The Iron possum
Newbie
I’m looking at heat boots now for the new set of wires. Hadn’t thought about megging plug wires. Would be nice if the parts stores carried a plug wire tester.
Thanks for feedback guys!
Thanks for feedback guys!
95 TBI Hot Miss troubleshooting
- Thread starter The Iron possum
- Start date
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Hey lron Possum, did the plug wires fix your problem. I'm having the same issue. Just flushed one $50 down the toilet (ICM). Trying to avoid flushing too many more. I did replace plugs recently, that didnt fix it either. I had the exact same thought, ignition switch. I have headers as well and taylor 8.8s. I have heat boots on mine though. Like you my plug wires checked out or at least I think they did.
How hard can it be to test plug wires?
1. Ohmmeter across the two metal terminals. Typical carbon-rope plug wires are on the order of 4000 ohms per foot of length. You have a three-foot-long plug wire, you better have less than 12,000 ohms. "Helical"- or "Spiral"-wound plug wires are under a hundred per foot, and "solid-core" wires are about one ohm per foot.
I've seen cylinders run at idle or light load with a plug wire having in excess of 50 thousand ohms--but they may not run under heavy load. Also, this is very hard on the ignition coil, cap, and rotor including the carbon button built-into the cap.
2. Connect the ohmmeter (set to "high ohns" scale) to either of the two metal terminals. Run the other probe over the outside insulation. Anything less than "open circuit" means the insulation is cooked. Check the boots as well. Sometimes the insulation has little burn-marks where the spark has been escaping.
3. Look at the plug wires on a running engine IN THE DARK. Do you see them glowing? That's called "Corona Effect" and if they glow...they go. The insulation is in the process of breaking-down.
4. LISTEN for the SNAP!SNAP!SNAP! of an escaping spark. A cylinder-balance test can find which cylinder(s) are not getting spark across the plug gap(s).
5. IF (big IF) you have an automotive oscilloscope, (almost nobody does) look at the ignition voltage pattern for the secondary side of the circuit. Cooked wires show up clearly. Spark duration is very low, and there's little "ringing" of the waveform. If there's a short-to-ground, spark voltage can be very low.
1. Ohmmeter across the two metal terminals. Typical carbon-rope plug wires are on the order of 4000 ohms per foot of length. You have a three-foot-long plug wire, you better have less than 12,000 ohms. "Helical"- or "Spiral"-wound plug wires are under a hundred per foot, and "solid-core" wires are about one ohm per foot.
I've seen cylinders run at idle or light load with a plug wire having in excess of 50 thousand ohms--but they may not run under heavy load. Also, this is very hard on the ignition coil, cap, and rotor including the carbon button built-into the cap.
2. Connect the ohmmeter (set to "high ohns" scale) to either of the two metal terminals. Run the other probe over the outside insulation. Anything less than "open circuit" means the insulation is cooked. Check the boots as well. Sometimes the insulation has little burn-marks where the spark has been escaping.
3. Look at the plug wires on a running engine IN THE DARK. Do you see them glowing? That's called "Corona Effect" and if they glow...they go. The insulation is in the process of breaking-down.
4. LISTEN for the SNAP!SNAP!SNAP! of an escaping spark. A cylinder-balance test can find which cylinder(s) are not getting spark across the plug gap(s).
5. IF (big IF) you have an automotive oscilloscope, (almost nobody does) look at the ignition voltage pattern for the secondary side of the circuit. Cooked wires show up clearly. Spark duration is very low, and there's little "ringing" of the waveform. If there's a short-to-ground, spark voltage can be very low.
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The Iron possum
Newbie
My issue was burnt plug wire(s). They were Taylor pro and less than 6 months old when the issue started. Just ohming them cold didn’t show any issues. I put a cheap set of Autozone 7mm wires on just long enough to determine that was the problem. Now I’m running blue streak 8.5 mm with thermal sleeves. I also used a few extra wire separators to route plug wires away from the headers. No issues yet and now I have a set of cheap wires for troubleshooting.
Schurkey makes some good points above for checking while running. My problem didn’t show up with any tests.
Schurkey makes some good points above for checking while running. My problem didn’t show up with any tests.
