No Spark on 1988 4.3 ltr. engine

[Rivergator]

The engine has no spark on any of the 6 plugs. I pulled the plugs and had my wife crank the engine. I grounded each plug and visually checked for a spark, nothing. I even dared to touch the plug to see if I get zapped, nothing. Then I proceeded to follow the test procedure for the thunderbolt IV and this is how far I got. Battery voltage is 12.56. Key in RUN position voltage on the + side of the coil was 8.22 - 10.11. Then I disconnected the WHT/RED wire from each other and checked the end on the module side. It was 8.5. Then I checked the end that comes from distributor and it was .367. That's when I stopped because I am not quite sure that I did this right. In the next step it mentions a spark gap tester. I am not sure I know what a "spark gap tester" is and how to apply it in this case, which would be in the next test step. Also I have both test procedures in front of me, one for the TB IV and one for the TB V and they are not exactly the same. In the TB V it says to disconnect the WHT/RED bullet connector and measure it at the module end. If the voltage is 0.00 the ignition module is bad. But I have 8.5 Volts on it and according to that the module should be ok. On the TB IV instructions it doesn't say anything about disconnecting the bullet connection and maybe because I disconnected it the voltage reads 0.367, so I am not sure that I do this right. Btw. the coil is brand new and is the proper coil for the TB IV. Time to consult the experts

 

[nola mike]

The engine has no spark on any of the 6 plugs. I pulled the plugs and had my wife crank the engine. I grounded each plug and visually checked for a spark, nothing. I even dared to touch the plug to see if I get zapped, nothing. Then I proceeded to follow the test procedure for the thunderbolt IV and this is how far I got. Battery voltage is 12.56. Key in RUN position voltage on the + side of the coil was 8.22 - 10.11.

you should have battery voltage at the coil. this needs to be corrected before proceeding. a first cheater step would be to jumper a wire to the coil pos and see if you get spark then (note that you'll need to disconnect the jumper to shut down the engine if it starts, or put a plug or spark tester on the coil tower to keep it from starting)

 

[Rivergator]

you should have battery voltage at the coil. this needs to be corrected before proceeding. a first cheater step would be to jumper a wire to the coil pos and see if you get spark then (note that you'll need to disconnect the jumper to shut down the engine if it starts, or put a plug or spark tester on the coil tower to keep it from starting)

Nola, I am in the process of doing this. I will check the purple wire from the + side of the coil through all its connecting points back to the battery. I am curious though. I removed the ignition module and its on my bench. I checked the harness to make sure there are no broken wires in there. That checked out fine. I was wondering is there an on the bench test that I can do to get an idea if the ignition module is bad or not. The same question goes for the distributor sensor. Can it be bench tested? Once I get done checking the voltage discrepancy it really boils down to these 2 components, the dist. sensor and the ignition module. I did an on the bench spark test of the coil and it sparks just fine. It should, because the coil is brand new.

 

[Rivergator]

Ok, I followed and checked the PURPLE wire starting at the coil to the alternator, then to the 5 gauges, then to the ignition key switch, all the while trying to scrape away possible corrosion by twisting and moving connections I could reach, which improved voltage quite a bit. The best reading I got up to that point was 11.53 VAC at the ignition key switch. From there I followed the RED/PURPLE wire back to the alternator, the slave solenoid, the 50 Amp circuit breaker. All these points are having battery voltage of 12.59 VAC. Then I checked the voltage again on the + side of the coil and now I got a better reading of 10.39 VAC, an improvement but not the same as the battery. I assume one can expect some loss due to resistance in the wiring and old age. But anyway before I put the ignition module back in the boat and continue with the test procedure I hope somebody can answer my questing about on-the-bench testing of the ignition module and dist. sensor

 

[nola mike]

. I was wondering is there an on the bench test that I can do to get an idea if the ignition module is bad or not. The same question goes for the distributor sensor. Can it be bench tested?

no, and no real reason to. the troubleshooting basically tests each component. each step that you reach ensures that all the prior components work.
look up how to do a voltage drop test to determine where your wiring issues are. 10.4v at the coil sucks.

 

[Scott06]

Ok, I followed and checked the PURPLE wire starting at the coil to the alternator, then to the 5 gauges, then to the ignition key switch, all the while trying to scrape away possible corrosion by twisting and moving connections I could reach, which improved voltage quite a bit. The best reading I got up to that point was 11.53 VAC at the ignition key switch. From there I followed the RED/PURPLE wire back to the alternator, the slave solenoid, the 50 Amp circuit breaker. All these points are having battery voltage of 12.59 VAC. Then I checked the voltage again on the + side of the coil and now I got a better reading of 10.39 VAC, an improvement but not the same as the battery. I assume one can expect some loss due to resistance in the wiring and old age. But anyway before I put the ignition module back in the boat and continue with the test procedure I hope somebody can answer my questing about on-the-bench testing of the ignition module and dist. sensor

No on bench testing of the module. There is a thunderbolt igntion diagnostic flow chart in the stickies at top of mercruiser section to diagnose no spark in TB system. I think first thing is measure 12 v at coil ….if you have 10.4 youre loosing voltage . Make sure batt is good and fully charged run a jumper from battery to positive side of coil See if you get 12 plus volts. See if it runs with 12 v at coil before you waste time on the module

How Mercruiser Thunderbolt ignition systems work.

Mercruiser Thunderbolt ignition systems. Mercruiser introduced the Thunderbolt IV onto their engines in 1982, alongside the introduction of the 1-R drives. The TB-IV system was used until the introduction of TB-V mid-way through 1996. Thunderbolt V was an improvement on an already exceptionally...

forums.iboats.com

 

[Rivergator]

Make sure batt is good and fully charged run a jumper from battery to positive side of coil See if you get 12 plus volts. See if it runs with 12 v at coil before you waste time on the module

Sounds good Nola Mike and Scott06. I will do that. The article "How Mercruiser Thunderbolt ignition systems work" Great explanation and education how the system works. Thanks!

 

[ROY WILLIAMS]

Sounds good Nola Mike and Scott06. I will do that. The article "How Mercruiser Thunderbolt ignition systems work" Great explanation and education how the system works. Thanks!

change that ignition coil ....did the resistor ohm meter of that coil ..........

 

[nola mike]

change that ignition coil ....did the resistor ohm meter of that coil ..........

No, don't change the ignition coil. A bad ignition coil isn't why he's getting 10.4v at the ignition coil

 

[ROY WILLIAMS]

No, don't change the ignition coil. A bad ignition coil isn't why he's getting 10.4v at the ignition coil

the troubleshoot of that ignition coil ......the OHM METTER ...take it of all those wires and do the ohm meter
positive ,negative , and the distributor wire ..
did the YouTube of the coil troubleshooting ..did the resistance ...
I was the electronic tech ...

 

[Rivergator]

the troubleshoot of that ignition coil ......the OHM METTER ...take it of all those wires and do the ohm meter
positive ,negative , and the distributor wire ..
did the YouTube of the coil troubleshooting ..did the resistance ...
I was the electronic tech ...

Your posts sound like telegrams from the 1850s where the Indians cut the wire in mid air - LOL. I am still trying to figure out what the hell you are trying to say. But never mind! I think I know what to do

 

[Scott06]

Your posts sound like telegrams from the 1850s where the Indians cut the wire in mid air - LOL. I am still trying to figure out what the hell you are trying to say. But never mind! I think I know what to do

From seeing his posts dont think english is his first language but seems to have worked on engines etc. and has some knowledge base.

He is saying test the coil with an ohm meter before you replace it. You can find a bunch of you tubes on how to test primary and secondary side (thats what he means by " do the ohm meter positive ,negative , and the distributor wire ..")

 

[ROY WILLIAMS]

Your posts sound like telegrams from the 1850s where the Indians cut the wire in mid air - LOL. I am still trying to figure out what the hell you are trying to say. But never mind! I think I know what to do

yes my stone tools in my property .. did the Wamesit Indians ...
the arrow heads ,spears and the hammer tools ...

 

[Rivergator]

Well, I am very happy to tell you all that the great TB IV ignition system is AAA OK. Nola Mike and Scott06 you were dead right from the start when you said that I needed to fix that 12 V problem on the coil first before I could proceed with the ignition test. Well, as you suggested, I jumped a line from the battery directly to the + side of the coil and then did the test. It all checked out like a dream. I then reconnected everything the way it should be including the shift interrupt wire and the gray wire from the tach. I then spark tested each plug by cranking the engine and boy did they spark. I then disconnected the jumper and did the test again. Each plug still fired but the spark was a lot weaker with 10.39 V on the coil. When I first started out I had only 8.22 V on the coil but after some rubbing and scraping of all the connections I got it up to 10.39 V. Either the 8.22 V was not enough to produce a spark or it was so weak that I missed to see it, thinking my ignition system was bad. Now that I know that everything works my next priority is to restore a good 12 V on the coil. Thanks to you all I learned that it is essential and important to have 12 volts on the coil in order to have a healthy ignition system.

 

[ROY WILLIAMS]

so you did of that ignition coil ... OHM METER OF THE RESISTANCE .. YOUTUBE COIL IGNITION .. look it up ....

https://www.amazon.com/AstroAI-Digi...d2lkZ2V0TmFtZT1zcF9zZWFyY2hfdGhlbWF0aWM&psc=1