Mercruiser 4.3 no spark

Bill_C

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Joined
Jul 9, 2012
Messages
9
I have read and read about possible causes for this the last week and I have not been able to fix the problem yet. Here is the Info on the boat;

it is a 96 Maxum with 4.3LX with Alpha 1 GenII outdrive. Has Thunderbolt IV ignition.
I can reply back with serial number when I get home.
Here is what I have done so far to try and fix the issue;
I have used the trouble shooting map to to try and determine what the issue is and it came down to needing the module after not getting any voltage at pick up coil leads. I originally had 807829-1 and I ordered a used replacement off ebay 861251-1 (the superceeded part number) and I spliced this into my wiring harness. The only thing I did not hook up was the yellow wire that goes to the oil pressure switch. I assume this is a ground to kill circuit and leaving it taped up should not cause any harm. let me know if I am wrong on that. I did not hook it up as the old ICM did not use this and I dont know what wire I am supposed to hook this to on the oil pressure switch. After I hooked up the new ICM the boat it fired right up and ran at idle for about 5 min on the muffs. I then took the boat to the resovoir and dropped it in the water. I idled until I got out of the no wake zone (1/2mile)and tried to give it some throttle and it died immediately. and I could not get it to restart again. Now I do not have spark again. This afternoon I am taking the ICM to a coworkers house and hooking it up on his boat to see if his boat will start with this used ICM that I bought. Here are some other things I threw at it in fustration. New cap and rotor, new coil, and new plugs. The only thing I have not changed is the pick up in the distributer. When I unplug the white/green and White/red wires from coil and check the voltage coming from the ICM I get 2 volts at the white/red and I get 10.8 volts at the white/green wire (not sure if this is normal). Things I have tried; it is not the kill switch, this is evident with the fuel pump still turning on. I unhooked the shift interrupter switch and made no difference. I unhooked the tach wire from coil and tried no success. I tried another coil wire no difference. I will post back with the results from trying my ICM on another boat tomorrow. Any Ideas or suggestions would be great as I am not the person who typically runs into something I cant fix or diagnose right away and this is drivign me crazy.
 

Don S

Honorary Moderator Emeritus
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62,321
Re: Mercruiser 4.3 no spark

I don't know what you have, but the the module you need is 805361T1. You don't go by the number on the module, that wasn't a PN and does not cross to anything. The modules also do not have yellow wires in them and nothing hooks to the oil pressure switch.
 

Bill_C

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Jul 9, 2012
Messages
9
Re: Mercruiser 4.3 no spark

I don't know what you have, but the the module you need is 805361T1. You don't go by the number on the module, that wasn't a PN and does not cross to anything. The modules also do not have yellow wires in them and nothing hooks to the oil pressure switch.


http://www.crowleymarine.com/parts/237577.cfm Here is a link to the OEM PN that I took off and in the top it shows the supersession chain with the 861251A1 PN. The A designation means that it is shipped as a conversion kit with the new pigtails to splice into the harness. They previous superceded part number 807829T1 cannot be ordered any more.

in the attachment in C3 is the oil pressure switch that the yellow lead goes to on a newer boat.
 

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Bill_C

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Jul 9, 2012
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Re: Mercruiser 4.3 no spark

I stopped by my friends house yesterday to plug up my module on to his boat only to find out he had a completely different system than my original and the one I switched to. Anyone have any ideas as to what else to try. or any way to determine if the ICM I bought is any good or not. As I said earlier I get 12 V at the green/White wire coming out of ICM going into the pick-up coil. Should I Have voltage coming out of the pick-up coil at the red/white coil? I dont and I may be thinking that my issue is the pick-up coil as this is the only hting I have not replaced yet. I have tried moving the wires around going into the pick up but the voltage values do not change. Does anyone know if there should be voltage at the red/white lead coming out of the pick-up if I have voltage going in at the green/White? would someone mind probing theirs for me and let me know what you find.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Mercruiser 4.3 no spark

There is no 'pickup coil' ... If you still have the original system as per factory delivery, it has a sensor assembly inside the distributor...

Both the drawing you posted and the module in the link are of a Thunderbolt V, not IV...

Please post your engine serial number...

Chris.......
 

Bill_C

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Jul 9, 2012
Messages
9
Re: Mercruiser 4.3 no spark

Pulling rotor/shutter wheel off and checking for voltage again.
 

Bill_C

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Jul 9, 2012
Messages
9
Re: Mercruiser 4.3 no spark

There is no 'pickup coil' ... If you still have the original system as per factory delivery, it has a sensor assembly inside the distributor...

Both the drawing you posted and the module in the link are of a Thunderbolt V, not IV...

Please post your engine serial number...

Chris.......

I will post this afternoon when I get back to the boat.
 

Bill_C

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Jul 9, 2012
Messages
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Re: Mercruiser 4.3 no spark

Just looked and the SN is OF818152. I also just replaced the pick up sensor, no change.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Mercruiser 4.3 no spark

Just looked and the SN is 0F818152. I also just replaced the pick up sensor, no change.

Yes, you can keep throwing new parts at it until you fix it, or you can diagnose it properly and methodically...

To that end.... You have a Gen+ engine, and so you have Thunderbolt V, not IV...

As such, you should be using the Thunderbolt V troubleshooting chart..

Chris......
 

Bill_C

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Jul 9, 2012
Messages
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Re: Mercruiser 4.3 no spark

Just printed off the TB5 chart, doesnt look much different that the one I was using previously, I will follow this again when I get home. Thanks for looking that up for me.
 

Bill_C

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Jul 9, 2012
Messages
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Re: Mercruiser 4.3 no spark

Went through the TB5 trouble shooting chart and it is pointing me back to a bad ICM again. It appears the used one I bought off ebay was junk. Im sending it back today and ordering another one and I will post back what I find out.
 

Audiogod21

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Jul 13, 2010
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Re: Mercruiser 4.3 no spark

Went through the TB5 trouble shooting chart and it is pointing me back to a bad ICM again. It appears the used one I bought off ebay was junk. Im sending it back today and ordering another one and I will post back what I find out.

I had the same problem in my boat. The white and red wire from the ICM powers the ignition sensor, the white and green wire is th return signal to the ICM. The white and red wire should have 12V, ifnot replace the ICM, if so take a test light and clamp on a 12V source and put the tip on the white and green wire and have someone crank the engine, if the test light flashes as your cranking the engine ignition sensor is good, if not replace the ignition sensor, also check and see what color your spark is on the in-line spark tester orange is week blue is good! To test the coil by itself disconnect the white and green wire at the ICM to the ignition sensor, hook up a jumper wire to the white and green wire going to the ICM with the ignition switch to the run postion and rapidly strike the jumper to a good cleen ground to simulate a running engine, again check the spark color. weak or no spark replace the coil.
 

Bill_C

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Joined
Jul 9, 2012
Messages
9
Re: Mercruiser 4.3 no spark

I had the same problem in my boat. The white and red wire from the ICM powers the ignition sensor, the white and green wire is th return signal to the ICM. The white and red wire should have 12V, ifnot replace the ICM, if so take a test light and clamp on a 12V source and put the tip on the white and green wire and have someone crank the engine, if the test light flashes as your cranking the engine ignition sensor is good, if not replace the ignition sensor, also check and see what color your spark is on the in-line spark tester orange is week blue is good! To test the coil by itself disconnect the white and green wire at the ICM to the ignition sensor, hook up a jumper wire to the white and green wire going to the ICM with the ignition switch to the run postion and rapidly strike the jumper to a good cleen ground to simulate a running engine, again check the spark color. weak or no spark replace the coil.

Thank you very much Audio God, I was not able to get anything out of the ICM it appears that the ICM that I just bought was bad. I returned today and now the boat is running again just need to reset base timing. I dropped my timing light and broke bulb when I was climbing in the boat. Just my luck.
 
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