5.7 mercruiser not getting sparc from coil

Greetings, I have 1986 Formula w/2 5.7 mercruisers and one runs fine the other wont start and has no sparc from coil, I have tried 2 other coils, still no sparc. <br />Engine did start the 1st time in the water but was missing/popping really bad, sounded like it would blow up or catch fire so I replaced the plugs, wires, cap and coil. Boat has no points, somebody must have updated the ignition, it has soemthing called a "micro switch" where the points should be. After the new parts it wont start and has no sparc. Thanks for any help you can offer as I have spent the last 4 weekends trying to chase down the problem.

Re: 5.7 mercruiser not getting sparc from coil

I would suggest you get an OEM Mercruiser service manual for your engine and at least learn the name of the parts you want to FIX.<br />You should have a Thunderbolt 4 ignition system on that engine, and just because it doesn't have spark from the coil doesn't mean it's a coil problem.<br />Here is a troubleshooting chart from the manual you should have.<br /><br />

Re: 5.7 mercruiser not getting sparc from coil

I just went through this exact problem last week! You will need to see if you have power on the puple wire to the coil '+' side when you turn the key to the 'run' position. Your going to need a volt meter and preferably one that has an 'audio' continuity mode. If you don't have power there let us know and we can go to the next step.

Re: 5.7 mercruiser not getting sparc from coil

Don s - Thanks for your time and the information, the diagram should be very helpful. Regarding the coil, I didnt mean to imply that the coil was the problem, in fact I thought I was proving that the coil was not the problem by pointing out that I used several different coils and still had no sparc. Or of course all three new coils are bad!<br />Could you please point out to me what parts I named incorrectly. The only part that I was not familar with was the part that is stamped "micro switch" under the distributor cap where one would normally expect to find a set of points on a 1986 GM 350. Again, I appreciate any and all of your insight.<br />Boiling Point 212- In anser to your question, I do have an audable alarm on my volt meter and I will test that wire ASAP. I also was thinking about connecting a wire from the pos term on the batery to the pos term on the coil to see if I could get the engine started and see if it was still missing, I read about this in a a different topic, what else would it prove other then I have ignition issues? <br />Thanks for all your help, its great that people take the time and have the patience to share the knowledge/wealth

Re: 5.7 mercruiser not getting sparc from coil

To your point about what does it prove? - Well The '+' from your battery goes to the starter, then to the slave solenoid, on to the circuit breaker, on to the alternator, and ends up on female end of the 10 pin connector at position #6. The male end of the #6 connector picks it up from there and carries it up to the ignition switch for that particular engine. When you turn the key to the 'run' position, that powers up the purple wire which powers your instruments and comes back down from the dash to the male pin #5 of the ten pin connector. From there, the the female side on #5 carries that voltage on the purple wire up to the coil ~ No voltage - No Joy. You can use the continuity setting on you meter to verify there are no breaks in the path from the battery to the coil. Now if this all checks out then we go to the next step.

Re: 5.7 mercruiser not getting sparc from coil

your gonna have to post a pic if someone has altered the ign system from stock, its exactly why I always reccomend AGAINST modifiying one.<br />unless the mod is done with factory parts so I can identify it 5 years later.

Re: 5.7 mercruiser not getting sparc from coil

Thanks guys for your help, the diagram is very helpful. I am on the boat now and I dont quite understand the last part of the trubleshooting process about removeing the wht/green lead? I am getting sparc at the coil positve lead and at the red/wht lead on dist. I tried using the ignition module from the other engine but no difference, so im thinking the sensor they talk about but want to prove it. Is anybody OL now?

Re: 5.7 mercruiser not getting sparc from coil

Ok boys and girls, I got the engine to start, it appears to have been the distributor sensor, alis (micro switch). Now hoever im back to the horrable popping and missing, the popping sound like its comming thourhg the carb, could this be a vacum problem? My brother did the winterizing last year and I found at least one frost plug not put back on and it started shooting water out the top of the riser/manafold, i put one in that spot but maybe i missed another one. What do you think?

Re: 5.7 mercruiser not getting sparc from coil

There is no such thing as a frost plug, so you really need to explain or post a picture of what plug you are talking about. <br />There are plugs commonly called freeze plugs, but you don't just take them out and put em back.<br />Did you "Read" the old spark plugs when you took them out? They could tell you a lot about the condition of the engine.<br />I would suggest you do a compression test as the first test. It's easy and eliminates a LOT of potential serious problems right from the start.<br /><br />Here is how to do a proper compression test that means something.<br /> http://www.boatfix.com/merc/Bullet/97/97_25.pdf

Re: 5.7 mercruiser not getting sparc from coil

I would do a compression test if I had the equipment, thats not an option this weekend. Forgive me miswestern slang, yes I did mean the freeze plugs that we took out to drain the block last winter when we fogged the engine and put it up for the winter. I think y brother who just happens to own a marina and small engine repair in northern Mn had a few to man beers in the process and it was dark and cold. As I said one engine runs just fine but the other when first started was shooting water out of a hole on the top rt side of the motor so I out the plug I found back in and it stoped but right from the start the motor was popping and backfiring through the carb and then the sensor was blown due to a loose distributor ground. SO my question is can a vacum issue cause missing like that ? Except, I dont see any water shooting out, is there any freez plugs that wouldnt shoot water? Thanks again for your help..