Strange misfire, 94 3.0

[stretchpdx]

I have a strange misfire that developed when I changed spark plugs. The ignition module was new, the stator was fairly new, and new plug wires did not help. One or two cylinders miss at idle and while driving. Ignition advance improves it a bit at idle. I pulled the plugs out and gapped them wide, like the old ones were, and the miss went away. Now after a year the miss is back, so I need to find the source. Any ideas? Coil, plug wires, and cap/rotor replacement did not cure it.

[Froze_Tread]

could be weak cyl but i doubt or a leaking fuel injector. OBD1 cars are hard to pinpoint misfires on. grrrr.

[sahib]

Is the mis-fire steady enough where you can pull a plug wire one at a time to see if the engine "tone" changes? If so do that and when you come to one that makes no differenc in how the engine runs you'll have located the cylinder(s) causing the grief. Pull that plug and see if it is firing. If it hasn't been firing it may be wet or damp. You can also check by connecting the plug wire and laying the plug on the engine (so there is metal to metal contact) and turn engine and see if there is fire across electrode tip. There are many different factors that could cause your problem including bad injector. Stuck valve or burned valve could be suspect. Place your hand over the tail pipe and see if there is any suction when running. If there is you have a valve problem. It should be a steady push on your hand. Use a gloved hand, especially if the engine is hot. Check these items out and then post back which ever way it turns out. One other thing, you can check for wayward plug wires by misting the engine while dark. Take a bottle of water in a Windex bottle or something similar and spray light mist over the engine (while dark) and if there are any weak plug wires. The fire will jump and you'll be able to see where if there is. Good luck.

[Car Pal]

pull the coil wire and see if there is corrosion on the coil.

[Froze_Tread]

Pulling the plug wire can easilty destroy the coil. Better way is to use a piece of black vacuume hose between the plug and wire which will allow it to fire. Then use a test light thats grounded out "NOT TO THE BATTERY" and touch the tip to the vaccuume line then ud just be looking for the cyl with no change. its a bit of work but saves on buying coils later.

[Willyum]

Did you put the old plugs back in to see if it acted the same?

[stretchpdx]

Thanks for the tips. Yes, I did sub the old plugs back in, no change (about a year ago). I chose not to endanger the coil by unplugging wires from a running engine, but I did unplug the injectors one at a time today and found the center front plug wiring was the culprit. This could explain the temporary loss of power on a recent trip also. No corrosion anywhere, but a vaporized section (white instead of black) of plug wire at the connector. Will try to gap the plugs back down again to see if the old problem really went away.

[Froze_Tread]

One last tip i forgot to mention was using a mixture of soap and water or i prefer salt and water sprayed on the plug wires while running. if the wires are leaking like yours where the engine woulda bogged down. Glad to here your backup and running