LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

intermitent spark at plugs

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Old Oct 13, 2003 | 12:14 PM
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94-3.4's Avatar
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From: Fort Collins, CO
Unhappy intermitent spark at plugs

my car has been running poorly and i thought it was plug wire related so last night i put a new set of wires on and it ran the same. The car feels like its missing on multiple cylinders at idle so we started pulling plug wires and to our surprise it ran the exact same with any one plug wire removed. So i stuck 4 different wires next to a bolt and started the car, each time we did this you could see the spark arcing to the bolt on a constisten basis for about 4 seconds that it would stop and then start again. So i am not gettinga constant spark which is why i am having a low rpm missfire. With that said i am guessing its the optispark which i replaced 2 months ago Can anyone clarify this for me? Thanks
Old Oct 13, 2003 | 12:34 PM
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My bet is weak coil...it sparks a few times after building up enough energy, then goes away for awhile...fairly common failure.

P.S. I'm assuming you changed the coil wire when you did the plug wires...if not, check it for white powder in the boot.
Old Oct 13, 2003 | 12:36 PM
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Ohh, and checking spark by grounding/arcing to a bolt can be very misleading...get a cheapo $5 spark tester at any parts store and ensure the spark is able to jump the appropriate sized gap. It's over 1/2" or so on a 4th gen if memory serves me...
Old Oct 13, 2003 | 01:32 PM
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I did not change the coil wire but i will now. What does white powder mean if i find any? Thanks for the info!
Old Oct 13, 2003 | 03:04 PM
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Originally posted by 94-3.4
I did not change the coil wire but i will now. What does white powder mean if i find any? Thanks for the info!
Ohh, that's a definite "must do" on these cars. It's VERY common for white powder to accumulate in the coil wire boot and corrode the connection. Not sure where it comes from myself (arcing?), but it's been a known fact for years and is the first thing to check/change when having ignition problems...start there and hopefully it's as simple as that!
Old Oct 13, 2003 | 05:59 PM
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Well i replaced the coil wire and the coil and it runs exactly the same. Any other suggestions? Some other simptoms are noisy rockers, low vacuum as well. Thanks
Old Oct 14, 2003 | 08:56 AM
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Bummer... I'd try the spark tester next to confirm whether you're really getting strong consistent spark at each cylinder...

When you did the OPTI, was it a full new OEM one or rebuild kit, etc.?
Old Oct 14, 2003 | 09:14 AM
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Double/Triple Check your wires.... When you check the coil wire.. It should have ZERO resistence?
Old Oct 14, 2003 | 09:33 PM
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How can i check for resistance? Will this show anything on the other plug wires as well?
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