[BLACK KNIGHT]

Car keeps losing power and running rough on an intermittent basis. Took it to a shop, they thought they fixed it but didn't. They said that some short in the wiring is causing one side of the fuel rail to stop working at the fuel injectors so basically it's running on only 4 cylinders. Not sure how to test this?

Also where would be a good place to buy a whole new wiring harness?

 

[steveo]

you can probably repair your harness

if that entire bank is intermittent.. it simply has to be the +12v.

there's a splice inside the harness itself (key power) that splits off a single wire, then powers that entire bank of injectors from one of the injector fuses.

either the splice has broken down, or the wire between the splice and the connector under the dash is sketchy somewhere

you could always bypass too, just take all the injector power wires, splice 'em together, and power them from somewhere else ignition switched.. wouldn't hurt, and would be an easy fix..

 

[BLACK KNIGHT]

So to test I could simply just use a voltmeter?

 

[shoebox]

So to test I could simply just use a voltmeter?

Sure. Just use the schematic. It would be highly unlikely that "one side of the fuel rail" is not working, since the injector power is split evenly over both rails. It might be something as simple as a problem at one of the fuses.

All of your injectors have a pink wire. That is where your power comes from and back to the fuses. Since your problem is intermittent, set up your meter to look for power on the pink wire at an injector connector and jostle your harness to see if it cuts out.

 

[cocobolo95]

If you get to the point where you need to do some major re wiring, may I suggest you search craigslist for a engine wiring harness.

Here in Florida, I see them on a regular basis. I use lt1 as my search query. Don't just search your local area, search out as far as your willing to drive.

And don't give up if you find nothing at the time. Search every day, people post new stuff up all the time.

 

[BLACK KNIGHT]

Well thanks for the info! Getting closer, the injectors connected to Fuse 10 intermittently seem to lose power even when the car is just sitting and the engine is off but the ignition on. Thinking it's a problem at the S102 junction. Plan to try and trace it this weekend.

 

[steveo]

a shitty connection under the passenger kickpanel is possible too..

testing wiring with a voltmeter sucks for intermittent problems.

you need to load test wiring to diagnose correctly. check voltage at the end, apply a couple ohms of load to that wire (say... a spare headlight bulb), check voltage again.

since a voltmeter provides no load, you could have a single strand of wire holding it together and never know. if you apply a load and there's a problem, it'll probably show up.

even better, if you give it enough load, you'll hear a nice fizzle and see smoke where the fault is....

 

[shoebox]

a shitty connection under the passenger kickpanel is possible too..

testing wiring with a voltmeter sucks for intermittent problems.

you need to load test wiring to diagnose correctly. check voltage at the end, apply a couple ohms of load to that wire (say... a spare headlight bulb), check voltage again.

since a voltmeter provides no load, you could have a single strand of wire holding it together and never know. if you apply a load and there's a problem, it'll probably show up.

even better, if you give it enough load, you'll hear a nice fizzle and see smoke where the fault is....

As a note of caution, NEVER use a test light on anything going to the PCM. A high current load will immediately fry any solid state electronics. You don't want that fizzle to be your computer. If a circuit goes to a fuse, you're ok.

 

[steveo]

oh, for load testing a wire you need to disconnect it at both ends for sure

i suspect that's what happened to my last dead ecm....

 

[BLACK KNIGHT]

Well I think we got it fixed. We traced the four injectors I think #1, 4, 6, &7 to a power wire that seem to go all the way to a harness connection near the PCM over the passenger side wheel well where it then ran all the way back to the fuse box. We weren't able to pinpoint exactly where the issue was, continuity from the fuse box to the wiring harness seemed good as well as ohm readings. Going to the harness back to the injectors the ohms weren't quite as good but we weren't seeing why. So we said screw it and just cut the power wire where it tied into the 4 injector wires and ran a new wire straight from there to the fuse box. Now instead of a power wire going all the way around the engine bay, there is a 2 foot wire going straight from the fuse box to the injectors. We left the original power wire active in case it feeds anything else and sealed it off where it used to feed the injectors.

So far so good.