1989 MERCRUISER 4.3 V6 WONT SPARK

[Snipesvi]

I have a 1989 Mercruiser 4.3 v6 with thunderbolt IV ignition. I can?t get it to spark. I have been on a lot of forums and seen some of the more common problems. I have gone through the thunderbolt IV ignition troubleshooting chart. I have replaced the distributor cap and rotor, the sensor, the ignition amplifier (replaced with a used guaranteed to work amplifier) ignition coil, wires and plugs, starter, and battery. Could the wrong wires be to blame? I originally order plugs and wires together but the plugs ended up being the wrong ones and I had to get new ones. The wires fit correctly. But is there a chance that they are wrong too and causing a no spark? I have tried bypassing the shift shutoff and tried bypassing the main wiring harness by jumping the starter and straight wiring power to the coil from battery. Also have tried pulling off the grey wire from the tacho on the - side of the coil. I have 12v on + and - at coil,(is this normal? ) I did not have power on the red/white or green/white from amplifier to sensor until I replaced the amplifier wire harness. I now get 12v on red/white (with engine on run) with the original amplifier and with the used amplifier that I bought. I did manage to shock myself while holding the coil lead but didn?t see a spark at all. I also get 12v at top of coil and took distributor cap off and have 12v on red/white wire at sensor. I have little gas in the tank currently. Had to clean the carb (2 barrel) but once I did gas flowed nicely when called for manually. Engine has a manual pump so I don?t know if it?s working and if this could be a fuel problem but that wouldn?t prevent spark. Could I have ended up with 2 bad amplifiers? I turned engine over with cap open and rotor is spinning (how fast should it be spinning)? I haven?t checked compression but plan too) but not sure if that prevents spark. I was thinking about the timing chain being a problem maybe? Also the trim pump won?t trim down and I think that it?s just a bad solenoid (could the bad solenoid be grounding something out preventing spark)? Anyone that may have any tips would be appreciated. Thanks

 

[alldodge]

Howdy snipesvi

You provide some good info, but it sure was hard to read. Try less capital letters and maybe hit the return a bit more.

In any case, The TB-4 and 5 troubleshooting guide should have found the issue. Below is the guide for the TB-V but is also for the TB-IV.
The Wht/Red wire is checked for 12V coming from the amplifier, if 12V found, then reconnect.
The Wht/Green wire is removed and struck on a ground rapidly while checking for spark.
At which point by following this guide did it not work?

 

[Bondo]

I HAVE A 1989 MERCRUISER 4.3 V6 WITH THUNDERBOLT IV IGNITION. I CANT GET IT TO SPARK. I HAVE BEEN ON A LOT OF FORUMS AND SEEN SOME OF THE MORE COMMON PROBLEMS. I HAVE GONE THROUGH THE THUNDERBOLT IV IGNITION TROUBLSHOOTING CHART. I HAVE REPLACED THE DISTRIBUTOR CAP AND ROTOR, THE SENSOR, THE IGNITION AMPLIFIER (REPLACED WITH A USED GAURANTEED TO WORK AMPLIFIER) IGNITION COIL, WIRES AND PLUGS, STARTER, AND BATTERY. COULD THE WRONG WIRES BE TO BLAME? I ORIGINALLY ORDER PLUGS AND WIRES TOGETHER BUT THE PLUGS ENDED UP BEING THE WRONG ONES AND I HAD TO GET NEW ONES. THE WIRES FIT CORRECTLY. BUT IS THERE A CHANCE THAT THEY ARE WRONG TOO AND CAUSING A NO SPARK? I HAVE TRIED BYPASSING THE SHIFT SHUTOFF AND TRIED BYPASSING THE MAIN WIRING HARNESS BY JUMPING THE STARTER AND STRAIGHT WIRING POWER TO THE COIL FROM BATTERY. ALSO HAVE TRIED PULLING OFF THE GREY WIRE FROM THE TAC ON THE - SIDE OF THE COIL. I HAVE 12 V ON + AND - AT COIL,(IS THIS NORMAL? ) I DID NOT HAVE POWER ON THE RED WHITE OR GREEN WHITE FROM AMPLIFIER TO SENSOR UNTIL I REPLACED THE AMPLIFIER WIRE HARNESS. I NOW GET 12V ON RED/WHITE (WITH ENGINE ON RUN) WITH THE ORIGINAL AMPLIFIER AND WITH THE USED AMPLIFIER THAT I BOUGHT. I DID MANAGE TO SHOCK MYSELF WHILE HOLDING THE COIL LEAD BUT DIDNT SEE A SPARK AT ALL. I ALSO GET 12V AT TOP OF COIL AND TOOK DISTRIBUTOR CAP OFF AND HAVE 12V ON RED/WHITE WIRE AT SENSOR. I HAVE LITTLE GAS IN THE TANK CURRENTLY. HAD TO CLEAN THE CARB (2 BARRELL) BUT ONCE I DID GAS FLOWED NICELY WHEN CALLED FOR MANUALLY. ENGINE HAS A MANUAL PUMP SO I DONT KNOW IF ITS WORKING AND IF THIS COULD BE A FUEL PROBLEM BUT THAT WOULDNT PREVENT SPARK. COULD I HAVE ENDED UP WITH 2 BAD AMPLIFIERS? I TURNED ENGINE OVER WITH CAP OPEN AND ROTOR IS SPINNING ( HOW FAST SHOULD IT BE SPINNING)? I HAVENT CHECKED COMPRESSION BUT PLAN TOO )BUT NOT SURE IF THAT PREVENTS SPARK.) I WAS THINKING ABOUT THE TIMING CHAIN BEING A PROBLEM MAYBE? ALSO THE TRIM PUMP WONT TRIM DOWN AND I THINK THATS ITS JUST A BAD SOLENOID ( COULD THE BAD SOLENOID BE GROUNDING SOMETHING OUT PREVENTING SPARK? ANYONE THAT MAY HAVE ANY TIPS WOULD BE APPRECIATED. THANKS

Ayuh,.... Welcome Aboard,.... WHY ARE YOU YELLIN" AT US,..??

Unlock the cap button, 'n use a few paragraphs so that yer posts are Readable,...

Like AD says, the diagnostic tree will point out the failin's of the system,...
You say you went through the diagnostics, What, Exactly did ya find,..??

 

[Snipesvi]

Alldodge- I apologize for the state of my post. I will correct the appearance tonight. I posted late last night and didn't even notice the all caps. Probably should not have done it on my phone.
Anyway, that is the chart that I followed. However I never tried striking the green/white to ground. I skipped this step because I had already replaced the coil, sensor, and amplifier. I will try that tonight.
Do you know if I should be getting stready 12v at coil on + and -? Some people say it's normal due to low resistance and some say it should be a pulsing signal. Thanks

 

[Snipesvi]

Bondo- completely unintentionally did the all caps. First problem was no power at coil. So I purchased new coil to no avail. I found a problem in the purple wire coming from the ignition to positive on coil and I replaced that wire. (Which I know I should have checked first)
Next, I had no power from the red/white coming from the amplifier. Since the amplifiers are not cheap I elected to go ahead and replace the sensor first. New sensor was installed but still no power at red/white.
So next I replaced just the amplifier. Still I had no power at red/white. I unhooked the green wire from shift switch and took grey from tac off the coil but still no power on red/white. So I decided to purchase a new harness for the amplifier. This fixed the red/white issue. I have 12v from amplifier red white and from sensor when connected. But still no spark. I also replaced the rotor and cap but that didn't help anything.
The only sign I've had of a spark is when I connected straight positive from battery to coil and jumped the starter with the wiring harness unplugged I received a pleasant shock! But I have yet to see a spark.

 

[alldodge]

Do you know if I should be getting stready 12v at coil on + and -?

Yes, there should be 12V on both sides, if the sensor is not shorted.

 

[Snipesvi]

Ok, I am re-writing my post so it can be read easier...

Here is what I have. 89' mercruiser 4.3 V6 with thunderbolt IV ignition. The engine is trying to crank but I cant seem to get a spark. I have replaced the following battery, starter, the ignition amplifier and harness, the coil, the dist. cap, wires and plugs, sensor, and rotor. I now have 12 v on positive and negative at coil. I also have 12v at red/white wire from amplifier. I had no power at red/white wire until I replaced the amplifier wire harness. Both of the amplifiers I currently have seem to work. I also have 12v coming from sensor wire which I tested with the cap off. I have used the Thunderbolt troubleshooting graph and followed it fairly closely. However I have not tried striking the green/white wire to ground with key on yet but will tomorrow. I'm not sure if this will matter considering I have replaced all the ignition components already. I have also tried bypassing the shift cutout switch and the throttle remote (in case there is a neutral safety stuck in there).

​Now one sign of life was when I connected power straight to coil and pulled lead off the cap I got a shock when jumping the starter trying to see a spark. I got a shock but saw no spark. My method was laying the wire on top of engine because I figured that would be a good enough ground to see an arc. Perhaps I am not doing something correctly? If all of my parts of the ignition are good then what else could I have going on?

​Just in case anyone wants to know as far as fuel I have great spray at carb when I manually depress the throttle. I have not checked the fuel filter as of yet but I have replaced the fuel line on both sides of the carb. I have also pulled the gas tank and siphoned out the old gas and put in an additive when I added new gas for testing purposes. However there isn't much gas in the tank (not that that matters if I don't have spark).

​There is a oil pressure switch on the top of the engine that has a blue wire ran to it. Does anyone know if I am supposed to be getting 12v there? I am only getting 6v. Reason I am asking is that some setups the engine wont run if oil pressure sensor is bad. Not sure that mine does anything more then give me a reading on the gauge but thought I would throw that out there.


​

 

[alldodge]

I think you mean the man overboard switch. This switch removes 12V from the coil, so if its is present then this isn't the issue. The neutral safety switch disconnects 12V from the starter solenoid so the engine will not crank.

If a plug wire was removed from the cap and laid on the block you would not see a spark. You would need to remove the coil wire from the cap to see spark in this method. If a plug wire is removed at the plug end, a screw driver is inserted and the metal part of the drive is held next to the block you should see spark. When striking the Wht/Grn wire you need to pull the coil wire from distributor and hold it near the block

With gas removed, you might just have a fuel issue and not spark. To find this out, take a tablespoon of fresh new gas and pour down the carb, then try cranking

 

[Snipesvi]

So here is where I am at. I do in fact have spark from coil when striking the green/white wire against ground. However I have not been able to get a spark from my spark plug wires using the screw driver method. According to the chart this indicates that the sensor is bad in the distributor. I have already replaced that with a new one. Could it also be something else or did I get a dud? I have also replaced the rotor and have verified that it is spinning. I also tried pouring some gas straight into carb but that didn't change anything.
Thanks

 

[alldodge]

So here is where I am at. I do in fact have spark from coil when striking the green/white wire against ground. However I have not been able to get a spark from my spark plug wires using the screw driver method. According to the chart this indicates that the sensor is bad in the distributor. I have already replaced that with a new one. Could it also be something else or did I get a dud? I have also replaced the rotor and have verified that it is spinning. I also tried pouring some gas straight into carb but that didn't change anything.
Thanks

Maybe

If you are getting spark with the White/Green wire then your ignition systems is working and maybe the sensor or the wheel which passes by the sensor.

I hope you have help, one crank the key and the other hold the plug wire. You can do this by your self but should use a spark gap gauge. This gauge allows the plug wire or coil wire to be connected to the gap gauge and ground. This way you can clearly tell if it works.

Take a pic of your distributor and sensor with cap off and rotor in place, and another with rotor removed.

Need to see what your seeing

 

[Snipesvi]

I will try this in the morning weather permitting. Thanks

 

[Snipesvi]

pics of rotor

 

[Baylinerchuck]

Obviusly you have the coil wire landed on the center post of the distributer cap..... this may sound dumb, but I noticed this on my new plug wires. I think I bought ones like you. The post contact in the wire plug boot slid back into the boot. When you put the boot on the coil or the distributer, you should feel a distinct click as it snaps on. I struggled to get the coil wire on since the boot was so tight and I was having trouble with the contact sliding back into the boot. It would be worth a look. You can also check continuity on the coil wire itself to ensure it was manufactured properly.

 

[alldodge]

Was hoping the pics might show something, but there was nothing obvious. The sensor is powered by the White/Red and Grounded by the Black wire. When the rotor tang passes it sensor closes and spark fires. Assuming the White/Green remains unconnected to the shift interrupter and the Black wire has a good ground, it would tell me the sensor. The TB systems is pretty simple, and its not unheard of getting a bad new sensor. Some vendors will even exchange them

 

[Snipesvi]

I'll get a replacement sensor and give it a try.

 

[Snipesvi]

Received my new sensor today. That was the problem. The first sensor I ordered must have been bad. Got a big backfire and burned the gas I put in the carb a couple days ago. Didn't actually start but it fired a few times. So ignition is working. This engine hasn't been started in at least two years. On to the next issue I suppose. Which seems to be fuel delivery. Thanks for the help!

 

[alldodge]

Thanks for the follow up, hope the next issue is easier

 

[achris]

Just a quick note... I changed your initial post to a more manageable 'font'.

The fuel system on your engine is very simple. Mechanical (camshaft driven) fuel pump pulls fuel from the tank and sends it to the carburettor. That's it! Check for air leaks in the lines between the tank and the pump.. You should find a filter somewhere there too. check the housing. Sometimes people over tighten the inlet and outlet fittings and crack the filter housing. Very difficult to see (almost impossible most of the time), but sucks air instead of fuel... Can be a very difficult to find....

Chris.........

 

[Snipesvi]

Thanks! I had more trouble trying to figure out how to change the font and initially post a question then I did figuring out this ignition problem.
I'm thinking since it's been sitting I will go ahead and replace the filter. Also I have change two of the fuel lines. The gas tank was exposed when I acquired the vessel so before replacing the floor I figured best to go ahead. I did not change the fill line though. Thanks for the fuel system knowledge!

 

[Slimd11]

Howdy snipesvi

You provide some good info, but it sure was hard to read. Try less capital letters and maybe hit the return a bit more.

In any case, The TB-4 and 5 troubleshooting guide should have found the issue. Below is the guide for the TB-V but is also for the TB-IV.
The Wht/Red wire is checked for 12V coming from the amplifier, if 12V found, then reconnect.
The Wht/Green wire is removed and struck on a ground rapidly while checking for spark.
At which point by following this guide did it not work?

View attachment 246475

Have the same problem except mines was reading 11.7 volts at the coil getting no spark