1G TMO - Fuel Pump Relay

DSM90AWD · Feb 26, 2006

I've just finished installing an aftermarket fuel filter/feed line and went to prime the pump to check for leaks (were none

) using my TMO datalogger's feature for the pump relay but the pump did not come on. The pump also does not come on for a few secs when ignition is turned to the "ON" position as it used to do.

The 90-91s have a separate Fuel Pump Relay mounted under the ECU (P/N E8T07071) which has two internal swiches, one I assume is for the Ignition On (to prime) and one for the Engine On. Both swiches when jumpered directly from the battery worked ok (i.e. close) so assume this is not the problem. I also took the cover off and saw no internal damage other than a slightly misaligned switch contact.

I assume the TMO Dataloger and Ignition ON swich triggers this relay, but neither seem to work (e.g. no audible "clack" as was when manually jumpered).

What could be the common break in the communication to this relay :confused:

I might add that the car starts/runs fine, so obviously whatever is wrong is specific to both the TMO Fuel Pump Relay activation and the "ON" swich of the ignition. I was thinking ECU, but I had the CAPs replaced by JeffO a few years back and was told it had no board damage.

Also the manual fuel pump relay harness (the one behind the battery) did work when applying 12V power.

Quasimondo · Feb 26, 2006

That's weird. When I had my '90 Talon, I never encountered that problem. I used MMCD to work the relay, did you try using that to see what happens?

DSM90AWD · Feb 26, 2006

Quasimondo said:
That's weird. When I had my '90 Talon, I never encountered that problem. I used MMCD to work the relay, did you try using that to see what happens?

It used to work (the TMO Trigger), but not right now. I know it's not the software as I have it loaded on two laptops, both connected/datalogged fine but neither would trigger the relay, now would the ignition to "ON" switch

Quasimondo · Feb 26, 2006

I've been looking over the diagrams. It appears that the MPI for the fuel pump has two coils. One is powered by the starter relay, the other is powered by the igniton switch and ecu. We can pretty much ignore the coil from the starter relay, that only engergizes when you're starting the car (which would explain why the engine has no problem starting)

The other coil gets its power from the ignition switch and the the ecu (pin B56). When that pin grounds out, it energizes the coil (that's how it looks to me). I would assume that pin isn't grounding out, but that doesn't explain how your car can still run. I doubt it's a break anywhere in the ignition switch wiring because your fuel pump wouldn't work. The same wire that powers the coil on the relay also provides power to the fuel pump.

The the last part of the wiring is a wire that is between the relay and fuel pump. That wire runs back into the ecu (13C) and it looks like a signal wire to let the ecu know that the fuel pump is running. If that wire doesn't get any voltage, it throws a CEL.

This makes me believe it's software related. If it was anything with the wiring on either the ignition wiring side or the ecu side, then the car wouldn't run.

DSM90AWD · Feb 26, 2006

Thanks for the help, unfortunately I have an unrelalted problem which is going to put a hold on my troubleshooting for few days (defective Summit Racing 90* AN hose end = fuel leak :mad:

).

Curious which of the two switches the TMO activates and how it goes about it.
Come to think about it, the "clicking" that normally comes from a bad ECU (caps leaking) is likely that ignition > pump relay. Is it possible that somehow that circuit burned out in my ECU and just affected that part of the relay (i.e. pump still runs when car is turned on) :confused:

steve · Feb 26, 2006

I've never seen a '90 turn the pump on when you turn the ignition on (RUN). All the rest of the 1G's turn the pump on when you turn the ignition to START.

Quasimondo said:
I've been looking over the diagrams. It appears that the MPI for the fuel pump has two coils. One is powered by the starter relay, the other is powered by the igniton switch and ecu. We can pretty much ignore the coil from the starter relay, that only engergizes when you're starting the car (which would explain why the engine has no problem starting)

Correct. The MPI relay has two functions. MPI power and Fuel Pump power.
The Fuel Pump power relay has two coils, one activated by the starter circuit getting 12v and the other activiated by the ECU pulling the pin to ground. The power feeds for these come from either the MPI fuse or the ignition fuse on the battery.

Quasimondo said:
The other coil gets its power from the ignition switch and the the ecu (pin B56). When that pin grounds out, it energizes the coil (that's how it looks to me). I would assume that pin isn't grounding out, but that doesn't explain how your car can still run. I doubt it's a break anywhere in the ignition switch wiring because your fuel pump wouldn't work. The same wire that powers the coil on the relay also provides power to the fuel pump.

Close. One of the two coils is powered by the starter circuit and it's other end is grounded where the other coil has the hot side tied to the same power source as the FP side is switching and it's other end goes to the ECU. So the starter circuit coil is activated by getting 12v and the ECU circuit coil by grounding it.

Quasimondo said:
The the last part of the wiring is a wire that is between the relay and fuel pump. That wire runs back into the ecu (13C) and it looks like a signal wire to let the ecu know that the fuel pump is running. If that wire doesn't get any voltage, it throws a CEL.

Correct. ECU Pin 13 isn't shown in most FSM but it's the sense line to the ECU that the fuel pump is getting power and the ECU throws a 42 fault code if the pump is activated by the ECU and 12v isn't seen on Pin 13.

Quasimondo said:
This makes me believe it's software related. If it was anything with the wiring on either the ignition wiring side or the ecu side, then the car wouldn't run.

The traces for running the fuel pump on the ECU run through the danger zone on the ECU for capacitor leakage damage. I fix a few a month where the cap leaked and the electrolyte eat the trace up disconnecting the edge connector from the logic.

Steve

DSM90AWD · Mar 27, 2006

For the archives, I found that the TMO Datalogger Version 1.16.03 (the Beta version that allows an external 0-5V sensor to be logged via the EGR-T input) has a a bug that prevents testing of the fuel pump relay. The CEL Code display / reset is also buggy.

I recently picked up a Palm running MMCD v.1.71.01132005 and was and sucessfully able to test my pump relay via that application.

Wish someone could of talked Todd into publishing the source to this application so someone else could have taken over the reins as he hasn't touched/upgraded it (or even been heard from) in years and I actually forked over the $300 years ago for the full version w/ upgrades

steve · Mar 27, 2006

DSM90AWD said:
The CEL Code display / reset is also buggy.

Depending on what code is in your ECU, it might be buggy because the '90 ECUs datalogging interface doesn't have/support the command to clear the error codes. It's in E931 and later but missing from the E742/E743.

DSM90AWD · Mar 27, 2006

My ECU is the 1990 with the 91-94 EPROM coding/trims from JeffO.

My error code(s) display under the ECU Info Tab, and my ECU Info on the Error Codes Tab. Yes, the clear codes never did work even in the non-BETA version, nor do they seem to work on MMCD as I still seem to have stored codes (forgot to hookup my MAS on Sat) which I could not clear.

Guess a hard reset is in order (e.g. negative battery cable) unless there is a better way?

jonheslop · Jul 15, 2006

I have the same exact problem with my MPI relay. It will work when the car is running but it doesn't turn on the prime the system. Also, the check wire under the hood doesn't work. I know the relay is getting power because when I turn the key, there is 12v going to the relay, just not 12v coming out. So I had to hook a jumper wire before the relay to the fuel pump and my car works fine. However, I don't like the pump being primed so long, the relay is only supposed to let it prime for a few seconds. I was following along for a while with you guys but then you lost me. Did you ever fix the problem? If so, what did you do? BTW, I don't have a TMO.

92awddsm · Jul 15, 2006

I would also be interested in knowing a solution. I normally just spin the engine over a couple of times and let off of the key so the system will prime. It then fires right up. My car has never primed with the key on in the 6 yrs Ive owned it. My fuel pump test terminal works fine under the hood.

steve · Jul 15, 2006

92awddsm said:
My car has never primed with the key on in the 6 yrs Ive owned it.

Like I said 17 months ago. The fuel pump doesn't turn on until you turn the key to START.

That's when the fuel system pressurizes because the starter circuit feeds 12v to pin 9 of the MPI relay. That energizes one of the coils on the FP side of the MPI relay and powers the pump. Once the ECU sees the engine turning over (CAS pulses) it will pull pin 7 on the MPI relay low, energize the other coil on the FP side of the relay and keep the pump powered when you release the key from the START position.

The power for the fuel pump comes from the Ignition switch and Ignition fuse to pin 3 on the MPI relay and go out on pin 2 to feed the pump. Late 2Gs have a separate Fuel Pump Relay and only the ECU runs the pump.

link16 · Sep 25, 2010

I just did some digging for a guy that called me today at work and gave me the "part number" listed in this post...I know it is old but I thought I would update this a bit.

E8T07071 is the stamp number on the part, the actual part number for the relay is MD119202.

I hope this helps people out when they are looking to buy. This part currently LISTS for $91.93.

Thanks,
Alex

snakeyes711 · May 18, 2013

I know this is a very old thread. Is there a way of testing the fuel pump relay with a meter? Is there a way to tell if its bad? My car starts and runs, but it has zero power, It builds no boost over 2-4 psi, and everything I've looked at checks good except that relay. It sounds like I hear the pump run low like the volts going to it are going down past. and its a walbro 190, I ought to have plenty of pump pressure.

http://www.dsmtuners.com/forums/tuning-engine-management/458951-1gb-no-power-boost-lean.html

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