ls1racer1999

hey i have a 99 trans am i had wrecked it and am almost finished re building it the car has been running no problems for months now then suddenly one day i park it then the next afternoon after work the car will start up run ok at idle then the fuel gauge cuts out and the coolant temp gauge and the tach and i cannot connect my laptop to it ive tested wires and fuses and grounds i replaced the the pcm pcm was programmed for some reason theres no signal from the dark green wire pin 58 on the blue connector and im not sure what controls that circut and everything . but still the same problem im stumped and its very frustrating dose anyone have any ideas please? thanks


scott

wssix99

iTrader: (5)

How much voltage does your gauge show? Or is that one out also?

ls1racer1999

the voltage on the gauge shows 14,5 ish brand new alt the old alternator had been messing up going from 7 to 14,8 and just going back and forth for a day or two then i replaced it could it be a ground ? if i let it sit for a few hours and then try it everything will work for about 2 min then drops out again almost as if something is getting hot and opening or maybe a ground getting hot? i originally thought it was the pcm i had tested everything up to that point so i ordered new pcm same model year and with my vin and it worked then cut out again so i know its not in the pcm now since the new one dose the same . im stumped lol im going to go through all the grounds i can see and clean them super good and then change fuses anyway and see what happens but if u have any ideas or have seen this before help please !!!!!!!!!!!!!!!! lol thanks for responding i really appreciate it

wssix99

iTrader: (5)

So, the voltage gauge still works when the others shut off? This kind of thing will happen to folks when the alternator isn't putting out enough juice. I'm wondering if something is weird with the alternator.

How much time has gone on from your alternator install to this gauge issue?

ls1racer1999

it was doing it before the alt what happened was i was driving it then one day the alt started fluctuating from 7 to 14.8 then about 2 days after that i oarked it in the garage for the night and when i got home from work the next day i started it up and was letting it warm up then when i got back in i noticed the temp,tach,fuel not working so i tried to hook the hp tuners i have up to it to scan it and it wouldnt connect so i started testing and everything i figured it was the computer i ordered new one with my vin and model year tried it worked for about 5 min then went out again. if i let the car sit for a day or 2 everything works fine then drops out after about 2-5 min and i cant for the life of me figure it out

ls1racer1999

sooo i found out what the problem was after going nuts for almost 2 weeks the gauge cluster i had bought was bad i found a resistor in the data wire on the cluster side burnt out well burnt out finally but owuld get hot and open causing the data being sent from the computer to get all jumbled and when that resistor would heat up it would spike the computer . i unplugged the cluster and hooked right up . its always something stupid lol

wssix99

iTrader: (5)

Wow - how did you test for that? Was the resistor on the cluster? Did you have to pop the thing out to test it?

ls1racer1999

i had everything i needed at the computer and everything was comming from it so the next thing was to check the cluster and all the gauges that did wourk all had seperate signals and the 3 that didnt work came from the logic in the cluster. theres a termination resistor in the data wire 60 ohm and one on the pcm side thats 60 ohm and since its can bus it has to talk back and forth down the same wire well those resisors terminate the signal after its beed used and since the one on the cluster side had been heating up and thats why the gauges would drop out because it would cause digital relfection in the line causing the signal to get all scrambled and the and the logics ic's couldnt convert the signal into something the computer or the cluster could use so in short i unplugged the gauge cluster hooked in the computer and it fired right up since the signal wasnt getting scrambled from the gauge cluster
always someting stupid and small i spent 2 weeks on this damn car and fianlly it came down to a 30 cent resistor lol

ls1racer1999

i work on electric forklifts and other electrical things at work and just kinda used that to diag the car since i couldnt see there being to much of a diffrence in how there canbus set ups also after check every damn thing on the car i had narrowed it down to either short in the fuel injection harness or the cluster

wssix99

iTrader: (5)

Wow - very clever. Good move on looking at the PCM at the same time to see that it was returning a signal at the data connector.

So, of these resistors, its possible that one at the PCM side of things could go out as well, eigh? Are they inside the gague cluster or PCM case or are they actually in-line with wires and dangling around in the dash? (Very curious)

ls1racer1999

bolth sides have a 60 ohm resistor 120 total and its at the end of each side to terminate the signal after its been sent so that it dosent reflect back into the line and mess or scramble the signal