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No Start - Spark at Coil - No Spark at plugs

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ThaBiggT

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I have a 1997 4.3lx with the Thunderbolt ignition. Getting a great spark from the coil, but nothing at the plugs. Bought a new cap and rotor. still nothing. Thought maybe the spark looked good off the coil but wasn't hot enough to get through the distributor, so I replaced the coil. Still nothing. Kill switch is working properly (no spark from coil when in down position). Getting voltage on the red/white wire at the distributor. Any ideas? Am I missing something easy? If I'm getting spark from the coil the P/U in the dist should be working properly right? I'm stumped... or stupid. lmao
 
If the coil sparks, the pickup coil & wiring are functioning.

If you have spark from the coil but not the plugs, and you replaced the rotor and cap, the only thing left is the high tension leads....
 
See if the carbon "finger" that sends spark to the rotor is still there. They can fall out and open the connection.

Jeff
 
Thanks for the replies. Sorry, should have stated in the original post that the wires are new, but that I have used multiple new and old wires to test for spark on every cap lead. All with no avail. Swapped the new cap and rotor out for one off my buddy's boat that is a known good one. Nothing. I've diagnosed dozens of thunderbolt systems and I'm very familiar with the process and system. I've never seen this before and it's got me bumfuzzled.
 
was it running with the old cap and rotor?..

did the distributor get turned (engine backfire?) so the contacts in the cap no loner line up to pass the voltage?..

you've said you are very familier with the systems, but sometimes, even the best can overlook a simple thing and have a problem...

its a simple system and if you are getting spark out of the coil and out the end of the high tension coil lead at the cap, then its going into the cap....
......at this point the voltage needs to pass thru the center contact in the cap to the rotor contact....
which then passes out the end of the rotor, which needs to be aligned with a contact to feed the spark plug in the cylinder.....

if there is no spark out the cap at one of the spark plug wires, there is either a disconnect somewhere at either end of the rotor (possibly out of time and the spark has no where to go out the end of the rotor) or continuity to ground (short) in the rotor..

also, I dont know what engine your working on, but just because, check to make sure the distributor gear pin hasnt sheared, which would cause it to be out of time and not allowing the spark to get out of the distributor.... which could also affect the oil pump (usually its a bad/stiff turning oil pump that causes the pin to shear)....
 
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centerline said:
was it running with the old cap and rotor?..

did the distributor get turned (engine backfire?) so the contacts in the cap no loner line up to pass the voltage?..

you've said you are very familier with the systems, but sometimes, even the best can overlook a simple thing and have a problem...

its a simple system and if you are getting spark out of the coil and out the end of the high tension coil lead at the cap, then its going into the cap....
......at this point the voltage needs to pass thru the center contact in the cap to the rotor contact....
which then passes out the end of the rotor, which needs to be aligned with a contact to feed the spark plug in the cylinder.....

if there is no spark out the cap at one of the spark plug wires, there is either a disconnect somewhere at either end of the rotor (possibly out of time and the spark has no where to go out the end of the rotor) or continuity to ground (short) in the rotor..

also, I dont know what engine your working on, but just because, check to make sure the distributor gear pin hasnt sheared, which would cause it to be out of time and not allowing the spark to get out of the distributor.... which could also affect the oil pump (usually its a bad/stiff turning oil pump that causes the pin to shear)....
Click to expand...

Thanks for the input! I wouldn't say I was one of the best, but like you stated, It's one of the easier ignition systems to diagnose. It was running down the river when it cut off. No backfire or strange noises. Just cut off and wouldn't start up. I'm going back to the marina today to check the timing and I've pulled the P/U out of my buddy's distributor. Gonna swap that out just so I can rule it out. The engine is a 1997 4.3l lx. I will post what I find later today. Thanks again!
 
ThaBiggT said:
Thanks for the input! I wouldn't say I was one of the best, but like you stated, It's one of the easier ignition systems to diagnose. It was running down the river when it cut off. No backfire or strange noises. Just cut off and wouldn't start up. I'm going back to the marina today to check the timing and I've pulled the P/U out of my buddy's distributor. Gonna swap that out just so I can rule it out. The engine is a 1997 4.3l lx. I will post what I find later today. Thanks again!
Click to expand...

you should pull the whole distributor from your buddys engine and try it... as you will likely have to pull yours to check it anyway and its probably just as easy as pulling the P/U coil out of it (which must be working fine if its sparking).... when the engine is at top dead center the end of the rotor should be pointing at the contact for either #1 or #4 cylinder...
 
I don’t think you would have any spark if the pin sheared on the distributor gear as the trigger wheel wouldn’t move and pick coil wouldn’t get triggered.

You can also verify without pulling the distributor by taking the cap off and cranking the engine , the rotor should turn.
 
We ordered a new cap and rotor from Sierra,at shop this year it was a 3.0 but the rotor arm was to short. Called Donavan and told them.
 
Thank you for all the replies! I wasn't able to make it back out to the marina this week, but I will be back out there Monday or Tuesday. Gonna check the timing, Swap out the P/U module and report back.
 
Couldn't help but reply to this thread, I recall a little while ago I was reading a thread about someone having similar issues with the same engine in this forum, also a 4.3. He replaced all the plug wires, cap, rotor, but the fix for him was replacing the entire dizzy. Apparently it was something of the sorts that it would ground out internally. Ill see if I can find that thread.
 
First, pull the cap and make sure the shaft in the dist housing does not move side to side in any direction. If it does replace the distributor.

Look at the distributor shaft and make sure that there is not a broken piece of rotor in the key slot.

The ark from the coil wire should be strong, really strong. You can have low voltage or a bad /incorrect coil that will jump a weak spark across a gap but not through the cap and rotor.
 
Dieter said:
I don’t think you would have any spark if the pin sheared on the distributor gear as the trigger wheel wouldn’t move and pick coil wouldn’t get triggered.

You can also verify without pulling the distributor by taking the cap off and cranking the engine , the rotor should turn.
Click to expand...
ive seen the pins shear and get caught so the shaft still turns but out of time.... I had a old gm 307 in a blazer when i was a kid that engine that ran great but wouldnt stay in time (kept dying). I couldnt figure it out until someone else told me what to look for.... so yes, it can happen, and so I suggested the OP to look as his more closely..
 
centerline said:
ive seen the pins shear and get caught so the shaft still turns but out of time.... I had a old gm 307 in a blazer when i was a kid that engine that ran great but wouldnt stay in time (kept dying). I couldnt figure it out until someone else told me what to look for.... so yes, it can happen, and so I suggested the OP to look as his more closely..
Click to expand...


Ok could see that happening for sure, but would think he would see spark as you must have to retime your blazer, Or a backfire, or spark coming out of center post of coil to ground.

one time I thought I had grounded my coil wire to the manifold so I could turn it with the spark plugs out to get oil circulated on spring start up...high tension wire wasn’t grounded properly. I saw spark coming out under the distributor wire boot on center post of coil finding it’s way to ground on the negative post.

this really amazed me how strong a spark a thunderbolt ignition will put out, nice blue and you can hear it crack. Likely that Chris’s comment about spark strength may be the root cause here.
 
You should really start your own thread but if your getting spark at the end of the plug wires using a screwdriver but no spark using a plug, and if using the fine wire type of plug, replace the plugs with standard ones
 
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