Finding Ground Issue

ncgoblin

ncgoblin

Goblin Guru
Hey guys I have an odd ground issue. Driving my LSJ is great but as soon as I come to idle the throttle becomes nearly unresponsive and rough idle. I can power the engine off and back on and all is normal while driving.

I checked the voltage at the PCM module positive terminal and it was like 16-17v but checking at the alternator was 14v. This winter I reorganized my wiring in the front of the goblin and re-soldered my grounds and merged to the foot pedal box. I did leave (1) ground not terminated but this I believe was for Aux power.

1. Would it be possible for this un-grounded wire to cause issues?
2. What method would you take to identify a grounding issue? I noticed this part after watching a youtube video which may help. I was also thinking of removing all fuses except for mandatory fuses to run.

Thanks all
 
G

Gtstorey

Goblin Guru
What makes you think you have a grounding issue?

I'm not sure that any ground is for auxiliary only unless you added it in, but I would have to study the wiring diagrams to confirm that. Why not ground it and see if it fixes the problem.

I would be concerned with the 16-17v if that is a good reading. Not sure how you could get that at the "jumper post" and something different at the alternator that should be the same circuit (assuming you are reading it with the same meter) unless you have a bad connection on that circuit. But if that was the case, I don't know how you got more voltage at the PCM. If this is repeatable, see what you get at the battery.

Are you getting any trouble codes?
 
Corgithulhu

Corgithulhu

Well-Known Member
Gtstorey said:
Not sure how you could get that at the "jumper post" and something different at the alternator that should be the same circuit
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The alternator positive cable and the jumper post on the fuse box should be electrically identical. They meet with the battery cable at the starter lug.
 
ncgoblin

ncgoblin

Goblin Guru
Corgithulhu said:
The alternator positive cable and the jumper post on the fuse box should be electrically identical. They meet with the battery cable at the starter lug.
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I thought it odd that the fuse box positive terminal had differing results from the alternator. I will be pulling off the hood and checking the grounds and terminate the one that is not grounded to eliminate that from a possible issue. The oddest symptom is when I lose throttle response only at idle and not all the time. In fact I drove 10 miles last night for remote tuning to send off the ZZP no issues come to a stop sign and engine goes into a limp mode no throttle response. Thought maybe something to do with the breaking but when it idles in the driveway same symptom after warmup. The one reason I was leaning towards a grounding issue is the 17v from the fuse box. It may also be a vacuum leak at this point I need to check multiple routes to find the root cause...

Already swapped the throttle body I had a spare charger.
 
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Chubbs

Well-Known Member
I don't remember getting 17v, but I DO remember getting weird readings (and different readings) between the fuse box positive lug and the alternator lug. They should be the same. They weren't.

Take the biggest ground wire you have left over from your donor, and run it between the engine block and the frame grounding lug (the one in the rear where all the other ground wires go). See if that fixes your problem.

But the entire engine block was already secured to the frame using huge bolts, right? Yes, it was. Apparently, they weren't a good enough ground. I have no explanation why. Not only that, but when I checked resistance between the engine block and frame, it was 0. Shouldn't that have been good enough? It wasn't.
 
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Gtstorey

Goblin Guru
Different readings are possible depending on how good a ground you are using, but a perfect ground should be the highest voltage reading and a not so perfect ground would be lower. That’s why a reading of 16-17v indicates a problem, possibly a voltage regulator problem.
I don’t think it’s possible to go into true limp mode without throwing some sort of code.
With these cars I’ll always think loose wiring connector for intermittent problems. All it takes is for one pin on one fuse box connector to cause problems.
 
Corgithulhu

Corgithulhu

Well-Known Member
Make sure the tabs on the starter lug are all clean and free of corrosion. Since we jostle their position around on that starter stud during the disassembly of the Cobalt and assembly of the Goblin, it's possible to get a bad positive voltage connection. Mine were corroded (and a washer I accidentally left between two lugs), and I was having total power failure issues until cleaning them off. Basically I wasn't getting good voltage up to the fuse block and thus most of the car.
 
S

Scott #321

Well-Known Member
Chubbs said:
Take the biggest ground wire you have left over from your donor, and run it between the engine block and the frame grounding lug (the one in the rear where all the other ground wires go). See if that fixes your problem.
Click to expand...
Whatever you find I highly recommend a good ground wire between the engine and frame. I see bad grounds more often than any other problem with wiring.
 
ncgoblin

ncgoblin

Goblin Guru
Update:
@Scott #321 @Chubbs pointed me into the right direction. I got to thinking I have (2) 8 gauge wires grounded near the driver side engine mount but do not recall ever mounting a 2-gauge wire from the starter to the engine mount for grounding and guess what...I forgot to install the 2-gauge when I rebuilt my engine. I have now made up a new grounding 2-gauge wire and mounted to one of the extra motor mount holes. The engine has been stable now at idle after a long run cross fingers this is the cause but regardless it needed to be done.

Now back to the ZZP remote tuning for e85 and #80 injectors with Alan.
 
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