1990 5.7 mercruiser no spark

[johot321]

While moving at about 6-8 knots my engine just died. I'm pretty sure its an electrical/spark problem cause I'm getting good fuel. I was told that I should check the intrupter switch but I'm not quite sure how, or what to attack first. Would an interupter switch just stop working like that? Is there something that I'm missing? Or should I go through the motions of coil, distributer, etc? Thanks for any advice you can offer

 

[Trent]

Re: 1990 5.7 mercruiser no spark

First just check for voltage at the + side of the coil. Then disconnect the tach wire and the shift interrupter at the coil and see if she starts. If she does re-connect one at a time to know which is your problem if any of them are your problem.

 

[johot321]

Re: 1990 5.7 mercruiser no spark

Thanks for the reply, however it did'nt work. I do have 12 volts on the + post of the coil, disconnected the interrupter switch and the tach wire and still no spark at either end of the coil wire. Also when I place my meter on both posts of the coil, I get NO reading. It only registers 12 volts when I ground the meter to the block.Is this right? If so what's my next step aside from sinking it. By the way it has thunderbolt electronic ignition. Thanks

 

[aeronutt29]

Re: 1990 5.7 mercruiser no spark

It is correct that you get no voltage reading between the two posts of the coil. You should get an OHMs reading here that only shows a few ohms worth of resistance. Since you have voltage that far, your next step is to make sure the trigger is sending a signal and that the brain box is working. Depending on the specific model (Thunderbolt was a generic name given to many different ignition setups over the years) you may need some special test equipment that only a repair shop is likely to own.

 

[Trent]

Re: 1990 5.7 mercruiser no spark

This is the Thunderbolt Ign system that was used on most of the engines of your year model. But you need to make sure you have this model. This guide might help you find your problem.... Thunderbolt IV

 

[johot321]

Re: 1990 5.7 mercruiser no spark

Turned out to be the ignition sensor. I used the trouble shooting diagram that you sent me to diagnose it. thanks

 

[Trent]

Re: 1990 5.7 mercruiser no spark

Glad you found your problem! Now go have some fun..I got to work