'91 5.7l TBI random interval misfire

Maldred said:

Hot and cold and a shudder that shakes the truck and drops the voltmeter bit by bit as it happens. Sometimes it's a one off thing for about 10 minutes or sometimes it will happen about 2 or 3 times in a few minutes. Would material of the plugs matter at all?

Click to expand...

Ya mine did the same thing and under load (mines a stick) so when u let the clutch out it would do it unless u really rev it

1994-5speedk1500 said:

My truck did this. Your plug wires may be bad. Check all your plug wires where they connect to the plug and look and see if any are touching the exhaust manifold heat sheild. If so thats most likely your problem. Simply spin the boot just a little bit so it isnt on the heat shield. My truck did the same thing. Under load it would misfire and run like ****.

Click to expand...

The issue is at idle and just above idle only. Under any kind of load, it behaves normally. It's also an automatic, not a manual.

Garbage in = garbage out. For a high one, pull your distributor cap, and pull the rotor off the shaft. Check the magnetic material in the pole for cracks. These cracks introduce additional lines of flux, and give the computer false signals.

You might need to get some good lighting, and use a magnifying glass.

Check out post # 2 in this link:

http://forums.superchevy.com/chevy-...mc-sle-tbi-350-57-runs-terrible-when-hook-to/
I had a link to a picture of one a while ago, not sure where it was but I will see if I can find it, I have posted it before.

EDIT: picture of cracks on pg 3 of that link

Maldred said:

The issue is at idle and just above idle only. Under any kind of load, it behaves normally. It's also an automatic, not a manual.

Click to expand...

Atleast check you plug wires and make sure they arent arching on the heat sheild. Its worth a shot and wuick n free

Earlier today, for the first time, it started doing it during hard acceleration.
EDIT: Today the issue got a bit worse, but I noticed that it's at least nearly undetectable at over 3000 RPM. Checked the temp sensor(not melted or anything), plug wires are intact, both injectors appear to be firing the way they should be. Might actually be the distributor at this point. Supposed to warm up in the next few days, so I'll take off the Dist. cap then and check out the condition of the cap and rotor.

Not trying to thread jack, but my 1992 2wd with 5.7 and auto trans is doing the same thing. I have read many threads about this problem, and there doesn't seem to be a definitive fix. I replaced the distributor and EGR. Still does it. So following this thread for ideas and results.

Maldred, You said the engine was remanufactured in 2015. Did you happen to check the teeth on the distributor gear? With a good amount of were on the teeth, can cause a misfire. You also stated that when it misfires the voltmeter drops. I would test and inspect all the connections to the ignition system. Especially the connections at the distributor. Tighten the pin connectors that connect to the module. They, if loose can cause a lot of hair loss trying to find the culprit. Also check the timing with the est disconnected, and reconnect and see if the computer is taking over the timing. If the timing is too far advanced it will cause a misfire at idle. Have you tested the coil? If you have another unit available that is good, install it and retest. Just a thought. Finding something like a misfire can be very frustrating. One more thought, have you completed a compression test on the engine? I know this may sound out of bounds but the more info you have the better it is to know what is good and not. Guessing doesn't usually work.

I should have pulled the wires to begin with. The wires looked perfect from the distributor to the top of the boot at the plug. When I pulled them off the plugs, 3-4 of them were crunchy and had a nice big crack and another one had a good chunk missing from the boot. Found that out when I decided to swap the plug wires on a whim and after I got done, the truck runs perfect now. Problem solved.

Try cleaning the MAF sensor with the airesol cleaner designed for it.

update, I did new plugs, cap, rotor, wires. All AC delco.

Still has misfire.