Plug and service manual question

287 Views 13 Replies 3 Participants Last post by BigMak, 13 d ago

BigMak

Discussion Starter · 13 d ago

Hopefully two easy questions. Car info below.
Firstly, what is this plug for? It is located just off the ecu harness.
Secondly in my trouble shooting I am following the manual and I do not understand what it means by check for a short circuit or short to ground. My take on it is, check to make sure the wire has continuity (i.e., between A8-108); then make sure there is no continuity between that wire and the ground.
1996 SL body
1991 vr4 engine & harness
1991 Chrome ecu

Thanks

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VR Thor

· #2 · 13 d ago

Haven't dug around in my console for awhile, but the only sensor I remember like that hanging by the ECU is the O2 sensor wire harness.

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mydecember1985

· #3 · 13 d ago (Edited)

At first glance, I thought it was the cruise control or active aero switch connectors that live in the ashtray area below the radio, but it looks like that is not the case. There's also the cruise control and anti-theft relays in that area, but they have the big prong connectors.
You've got me stumped, but I think Thor is onto something according to the manual. For the Non-"Trubo" models

And the wire coloring looks correct

1-2-3-4 would be W-B-R-B

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mydecember1985

· #4 · 13 d ago

BigMak said:
Secondly in my trouble shooting I am following the manual and I do not understand what it means by check for a short circuit or short to ground. My take on it is, check to make sure the wire has continuity (i.e., between A8-108); then make sure there is no continuity between that wire and the ground.

Correct. You are disconnecting both the ECU harness and whatever control relay you are testing. There should be continuity between pin A8 on the control side and 108 on the ECU harness. You'll need to either back-probe or insert a pin. Same goes for A4 to 12 and 25 on the disconnected ECU harness.
If continuity fails, you may have a break in the wire or it is pinched/shorting.

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BigMak

Discussion Starter · #5 · 13 d ago

Thanks for the replies. The o2 sensor would make sense, since I am going turbo do I need to worry about that connector?

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VR Thor

· #6 · 13 d ago

BigMak said:
Thanks for the replies. The o2 sensor would make sense, since I am going turbo do I need to worry about that connector?

Considering you are running a Chrome ECU, probably not. But the other O2 sensors are probably going to make a difference.

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BigMak

Discussion Starter · #7 · 13 d ago

Sounds good. I have not gotten to wiring in the o2's yet but its on the list to do. Right now I'm trying to figure out why I have no spark.

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mydecember1985

· #8 · 13 d ago

BigMak said:
Sounds good. I have not gotten to wiring in the o2's yet but its on the list to do. Right now I'm trying to figure out why I have no spark.

Is your CAS hooked up on the rear head? I would start with those connections. I find that is the easiest way to disable fuel/spark on these cars. Unhooking that and no more ⚡

Stealth 316 - 3S Ignition System (DOHC)

Stealth 316 - CAS Replacement - DOHC 1991-1992

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BigMak

Discussion Starter · #9 · 13 d ago

Yes I have double checked the CAS, and tried a verified used one as well and no change. But I'll take another look at the wires and connector.

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mydecember1985

· #10 · 13 d ago

Hopefully someone more versed in the ECU logic can chime in, but also check your PTU connections again.

This details how to inspect the PTU:
Stealth 316 - Power Transistor Unit

Outside of CAS, PTU, and good coils, checking your grounds are my basic troubleshooting skills. Harness transplants are too much for me. But your car is turning over, so the block must be well-grounded enough to do that.

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VR Thor

· #11 · 13 d ago

Typically the Chrome ECUs are not known to fail (to my knowledge I believe they are just converted newer ECUs, so I'm assuming some refurbishing has been done / newer ECUs lack the failure rate of older models.) However, it's not out of the question.

I'd suggest with the simple things first like ensuring all plugs and wires are well, and move down the line from there.

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BigMak

Discussion Starter · #12 · 13 d ago

It has been quite the process trying to figure it out, I know I'm getting close. But on the bright side, I went from fearing automotive wiring to kinda figuring it out and using the manual to trouble shoot instead of the parts cannon.

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mydecember1985

· #13 · 13 d ago

VR Thor said:
Typically the Chrome ECUs are not known to fail

What is someone has a bad IACV that they transplanted from another engine not knowing it was internally shorted?

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BigMak

Discussion Starter · #14 · 13 d ago

I have a new one of those, not oem. I kind of remember testing it a couple months ago before I took a break for the winter.

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