low voltage from coil (Thunderbolt IV ignition)

[ABackman]

Engine started fine first time out from winter storage. Ran for app. 20-30 seconds and shut off with no warning. Hasn't cranked since. Plenty of fuel, no fire. Long story short, I have now replaced module, coil, cap and rotor, and ignition sensor......plugs and wires app. 1 year old. I'm getting fire from the coil into the cap but is extremely week. Getting 12 volts to coil. Have tried two new coils now. I'm at a dead end. It acts like it's not getting a good ground. Any ideas would be much appreciated. I'm up to $1000 so far and going further in the whole. Thanks for your time, Adam

 

[FreeBeeTony]

Re: low voltage from coil (Thunderbolt IV ignition)

Ran for app. 20-30 seconds and shut off with no warning. Hasn't cranked since.

Does this mean it doesn't turn over?

 

[ABackman]

Re: low voltage from coil (Thunderbolt IV ignition)

Does this mean it doesn't turn over?

Sorry for leaving that very important detail unclear. The engine does turn over but no fire is being sent to the plugs. I'm getting fire into the cap but it's extremely weak.

 

[gadget73]

Re: low voltage from coil (Thunderbolt IV ignition)

Have you tried a different coil wire? I once had one burn open and cause similar symptoms. I also had a coil crack a tower, and it was arcing through the tower to one of the low voltage terminals on top of the coil.

 

[ABackman]

Re: low voltage from coil (Thunderbolt IV ignition)

Well I'm pretty positive it's not the coil wire cause I replaced the coil wire with a brand new high dollar in-line spark gap tester which would have basically been the same thing as a new coil wire, just with a sight glass in it to see the spark. Any other ideas? lol

 

[ABackman]

Re: low voltage from coil (Thunderbolt IV ignition)

Can anyone tell me how to thoroughly check to make sure I'm getting a good engine ground? Considering I've replaced everything in the ignition system I'm starting to think the weak spark might be due to a bad engine ground.

 

[ezzymonie]

Re: sparking from post and neg leads on coil (Thunderbolt IV ignition)

Re: sparking from post and neg leads on coil (Thunderbolt IV ignition)

I have a 1989 205 hp v6 with thunderbolt iv ignition. i have spark coming from coil tower to the positive and negative leads. changed coil and wire that goes to distributor cap ran fine for a few minutes than did the same thing on other coil. engines runs fine at idle not under a load very dangerous with spark any suggestions?

 

[Bt Doctur]

Re: low voltage from coil (Thunderbolt IV ignition)

Try removing the tach lead fron the neg side (grey wire from harness side NOT module side)

 

[wire2]

Re: low voltage from coil (Thunderbolt IV ignition)

Can anyone tell me how to thoroughly check to make sure I'm getting a good engine ground? Considering I've replaced everything in the ignition system I'm starting to think the weak spark might be due to a bad engine ground.

You won't get zero ohms to engine ground but that's not an issue.
The coil is wired like an autotransformer, meaning it has one end of the secondary winding tied to one end of the primary.
The ~10,000 volts from the coil will try to get back to the battery, and it's inconsequential whether it gets back to the + or-. (You might drop down to ~9,988 volts, going to the + post)

 

[wire2]

Re: sparking from post and neg leads on coil (Thunderbolt IV ignition)

Re: sparking from post and neg leads on coil (Thunderbolt IV ignition)

I have a 1989 205 hp v6 with thunderbolt iv ignition. i have spark coming from coil tower to the positive and negative leads. changed coil and wire that goes to distributor cap ran fine for a few minutes than did the same thing on other coil. engines runs fine at idle not under a load very dangerous with spark any suggestions?

First, welcome to iBoats.
You should really start a new topic for this question, but briefly, you have a very high resistance in your hi voltage circuit somewhere. The spark can't easily get to the plugs, so it jumps from the tower to the + and/or- terminals.
There may be a large gap between the rotor and dist. cap (due to a wrong or burned rotor, or the rotor end is not adjacent to the dist cap pin when a spark occurs). Or the wires may be open. Check with an ohmmeter on Rx1000, ball park is ~1,000Ω per inch.