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Old 01-20-2010, 10:46 AM   #21
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Anyone know where exactly the ECU gets its power?
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Old 01-20-2010, 11:09 AM   #22
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Originally Posted by MartinezA92 View Post
Anyone know where exactly the ECU gets its power?
Stock 92 ECU yes?

10A Room Fuse feeds Pin 1A - constant
Ign feeds 1V - startup (neutral or clutch switch)
Main Relay feeds 1B - ign on
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Old 01-20-2010, 01:01 PM   #23
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Originally Posted by BarbyCar View Post
Stock 92 ECU yes?

10A Room Fuse feeds Pin 1A - constant
Ign feeds 1V - startup (neutral or clutch switch)
Main Relay feeds 1B - ign on
So testing at 1V would eliminate the ign SWITCH, correct?
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Old 01-20-2010, 04:52 PM   #24
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So testing at 1V would eliminate the ign SWITCH, correct?
No, It would eliminate only the switch during start up and only IGN2.

To test the switch: With IGN turned on, check for +12V at the Black/Red and Blue wires from the switch (or check for +12V at the 30A Heater and 15A Engine fuses. (Note that there are two switches inside the ign switch, IGN1 and IGN2. Main relay coil is fed from IGN1.)
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Old 01-20-2010, 11:02 PM   #25
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Main Relay is working so I'm ruling that out.
Got home from school, put the key in, plugged the harness in, and my CEL was on. Steady. Cranked it and....it started. Misfired like hell for a little bit then after some nudging and caressing it ran fine. Then after a minute of messing with wires under the hood trying to see if it shut off...We touched the AFM plug and it died. Instantly. I don't think the fact that we touched the AFM has anything to do with it though, just coincidence...AFM isn't anywhere on the wiring diagram for the ECU...

CEL is back off, ECU still not working...
I'm chasing gremlins, FML.
Though it seems like I eliminated variables, my no spark is not related to faulty components like ignitor/coilpacks/etc.
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Old 01-20-2010, 11:13 PM   #26
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Not to sound like a broken record but, CAS. If you can get your hands on one you can swap it in about 5 mins. My car did all kinds of weird **** when mine went, twice.
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Old 01-20-2010, 11:23 PM   #27
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If someone can prove to me that a bad CAS will cause the ECU to not function, I'll beleive you. I have a wiring diagram and a bad CAS does not make sense to me, especially since the car was running today.
Guess I'll try it but I'm really not expecting anything to change.
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Old 01-21-2010, 12:22 AM   #28
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If the CAS or AFM is shorted to ground internally then the ECU will do all kinds of crazy things.
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Old 01-21-2010, 12:25 AM   #29
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If the CAS or AFM is shorted to ground internally then the ECU will do all kinds of crazy things.
Now you're starting to make sense. AFM. I got the car running and when I touched the AFM the car died. Now, couldn't I eliminate these by unplugging them and seeing if the CEL turns on?
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Old 01-21-2010, 01:01 AM   #30
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Wow.
Unplugged AFM. Consistent CEL. Plugged in a spare I have that has been tuned for SM or something like that, and CEL is still on. Kinda hard to get running at all, but this has narrowed it down. I still don't understand how the AFM is doing this though, I've been staring at the diagram and I don't get it.
EDIT: No tach signal, and car won't stay running. =/
From what I see on this diagram, the only thing that sends a tach signal is the igniter. Correct me if I'm wrong?

Last edited by MartinezA92; 01-21-2010 at 01:36 AM.
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Old 01-21-2010, 09:05 AM   #31
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Originally Posted by Joe Perez View Post
The fuel pump isn't driven by the ECU at all on the '90-'93 cars- the relay is wired to the AFM and to the starter.

Was searching for my problem, hope this is it? Installing a MSPNP with MAP and got rid of the AFM, go when I got to check if I have any fuel leaks (after putting 430cc injector and a 255L pump in) my pump isn't coming on. Jumped the diagnostic pins and the pump came on just fine. I thought about the AFM and plugged it in but also no pump, mind you this is with the key "on" postiion, no cranking. Anyway, what else is there that's keeping my pump from coming on? I have a '91.
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Old 01-21-2010, 09:52 AM   #32
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The pump doesn't come on unless you ground it at the diagnostic box, or you're cranking. Ground it when the key is in the on position. Just having the key in the on position does nothing.

Last edited by MartinezA92; 01-21-2010 at 10:48 AM.
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Old 01-21-2010, 01:19 PM   #33
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Wow.
Unplugged AFM. Consistent CEL. Plugged in a spare I have that has been tuned for SM or something like that, and CEL is still on. Kinda hard to get running at all, but this has narrowed it down. I still don't understand how the AFM is doing this though, I've been staring at the diagram and I don't get it.
Don't you have to clear the CEL manually (on my 2000, I do).

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EDIT: No tach signal, and car won't stay running. =/
From what I see on this diagram, the only thing that sends a tach signal is the igniter. Correct me if I'm wrong?
The tach gets power from the 10A Meter fuse. It shares common grounds with Fuel, Water and Oil Pressure gauges. It gets its signal, as you say, from the igniter.

I've got the circuit laid out in front of me. It looks like Igniter, CAS, AFM or Circuit Opening Relay (Fuel Pump Relay) or a combination of any of these will be your problem.

Last edited by BarbyCar; 01-21-2010 at 02:02 PM.
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Old 01-21-2010, 05:05 PM   #34
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Don't you have to clear the CEL manually (on my 2000, I do).


The tach gets power from the 10A Meter fuse. It shares common grounds with Fuel, Water and Oil Pressure gauges. It gets its signal, as you say, from the igniter.

I've got the circuit laid out in front of me. It looks like Igniter, CAS, AFM or Circuit Opening Relay (Fuel Pump Relay) or a combination of any of these will be your problem.
Yes, in this case having a CEL is a good thing, it means my ECU is operational.
I'm picking up an igniter later today from a parts car, an AFM I'm pretty sure has absolutely nothing to do with a tach signal? Also picking up a CAS, so I'm going to eliminate a bunch of variables at once.
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Old 01-21-2010, 05:57 PM   #35
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an AFM I'm pretty sure has absolutely nothing to do with a tach signal?
I would like to agree except

1) That there is a switch in the AFM connected to one of the coils in the Circuit Opening relay, the other side of which is connected to the Main Relay, CAS, Purge Solenoid, ISC Solenoid and ECU Pin 1B (ie switched ECU +12V).

2) The AFM is connected directly to the ECU.

If any of these are affecting the ECU then the igniter, which is connected to the ECU, and hence tach signal may be affected.

I'm not saying it is the problem, just don't rule it out because it isn't directly connected.
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Old 01-21-2010, 07:07 PM   #36
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Well...getting spare AFM, coil packs, igniter and CAS. Gonna see what happens. **** this.
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Old 01-22-2010, 11:17 PM   #37
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Just as an end to this thread, the problem was a combination of the AFM and igniter going bad. I guess the AFM was internally shorting and unplugging it caused the ECU to turn back on. The lack of a tach signal was the igniter going bad, thats the only thing that feeds the signal to the tach from what I can understand on this wiring diagram.
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Old 01-23-2010, 11:05 AM   #38
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Glad you got it sorted. Well Done.

Gary
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