# [SOLVED] Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC



## GZ (Jan 31, 2010)

My buddy Keith and I are troubleshooting an issue with the Fuel Pump relay/MFI circuit.

The previous owner tied a switched ground into the Black/Blue wire coming from the fuel pump relay. The wiring diagrams I have found don't have that wire listed.

The issue is that, occasionally, the car will stall and refuse to run (when the switch is in the off position). When it is in the on position, the car seems to run fine all the time.

I don't understand the reason for the switched ground... my first hypothesis was that it was added as a fuel cut-off switch, but it is still tied to the original circuit. Also, for all I can tell the black/blue wire runs into a loom that may go into the MFI control unit.

When the switch is closed, the car seems to run... but when it is open, the car may run or it may not run... so I am thinking that the switch may have caused the issue and damaged the MFI control and or the MFI/Fuel pump relay.

Any ideas are welcome.


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

Just drove the car around and there were no issues with it running as long as the added ground circuit was closed.

The factory part number is E8T07071, apparently it also communicates with the MFI control unit. I have seen it referred to as the MFI/MPI relay as well.

Still trying to figure out the black/blue lead. I did, however find this diagram.

I will keep updated on progress.


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

According to this diagram, the Black/Blue wire is the lead #6 and is connected to the MFI relay control... I would assume that this is the wire that controls the active state of the relay... 

What would cause the MFI to turn the relay off while running?


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

I am starting to decipher what the relay is for. There are two coil windings inside the relay and one controls power to the MFI the other controls power to the fuel pump.

I am in the process of testing the relay now.


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## Wrench97 (May 10, 2008)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

If not grounded it should not be running, I too think someone added the switch as a anti-thief device, what happens if you simply disconnect the switch?
It could be the switch has enough resistance across it to hold the relay closed, especially if it's the type with a pilot light in it?


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

With the switch disconnected the car will run, but will eventually stall out and not run, then the ground will need to be connected to activate the relay.

I initially thought the same thing about anti-theft, but the wire running to the MFI relay control is still connected, the extra ground is just spliced in.


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

The relay tests fine. Both windings are working properly and the volages are even across the leads.

I have to assume that the issue lies somewhere else.


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## octaneman (May 13, 2009)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*



gavinzach said:


> According to this diagram, the Black/Blue wire is the lead #6 and is connected to the MFI relay control... I would assume that this is the wire that controls the active state of the relay...
> 
> What would cause the MFI to turn the relay off while running?



Gav,


From what I see on the diagram the coil on the L3 is connected to the transistor on pin 8, the transistor switches on when the ignition switch is in the run position. If the engine dies for whatever reason, the S2 will click off and the diode will prevent any kickback voltage when the relay shuts off. The L2 coil will switch the relay on only if the neutral safety switch is either in park or neutral.


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

I'm sorry... I meant lead #8 not 6...

My buddy and I usually work well together when troubleshooting... He usually goes one way and I go the other way then we meet in the middle and find the problem. It's kind of nice... but, when it comes to electical, he just muddles my thoughts.

I think that this is actually two issues...

When we first went over to his sisters to pick up the car, it would run for a moment then sputter and shut down. I noticed that the IAC was making some nasty noises, so we disconnected it and after a little sputtering, ran fine, albeit at 1500RPM idle.

It wasn't until we got it back to his place that he noticed the switch and started playing with it. The car just quit... no sputters.

After testing the relay, we reinstalled it (I kept the added ground circuit open) and the car ran relatively well. Idle was a little rough (the IAC was reconnected) but didn't have any issues. Drove it around for about 15 minutes... When we got back, I closed the circuit and the car continued to run until I opened it again, then it quit.

After that, the car would not start or run unless the ground was closed. I think that the added ground is causing an issue with the ECU. 

Sorry about the confusion with the leads. I understand what you are saying with lead 8 (which is grounded anyhow), but the added ground circuit is spliced into lead 6 which goes to the ECU.


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## octaneman (May 13, 2009)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

From my understanding the switch is connected after the relay. 

Need to know 3 things: 

1)Where is the switch getting power from ?

2)Is it a 2 prong or 3 prong switch ? If 3 prongs is the ground pin connected to the chassis ?

3)Have you tested the switch from open short to ground ?


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

The switch is not getting power (tested with multimeter).

The switch is 3-prong, a simple open/closed circuit with an LED indicator that is not connected.

The switch is connected directly to ground.


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## octaneman (May 13, 2009)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

Gav, 

Your switch is not connected properly, the ground pin on a 3 prong switch has to be connected to the chassis not to a wire ground. The other pins are power in after the fuse and power out.


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

The switch shouldn't be there at all. It was added by the previous owner for reasons unknown.

One end of the lead is spliced into the Black/Blue wire (lead #8) between the ECU and the relay. The other end is grounded to chassis. The switch is a simple open/close.


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## Wrench97 (May 10, 2008)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

If the ground to the chassis appears to be original wiring I would just eliminate the switch and splice the wires together.


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*



wrench97 said:


> If the ground to the chassis appears to be original wiring I would just eliminate the switch and splice the wires together.


No, the chassis ground is not original. The black/blue wire is part of the harness taht connects to the relay. the entire switch/ground is spliced into it right before it enters the loom.

According to the electrical diagram, it connects to the ECU. I would assume that the ECU is supposed to control that relay (R1).


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## Wrench97 (May 10, 2008)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

That's sounds correct, the ECU would supply the ground to control the relay, so I take it the switch does not interrupt the circuit but when turned on supplies an additional ground to the circuit? 

We'll need to find out under what conditions the ECU would interrupt the circuit, I.E. no oil pressure, collision, or it may simply be a bad connection between the harness and ECU.

With the switch off does the check engine light come on as it shuts down? Are there any codes stored in the ECM?


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

That seems right. It bypasses the ECU and grounds the relay, causing it to close which supplies power to the the ECU and various sensors according to the wiring diagram.

I am assuming that tripping that ground causes a fault in the ECU, effectively breaking it's control of the relay, which causes the engine to cut.

Unfortunately the car is pre-OBDII so my scanner will not work. There, however is no indication of the check-engine light either.


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## Wrench97 (May 10, 2008)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

It should be supplying the ground to the relay from the ECU not the relay to the ECU.
Closing the switch simply grounds the relay and runs the pump.

Back the Check light, does it light up with the key on engine not running, and go off after starting?


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

Yes, it does supply ground to the relay... but in one of my observations, the vehicle was running fine until the switch was closed, completing the ground circuit. Once that ocurred, the engine would not run (nor start) with the switch in the off position after that. This also is not the relay that controls the fuel pump. That is R2 and is actuated with the ignition switch. The second relay seems to control power to part of the ECU and some of the sensors. Both relay switches are completely independent of each other, which surprises me that they are in the same housing.

I believe that this may be one of the most over-engineered systems I have seen...

Unfortunately the car is at Keith's house up in the Poconos, so I can't check myself, I will have to ask him. He was the one behind the dash, I was under it :grin:.


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## octaneman (May 13, 2009)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

If you jump the pins on the ALDL connector does the fuel pump run ?


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

Unknown. Which pins should be jumped? I can send a text to Keith and have him try.

AFAIK, the fuel pump portion of the relay functions without issue.


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## octaneman (May 13, 2009)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

Is the ALDL like this ?


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

The funny thing is, Keith sent me a photo of the ALDL quite some time back and I had forgotten to post it... I just deleted my message inbox the other day!

Well, the last few months have been rough for Keith, lot's of health issues and I haven't had the time to get up there and help him with the car until yesterday.

My observations... 

I removed the switch before connecting the battery.

Car started on the first try. Keith told me the IAC was disconnected.
Connected the IAC, car started up right away and ran fine until I shut it down.
After shutting it down, I noticed noises coming from the area of the IAC. (ignition OFF)
Disconnected the battery and reconnected it, no noise from the IAC. 
Vehicle started immediately again and when turned off, noise coming from IAC.

The IAC will be the first thing being replaced once we get a chance to get out.


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## Wrench97 (May 10, 2008)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

Idle Air Control?

That just opens and closes an orifice to control idle speed.


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

Right, and on this car it seems to be electronically controlled... There is definitely a buzzing sound emanating from the IAC. I verified this by disconnecting it...


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## Wrench97 (May 10, 2008)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

It is, the electric motor is controlled by the ECM to open or close the size of the orifice, for example in the summer when the A/C compressor cycles on and off the IAC keeps the engine at a constant idle speed despite the varying load.

I've seen some that will run a few seconds after the engine is shut off but no longer then that, often a good cleaning with carb cleaner will straighten them out, if it continues to run longer then that look more to a control issue then the IAC itself.


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

I am pretty sure the valve is shot... shouldn't be making that much noise. As for how long it runs after the engine is shut down... I think that it has to do with the relay in question...


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## Wrench97 (May 10, 2008)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

It may, but the ECM should know from the engine speed sensor it's no longer running an stop commanding the IAC.


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## GZ (Jan 31, 2010)

*Re: Troubleshooting electrical problem 1992 Eclipse 2.0 DOHC*

I know it's been a while but I figure an update is in order.

The IAC was definitely bad. The motor was buzzing like crazy.

After a whole bunch of confusion, multiple trips to the scrapyard, a bunch of research and some argument, (Keith thought the TCU was the ECU...) we finally got the ECU issue sorted.

Apparently there is a high occurrence of failing capacitors amongst other issues with the ECU in that car. When I opened the ECU to check it out there was a load of corrosion along the riser PCBs and on the contacts of all the ICs and other components... Apparently the switched ground wire was the last owner's idea of a workaround. That hack and the corrosion is likely what led to the IACs failure. Of course, the IAC is another common problem in those models... Keith replaced it with the updated version and replaced the ECU with one he found on eBay and the car is running well, albeit a slightly high idle.

In case anyone needs to differentiate between the ECU (engine control unit) and the TCU (transmission control unit) the ECU is mounted in the center console directly behind the stereo/climate controls. The TCU is mounted on the floor behind the center console, closest to the firewall. 

Thanks for all of your help and insight once again!


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## GZ (Jan 31, 2010)

Update... The idle situation is now under control.

Keith had replaced the ISC (formerly referred to the IAC) due to the noises it was making. Since he replaced it, he didn't think to check it. We spent the last few hours checking system after system... Finally I pulled the ISC to test it and it was not functioning.

Long story short... The old IAC tested good, so we put it back in... Idle is fine now. The buzzing was likely due to bad voltage from the ECU.


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## Wrench97 (May 10, 2008)

Good to hear it's sorted out, and I take it everyone is still living


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## GZ (Jan 31, 2010)

:lol: Yeah... as far as I can tell at least!


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