What is this wire?

[showman]

My 84 vette for the past rear would intemittently run rough, take about 5 seconds before injectors would fire - again intermittent.

Last week, taken a right turn off freeway, goes dead. Cranked it for over half an hour, then it just started up and ran fine. Two days later, take a right out of a restaurant, same thing, but never started up agaiin. Had it towed to house. Checked all the standard stuff (fuel pump pressure, yadayadaya).

No luck, started just pulling on the clusters of wires thinkin one is a bit loose...boom, started up immediately. Started it 30 times in a row, injectors fired immediately. Took it down the street ran great, took a left, zoomed it, ran great, took right...boom, shuts down.

Yanked on wires over and over, then after 20 minutes it starts no problem.

Got it home in garage, starts everytime.

Three things:

1. My instrument panel had only half of it's light working, after my wiring pulling fiasco, all lights are on, even when the car went dead on me.

2. I took out the fuel pump regulator, and it still runs great!

3. What is this wire coming from the battery (having running through brake cylinder so you can see). If I disconnect it, the injectors don't fire.

Mechanics are baffled!

Thanks guys/and dolls!

 

[boomdriver]

I am not the least bit surprized at what you've discovered.
I've preached for yrs that the wire harness is crap. The DOT issued some complaints to GM for their wire harness lifespan & durability back in the 80s.
The wire is undersized, the insulation is not chemical resistant, and the quality of the wire itself was poor...corroded and rotted too easily. Nowhere near the DOT mandate for a lifespan.

I've had to chop out whole sections of my current harness under the hood because it was so rotted and brittle that inj got cross signals from other things and the inj sent false signals to other sensor inputs. In a system that operates on sensitive resistance values as reference for engine control, the harness is the nervous system of the car. It needs to stay in good shape, clean and not have its ability to carry a signal compromised by age and enviroment.

You;re going to have to go thru the harness and test each circuit and replace the bad wire or the whole harness. I replaced my left inj harness with all the sensor circuits and other misc things because every strand of wire was junk. Insulation broken and cracked on each wire. Chopped out, new wire soldered in, new plugs for everything and it ran like new again. The same harness section on the rt side was totally undamaged and the original wire is still in service......Mine had a misfire that moved from #3 to #7 to gone, then reappear again at #1 then #7....hell to pin down for a diagnosis. Always had a mis that acted like a dead hole but could'nt find it. Discovered the bad harness by grabbing a handful of wire behing the valve cover and jerking it around. For all of you that think you are running 80 psi oil pressure,....you;re NOT. Its the rotten wire. Wiggle it and see....

Your odd wire...probably a replacement for a dead circuit. Look at the ECM and at the bulkhead seal for a wire thats been cut off. See where it ends up...spliced into something.
For whatever reason somebody felt it necessary to run a new path for a power or ground circuit. You have a series of power circuits that are NOT fused, that are on a bolt behind the battery called the "jumping post". That post supplies the power for all the critical system and has fusable links under the battery that do NOT run thru the fuse panel. It may have come from there originally. I've seen lots of jury rigged wire when a fusable link blows and nobody can find it.....they usually just run a new wire.

As far as the dying...look at the wires to the dist and find one thats got bad insulation or loose. They will ground on something and short out the ing system. The wires inside the cap get pinched and the module gets shorted out.

That wire might even be a bubba style VATS bypass of some sort. Thinking that supplying power to the vats module will eliminate it and allow the sure starting of the car. All it takes is a 4" jumper wire in the right place, but I can see bubba running a wire from the battery to the decoder module if thats what was cutting off inj signals. Sure would be nice if barnyard engineers would leave a diagram behind with thier handywork.

 

[indafreebird]

I had an earl 80's GM HEI dist. that one of the control module wires had worn through it's insulation causing a short to ground conducting a right hand turn.