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no spark

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infinityron

Contributing Member
folks....this is actually about my Mercruiser 7.4 mie w Hurth trans, but I don't see a section for Mercruiser MIE. It's close enough to Crusader 454 to ask this distributor question........yesterday I was going to check my timing on starboard engine only because I wanted to make sure it was still where I wanted it. But with it idling at about 800 rpms, I inadvertantly knocked off the coil lead from top of coil and of course killed engine. But when put the lead back on top of the coil, now engine just cranks like no spark. Thinking the coil may have shorted, I swapped coils port to starboard and the port side coil now connected to starboard engine still resulted in no fire. The starboard coil now on port, started the engine. So.......any ideas on what has happened? These distributors appear to be factory original 1990 but no identification on them. My parts manual gives me a part number and the illustration looks like the same units I have. I do not see points. There is a small white plastic sensor in the distributor that bears "microswitch" lettering and has two wire leads connected to it on outside of distributor.
help appreciated
 
You can post MIE questions in the Mercruiser Stern Drive section with no issues...
On the distributor, you probably have the ThunderBolt-IV electronic ignition. The troubleshooting procedure has been posted in the Mercruiser section several times and is readily available from a google search as well....
Follow that and it should identify the problem. If it turns out to be the module, they are NLA from Mercruiser. There are many sources for used but they are greedy. that discussion has been had a few times in the Mercruiser section, too!
 
makomark said:
You can post MIE questions in the Mercruiser Stern Drive section with no issues... On the distributor, you probably have the ThunderBolt-IV electronic ignition. The troubleshooting procedure has been posted in the Mercruiser section several times and is readily available from a google search as well.... Follow that and it should identify the problem. If it turns out to be the module, they are NLA from Mercruiser. There are many sources for used but they are greedy. that discussion has been had a few times in the Mercruiser section, too!
Click to expand...

Thanks Mark. I will go check out the mercruiser sterndrive section. FYI, I swapped the coil between port and stbd, ruled out the coil. I swapped out the ignition module, ruled out the module. I think its the internal sensor and I will order one as well as new rotor. That rotor is rusted on and I see from youtube that it is commonly frozen on and requires persuasion.
 
the pickup coil...and they are known to fail (usually with decent service lives)...
when I was working for the dealer, the TB-IV rotors came in with red locktite and they left with it as well...we usued to use a torch to break down the adhesive w/o breaking or bending anything ....
 
makomark said:
the pickup coil...and they are known to fail (usually with decent service lives)... when I was working for the dealer, the TB-IV rotors came in with red locktite and they left with it as well...we usued to use a torch to break down the adhesive w/o breaking or bending anything ....
Click to expand...

Mark, thanks again. Just what do you think I'm curious as to the coincidence of total loss of spark immediately after the coil lead was inadvertantly pulled off with engine idling. The reason I wanted to check the timing was increasingly stubborn starting on that engine. Could it be that the internal sensor just freakishly died at same time the coil lead was popped off, or did the coil lead coming off while engine running cause a failure?
 
hard to say with certainty...I'd be inclined to think the hard starting was coupled to the pickup coil degrading.
Pulling the high tentsion lead when the engine is running leaves a decent amount of energy no place to go....and that usually takes out unprotected active components...the pickup coil is passive and fairly well isolated from the high tension side...
 
makomark said:
hard to say with certainty...I'd be inclined to think the hard starting was coupled to the pickup coil degrading. Pulling the high tentsion lead when the engine is running leaves a decent amount of energy no place to go....and that usually takes out unprotected active components...the pickup coil is passive and fairly well isolated from the high tension side...
Click to expand...
Hey Mark, just wanted to update you on this. I think you are calling the "pick up coil" what the parts manual calls "ignition sensor"? At any rate, yesterday I changed out that sensor, rotor and cap and when back together and turned the key, the engine started INSTANTLY, no throttle pumping or cranking whatsoever. It actually took me by surprise. I then put timing light on it and I made a very slight advance adjustment to 8 degrees BTDC at idle and locked it down. That's where I usually set my timing on other 454's with satisfaction. I've now decided to change out the same distributor parts on the other engine. Easy peasy vast improvement. Thanks for your feedback as always.
 
probably a good idea...
I'd also suggest making sure you check to make sure you get full ignition timing advance per the manual.
 
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