I jsut had my 1991 start dying intermittantly, and it was traced to a faulty wire in a junction box under the battery. After fixing the wire, it appears that there is now 12V going into the ECM, but only 10.5-11 coming out.

Anyone seen anything like this? Am I stuck with a new ECM?

Thanks in advance!

 

hm. Thats interesting. I wonder if your charging system is up to snuff.

 

Andy,

Is there a rational way to go about checking the harness? Do you know of any references that might help? I'm electronic, not electrical - until I got the 1985, I hadn't used a multimeter since 1989.

 

Sadly, John, the only tool is your eyes.

Check all the ends on connectors. If you start to get errors revolving around things like ground faults and the like, you will then want to pull out the multimeter.

There is no curtainty that this WILL happen, it just can. A lot of these cars might be just fine, but those that have more miles, questionable service histories and a lifetime in hot climates are more susceptable. I have seen some mid 80s harness that look perfect, others, look like hell.

What I can't see - and none of us can - is what is happening behind the convolute. Those wires are insulated - and the heat is stored in there. Add in friction, and all hell can break loose.

This sounds trite, but the best you can do is monitor things. Once the glitch begins, hook up a scan tool and see what it says. Also, a DDM is a great way of testing the circuit. A test light is a huge help, too!

A Helms Manual is the more important tool you can buy! Without that, everything else is a waste of time.

 

Check this out.

My stupid little (free) white car was running badly, you'll remember the catalytic converter came apart recently and plugged the exhaust.

The backpressure spiderwebbed and caused a myriad of new problems, the first of which, the MAP sensor has a small filter so that fuel does not find it's way in there. The backpressure had flipped a diaphram in the filter and the MAP sensor no longer got any input. After a few hours I found that, blew into it the right way, and the car ran great.

Then the (small) inlet(intake) manifold leak that started when the ceramic decattified grew into a much bigger leak and was dousing all sorts of things in flammable liquid. I changed the inlet manifold gasket, and voila, the car ran great.

Recently the car would just die for no reason and didn't really seem to have much throttle responce. I removed the (one month old) spark plugs and they were all coked to hell. One, on a test, actually prefered to jump the dielectic(ceramic white deal) instead of the gap about 3 out of 5 times. I changed the plugs, thinking that maybe the cat-plug had caused it. The car didn't run any better.

Just to check the dryness of the newly deleaked inlet manifold, I took the air filter assembly(about the size of the 1.392L engine) and noticed quite a bit of exposed copper on the potentiometer (Throttle Position Sensor) and the the wires were twisted together quite nicely. I touched the insulation, and it dissintegrated in my fingers. The fuel had slowly been eating that particular wire assembly...none of the other wires were effected, but then again, none of the other parts on my imported Ford say, "Made in the UK" (The home of the positive earth). So, instead of buying a new one...only £60($110), I cleaned it up really good, cleaning off all of the burned carbon(a definite sign that there was shorting) I wrapped first the wires in aviation quality F4 tape, and then the whole assemblage.

Car runs great, drove it 440 miles this weekend, and no worries at all.

 

That's not a fair comparison... You are dealing with a British car!

 

Bogus......Any chance you can get me a complete (even used) harness off a vette ??? If so I can make the new ones. I'm making conversion harnesses for the overhead consoles in the S10 trucks & I have damn near all the GM tools needed to make just about any connection. Also I have access to GM connectors, approved wiring, etc......

Just a thought. I wouldn't mind doing one just to see how hard it'd be but I'd need a harness to follow or one hell of a wiring schematic.

 

I can't touch a connector on my 84 without replacing it!

 

That would be way cool... if I had a spare harness.

I wonder how much one would cost, used???

 

and thanks for this heads up!

But I may be confused, which wouldn't be unusual!

Are we saying here that wire harnesses pre 1990/91 are suspect? Is this true for vettes only or all cars?

I have an 82 Camaro which so far doesn't have any problems, should I be concerned?

The wiring in my 88 vette with over 120,000 miles seems to be holding up just fine. Even the vacuum hoses and fitings are doing just fine. Am I the exceptiion?

Thanks for your valuable input

Jack

 

All cars are suspect to this problem, or at least all GM cars.

it's hit and miss, really...

Glad I could help!!!

 

 

I just noticed tonite that this post has 4200+ views!!! That is GREAT!!!!!!

I am glad the word is getting out!!!

 

Bringing it back.

Has anyone heard anything new about this? Is there a GOOD replacement harness. Like if I was to order one, would it be NOS or a repo using newer wire( I ask this now, because I just read this & no one is open right now)
I was about to redo all the connections starting tonight. But if there is an upgraded harness I wont bother, i'll just buy new( which I might just do anyway).
TIA

 

Painless is one of the biggest makers of harness. I don't know if they are doing C4s quite yet, but they are going to have to.

 

Yeah, I used to deal with painless all the time back in the early to mid 90's. I'm going to call them on Monday to see what they have.

I just have too much to splice back together, & connectors replace after the engine fell. It cut more wires than I thought. This harness may not be worth saving.
The year long resto drama continues...

 

you can always go with new GM... even if it is old style it will last 15+ years of daily use...

 

Damn, just a few weeks ago my car caught of fire because of the brittle wiring shorting out on each other that go into the front of my distributor/ignition module, fortunetly I was only backing in the garage and not driving on the streets or my car would not be here right now.

 

I am sure your problem is amplified by the hot climate in Hawai'i!

 

Replacing the wire is not the only concern but you will more than likely need to replace corroded pins/ sockets and broken connectors. Typically if you do not need to go directly into a component (alternator plug, TBI or ECM) you can replace connectors on where they mate together using any good moisture resistant connectors. Don't use bullet connectors, especially for sensors or feedback to the ECM as they will corrode and allow moisture into the wires and across the connection itself. If I could get a reasonable good wire harness for a 84 and up with all the connectors in place and the basic wiring in fair shape it would not take long to build a harness board and from there it is duplicating the wire runs, terminating connectors (if available) and then finallizing the breakout (tape or convoluted tubing ) so the wires would go to the proper place when set in the vehicle.
Good luck
Woody