I know there are several well writen articles on properly grounding the ECU, unfortunatly I'm picking up a project which is full of wireing gremlins from the prior owner, I'm not sure what's stock and what isn't any more.
SO... I'm regrounding the electrical system, and I'm up to the ECU. Pulled the floor cover and found a nice little rats nest highlighted w/ Duct-tape...


Question one:
In my gallery I've posted six photos of my find. I think I can figure out most of the re-wireing by gauge / color markings, but one of the wires has me courious if it's stock or a bizzar addon.

This gray cable has the center wire properly set into one of the connectors w/o spliceing, but it had a sheild wire which is conected to one of the black/red wires in the primary harness.

Secound question:
I was planning on running two ground wires back to the engine, but not using the location under the UIM. Is there any reason NOT to ground to a different location on the block that is easier to get to w/o disasembly?

 

The grey cable with the black center conductor is the 02 sensor output wire to the ECU. The shield is for obvious reasons.

Also look at the series four wiring diagrams and you will see the shield symbol on the 02 sensor wire.

 

That makes sense! Thanks. I just sat down to pull out the service manual to see what pin that gray cable was connected to. I will assume the ground cable that it's connected to is stock. I'm going to tape that one up and move onto the next three cut grounds.

 

The two black wires are ECU gnds wires coming from 3A, 3G and 2R and the gnd wires terminate on top of the engines rear rotor housing (can only be seen if the upper intake manifold/throttle body is removed. That gnd wire is also tied to the black wire of the two wire Fuel Pump Circuit Terminal (Yellow two wire fuel pump check connector in the engine bay).

See the 88 wiring page 50-31 and the left side of that page.

 

buy an uncut wiring harness, it's an s4 n/a

 

I knew about 3A and G from the grounding write up and was going to re-run those two grounds. I had not seen 2R in the write ups as needing to be re-run. But easy enough.

Right, and thus my 2nd sudo-question, would there be any reason not to run the redundant grounds to a different location on the block? (somewhere easily accessable)

Is it worth while to re-gound these connectors seperately?

Thanks for pointing that out!
-=BOFHmike=-

 

I'm actually looking to buy an '88 gxl as a parts car. The one I found isn't running at all, and is priced right for the odds and ends I need to complete my '87. This harness should be the same.

 

Keep in mind that if your car is any early '87, you'll have a resistor pack & low impedance injectors. Late '87s and all '88s will use high impedance injectors and have interchangeable harnesses.

 

Thanks for pointing out the injector differance. Fortunatly, the majority of the parts I need are trim level so I'll be ok. But the harnesses are a bit of a concern.

 

Right, and thus my 2nd sudo-question, would there be any reason not to run the redundant grounds to a different location on the block? (somewhere easily accessable)

Some people like me go to that wire splice where the three black and shield are and solder a new wire to them. Then gnd the new wire to a known ground point. I used one of the studs that hold the bracket for the ECU to the body. It cured my 3800 hesitation. Worked for me and several other people like NZConvertibe. Did not work for other though. Usually only needed to be done on series four, not series five.

 

I'm not having hesitation issues at this point in time, my problem is lack of sustainable low idle. I had between 2 and 45mV between negative post and random body and block location I tested. I've since pulled/cleaned/replaced the ground points on the driver side strut-tower, the one bellow the traling coil, and the one from the firewall to the trany. The ECU just happens to be the next item on my list to work on. I'm going to clean up the wireing mess I found, but use your idea of adding a ground point at the ECU from the three lines plus the sheild wire, as well, I'm going to run another ground line from the ECU grounds to the engine block. Perhaps overkill, but it can't hurt.

 

Update - Damn, I should have done the grounds sooner!!!! Amazing! Idel problem nearly gone! I seperated the rats nest at the ECU and used some 12G stranded wire w/ crimped eyes to ground each of the three ground leads plus the O2 sheild. She idled like a champ for over 40 min.
Amazingly now my TPS, when adjusted using the lamp method, was nearly dead on w/ voltage. I have it sitting at .995V My hand isn't steady enough to hit 1.0