'96 4.3L mis-fire
October 29th, 2016, 3:35 PM
#1
CF Beginner
Thread Starter
'96 4.3L mis-fire
Hi! I'm new to this group. I joined because I'm stymied with a problem.
>History: Engine has 130,000 miles. Oil changed 3 weeks ago. Unknown as to when last tune-up and/or fuel filters changed. Bought it used, cheap.
It has run fine up until 2 weeks ago. I drove it about a mile and parked. After shopping, maybe 15 minutes in the store, I came out and fired her up. I sat there for a few minutes doing some things and it suddenly began to run rough and buck then stalled. It would not re-start. I called the hook which arrived about a half hour later. We tried to start it and it fired right up! Ran nice and smooth UNTIL it had run about 5 minutes then the same symptoms re-appeared and it stalled. It re-started once, bucked, ran rough and had a spark knock sound then stalled. Towed it home.
>>Problem found, (1): After figuring out just how to remove the interior engine cover, I discovered that the distributor cap was loose. The housing on the OEM distributor is plastic. One ear where the cap screw goes into the housing was cracked, the other was half broken off. Distributor was junk. Cap and rotor were both worn and burned. I ordered a replacement distributor from Rock Auto with a full metal housing. It came with cap and rotor. As GMC made the replacing of the distributor pretty much idiot-proof, I changed it with no problem, reattached the spark plug wires and coil wire, attached the wiring harness to the side connection and fired it up. It ran just fine, then, after running for about 2 minutes, it exhibited the same problem and stalled. Tried to start it again and it fired but ran extremely rough, bucking and knocking before stalling yet again.
>New Problem.THIS time a crackling, arcing sound was coming from INSIDE the distributor cap while the key was on. Shutting the key off stopped this noise. I disconnected the three prong connector from the side of the distributor and turned the key on. The noise reappeared. Shut the key off, pulled the COIL wire (which inadvertently rested on the tranny dip stick tube) and turned on the key. The coil wire immediately started arcing to the tube very sporadically.
>New Problem: The coil is being told to fire even though the engine isn't running when the key is turned on. It fires very unevenly but, constantly until the key is turned off. The ignition system is coming on without the engine being cranked.
I'm no good with these new (to me) electronic ignition systems. Adding electronic fuel injection has placed this way above my pre-1995 engine experience. Hall effect pick-ups, MAP sensors, crank and cam positioning sensors are alien to me. About the only things I'm comfortable doing on these newer (post-1995) engines is changing the oil, fuel and air filters, and the spark plugs. I am capable of changing parts, even electronic ones but, diagnosing a problem like this one is far, far beyond me.
I don't want to get rid of this little van as it's engine is tight (no oil leaks, no rattles or squeaks, etc) the tranny is fine and it's great on gas. It seats six comfortably and gives me the ability to grab the grand kids and go have fun. So, any help as to wear to begin, what to do or even step by step instructions would be GREATLY appreciated.
>History: Engine has 130,000 miles. Oil changed 3 weeks ago. Unknown as to when last tune-up and/or fuel filters changed. Bought it used, cheap.
It has run fine up until 2 weeks ago. I drove it about a mile and parked. After shopping, maybe 15 minutes in the store, I came out and fired her up. I sat there for a few minutes doing some things and it suddenly began to run rough and buck then stalled. It would not re-start. I called the hook which arrived about a half hour later. We tried to start it and it fired right up! Ran nice and smooth UNTIL it had run about 5 minutes then the same symptoms re-appeared and it stalled. It re-started once, bucked, ran rough and had a spark knock sound then stalled. Towed it home.
>>Problem found, (1): After figuring out just how to remove the interior engine cover, I discovered that the distributor cap was loose. The housing on the OEM distributor is plastic. One ear where the cap screw goes into the housing was cracked, the other was half broken off. Distributor was junk. Cap and rotor were both worn and burned. I ordered a replacement distributor from Rock Auto with a full metal housing. It came with cap and rotor. As GMC made the replacing of the distributor pretty much idiot-proof, I changed it with no problem, reattached the spark plug wires and coil wire, attached the wiring harness to the side connection and fired it up. It ran just fine, then, after running for about 2 minutes, it exhibited the same problem and stalled. Tried to start it again and it fired but ran extremely rough, bucking and knocking before stalling yet again.
>New Problem.THIS time a crackling, arcing sound was coming from INSIDE the distributor cap while the key was on. Shutting the key off stopped this noise. I disconnected the three prong connector from the side of the distributor and turned the key on. The noise reappeared. Shut the key off, pulled the COIL wire (which inadvertently rested on the tranny dip stick tube) and turned on the key. The coil wire immediately started arcing to the tube very sporadically.
>New Problem: The coil is being told to fire even though the engine isn't running when the key is turned on. It fires very unevenly but, constantly until the key is turned off. The ignition system is coming on without the engine being cranked.
I'm no good with these new (to me) electronic ignition systems. Adding electronic fuel injection has placed this way above my pre-1995 engine experience. Hall effect pick-ups, MAP sensors, crank and cam positioning sensors are alien to me. About the only things I'm comfortable doing on these newer (post-1995) engines is changing the oil, fuel and air filters, and the spark plugs. I am capable of changing parts, even electronic ones but, diagnosing a problem like this one is far, far beyond me.
I don't want to get rid of this little van as it's engine is tight (no oil leaks, no rattles or squeaks, etc) the tranny is fine and it's great on gas. It seats six comfortably and gives me the ability to grab the grand kids and go have fun. So, any help as to wear to begin, what to do or even step by step instructions would be GREATLY appreciated.
October 29th, 2016, 3:58 PM
#2
CF Monarch
The ignition is "on" with the key switch on, not just crank. I'd suggest with the distributor rotor see how much play it has. With what you are describing sounds to me like the distributor is worn, and shifting when the engine is running causing the problems with the rotor/cap you describe.
October 29th, 2016, 4:06 PM
#3
CF Beginner
Thread Starter
The ignition is "on" with the key switch on, not just crank. I'd suggest with the distributor rotor see how much play it has. With what you are describing sounds to me like the distributor is worn, and shifting when the engine is running causing the problems with the rotor/cap you describe.
October 31st, 2016, 5:40 PM
#4
CF Active Member
Join Date: Jul 2016
Location: Wisconsin
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I had an 89 Caprice with a 305 that had a similar problem. When cold would start and run okay but then would die out after a couple minutes. I found the was a crack in the coil's body that would open up when it got warm and basically ground itself out on the intake manifold. Replaced the coil and all was well. Sounds like you should at least replace the coil wire, might consider a complete set of ignition wires.
November 1st, 2016, 2:50 PM
#5
CF Beginner
Thread Starter
Perhaps I'm not being clear. I put a screwdriver into the distributor end of the coil wire and hold it close to a ground. When I turn the key "on" NOT to "start" the coil begins throwing a spark, This is NOT normal. I have been under the impression that the ignition system doesn't function until the engine is cranking then continues when the engine starts. If the engine stalls, shouldn't the coil de-energize? It doesn't. And, remember, this only happens after the engine has warmed up a little. Not quite operating temp.
