Bad computer ground?? 1991 454 motor home Class A

10

Asked by Apr 21, 2018 at 06:58 PM about the 1991 Chevrolet R/V 3500

Question type: Maintenance & Repair

I grounded out my alternator wire (by accident!!) on my 1991 GMC 454
motor home while it was running. Stopped it dead. Now barely runs; won't
idle, rpms up and down as you feather the throttle just to keep it running.
Even though it was the hot wire, I'm guessing I compromised a ground and
the engine computer is all over the place. Any ideas? Had just installed
rebuilt engine, and even though running fine, it would randomly stall after
about 45 min of idle. after shorting out hot wire; everything is bad...

7 Answers

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Haven't sorted everything out yet, but computer ground was bad; now at least it runs, but still surges at idle. braided frame to engine got that cleaned up and shiny and there was improvement. I'm going to clean up the battery ground to frame next. Each ground I clean up, there is improvement. Motor home has been sitting for at least 3 years. Have no idea how it ran with the old engine. They used only water for coolant and completely rusted up all the water passage ways and overheated/ruined both the heads and the block. Idiots. Never use only water. Antifreeze is ALSO anti-boil, has rust inhibitors, and has lubricant for the water pump.

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computer sensor or computer itself makes sense in my scenario. When I shorted out the main hot wire, everything changed. What sensor causes surging idle and makes acceleration almost impossible. I did clean the main battery to frame ground with zero improvement. Also determined that timing is correct and doesn't vary (with engine surging up and down). Runs better with largest vacuum line wide open, meaning most likely running rich; needs more air. Changed TBI and zero improvement. Cousin/mechanic old school, thought coolant sensor might have been compromised when computer wasn't grounded correctly, and is telling the computer it's 40 below temps (ambient temp here in FL around 80). Haven't changed sensor yet. Just bought one. Anything else that would tell the computer to run rich? Again, after running fine prior to shorting wire out... Anyone feel free to jump in here. Others receive responses, but it appears I am invisible.

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Unplugging/changing Idle Air Control changed zero. Revs up and down; up and down. By changing TBI I changed the fuel regulator (haven't checked fuel pump pressure). Seems to be running rich though, not lean... Runs better when I removed the TBI base gasket and started it by mistake. More air through missing gasket and it ran much better, though still up and down rpms; same as leaving PCV hose off TBI, runs better, but not right. Stalled when I hooked vacuum line back up

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Coolant sensor was telling computer 40 below so full on gas; way too rich to run right. Changed sensor and it ran fine for 30 seconds, then fuel pump rubber line in tank split, so low pressure. Just got pump changed, but low battery now. Waiting for it to charge.... A run of unrelated problems. Unbelievable!! Good to weed out ALL the problems though

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New fuel pump, full pressure, fuel to the TBI, no fuel OUT of the TBI. No start. No fire. Finally checked spark; no spark. Took electric panel apart behind grill, main ground wire melted to computer and dash etc... Melted into the wires around it. With bad grounds when I first started engine after replacing engine (I bought it with non running engine), I smelled burnt electrical, but alternator went down to 12.9 volts, so I thought it was that. Even after alternator started charging correctly again, I simply thought it was a glitch. Nope. I fried the main ground to the dash/computer. So far and can't find the terminus to that ground wire. Can't take the dash apart as all the screws have nuts on the back that spin, and you can't get to the nuts.... One day I'll get back on here to say, IT'S RUNNING

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But it appears I am invisible to others, so this may be the world's best kept secret Computers need GOOD GROUNDS

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Loose terminal in Distributor from pickup coil to the ignition module. Decided to just put new distributor in instead of changing pickup coil. Started right up. Runs fine. Bad grounds. Bad fuel pump (rubber hose split). Bad connection to ignition module. End of story...

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