Can't solve this no CEL issue!!!

[SeeUSmile]

Can't wrap my head around this. I have an 89 gt limited and the engine-light won't appear.

The only time it lights on is whenever I disconnect;
-EFI fuse
-EFI, Main
-Ign fuse.

As soon as I put them back on, cel turns off and back to square one again.

I grounded W terminal on ecu side and cel lit up. Checked continuity for E1 from ecu pin, M1, afm and manifold ground and they all checked out. Got the same result from another test ECU although it suddenly fried itself shortly after leaving it connected for unexplained reasons. Car originally had a jdm ecu and the one i tested on it was non jdm grey plug. :/

 

[jetjock]

Since removing those fuses should *prevent* the MIL from coming on it appears your wiring may be fubar. That said check the 5 volts (Vc) at any of the sensors. Or try unplugging them all. A Vc short to ground will paralyze the ECU.

 

[Rollus]

Does the CEL light up after starting, while car is running?

 

[SeeUSmile]

Thanks for the reply guys appreciate it.

No cel light at all running/not running rollus.

Thanks for the help Jetjock. I went and checked VC between E2 and ground at AFM plug and TPS plug, and I get 5V with ign-switch on, also checked continuity between VC and ground incase there was a short and so far nothing, double checked voltages with ignition switch off incase there was something playing up with the wiring on that end.. Unplugged tps, afm and VC @ 16pin ECU plug all together and still no engine light.

Engine light switches back on whenever I disconnect the 22 pin ecu plug as long as 32P plug is still connected, also disconnected ecu completely to see if it didn't magically stay on. To which it didn't.

The car still turns on and seems to drive fine, minus the exhaust leak.

 

[SeeUSmile]

Just wanted to clarify this procedure

At first I think I was doing it wrong, I was grounding from the engine check light wire-side instead of the ecu since they use the same color wire at the m1 plug and cel lit up as expected.

but when I tried to ground Ecu side it just sparked and efi fuse popped.

I'm a bit puzzled, is the W terminal like a power to ground switch for CEL? assuming gauge is a supply wire? Was reading in the tsrm troubleshoot that with the engine running there should be voltage between W-E1. Because atm with just ign-switch on without the engine running, it's reading 12 volts to ground.

Edit* Now that I think about it. I believe it would come down to wiring now that you mentioned it JJ.

Gonna look at the wiring see what's making the cel go on with those fuses disconnected since I was looking at the wrong place for the problem initially.

 

[SeeUSmile]

Update. Ok some retarded magical miracle just happened. Went to investigate what happens to W terminal when I disconnect either of the ign fuse, efi or efi main.

First thing being efi fuse, W had no voltage came up as 0.L/infinity? although this time, Cel was off instead of being on during the first issue. Connected efi fuse back on and cel went back on, thought this was too good to be true so I jumped te1 and e1 and it's flashing trouble codes! only came up with code 51 maybe tps gone bad or tps wiring who knows but will dig into that some other time.

So yay, suddenly by fluke it's fixed but at the same time i'm pissed cause now I don't know what I did that fixed it and whether it's permanent or not. Perhaps it's was when I was jiggling the wires while trying to diagnose the issue when backtracking it or something else I missed. The areas I've been working around was just placing with the fuse box, ecu and wiring around that area.

Closest verdict I believe would be the wiring as you pointed out JJ. :bowdown:

fingers crossed it doesn't play up again when I put everything back together again.

Thanks all!

 

[jetjock]

Huh. That's powerful queer alright. Since you didn't mention in the first post the engine runs the advice about Vc was unnecessary. Second, externally checking the W circuit does involve grounding the engine side of the harness. As you can see by the schematic the MIL has 5 vdc on one side and the ECU supplies ground to illuminate it.

Based on the light being on when the IGN fuse is out it definitely sounds like wiring though. If it were me I'd want the issue to come back so as to fix it properly. If it does, try taking the opposite approach: rather than troubleshoot why the MIL won't come on, focus on why it's on when it shouldn't be.

 

[hvyman]

What happens when you ground te1?

Ecu controls ground to w when te1 is ground or when a certain codes are set.

 

[Nick M]

I thought he wired it like an old school battery discharge light.

 

[SeeUSmile]

Huh. That's powerful queer alright. Since you didn't mention in the first post the engine runs the advice about Vc was unnecessary. Second, externally checking the W circuit does involve grounding the engine side of the harness. As you can see by the schematic the MIL has 5 vdc on one side and the ECU supplies ground to illuminate it.

Based on the light being on when the IGN fuse is out it definitely sounds like wiring though. If it were me I'd want the issue to come back so as to fix it properly. If it does, try taking the opposite approach: rather than troubleshoot why the MIL won't come on, focus on why it's on when it shouldn't be.

Yes will definitely look into it. Was actually about to do it but then it fixed itself before I could >_<.

What happens when you ground te1?

Ecu controls ground to w when te1 is ground or when a certain codes are set.

Hmmm i haven't tried doing that approach. I only grounded it to E1 which did nothing at the time.

 

[hvyman]

Grounding te1 to e1 is just grounding te1. What happens when you do that?

 

[SeeUSmile]

:S not sure where you're going with this? Not sure if you meant grounding te1 to body instead of ecu ground on your previous post.

Jumping the diagnostic pins didn't make any difference to the cel appearing during that time with ign-switch on.

But everything is working normally now ever since that fluke fix.