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Old 04-26-2010, 01:18 AM   #1
Cameroonski
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Default Crazy Electrical issue with EFI system

My car was running great untill it decided not to start. It cranks just fine but the fuel pump isn't getting power. It has done this before- last time it randomly didn't work and an hour later it did. One time it happened I think and I replaced the power main relay and it fixed it(but i dont think these are even on the same circuit). But this time I am very confused.

I could not figure out why the EFI main relay wasn't clicking. I was getting power to it from the fuse, but not to the resistor side (my memory is being tested here so i apologize for errors). I go back to it a day later, try it, and the relay clicks... but the EFI fuse was blown(what!?). I replaced the fuse and the car still was running fine. I clean up, and thirty minutes later it didn't work again(crank, but still no power to B+ on the diagnostic grid by the junction box).

I made sure the ground from the EFI relay was good... and the circuit opening relay seems to be working. The only other thing going into that relay (besides power from the fuse through to the circuit opening relay... i think) is M-REL from the computer through the resistor to ground. So is my problem the computer? I know it isnt the relay... ive tested about six of them with the horn(cuz it uses the same relay) and the fuse is good (now) and the ground is good. AND, i replaced the junction box with another one. So... wth? (also.. if i run power to... what i think would be the resistor side of the relay terminal (memory is hazy) it works, but when the car is running with this rigged up it idles weird and gives codes for either RPM pulse or Air Flow Meter or something like that.)

Any help would be great. thanks.
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Old 04-26-2010, 04:15 PM   #2
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have you tried the fp & b+ jumper trick in the diag. box yet? (check tsrm to make sure my memory's not lying on those terminals to jumper before you connect anything 'cause I ain't exactly on form today!!!).

This should result in the fuel pump running permanently with the ign. on & IIRC bypasses the relays & fuses. If the car's then running but rough & with seemingly random codes as you described then it could possibly be the ECU or it's connections/earthing, I'd check/double check/replace the cheap stuff first though as you've started doing, maybe even swap the fuse again in case it looks fine but is duff, I've had 'em like that before. (if it is gone again maybe check how much current the pump is drawing too?) and only spend on an ECU after you've exhausted every other route.
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Old 04-27-2010, 12:25 AM   #3
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Yes that was the first thing I checked was the jump between B and Fp. But there isn't power to B in the diagnostic box... so this is what i did today.

I checked power at BATT on the computer, it has 12v. I checked M-REL, it had .08v when it should have 12 (with ignition on). So I ran a long line for the BATT line from the computer to the correct wire on the junction box... making sure EVERTHING else was right... power to relay, to BATT, good ground, whatever was going through that relay i made sure was good. It wasnt working and still no power to M-REL with BATT hooked up like this... so the problem must be M-REL i think.

When i jump power to the side of the relay that goes through the resistor (M-REL side) the car runs and drives but idles up and down and crazy. It actually didnt drive too bad though. I basically hooked a hot wire straight up to the M-REL side of the relay b/c that was what the computer was not doing correctly... i think. so... ECU? I have the privilege of a parts car with a good ECU, it is just a bit of a drive to get there, so i cant exactly just switch them out right now, mabe by the weekend.

Any input? Thanks!
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Old 04-28-2010, 02:06 AM   #4
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+B and +B1 are not the same circuit as BATT.
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Old 04-29-2010, 12:51 AM   #5
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Quote:
Originally Posted by cre View Post
+B and +B1 are not the same circuit as BATT.
The diagram says that BATT breaks off in between the fuse and the relay and goes to the computer. I was checking anything that had anything to do with that relay.
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Old 04-29-2010, 02:06 AM   #6
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Quote:
Originally Posted by Cameroonski View Post
there isn't power to B in the diagnostic box...
This is why I mentioned it.
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Old 04-29-2010, 02:26 AM   #7
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Okay, sorry... I looked back over what you're doing and see what you're doing... powering +B and +1B from the BATT line. IMO it would be better to bypass the relay directly than to introduce power from a line which is already running all over the place (noise) and may be suspect itself.


Oh, and the circuit opening relay which powers the fuel pump is switched by the main EFI relay AND the ECU has an emergency shutoff should it believe there is no air flow... so ECU and main EFI relay are both possibilities for no power to the fuel pump. The relay is more likely unless you've had a blown heater core steam the innards of the ECU.
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Last edited by cre; 04-29-2010 at 02:31 AM.
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Old 04-30-2010, 01:45 AM   #8
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I switched out the ECU and the ignition switch today and still no luck. All my relays are good, they have been tested and switched and juggled and they work. My problem is this...

M-REL only has .08 volts at the computer, as well as at the EFI main relay with the ignition on. When I apply voltage to the computer side of the the resistor side of the relay, it works and the car turns on but with funky idle issues.

What i will do tomorow is do this bypass and see if im getting voltage at M-REL... i think. If i am, I know the wire is good, if not there is another problem somewhere else and im SOL.

Cre, thanks. Any other advice? I am totally confused here...
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Old 04-30-2010, 11:11 PM   #9
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Here's the update...

The Check Engine light was not coming on with the ignition on. It DOES come on when terminal W is connected to E1 (computer ground) as well as a body ground. The computer ground into the engine block is good.

I'm also getting these voltages...

BATT has 12v
M-REL still has about .08v
IG S/W had about 1.23v
+B is not getting anything

Also, on the Diagnostic Box...

From +B and the battery i have 12v, and from Fp and the batter i have 12v, but both to the same side of the battery and when i test it in between them it is 0v. Im not sure if this means anything...

All of this seems like the ECU is funky, but i have tried two different ECUs, and i find it highly unlikely that the same odd problem would lie in both. So short circuit somewhere maybe?

Please i need some help..
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Old 08-13-2022, 12:22 PM   #10
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What was the problem here? I have exact thesame issue! who can help me bringing my fully rebuild 88' back on the road again?
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