1986 Corvette Ignition problem
Thread Starter
Intermediate
Joined: Mar 2009
Posts: 35
Likes: 0
From: Newton Ks
1986 Corvette Ignition problem
I have a 1986 Corvette that has a miss and runs rich. In the process of elimination I have tested the coil, pickup coil is new, Cap and rotor new, MSD spark plug wirers test with in range. I hooked it up to a timing light and the spark is very erratic on every cylinder. Timing light is working correctly have tested it on another vehicle. I can not seem to figure this out!!!! Any help will be greatly appreciated.
Drifting
Joined: Jun 2010
Posts: 1,853
Likes: 8
From: Westerly RI
You could still be getting a misfire to another plug wire or to ground. One test is to look for arcing under the hood with the engine idling in the dark. The spark will go to another cylinder or to ground if there is a weakness in the insulation, a crack, etc., because it takes more voltage to fire a plug inder compression and the spark will take the easiest path.
Drifting
Joined: Dec 2007
Posts: 1,647
Likes: 4
From: Argillite KY
^^^ I agree. I was typing while the sailor was answering. That just show to go you that great minds think alike.
Is the spark erratic or is the spark timing erratic? Is it firing every time just at different times or is the spark not happening? Hell, I don't know how to ask this. It does soud like spark problems. Go out tonight, just before you go to bed, turn out all the lights and look at each wire and the coil in the dark. The darker the better. If it looks like a thunderstorm under the hood, that's not good.
Is the spark erratic or is the spark timing erratic? Is it firing every time just at different times or is the spark not happening? Hell, I don't know how to ask this. It does soud like spark problems. Go out tonight, just before you go to bed, turn out all the lights and look at each wire and the coil in the dark. The darker the better. If it looks like a thunderstorm under the hood, that's not good.
Last edited by 1963SS; Jul 7, 2011 at 03:27 PM.
Thread Starter
Intermediate
Joined: Mar 2009
Posts: 35
Likes: 0
From: Newton Ks
The spark is erratic. The timing light flashes normal three or four times then nothing then back flashing normal. It does this over and over. I put the timing light on the other cylinders they are the same. The ground strap on coil is good.
Last edited by Jim Hannon; Jul 7, 2011 at 04:23 PM. Reason: addition
Thread Starter
Intermediate
Joined: Mar 2009
Posts: 35
Likes: 0
From: Newton Ks
You could still be getting a misfire to another plug wire or to ground. One test is to look for arcing under the hood with the engine idling in the dark. The spark will go to another cylinder or to ground if there is a weakness in the insulation, a crack, etc., because it takes more voltage to fire a plug inder compression and the spark will take the easiest path.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
7 Bolt-On Upgrades From Extreme Online Store to Level Up Your C6 Corvette
Pouria Savadkouei
How Likely Are These Five 2027 Corvette Rumors to Be True?
Brett Foote
9 Best Corvettes You Can Buy for Half Price (& 1 You Should NEVER Buy!)
Joe Kucinski
8 Very Best Corvettes of Amelia Island 2026
Joe Kucinski
Top 10 WORST Corvette Engineering Failures of All Time!
Joe Kucinski
10 Records the C8 Corvette Generation Has SMASHED (& 1 Glaring Failure)
Joe Kucinski
7 Wildest Corvette Concepts Ever Made
Brett Foote
Thread Starter
Intermediate
Joined: Mar 2009
Posts: 35
Likes: 0
From: Newton Ks
^^^ I agree. I was typing while the sailor was answering. That just show to go you that great minds think alike.
Is the spark erratic or is the spark timing erratic? Is it firing every time just at different times or is the spark not happening? Hell, I don't know how to ask this. It does soud like spark problems. Go out tonight, just before you go to bed, turn out all the lights and look at each wire and the coil in the dark. The darker the better. If it looks like a thunderstorm under the hood, that's not good.
Is the spark erratic or is the spark timing erratic? Is it firing every time just at different times or is the spark not happening? Hell, I don't know how to ask this. It does soud like spark problems. Go out tonight, just before you go to bed, turn out all the lights and look at each wire and the coil in the dark. The darker the better. If it looks like a thunderstorm under the hood, that's not good.
Thread Starter
Intermediate
Joined: Mar 2009
Posts: 35
Likes: 0
From: Newton Ks
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Are you sure the plug wires are in the right holes in the distributor cap?
Sounds like a bad module in the distributor. You can bypass it by disconnecting the connector near the wiper motor. This is the one you disconnect to set the base timing.
Another possibility is a bad ECM. The spark signal comes from the distributor module and the ECM calculates the advance and sends the signal back to the module. It goes to the coil from there.
You might have wiring problems between the distributor and ECM.
Sounds like a bad module in the distributor. You can bypass it by disconnecting the connector near the wiper motor. This is the one you disconnect to set the base timing.
Another possibility is a bad ECM. The spark signal comes from the distributor module and the ECM calculates the advance and sends the signal back to the module. It goes to the coil from there.
You might have wiring problems between the distributor and ECM.
Last edited by Cliff Harris; Jul 8, 2011 at 02:14 AM. Reason: Had a new thought...
Team Owner
Joined: Jan 2003
Posts: 20,222
Likes: 207
From: Summerland B.C. Canada
Team Owner
Joined: Jan 2003
Posts: 20,222
Likes: 207
From: Summerland B.C. Canada
Re-reading your posts, I see no mention of testing or replacing the ignition module.
Might want to check it out.
http://dankai.shawwebspace.ca/asset/...5/ignition.pdf
Might want to check it out.
http://dankai.shawwebspace.ca/asset/...5/ignition.pdf
Thread Starter
Intermediate
Joined: Mar 2009
Posts: 35
Likes: 0
From: Newton Ks
Tested the timing light it is good. Replaced spark plugs and wires, new coil, new pickup coil, new cap and rotor. Tested the ICM six times and is good. Pulled Dist. and checked the Dist. gear and is OK. I am open to any suggestions. Thanks in advance.
Thread Starter
Intermediate
Joined: Mar 2009
Posts: 35
Likes: 0
From: Newton Ks
Re-reading your posts, I see no mention of testing or replacing the ignition module.
Might want to check it out.
http://dankai.shawwebspace.ca/asset/...5/ignition.pdf
Might want to check it out.
http://dankai.shawwebspace.ca/asset/...5/ignition.pdf
Team Owner
Joined: Jan 2003
Posts: 20,222
Likes: 207
From: Summerland B.C. Canada
I was looking over the link that you posted and was wondering is there any spec. on the amount of end play on the dist. gear? On inspection of my dist. gear is that there is at least an eighth of an inch play between the dist. gear and the housing. There is a washer with tangs and another washer that has visible wear. Is this something that I should be concerned about? Thanks for your input.
Is the dizzy out right now ?
Is there a chance your rotor is not making full contact with coil carbon, 100% of the time.
Thread Starter
Intermediate
Joined: Mar 2009
Posts: 35
Likes: 0
From: Newton Ks
Way out of spec, I believe .020 is what you would like to have. Not sure if that could cause your problem, but having the rotor being able to jump up and down that much, can't be good.
Is the dizzy out right now ?
Is there a chance your rotor is not making full contact with coil carbon, 100% of the time.
Is the dizzy out right now ?
Is there a chance your rotor is not making full contact with coil carbon, 100% of the time.
Thread Starter
Intermediate
Joined: Mar 2009
Posts: 35
Likes: 0
From: Newton Ks
Was wondering about injectors? Had a fuel pressure guage on and when I turn key on I get an immediate 42psi and then it drops 10psi after pump goes off to 30psi in less than a second. It zeros out within 5 to 10 seconds. Is this normal or do I have some leaking injectors? If so could this be the cause of the erratic spark showing up on the timing light because of a weak spark from flooding and the motor to miss?