1990 mercruiser 4.3 no spark

[mgeorge15]

I am getting no spark out of the distributor to the plugs,i have power on both sides of thecoil. tried replacing the coil and that didnt fix it. Was going to order a new ignition sensor in the distributor but thought I would pick some peoples brains first. Its a Thundervolt system. Last year at the end of the year the boat would run for about 10 minutes and then it would bog down and lose power, never tried to fix it, just put it in storage and now this year it wont start at all. Any help would be awesome.

 

[cny boater]

Re: 1990 mercruiser 4.3 no spark

With a 12v test light, probe the negative side of the coil while cranking and note the light. If it is NOT blinking, then most likely the sensor in the distributor is bad. If it is blinking, check for spark at the COIL WIRE, not at the plugs. Post your findings.

 

[Don S]

Re: 1990 mercruiser 4.3 no spark

Here, might as well check it right, and stop throwing parts at it. <br /><br />

 

[mgeorge15]

Re: 1990 mercruiser 4.3 no spark

The light is not blinking, I have checked for spark at the coil wire and you get no spark from the coil wire either.

 

[Don S]

Re: 1990 mercruiser 4.3 no spark

Then use the troubleshooting chart I just posted......

 

[cny boater]

Re: 1990 mercruiser 4.3 no spark

That flow chart is the reason why I don't like flow charts - - there are 2 huge problems with it that have you throwing a coil and an ignition module at the problem for possibly no reason.<br /><br />Mical, sounds like you need a new ignition module or distributor sensor. I am not familiar enough with that system to know the components used. The distributor "sensor", in this case, may actually be an ignition module.

 

[Don S]

Re: 1990 mercruiser 4.3 no spark

That flow chart is the reason why I don't like flow charts - - there are 2 huge problems with it that have you throwing a coil and an ignition module at the problem for possibly no reason.<br />

It eliminates the sensor, and the wiring as a potential problem, then it has you replace the coil with a good one because very few people have a coil tester. Do you???. Then and only then does it tell you to replace the module as the final step. Since the module is a "Black box" type unit, there really isn't any way to test it, so eveything but that was checked first.<br /><br />

I am not familiar enough with that system to know the components used. The distributor "sensor", in this case, may actually be an ignition module.

Then giving advise on how to troubleshoot it isn't a real good idea either. The sensor is not the same as the module.

 

[cny boater]

Re: 1990 mercruiser 4.3 no spark

Flow chart problem #1: Substitute a new ignition coil. That is shotgunning parts too! Did you ever wonder why no one has a coil tester? It's because they are not necessary.<br /><br />Flow chart problem #2: No where does this flow chart take into account for the possibility of a faulty coil wire. If there was an open in the coil wire and you used this flow chart, then you will have successfully replaced a good coil and good ignition module.<br /><br />Flow chart problem #3: Replace igniton module harness without ohming it out first?? More shotgunning.<br /><br /><br />By grounding the wht/grn wire, you are basically taking the place of the RPM sensor (crank sensor or distributor sensor) and proving that the ignition module, wiring, coil and coil wire are ok. This is really kind of an outdated method. I prefer a labscope to monitor a crank position sensor output, but I doubt the fellow here in need of help has one or knows how to use one.<br /><br /><br />My bad on the module/sensor confusion. I was thinking in terms of later model ignition systems that only had a sensor mounted in the distributor.<br /><br />In any event, given that the test light is not blinking (it does light, correct?) and the coil is now new, I would suggest, if you have the capabilty, to ohm out the coil wire or replace it with a new one (they are cheap and just a "testing" one is readily available). <br /><br />If there is still no spark, perform the crank sensor "substitution" test outlined above. Make sure you have a good ground!! If you now have spark, the crank sensor (pick-up coil, rpm sensor, Hall Effect switch - pick your terminology) is defective. If you still don't have spark, then the ignition module is bad.

 

[mgeorge15]

Re: 1990 mercruiser 4.3 no spark

i followed the chart and it is pointing me to the ignition sensor in the distributor. Only problem is no auto parts stores carry them so I have to order it. Thanks for all the help.

 

[Don S]

Re: 1990 mercruiser 4.3 no spark

Good grief cny boater, get a grip. He has a 1990 4.3 carbed engine with a Thunderbolt IV ignition, not an MPI engine you have crank sensors on, and he damned well doesn't need a labscope to check out a crank sensor he doesn't have.<br />The "substitute the coil" is the NEXT TO LAST step in the process and the ignition module is the LAST step.<br />Your problem with the flow chart is not knowing how to use it.<br />mical used it and found a bad ignition sensor in the distributor, which is a fairly common problem on the TBIV ignitions. <br /><br />It's a Mercruiser distributor mical, which is why you don't find the parts at an autoparts store. It's ONLY used on Mercruiser engines.

 

[cny boater]

Re: 1990 mercruiser 4.3 no spark

Don, what type of signal does the pick-up coil produce on a Thundervolt IV system and how do you measure it? Sorry for my lack of marine terminology, but an "RPM signal generator", be it a crank sensor on an MPI engine or a pick-up coil on a carbed engine, basically does the same thing, and that is to provide engine speed to either an ignition module or ECM.<br /><br />I stand by my comments on the flow chart. Someone could very easily be led into an improper diagnosis by using that chart, and in more than one direction. <br /><br />Who pays for the parts if you were to follow that chart and replace both the ignition coil and ignition module only to find out that the coil wire was bad?

 

[Bondo]

Re: 1990 mercruiser 4.3 no spark

Good grief cny boater, get a grip. Your problem with the flow chart is not knowing how to use it.

Ayuh,..................<br /><br />cny boater,... You wouldn't be Complaining if that Manual said Seloc on the cover.........<br />I KNOW I can say it Here,+ You won't be editing My posts here at iboats, like You did at BoatingABC.com a couple of months ago..........<br /><br /> Seloc Manuals $uck........ <br /><br />Now,... You run right back over to Your forum,+ Tell Kevin that I'm Trashing His So Called Manuals.......Ya,... Kevins Manuals are right up there with a Sears catolog,.... Good for Wiping your Arse,..... NOT working on Engines......<br /><br />Ayuh,..... You go get Kevin,+ You 2 can TRY to defend his manuals here,.... Where Neither of You can Edit,+ Delete My posts that point out the Major Short coming of Seloc So Called Manuals..............<br /><br />I Dare You,........ I Double Dare You..........<br /><br />You sir,+ Kevin from Seloc are the Reasons I went over to boatingabc,.....<br /><br />To TRY to STOP the Major MIS-Information being thrown about to the Poor Unknowning boaters at boatingabc..................<br />And,... Now You're doing it Here......<br />

quote:<br />--------------------------------------------------------------------------------<br />I am not familiar enough with that system to know the components used. The distributor "sensor", in this case, may actually be an ignition module. <br />--------------------------------------------------------------------------------<br /><br />Then giving advise on how to troubleshoot it isn't a real good idea either. The sensor is not the same as the module. <br /><br />

 

[marinemech1]

Re: 1990 mercruiser 4.3 no spark

i,ve found this is a fast way to test pick up coil<br />put a spark tester in coil<br />turn on key <br />find shift interupt switch<br />flick switch coil should spark if it does replace pick up coil<br />note: this test assumes coil has power

 

[Don S]

Re: 1990 mercruiser 4.3 no spark

Bondo, sounds like you might have had conversations with cny boater before and I might be better off to save my typing fingers.

 

[Don S]

Re: 1990 mercruiser 4.3 no spark

marinemech1<br />Sounds a lot like the section of the flowchart just prior to "Substitute coil"

 

[Bondo]

Re: 1990 mercruiser 4.3 no spark

I'm Pretty Certain that This cny boater, is the Same cny boater who has Moderator's powers over at boatingabc.........<br /><br />Him,+ Kevin, the publisher of Seloc Really Didn't like Me pointing out the Serious Short Comings of the Seloc Manuals..........<br />Of Course, Things escalated from there.....<br />My posts were edited by cnyboater to make Me look like the Idiot that Both of them Truely Are............<br /><br />That's where I met cclancer,.... He's the 1 that started the thread about the Screwed Up Manual....He was Questioning wether the Pictures, OR the Text was Right,.... Because they Didn't Match............

 

[marinemech1]

Re: 1990 mercruiser 4.3 no spark

its quick no meters required and it works

 

[cny boater]

Re: 1990 mercruiser 4.3 no spark

Bondo, what in the world are you talking about??<br /><br />Again, my jaw is still on the ground.<br /><br /> I have nothing to do with moderators on BoatingABC. I have never edited or had anything to do with editing any post on BABC. In fact, I had nothing to do with that thread at all. You are surely mistaking me with someone else. Maybe you should get your story straight.<br /><br />If you hate BABC so much, then why did you pop in recently to say hello?<br /><br />If you need to know the truth, I don't hold aftermarket information sources in high regard. I have only OEM Merc service manuals for my boat and I have made my opinion known on aftermarket information sources on BABC. That does not preclude Merc from printing bogus information from time to time. This, IMO, is one of those times.<br /><br />Man, some of you guys have problems over here...

 

[tommays]

Re: 1990 mercruiser 4.3 no spark

if you cant follow that chart then you cant do your own repiars<br /><br />it could not be more clear and involve less steps to get directly to the problem<br /><br /><br />tommays

 

[Bondo]

Re: 1990 mercruiser 4.3 no spark

OOOOppss,.......Boy, O Boy am I a Total Idiot...................<br />I've mistaken you for someone you're Not..........<br />I'm Truely Sorry....... Really Sorry....... Really, Really Sorry...........<br /><br />I went over there after being Invited to see the thread by someone from here........After all,... I was being Welcomed by someone in the off topic section,.... There I Never go.....<br />I Still wander over to the engine section on occassion.... But Rarely.....