lionj

Hi,

Does anyone know the procedure to change the fuel pump ecu(control curcuit) thanx

London Bill

Changing the Fuel pump ECU is quite easy:

Remove rear seats, lift up the seat base at the front edge. the upright part is held in by the now exposed bolts (2 or 3 of them).

Remove the exposed left side panel (the ECU is in here on the RHD models, could have been re-located to the right side for the US models).

Unplug harness and remove single bolt.

Heres a photo of the internals, it's all set in epoxy so replacing any bits is a real no-no.



Picture replaced with one courtesy OLT

philauldridge

The fuel pump ECU (at least for SC300) is located on the side panel, rear seat, driver side, just below the side window. Just remove the side panel, and you will see it there.

The only purpose of the fuel pump ECU is to supply lower voltage to the fuel pump when the main engine ECU determines max fuel pressure is not needed. Many owners, especially with turbo upgrades, have bypassed the ECU entirely, which just sends a full 12V to the fuel pump at all times. Doesn't really seem to lower pump life and eliminates any problems with the FP ECU. (This voltage jump does NOT affect fuel pressure to the engine, this is controlled by the pressure regulator up front). For details on how to simply accomplish this modification, look in the technical section for 12V Fuel Pump mod on the Supra site: wwww.mkiv.com

Phil

Camshaft

Will bypassing the fuel ECU increase power? If there is an increase in fuel pressure, shouldnt there be a slight drop in MPG but an increase in throttle response?

philauldridge

The Fuel Pump Pressure has no DIRECT effect on actual fuel flow to the injectors or air/fuel mixture. That function is all handled by the fuel pressure regulator (with signals from the main engine ECU) mounted on the engine. Fuel in excess of that needed at any given moment is routed through the fuel bypass line and back into the fuel tank. Only when fuel flow from the pump is LESS than needed by the engine management system will there be an adverse effect on the overall air/fuel ratio.

The Fuel Pump ECU is designed to detect lower power engine situations (as determined by the main engine ECU) which do not require full fuel pump pressure, and send a lesser voltage to the pump, hence lower fuel flow output. This is presumably to add life to the pump itself, but, again, has no direct effect on actual fuel usage, or engine power output. Many owners bypass the FP ECU completely, giving it full 12 volt power and full flow continuously to insure that any add-on after-market electronic devices which might 'trick' the main engine control unit into assuming less than normal power and hence not give the Fuel Pump ECU the correct signal. This could result in a lean fuel mixture and possibly damage the engine!

The only adverse effect of bypassing the Fuel Pump ECU is the possibility of shortened pump life since it WILL be working at full bore all the time. This does NOT seem to be a problem or concern among owners who have made this mod. Worse case, the replacement pump is a $150 or so item, and replacement is a hour or less!

PERRYinLA

Wow- what kind of design logic is this, where a $150 fuel pump is "protected" by a Fuel Pump ECU that approaches the same cost.

And what happens when a FP ECU fails? Does the fuel pump:

1) stop working altogether, stalling the engine? Or does it just...
2) stop lowering the voltage at times, sending 12 volts full time- the very same effect as bypassing it?

If it is 1), then you theoretically make your car MORE RELIABLE by removing it! This has got to be the TIP OF THE MONTH!

If it is 2), then you'll never know it fails! But then I doubt "lionj" would have posted this question in the first place!

So I must be missing something here- maybe when a FP ECU fails you got another condition besides 1) or 2).

philauldridge

Good points you've made about the necessity for the ECU. I'm not a Toyota engineer, so can't guess. I'll just pass along my own observation and experiences with this critter.

I've done the bypass to my SC300 (which, admittedly, now has the Supra Twin Turbo engine, and the higher-capacity Supra fuel pump), and it has worked flawlessly. Sorry, I'm not gonna tear into the upholstery again to look at my bypassed ECU, but, since the info on the SUPRA site IS specific to the very similar but sometimes different Supra setup, I DID review my factory manual for the SC300. Here's the scoop:

When you unplug the connector to the Fuel Pump ECU, here is what you will find:

The connector should have 5 pins and/or wires coming out. According to the manual, from left to right, (or vice versa, depending on which way you are looking at it):

Left: GROUND White/Black
Diagnostic Connector Purple
Input from Main ECU Red/Green
12v Power fm EFI Relay Black/Red
Right: Power TO Fuel Pump GREEN

First, I would get out my voltage tester, and confirm with ignition switch on : 12 volts on the Black Red Wire, 8-12 volts on the GREEN wire. If this checks:

1. DISCONNECT THE BATTERY!!! Can't be too careful with that main Engine ECU
2. Leave about 2 " of wire on the ECU connector in case you want to reverse the process later
3. Cut BOTH the BLACK/RED Wire (main 12V power from the EFI relay), AND the GREEN wire (power TO the fuel pump)
4. Join the two wires together you've just cut (NO!! NOT the short ones still on the connector, but the other two ends!) DON'T use the hokey household romex twist connectors as shown in the pics on the SUPRA site. Do it right, with a good solder connection and heat-shrink wrap over. After all if this connection fails, you are definitely gonna be WALKING! (not an easy roadside fix)
5. Tape over the two separate ends of the 2 inch wires left on the connector (shouldn't be necessary, but just to be safe.

That's it! You've successfully eliminated the Fuel Pump ECU!
2. Cut BOTH

JPI Racing

I don't see why we have to use this method to raise the fuel pressure. Increasing pressure fuel can damage injectors, injectors seals etc . Why don't we use a bigger pump, bigger injectors?
JPI

London Bill

A reported "downside" to the fuel pump bypass;

The fuel ECU delivers three states, OFF/LOW FEED/HIGH FEED, this is determined by the running conditions, if the engine is stalled the ECU would go to OFF, with the bypass in place this option is not available, so in worst case scenario if you had an accident and killed the engine or fractured a fuel line the ECU would not be able to go to OFF and would continue to pump fuel round the system or into the engine bay or just dump it onto the road.

CrazeeSC

i think you can run higher pressure safely how can you say it will damage the injectors?????

Fred Smith

The ECU is NOT there to protect the fuel pump. It is there to make less noise and heat the fuel less under light load conditions.

Bypassing does NOT raise fuel pressure. Only messing with the regulator can do that. Bypassing is just done by turbo cars that are afraid their upgrades may mean fuel starvation when the ECU thinks the engine only requires low flow from the pump. Anyone with a Supra TT pump should do it as well, because the FP ECU probably can't handle the extra current required to operate this pump, and would most likely burn out or shut down. The safest way to do this would be with a heavier, fused, direct 12V from the battery, switched by a high current relay. The FP ECU operates the relay. You need to find a high current one so it thinks the relay is the pump and doesn't shut down due to "pump missing".

craaaazzy

iTrader: (4)

sorry to bring back an old thread but at least i searched. hopefully someone can help and i don't have to start a new thread...

i've in the process of tuning the na-t. boostlogic stage 2 w/ 525cc injectors, tt denso fuel pump, and aem 1101.

idle is good but car is sputtering under 3k RPM's under full throttle. i have not done the 12v mod yet but could this be causing the sputtering issue? here's my theory...since i'm running the aem, the fuel pump ecu does not get the "high speed" mode signal it would normally get w/ the stock ecu. thoughts? tia.

craaaazzy

iTrader: (4)

after some further research, i found dejacky's thread where he mentioned that this mod was required or "car would not get proper fuel when the throttle was applied more than a "little bit."".

i'd like to know people's thoughts though so let me know...i'll see if this resolves my issue as well later on next week.

Sc4004me

Well my 92 sc400 has been sitting for 6 months.I just changed out the crank seal.Now i traced a no fuel problem to the fuel pump ecu .I got a bad wire "no continuity between fuel pump ecu and engine ecu.

But thanks to this thread and its posters,You guys saved me 100's of dollars ,and maby a trip to a garage.I jumped out the pins as directed "strait 12 v to the pump,and i have fuel ,and now a running car.Thanks alot for posting this,you guys saved me hours of headaches and the cost of parts @!!!!!! yay ill be driving my lexus today

Loo-10-ant

I have the issue with my 93 LS400. Apparently the FP ECU has failed because I get no output from the module. I have 12v on the IGN terminal (Black/Red wire @ the connector) and only 4.56v from the Engine ECM, the Green / Black wire @ the connector. I measure 9.8V at the G/B wire out of the ECM so there is a Voltage drop between the ECM and the Connector. In order to get the car to run I had to run 12v directly to the pump from and external power source (Portable Battery booster) as I have just bought this car and it has been sitting for 3 years. It has a 1/2 tank of bad fuel and ran like a kangaroo when I first started it up.Siphoned the nasty turpintine smelling junk out of the tank, new pump, New gas with FI cleaner and after a couple of minutes of spitting and skipping the engine cleared up and purred like a Kitten! I first suspected the ECM module but I have all the correct voltages (That I know of) in order to get the pump to run, but not sure why I get the voltage drop. Reading this thread has given me the insight to do the inevitable!!! BYPASS!!!! i will still try to locate the voltage drop because I wanna know why it does. But this is a good thread because I have always wondered if bypassing the FP ECU would be feasible.

Loo