1994 5.0L Thunderbolt IV ignition module

[Mick66]

My 1994 Mercruiser 5.0L was running fine this spring but had a bad oil leak. I had to pull the engine to fix it and now that it is back in I do not have any spark. I have power to the condenser ( I bought a new one) and in the white/red wire at the distributer. Everything leads to a bad ignition module but I find it hard to believe the module happened to go out at the same time as I pulled the engine. I find it much easier to believe I screwed something up pulling and replacing the engine. The module is not cheap so before I buy a new one, is there some way of checking the module and does anyone have any idea of something else that could cause the no spark condition? Thanks

 

[Bondo]

Ayuh,.... Welcome Aboard Mick,...... There's a flow chart to diagnose the module in the factory manuals,....

The manuals can be found in Don'S Adults Only section, at the top of the I/O forums, or the link in my signature,.....

 

[Mick66]

Thanks Bondo, I've gone through the flow chart out of the Seloc online manual. It is a little confusing, or maybe too simple. Step 3 tells me to check to see if I have 12 volts at the positive terminal on the coil. If I have 12 volts, and I am checking a Thunderbolt IV, go to step 7. Step 7 tells me to install a new coil. I have done that. Then I am supposed to go back to step 6. (notice I was told to bypass step 6 before). Step 6 has me checking the ignition sensor by grounding the green/white wire from the distributor. If I get no spark then, I am supposed to change out the module. If I get spark, I am supposed to change the ignition sensor. For the Thunderbolt IV is there a ignition sensor and can it be checked by shorting the green/white wire?

Thanks again

 

[Fun Times]

There is a ignition sensor located under the distributor cap. If the sensor has failed, you won't have spark.

Are you using/following the ignition test like seen on page 1C-8 (on the left side/page)? http://www.boatinfo.no/lib/mercruiser/manuals/mercruiser17.html#/68

You may want to double check to ensure that none of the engines electrical wiring harness connector pins haven't been pulled/backed out not making contact to all of the ignition system components especially the wire harness that plugs into the ignition control module as that little wire harness tends to be issue with the wiring not making contact.

Be sure the Alpha designed shift interrupt switch is not activated as that could cause a no spark condition. See item number 18 for reference, http://www.mercruiserparts.com/bam/subassembly/31835/1014/320

Also try bypassing the boats wiring harness by starting the engine like seen in the following video, https://www.youtube.com/watch?v=NUoXFIo2Ab8

Then try these two quoted steps as well for testing,
http://forums.iboats.com/forum/engi...utdrives/10184655-icm?p=10185708#post10185708

 

[Mick66]

Thank you Fun Times. This just keeps getting interestinger and interestinger. I borrowed a used ignition module from the local boat shop. I hooked it up and turned the engine over and no spark. (I am checking for spark using a timing light around the high tension lead from the coil). I noticed the engine was turning over very slowly even though the battery had been on a charger for several hours. I hooked up some jumper cables to the battery and let it charge about 10 minutes. Turned it over and had spark. Wahoo. I decided to let it charge for about a half hour then see if I could start it. After the half hour I tried and I am back to the no spark situation even though it is turning over better. I think I have a short to chase down. I will try the method in the video to see if I get anywhere. I was also thinking of jumping a wire from the battery to the positive pole on the coil. I am getting 12 volts there now but, I was wondering, if there is a minor short or a frayed line, could I get 12 volts when it is not drawing power but the short would not allow enough current when the power is needed? Like a kink in a hose, you can have enough pressure but no flow.

I'll let you know how it turns out,

 

[Mick66]

I have spark. Using the borrowed ignition module with a charged battery ( my charger was not working) I am now getting spark. My module is the four (4) wire type attached to the distributor. The borrowed module is anchored to a plate that bolts to the exhaust elbow. To get spark using this module I am using jumper cables to ground this plate to the battery. My question now is, how is the module attached to the distributor grounded? It seems reasonable to me that when I removed the engine and the housings, etc. to get to the rear seal I disconnected a ground for the module. This could be causing my whole problem. Is there a way I can ground my original module to see if this is the problem?

Thanks again.

 

[Fun Times]

There should have been a ground wire going to one of the mounting bolts. Try running a ground wire to the base of your original module.

Is yours original mounted to the exhaust manifold/riser/elbow?

Also again, double check the wiring harness to the module, they do tend to lose connection especially after being moved around from servicing, etc..