1999 43L Merc Thunderbolt IV Ign low fire from coil

"Engine started fine first tim

"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"

You should have purchased the

You should have purchased the appropriate service manual for $ 75 and used the proceedure in it to troubleshoot your problem (ignition) and you would most likely have saved $925.00


This is for future reference!!!!

""...wires app. 1 year old

""...wires app. 1 year old"

It just means they are a year old; not that they are all still working.

"...fire from the coil into the cap but is extremely week"

What does the spark look like at the PLUGS? Coil wire? Try a new GOOD one. At 4,000 RPMs the coil wire handles 24,000 HV bursts/minute; needs to be a good one."

"What does the spark look

"What does the spark look like at the PLUGS? Coil wire? Try a new GOOD one."

I have no fire to the plugs what-so-ever. I replaced the coil wire with an inline high dollar spark gap tester. The tester is brand new and it takes the place of the coil wire. It's a tester that is basically a coil wire but has a sight glass in the middle to view the spark. Good idea though. If I hadn't had that type of tester and been testing it the old way by grounding the wire off at the exh elbow or something I would have probably done had a new coil wire on there.

Make sure the wire connectors

Make sure the wire connectors at the coil a very clean and shiney. Check the module ground; scrape the grounding point clean w/SP or a file. Reconnect the ground and dab w/some grease. Reset the timing since you replaced the optic sensor.

Ok sounds good. I'll doubl

Ok sounds good. I'll double check all above. Only question is would you happen to know where that ground would run to? Out of the module harness the ground wire tees into a huge wrapped up bunch of wires that could go anywhere. Thanks so much for your help btw.

"When you try and start the en

"When you try and start the engine are you getting a good crank from your starter? You state; "no crank since".
Check and clean your battery connections and the ground at the block, put a booster on your battery, and try and start your motor. Just because you've got 12 volts at the coil does not rule out battery/connector problems."

"...where that ground woul

"...where that ground would run to?"

No; mine has a connector that a screw holds in place. Follow the wire to see or check the ground to the engine block w/a digital voltmeter.

Ok will try thanks. It might b

Ok will try thanks. It might be a day or two before I can work on it but I'll keep you posted. Thanks so much!