Fuel Delivery


Damage Found:
ECU Upgrade:
Fuel Pressure Gauge:
HKS Vein Pressure Converter:
Injector Upgrade:
Split Second Unit:
Super AFC
Fuel Management Unit:
Free FMU
Split Second ESC1:
Final Recomendations:



I was very excited about my new TRD supercharger until I started having problems. Once problems started to surface I began testing to try to tack them down. There is no doubt in anyone’s mind that there is definitely enough air being supplied by the supercharger, but the question is whether the stock fuel system is up to the increase in demand to provide enough fuel to mix with the extra air being stuffed into the engine.

I have uncovered what I believe to be some short comings and some possible solutions.

Back to Index

Damage Found:

Before I installed the supercharger my 4Runner could easily reach the 108 mph speed limiter built in to the ECU. After installing the supercharger I had much more power and acceleration until I reached 90 mph when I started to loose power. If I backed off of the throttle slightly it seemed to have a little more power. This is a classic sign of fuel starvation.

About a month later I developed and exhaust leak at the front O2 sensor gasket and the front cat gasket. I tore it down to replace the gaskets and found that they had been burned through. Not just from erosion from a ongoing leak, but BURNED through! It takes a lot of heat to burn through these type of gaskets especially so far from the engine.

Back to Index

ECU Upgrade:

JET ECU Upgrade:

I was looking through the Performance Products catalogue and saw the listing for the JET Chip. It claimed a 17HP increase. Well that sounded great.

I visited a friend who owns a auto salvage chain. He was able to get a spare ECU for my 4Runner. I installed it in my 4Runner to verify that is worked, and then sent it off to JET. I had it back the second day.

I installed it and took it for a drive. I was very disappointed that I did not notice any difference. I called JET to inquire and was told it takes 100 miles for the computer to adjust itself. I drove for quiet a while and never really noticed a difference. I even swapped back and forth with my stock ECU and still could not notice any difference in the way it performed.

I do not recommend the JET ECU upgrade.


E L Prototypes ECU Upgrade:

The one on the left is a stock ECU, the one on the right is the ELP modified ECU. You can see the extra ROM board that is added in the upper left corner.

I was really impressed with the overall performance of my supercharger equipped 4Runner, but I did notice it started to loose power at about 90 MPH. It also would struggle to meet the 108 MPH speed limiter programmed into the stock Electronic Control Unit (ECU) in overdrive. It seemed to me that it might not be getting enough fuel and the mixture was leaning out causing a reduction in power.

E. L. Prototypes (ELP) developed a special ECU program for use with the TRD supercharger. I was leery about ECU upgrades due to my experience with the JET chip. I new that Ron was sending his off to have it reprogrammed by ELP and wanted to see what results he had. After getting his back he had nothing but good things to say about it. I then sent my spare ECU off the ELP.

I have been told that the stock chip in the Toyota ECU "CAN NOT" be reprogrammed. The chip has to be removed and replaced. The Stock ECU does not have a removable chip like on many of the domestic units.

Look at the picture above. The one on the left is a stock ECU and the one on the right is a modified by ELP. What ELP does is remove the top left chip and replace it with a ROM board. This new ROM board is equipped with a removable chip or EPROM. The nice thing is that if you make changes to you truck you can have a new program developed and sent to you on a pop in chip.

The ECU really improved the way the truck ran. It had a dramatic increase in low and mid range torque and was much more responsive. This was all without any boost. Under boost it is a real screamer. It accelerates very strong well past the old 108 MPH speed limiter (removed). I can not tell you what the top speed is, but I can say I left a Mustang and a Firebird behind at 124 MPH and just walked away from them.

The speedometer will peg on the odometer rest button at 115 MPH, so you will have to watch the highest obtained RPM on the tachometer. Then drive at half that RPM and read the speedometer and then double it to get the top speed.

I strongly recommend that anyone who installs the TRD supercharger on a 95-97 3.4L also have his ECU modified by ELP. The ELP modification really works, and works well.

Back to Index

Fuel Pressure Gauge:

This started me wondering if the engine was getting enough gas to meet the needs of the supercharger. I installed an Auto Meter fuel pressure gauge (see the section on gauges for more information). What I saw on this gauge is at about 4-5 psi of boost the TRD Fuel Management Unit (FMU)would kick in and jump the fuel pressure up to 65 PSI, so far so good. As the RPMs continued to climb the fuel pressure would drop. At the point of maximum demand the fuel pressure would drop below 50 PSI which is only 7 PSI over the idle pressure. If you then subtract the amount of boost from the fuel pressure it places the actual fuel pressure below the idle fuel pressure (more on that later).

I spoke to the folks at TRD about my fuel pressure loss and I was told that the supercharger only needs 53 PSI for proper operation. I told them all I was able to maintain was 50 PSI. The guy had no more answers for me. So, yes, it is leaning out! I knew I was going to have to fix it my self.

Back to Index


The FMU ups the fuel pressure so that more fuel can flow from the injectors under boost. The problem that I saw is that the fuel pump is not able to flow enough fuel to meet the demands of the supercharger. As a result as the demand would go up the supply of fuel would go down causing the mixture to go lean. This causes the exhaust gas temperature (EGT) to go way up and power to drop off.

I installed a Kenne-Bell Boost-A-Pump (BAP). The BAP works by increasing the voltage to the fuel pump under boost causing it to spin faster and deliver a greater volume of fuel. The BAP has a control knob that allows you to adjust the percentage of voltage increase to the pump. The BAP is activated by a pressure switch mounted in the supercharger plenum that activates at 3 PSI of boost. I adjusted the voltage with the control knob so that once the FMU kicked in I could maintain the 65 PSI of fuel pressure. This was 35% on the control knob.

I made a trip to the dyno and tested the results. I was amazed to see just how much it increased the HP where without the BAP it would drop way off. My dyno tests showed that a setting of 35% was ideal for the best power.

I called Mr. Bell at Kenne-Bell to discuss my results. Mr. Bell was very familiar with the TRD supercharger and that made things much easier. He confirmed what I suspected that supercharger was running lean.

Mr. Bell told me that there is a very easy test you can do to see if your supercharger is running to lean or not. Run a tank of 93 octane pump gas and then run your next tank with 100 octane unleaded racing gas. If you see an increase in performance you are running lean. If the performance stayed the same you are just right. If you lost power your are to rich.

Here is what is happening. The higher the octane the slower the gas burns. The richer the mixture the slower the mixture burns. The leaner or the lower the octane the faster it will burn. Also the leaner it is the more likely it is to cause detonation. When the engine starts to detonate the knock sensors picks this up and the ECU retards the timing. For every degree of timing retard you loose about 3 HP. When you richen the mixture you are suppressing detonation and this allows the ECU to run the timing more advanced so you get better performance. The BAP allows you to maintain a richer mixture where before it was leaning out due to fuel pressure loss.

As you can see there is a very dramatic increase in performance. These tests where done with the following setup: K&N FIPK, VPC, and ELP ECU.

The results speak for them selves. In the second gear pull showed 33.9 HP increase. In the third gear pull where the red line starts dropping badly there is an increase of 31.1 HP

Exhaust Gas Temperatures (EGT) where as follows:

Run 4 (BAP 0%) peak 1655 degrees F

Run 2 (BAP 35%) peak 1579 degrees F

Run 3 (BAP 50%) peak 1577 degrees F

What I found is that with the BAP the EGT would stay in the mid 1400s until the very end in each gear where it would suddenly spike to the temperatures indicated with a sudden reduction in fuel pressure. It showed up in the charts as a dip in the line toward the end of each gear pull. The runs without the BAP the EGT stayed very close to the peak through out the entire run.

I installed a digital EGT meter in the right side exhaust header. This meter has a recall function and would record the highest temperature recorded during the dyno run.

I set the BAP to zero for the first run on the dyno. The dyno operator saw the incredibly high EGT and aborted the first run. He then tried to talk me out of any further runs worried about engine damage. I explained to him that I have been running it like this for some time and wanted to press on. He reluctantly agreed.

The run with the BAP set to zero recorded an EGT of 1655 degrees F. The EGT was also that high through out the whole run. On the next run I set the BAP to 35% and the EGT meter showed a stable EGT in the mid 1400s until just before each gearshift where it would spike to 1579. On the next run I set the BAP to 50% and there really was no additional benefit. The dyno did record a maximum increase in HP of 33.9 HP with the BAP.

Keep in mind that these runs were done with the ELP ECU and the VPC that was already adding extra fuel. I simply can not imagine what the EGT was without the ELP ECU or VPC.

I do feel much better with the reduction in the EGT. There is no doubt that my engine will last much longer.

Back to Index

HKS Vein Pressure Converter:

The stock air flow meter is very restrictive. E. L. Prototypes is modifying an HKS Vane Pressure Converter (VPC) from a Toyota Supra for use on the 3.4L. This unit uses manifold pressure, an inlet air temperature sensor and a computer to replace the restrictive stock airflow meter. In place of the stock air flow meter, a three in pipe is inserted.

After installing the VPC I noticed an immediate increase in top end performance. I also found it that it takes a little time to get the adjustments set so the vehicle runs properly. Initial setting took about 10 minutes followed by fine adjustments over the next few days.

Installation involves:

  1. Removing the stock restrictive air flow meter and replacing it with a straight piece of pipe.
  2. Installing a temperature probe in the plenum. It replaces a allen headed plug on the rear of the plenum.
  3. Installing a manifold pressure sensor which is connected to the vacuum line going to the FMU.
  4. Splicing about six wires into the wire harness coming from the ECU inside of the dash.
  5. Mounting the control unit.

The black box on the fire wall is the manifold pressure sensor. The silver thing sticking out of the gray supercharger plenum is the temperature probe.

I installed the control unit in the glove compartment. I attached it to the roof of the glove compartment. This works out real nice. It is out of sight unless you stoop down and look up and provides easy access to the controls.

The VPC Control unit has four knobs: Response (works like an accelerator pump), Gain (overall mixture), Idle (idle mixture). The fourth knob is the "Option Out" knob. This is for piggy back HKS computers like the F-Con, or the GCCII. It is not used in my application.

There is a hesitation that remains after setting all the adjustments. This hesitation only occurs when pulling off from a complete stop with a rapid throttle input. I have tried everything possible to reduce the hesitation. I spoke to Eric at E. L. Prototypes and he agrees that it is most likely a slight bug in the program. Eric has sent me a total of four different chips and still the hesitation remains.

I have upgraded my fuel injectors and because I have not been able to get a new program to properly control the injectors from E. L. Prototypes, I have had to replace the VPC with a Split Second unit.

Back to Index

Injector Upgrade:

Left is the 270 cc Lucas injector, center is the stock 238 cc injector, and right is the 305 cc Toyota injector.

It was clear that I still was not getting enough gas into the engine. Remembering back to my first set of dyno runs the dyno operator told me I needed an injector upgrade. He pointed out the jagged saw tooth look to the lines on the chart and said every time he has seen this it ended up being to lean.

I sent one of my stock injectors to RC Engineering and had it flow tested. It flowed at 238 cc. That means that when locked full open it will flow 238 cc of fuel per minute. Locked full open is 100% of its duty cycle. The maximum recommended duty cycle of any injector is 80%. This is the industry standard to prevent erratic injector operation.

I used the fuel flow formulas on the RC Engineering web page and computed the max HP for the stock injectors out of my truck. At 80% duty cycle they will support 198 HP and at 100% they will support 247 HP. The 198 HP seems real bad and the 247 sounds a little more acceptable if the ECU will run the injectors at 100% duty cycle.

I called E L Prototypes and spoke with Eric the owner about my project. He told me that he had just installed injectors out of a 95 GS300 in his drag 4Runner. He had developed a new chip for the VPC he is marketing that would control the GS300 injectors. He said he would send me the chip to try out and if needed make me a new chip specifically for my size injectors.

I ordered the 270 cc Lucas injectors from RC Engineering. To install them I had to modify the wire harness connectors as the Lucas injectors use a different plug. At this I had previously removed the HKS VPC due to drivability problems and was hoping the ECU was capable of handling the new injectors by its self. The ECU could not control the new injectors effectively and tripped a check engine light.

I reinstalled the HKS VPC with the new injector chip. The chip was for injectors that where bigger and it ran to lean. I switched back to the original chip and it ran to rich. I called Eric and he said he would make me the chip I needed. Eric has many projects in the works and it was taking forever.

I was asked to try the Split Second MAF conversion kit. I installed the unit and was really impressed. It dialed in the injectors nicely.

The 270 cc injectors really made a big difference. It was making lots of power and the EGT was way down. The problem I was now having was with the TRD FMU that came with the supercharger kit. With the FMU connected it would run to rich at times due to the large rise in fuel pressure. With it disconnected it would run to lean. Thats right it would run to lean with 270 cc injectors without the FMU. You folks with stock injectors and no FMU on your TRD supercharger better re-read that a few times.

After a long talk with Mr. Bell at Kenny-Bell superchargers I was convinced that all forced induction engines needed an FMU of at least 1:1 ratio. See the FMU section on this page for more information on FMUs. I knew I needed an FMU but I also knew that the 270 cc injectors are not big enough for a 1:1 ratio FMU. I needed still larger injectors.

I did some math and figured that a fuel injector in the range of 300-320cc would be the perfect size injector for my needs.  I looked at different Toyota applications and learned that the 95 GS300 used a 305cc injector.  I obtained a set and had them flow tested and they were 305cc.  Toyota dealerships and they provided me with a Toyota part number of 23209-46031 and said this is the same injector used in the following applications:

  • 93-98 Toyota Supra NON-turbo
  • 94-97 Lexus SC300
  • 93-94 Lexus GS300 California Emissions
  • 93-97 Lexus GS300 Federal emissions

There is a guy (I am not going to use his name so he will not get into trouble) I know that works in one of the Toyota parts distribution centers and I was able to get two sets of these injectors at dealer cost. It was a one-time deal. One set was for Ron S one for me. I sent the injectors to RC Engineering and had them flow tested. They flowed at 305 cc. I was kind of disappointed that they were not 330s and was told by RC Engineering that Eric’s injectors were flow tested at 312 cc.

I went ahead and installed them. I also installed a Cartech model 20005 FMU that is completely adjustable for onset and rate of rise so I could test different fuel pressures to determine the ideal fuel pressure for these injectors.

The first test drive showed I had the perfect size injectors for my truck. I was able to back down the FMU down to as close to a 1:1 ratio as I could get and the injectors were working just fine. I was able to tune the Split Second so that it idled fine and at full boost I was able to get the EGT right at 1400 degrees F. My prior dyno testing showed that this EGT was the best power for my engine. With this EGT my air/fuel ratio meter was indicating a ratio of 13.2:1 as indicated by the first blue light solidly lit on my Split Second air/fuel ratio meter.

Split Second ARM1

I called Magnuson Products, the people that make the supercharger kit for TRD and they confirmed the ideal EGT for this engine at max boost is 1400-1450 degrees that made me feel great. I then called Split Second and to talk to them about the best air/fuel ratio. Split Second has been doing some development work for TRD by the way. They confirmed that the air/fuel ratio that I was running is ideal for my application. So I feel very confident that I have exactly the right size injectors for my truck.

I do not see any need to go any bigger. I have the high control on the Split Second dialed way back so I think that there is still plenty of room left in these injectors. I wish I had a duty cycle tester to see at what percentage of the maximum duty cycle on the injectors are at full boost.

I also think that my 270 cc injectors would work if I used them with the tunable Cartech FMU. It may just be a matter of finding the ideal ratio of fuel pressure to boost pressure. I know that with the TRD FMU it would be to rich at times so that would indicate that it is possible to flow enough fuel from the 270 cc injectors with the proper fuel pressure rise. I think I will leave that to someone else to iron out.

So if you want to do what I have done you do have a few options depending on the money you want to spend. The first is choosing the injector. The Toyota injectors that I am using will snap right into the wire harness without any modifications, but cost much more then the 310cc Lucas injectors from RC Engineering. So if you are trying to watch your money I would have to say go with the RC Engineering injectors. You also may be able to find some used Toyota injectors out one of the vehicles listed above. Before you install them make real sure the coil resistance is 13.8 ohms. Toyota uses injectors with different coil resistance and you must use high impedance injectors of about 13.8 ohms or you may smoke your ECU.

Split Second ARC 1

Split Second ARC 2

You will also have to use some type of injector driver or controller. I am using the Split Second 3" MAF conversion kit with an ACR2 controller. That will cost you around $1100 and replaces the stock air flow meter (AFM). You can go a cheaper route and get the Split Second ARC1 controller which is designed to work with the stock AFM and costs around $300. You can later upgrade to a Supra AFM for more airflow and more power. For information on the Split Second ARC1 go to the Split Second web page and down load their brochure.

Back to Index

Split Second Unit:


 I obtained one of Split Seconds MAF conversion kits and installed in on my 96 4Runner.  A custom air tube had to be made.

This is what the prototype installation looks like. I can not wait to see the final version. JT says he is making the production version out of spun aluminum.

I have been running upgraded injectors for some time and have been trying to get a new chip for my VPC that was tuned for my new injectors. Eric at E L Prototypes has sent me a total of four chips for my VPC and none of them were quite right. Given time I know that he will eventually nail it, but the problem with the VPC is that any time you change something you have to have a custom program done to match it. With the SS you just dial in the needed changes with the control panel and you are all smiles.

The vender I got the kit from sent me a wiring guide that was totally wrong and I had to sort all that out myself.  After sorting out the wiring connections I had the Split Second installed and running. I went on a test drive and was simply amazed on the difference in performance. The throttle response was incredible as was the top end power.

Simply by snapping the throttle I can break the rear tires loose at will. Low end, mid range and top end response and performance is simply perfect. This is the one modification that has brought all of the others together.


This is a picture of the three different AFMs side by side. Left is the SS 3", middle is the SS 3.5", and the one on the right is the restrictive stock AFM. You can see why the stock one is so restrictive. That big thing in the middle really cuts down on the space that air can flow through.

I prefer the stock airbox over the cone type filters mostly for the noise reduction and I know the K&N type filters are about the worse air filter on the market for filtration. The cone type filters is very loud. Once I get it I will test everything on the dyno and report the results.

I am sorry to say that even with my 270 cc injectors I still can not get enough gas into the engine to prevent a lean condition without the FMU connected. More proof that larger injectors are needed.

I used an air temp sensor out of a Nissan to substitute for the one that is built into the stock AFM that I removed.

The stock AFM has the induction air temp sensor built into the unit. When the stock AFM is removed the stock air temp sensor goes with it. JT takes the same approach that Eric at E L Prototypes did with the VPC. He includes a resistor that is spliced into the stock AFM harness. This resistor tells the ECU that the induction air temp is at 68 degrees all of the time. I decided to see if I could find a replacement air temp sensor that I could use as a substitute. Using the voltage values listed for the stock air temp sensor listed in the Toyota shop manual I set out testing all the air temp sensors I could find. I found that the induction air temp sensor on my 95 Maxima was a perfect substitute.

I visited the Nissan dealer and found that new ones are $65. I went to visit my friend at the junk yard. I got four used ones and brought them home and started to test them. Out of the four two were still good. I sent one to Ron and installed the other in the prototype air tube and spliced it into the harness.

I can not say that I have noticed any difference at all over the resistor, but I do feel better knowing that the ECU is now receiving the proper data to make its calculations from.

I spent some time prowling the junk yards and picked up a flanged 3" composite AFM and a air tube from the 99 Ford Crown Victoria. I cut everything off of the rear of the stock air box and the air flow meter was a perfect fit if it was turned upside down. I then sealed it with silicone. I then cut down the air flow tube and I also cut down the metal tube. Everything fit real nice and looks as if was OEM. I transferred the electronic module from the 3.5" Split Second AFM to the Ford AFM. The bellows in the air tube provide plenty of stress relief to allow for engine movement.

With the opening I cut in the front of my air box this setup emits a very pleasant hum from the front of the vehicle at idle. What I like most about this set up is that it is very, very quiet. I wanted to get away from the K&N cone filter for its lack of filtration and the noise it makes.

Although this todate was the best setup I had installed, the ARC2 controller just did not have enough precision for optimum tuning and it was removed along with the MAF.  I then went back to the stock MAF and used the APEX S-AFC for a controller.

Back to Index

Apex Super AFC:

I currently have the AFC installed above my rear view mirror.  It is easy to tweak
 it at stop lights.  I am planning to move it to the glove box soon.

There is a new device on the market that works like the Split Second ARC units.  It is made by APEX and it is called the Super AFC.  It operates on the same concept as the SS ARC units by modifying the signal from the MAF.  By doing so you can alter the fuel mixture and dial in larger injectors.

The thing that makes the AFC different from the SS is that you can make the air flow corrections at specific RPM and throttle settings and that can not be done with the SS units. 

The AFC is a very small compact unit that makes installation much easier.  It also has all kinds of data displays like RPM, correction factor, throttle position, air flow, and a few others.  

I really liked how easy it was to tune in.  I had removed the Split Second stuff and replaced it with my stock MAF and the AFC.  The truck ran really good with this combination, but I did loose some top end power with the more restrictive stock MAF.  

The Supra MAF is easy to adapt to the stock airbox.
Because the mounting holes are on the opposite side as on the
stock MAF, I had to rotate it 90 degrees to the passenger side.
The nice thing is that it just plugs in to the stock harness.
It also has the IAT built in just like the stock one.

I was able to obtain a used MAF from a twin turbo Supra.  It is very much like the stock MAF on my 96, but much, much bigger.  It is very easy to adapt it to the stock air box.  With the larger MAF all the top end power came back.  Overall I liked this combination so much I sold my ARC2 and 3.5" SS MAF.

With the stock MAF and my 305cc injectors, I had the low throttle settings on the AFC set at -15% and the high throttle settings at -10%.  The hot wire type is set to 01 and 01.  Works really nice.

I had to retune the AFC when I upgraded to the larger Supra MAF.  The low throttle settings are, +20% and the high throttle settings are +35% and +40% at 4000 RPM and up.  The hot wire type is set to 15 and 15.  As you can see with the larger Supra MAF the settings must be much higher to compensate for the greater air flow through the larger MAF.

The AFC is really popular in the sport compact car scene and they can be hard to find.  You can shop around on the net and find one at a good price.

HKS has come out with a similar unit called the AFR.  I have made connection guide for several people that got the HKS AFR and most all of removed them and replaced it with the AFC.  There is no graphic display and it seems that people loose track of where their settings are.  I suggest that if you get one you plot your correction factors out on some graph paper so you have something visual to look at during your tuning.  To date I know of one person that was successful in getting the AFR properly dialed in, most of the rest hated it.

I have since removed the AFC and upgrade to the Split Second Fuel Timing Calibrator (FTC).

Back to Index

Fuel Management Unit:

TRD includes, or at least did, a Fuel Management Unit (FMU). In theory what this thing does is increases fuel pressure under boost to cause more fuel to flow from the injectors.

The TRD unit is installed by removing the stock fuel pressure regulator from the fuel rail. The TRD FMU is then clamped on top of the stock fuel pressure regulator. The FMU has a diaphragm in it that is deflected by positive pressure in the manifold (boost). There is a pin attached to the diaphragm that pushes on the diaphragm in the stock regulator causing it to hold a higher fuel pressure then it normally would. The combination FMU/regulator is bolted to the firewall and the stock regulator is connected to the fuel rail with a high-pressure hose. A vacuum hose connects the FMU to the supercharger plenum.

By increasing the fuel pressure you are forcing more fuel from the injectors into the engine. Is this a Band-Aid fix for not having injectors big enough to do the job, or does the FMU just allow you to brake even?

I spent some time talking to Mr. Bell at Kenne-Bell about supercharger fuel needs. Mr. Bell is a wonderful guy and he is a real straight shooter. It is his opinion that all forced induction engines must have an FMU of at least 1:1 ratio of boost to fuel pressure increase. He explains that if your normal fuel pressure is 43 PSI and you increase your boost is 7 PSI with no FMU you have a negative affect on the fuel pressure and are essentially reducing the fuel pressure by 7 PSI. As the pressure increases in the plenum it restricts the fuel from flowing from the injectors. In this example you have a net affect on the fuel pressure by a reduction of 7 PSI so it is now 36 PSI. This further compounds the lean condition. By the way TRD does in fact sell a 1:1 FMU as an upgrade for the turbo Supra. Interesting don’t you think?

Here is the problem. Stock fuel pressure regulators and fuel pressure gauges work by comparing the fuel pressure in the fuel rail with the pressure of the OUTSIDE air and not the pressure in the manifold or plenum. This is fine for a normally aspirated engine because the manifold pressure never exceeds the outside or atmospheric air pressure. Forced induction engines are different. As the pressure in the plenum increases it has the affect of decreasing the fuel pressure by the same amount because it makes it harder to flow fuel from the injectors into the plenum. This is where an FMU comes in. It will adjust, or supposed to anyway, the fuel pressure in relation to the pressure in the plenum.

A big problem that I have observed with the TRD FMU is that it is very inconsistent. If I quickly apply the throttle the TRD FMU reacts very quickly and jumps up the pressure. If I ease into the throttle the TRD FMU dose not react until I get about 5-6 PSI of boost. This maybe why some 4Runners ping under light acceleration. The overall amount of fuel pressure increase is very inconsistent and does not seem to have a good relation to the boost pressure. In other words it is erratic as hell. As the boost goes up fuel delivery is being reduced until the TRD FMU kicks in.

TRD has deleted the FMU from the newer supercharger kits. We have been told that this was done to eliminate pinging on the 98 and later models. From my testing and the very high EGTs even when using the FMU, the thought of running the supercharger without an FMU is real scary at best. I wish TRD would replace the erratic FMU with a more stable and consistent one instead of just getting rid of it.

Ron has installed a Cartech FMU that allows him to adjust the ratio of fuel pressure increase in relation to boost pressure and the onset of the increase. What that means is it can be adjusted to a 1:1, a 2:1, a 5:1 or what ever you want. Not only that, but you can adjust it as to when the increase in fuel pressure starts. You can set it to start as soon as you have boost or what until you reach a certain boost level. Ron had such great results that I decided to order one so that I could test different fuel pressures with my new injectors.

The Cartech FMU is different then the TRD FMU. It is not installed on top of the stock fuel pressure regulator like the TRD one. Instead it is installed in the fuel return line that returns fuel from the regulator to the fuel tank. The way this FMU works is that it restricts the fuel leaving the stock regulator when needed to increase fuel pressure in the fuel rail.

This FMU is ideally suited for installation on the TRD supercharger kits with the deleted FMU, or to replace the erratic TRD FMU. The only thing is that you will have to replace the fuel return hose from the regulator to the tank with a section of high-pressure hose. Ron came up with the idea of upgrading this hose is when the supercharger is being installed. Because the newer kit do not remove the regulator from the fuel rail the only way to get to it is with the supercharger off of the engine. Everyone installing the supercharger should plan ahead and replace the return hose with a high-pressure hose at the time of supercharger installation. This way if you decide to install the Cartech FMU after installation you will not have to remove the supercharger to do so.

It is important to keep in mind that there is no way a FMU can make up for the injectors being to small. On the RC Engineering web page Russ has an example using a 240 cc injector. By upping the fuel pressure from 43 PSI to 50 PSI there was an increase of only 2.64 HP worth of fuel flow for that injector. Now if you subtract out the boost pressure differential of say 7 PSI of boost you really have accomplished nothing and really only broken even.

Cartech 20005 FMU

I installed the Cartech 20005 FMU along with my new 305 cc injectors. I was hoping that I would only need a 1:1 ratio of fuel pressure rise to boost pressure. My tests confirm that with my new 305 cc injectors a 1:1 ratio is ideal. I have found that the Cartech FMU is a very nice unit and is very consistent and reliable and will give the same results time after time. It performs as it should and not like the erratic FMU that was included with the TRD Supercharger kit. Those of you that are still running stock injectors and no FMU this would be a good one for you to get. It installs in the fuel return line from the stock fuel pressure regulator. You will need to upgrade the line from the stock regulator to the Cartech FMU with a high pressure fuel injection hose as the stock return line is not intended to hold pressure.

TRD Supra fuel pressure regulator (FMU)

Now that I have confirmed that a 1:1 ratio is ideal with the 305 cc injectors, I replaced my Cartech FMU with this TRD fuel pressure regulator. It is suposed to work just like the Cartech FMU and is fixed at a 1:1 ratio. I installed it and found out real fast it really is not any good.

I set it up just like the Cartech FMU. I adjusted the onset screw with the vacuum line disconnected from both the stock fuel pressure regulator and the TRD fuel pressure regulator so I noticed the slightest increase in fuel pressure above the stock regulator. Then I locked the jam nut.

I went for a test drive and found that it does not provided a 1:1 ratio increase in fuel pressure at all. It would increase fuel pressure about 3 psi at the most. So with 9 psi of boost indicated it would only increase fuel pressure by 3 psi. It was not any good for my purpose and I removed it and reinstalled my Cartech FMU until I discovered the "FREE FMU".

Overall, I have had little luck using these FMUs.  They all proved erratic, inconsistent and totally worthless.  I am convinced that all these pressure increasing FMUs are junk and are nothing more then a piss poor band aid fix.  The proper thing to do is to install the correct size fuel injector and control them electronically.

Free FMU:

While testing the Cartech FMU and the TRD Fuel pressure regulator I decided to see if I could run my 305cc injectors without an FMU stumbled across something. I removed the Cartech FMU and went for a test drive. I was surprised to see that my fuel pressure was increasing when I was in boost at a ratio of 1:1. How can this be?

I checked out my connections and found that I had the stock fuel pressure regulator (FPR) hooked to the boost port. The stock connection is to the main air induction tube which is really nothing more then a vent and gives a constant 43 PSI all the time.

With the FPR hooked to the boost port it will react to boost pressure and increase the fuel pressure under boost at a perfect 1:1 ratio. This offsets the boost pressure differential that I discussed earlier and really does a good job of stabilizing the fuel pressure in relation to manifold or boost pressure. The funny thing is that all the other fuel injected engines I have toyed with has the FPR connected to a port that allows it to read and adjust the fuel pressure in relation to engine load (manifold pressure).

Here is the benefit with the TRD supercharger. Like I explained earlier, as the manifold pressure increases in boost it will restrict fuel flow from the injectors. By reconnecting the FPR to the boost port you prevent this problem and it will give you 6-7 PSI of extra fuel pressure at max boost that you did not have before. Many people with the dreaded pining problem have tried this and it has in some cases eliminated the high gear, low RPM ping. All have reported an improvement.

I do not think for a second that this will be enough to prevent the fuel system from leaning out at max boost, but it will not be as bad.

Give it a try. It is FREE and you can easily switch it back. I have been told that TRD has heard about my little trick and is now recommending it as their own discovery.

I currently have my stock FPR connected to the boost port and I am using the 305 cc injectors.

Back to Index

Split Second ESC1:

With the larger injectors and the Split Second (SS) ARC2 controller I have solved my top end fuel delivery problems. There was still one spot in the power band I was not happy with. That was part throttle acceleration under boost. In this region I felt that the engine just was not producing the power it should and there was a constant surging.

I figured out what was causing the surging as soon as I installed my SS air/fuel ratio gauge (ARM1). It is from the ECU operating in "closed loop" operation. In closed loop operation the ECU it constantly adjusting the fuel mixture to try to find the "ideal" mixture. The mixture is being varied from rich to lean, then back to rich. This cycle takes about a second to complete. When it is on the rich side there is more power, when on the lean side there is less. So it presents as surging in power. More proof that this engine control system was not intended to support an aftermarket supercharger.

At full throttle the ECU switches into "open loop" operation and it is no longer cycling the mixture. It switches over and uses the full throttle fuel map, which is richer then cruise power and it makes more power. It would also switch into open loop if I continued to accelerate in 3rd gear for about seven seconds or more. As soon as it would switch into open loop the surging would disappear and there would be a noticeable jump in power.

I found I could adjust my SS ARC2 so that it would be real rich in the mid range while acceleration under boost with part throttle. This would cause the ECU to switch into open loop and would run nice in this narrow range, but would throw everything else way out of adjustment. I knew what had to be done, just not how to do it. I started making calls and spoke to Eric at SS. He said that they had just the thing I needed, the ESC1.

The ESC1 is a signal conditioner. They make a few different ones that modify the signal from the sensors to the ECU. This one modifies the signal from the front O2 sensor. Under boost it modifies the signal from the O2 sensor to the ECU causing the ECU to switch into open loop.

There are 4 wires that get spliced into the ECU harness, and a vacuum line that is connected to the boost port. I found that the connections have to be made behind at the ECU, which it located behind the glove box. The O2 sensor wires are shielded in the engine compartment to prevent interference so you can not make the connections there. I originally installed the ESC1 behind the glove compartment. I had a loud buzz under boost. It turned out to be whine from the supercharger traveling up the vacuum line. I then followed a friends lead and installed the ESC1 on the firewall next to the wiper motor.

I went for a test drive and found out right away, this thing is great! Shortly after going into boost the ECU kicks into open loop and I now have so much more power then I did before at the lower boost levels. The surging is GONE. Now for the very first time my supercharger feels like a factory installed unit. It is very smooth and very torquey at lower boost levels. It is amazing what just a tad more fuel will do for the drivability of the supercharger.

I live off of a long country highway with lots of hills. Using the cruise control was impossible due to all the downshifting. The installation of the supercharger made that a lot better, but it still down shifted more then I liked. Now with the SS ESC1 the engine makes so much more torque at highway speeds it no longer down shifts. It climbs the same hills with 2-3 PSI less boost then before. It is interesting to watch the boost gauge suddenly drop 2-3 PSI as soon as the ECU transitions into open loop.

I find that I can pass the slow pokes hogging the left lane and that are too rude to move over without down shifting. I just ease in the throttle and get lots of torque and I can add 20 MPH without down shifting so fast it feels like I have a 350 in it.

So, the SS ESC1 gets my seal of approval. It works and does exactly what SS says it will do. The ESC1 will work on all O2 sensor equipped trucks from 95-98.  Starting in 99 Toyota started using an wide band O2 sensor on some truck and the ESC1 is not compatible with that sensor.  Still some trucks were equipped with the old style O2 sensor, but there is no boost induced power surging on the 99 and later trucks so I do not recommend using the ESC1 on anything newer then 98.

Back to Index

Final Recomendations:

Fuel delivery solution has to be done in a package deal. One thing without the other is only a half assed approach. The first thing is everything is dependent on there being enough fuel available from the pump in the first place. You should install a BAP or a larger pump so that enough fuel will be available. I am using the BAP. Then you have to find a way to get it into the engine. I have chosen to install adequate fuel injectors. Another approach is to install extra injector(S) in the intake track. Then there must be a way to properly control the injectors so the right amount of fuel is injected at the right time. I am using the Split Second Unit. And lastly you must make sure that boost pressure is not going to restrict fuel flow from the injectors by installing an FMU.

You also must be able to monitor engine operation to make sure everything is working properly. I did this by installing a Split Second Air/Fuel ratio meter, a dual EGT gauge, and a fuel pressure gauge. This allows me to cross check engine functions and be able to spot a problem before I melt a piston.

After everything I have learned from my dyno testing I have developed the opinion that the TRD supercharger kit runs to lean. I have discussed my findings with several other supercharger kit manufacturers and all have agreed with my findings. The real kicker was a guy that worked for the company that developed the TRD kit for TRD. He says that he had told TRD that the kit in it current form without the TRD FMU is to lean and that TRD has flat out chosen to ignore him. He said, "it is the most expensive way I have ever seen to aluminize an exhaust system."


I have formed a company to market a fuel kit based on everything I have tried, learned and developed to date.  This is a complete kit that includes everything needed to solve the High RPM Lean Out problem, the HG/LR-ping, as well as provide a very nice increase in performance.

I installed one on a 2001 Tacoma and dyno tested better then a 40 HP gain.

Check it out at www.URDUSA.com.


Back to Index