Mechanics

CHEVY K1500 Z71 4WD PICKUP 5.7L TBI AUTOMATIC 126K BAD MISFIRE IDLE AND DRIVING

1995 Chevrolet Silverado • V8 4WD Automatic • 126,000 miles

1995 Chevy k1500 z71 4wd pickup with a 5.7L (350CI) Throttle Body Injected automatic with 126,000 miles. A while back I had bad misfiring (sputter, missing, and stumble) while accelerating and in the last gear under greater load i.E. Going up a hill (truck would shake and stumble) but not much while idling (slightly if at all) Replaced plugs (two plugs and ash deposits and one plug had oil on it) and fuel filter (filter poured out brown gasoline) and it ran like a champ for about a week.

Started doing the same thing again and also missing more at idle. Replaced wires, distributor cap, and rotor button. Wires had arcing spots, distributor cap was corroded and worn, rotor button was rusted onto the distributor and had lots of black deposits, the circular metal plate where the cap screws down on was solid green with corrosion, removed as much as possible but unable to remove it all. Solved the problem and ran wonderfully for a couple weeks to a month.

Now it is miss firing again while idle (worse than before) and while accelerating and cruising in last gear under load i.E. Going up a hill EXACTLY as before. Hoping it's not a warped or burned valve, especially since it ran like a champ for a while after every repair.

(As a side note, kind of unrelated, after the wires and distributor cap and rotor button, I had the intake manifold gasket replaced for leaking, valve cover gaskets replaced for good measure, and driver side exhaust manifold replaced because of a crack, done by a shop. The mis firing started a week or two after these repairs)

No black or blue smoke.

Stumped, any help would be greatly appreciated, Thanks in advance!

P.S. After replacing wires, the plastic clips unavoidably broke, some of the wires are touching metal brackets connected to the block, and I caught a couple wires touching the block, so I tied them back out of the way with zip ties. Should I wrap them in plastic electrical lume where ever they contact the metal brackets to prevent arcing?
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Ncfirefighter2011
February 8, 2011.



Try to avoid allowing the plug wires to touch the engine block where they can melt and arc. Check fuel pump pressure. Check crank sensor.

The odd thing about this is the fact that it works good for a period of time then changes back to the start. Therefore, I don't feel it is anything internal. I really feel it is ignition related. Check the things I mentioned. Also, if the new wires have any signs of arcing, they need replaced again. Also, I just re-read your comment about the metal brakets. There should be rubber grommets between the wire and the steel bracket.

I just got it back from the shop. Had original pickup coil and ignition module, apparently Chevy had a problem with these in the 90s. Mechanic said they were crappy and replaced them. He said he checked fuel system and O2 sensor. Don't know about the crank sensor. I assume he would have known, he plugged into the ALDL. It runs way better now, no misfiring while accelerating or cruising. However, there is still an occasional stumble or skip while idling, less than before, but still obviously present to me. I wonder about the actual ignition coil? I will check the wires for signs of arcing in the mean time. What do you suggest I use to keep them off of the metal since most of the stock clips broke? Thanks!

Tiny
Ncfirefighter2011
Feb 15, 2011.
I usually will use zip ties to keep things in place. Just for the heck of it, at night, start the engine, open the hood, and mist water on to the plug wires, coil. All ignition components. Do it in the dark so you can see even the slighest arc. Also, the crank sensor is mounted low near the crank shaft pulley. See if you see any arcing there too. Please keep you hands away from the fan and belts. As far as the ignition module, yes, they have always caused problems. Usually, a person would shut the engine and it just wouldn't restart (no spark).

Lol, he said 1995 K1500. It does not have a crank sensor, it has a distributor. Will have to remember not too listen to your advice

Tiny
Muddywaters68
Apr 20, 2014.