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2004 4.3l Mercruiser no spark

gotten

New member
2004 Sea Ray 185 Sport with 4.3l Mercruiser, Thunderbolt V ignition.
As a preventative maintenance routine, I replaced the distributor cap, rotor, ignition sensor module in distributor, and ignition coil. The boat ran fine the day before this maintenance. I started the engine immediately after the maintenance and it started. Now the engine won't fire the day after. Cranks strong but no spark. Also have new starter battery. I followed the Thunderbolt V troubleshooting flow chart, with the following results. Gray tach lead not shorted. 12.4 volts at the positive terminal on coil. 11.6 volts at the wht/red lead coming from the ignition module. No spark when striking wht/grn lead against ground. Kill switch was bypassed years ago. Carb getting fuel. Spraying carb cleaner and cranking gives no results. I can't believe the ignition module could have gone bad in one day. Disconnected the gray tach wire from coil and still no spark. Is 11.6volts from the ignition module a problem? Is there a neutral or other switch I'm overlooking that would allow cranking with no spark? Hoping to avoid replacing the ignition module if not necessary.
 

kghost

Silver Medal Contributor
Check shift interrupt switch on shift bracket where the two cables are. If that switch is made no spark.

It wouldnt be the first time a new part failed


Swap out the new for the old parts one at a time and see what fixes it if it does.

Tests for Thunderbolt Ignition:


Tests for Thunderbolt Ignition:
With ignition key on AND BILGE WELL VENTILATED OF GAS FUMES!!!

#1 - Connect your voltmeter neg. lead to the engine ground and pos. lead to the white/red wire terminal at the dist. It should read 12 volts.

#2 - If 12 volts is present, remove the coil spark wire from the distributor and connect it to a spark gap tester to ground. Remove the white/green lead from the dist. terminal. Turn the ign. key to on and strike the white/green lead to ground. If there is spark, replace the ignition sensor in the dist.

#3 - If there is no spark, substitute a new coil and repeat test #2. Now if you get spark, install a new coil. NO SPARK, replace ign. amp.

#4 - In #2, if there is No voltage present, disconnect the white/red wire and check it again for 12 volts. If 12 volts is present, replace the ignition sensor inside the dist. cap. If no 12 volts present w/it disconnected--ignition amplifier is shot and must be replaced.
 
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gotten

New member
Thanks kghost - More troubleshooting to go. I'll check the shift interrupt. I'm hoping I just got a bad (new) ignition sensor since its behaving the same as it did when the factory original sensor failed 5 years ago. Do you know where the kill switch circuit terminates? At the coil or at the relay panel under the dash? Trying to trace any possible electrical faults that would kill the spark in addition to component failures. Thanks for the input!
 

kghost

Silver Medal Contributor
The "Lanyard" switch interrupts the Purple wire going from ignition switch to lanyard back to dash (daisy chained to all gauges) then thru wire harness to ignition at engine. simply join the two wires together (after removing from lanyard) for TESTING ONLY. If you have 12 volts to ignition coil with key on then Lanyard is closed.

The shift interrupter switch is easy, One of the leads goes to ground, simply disconnect that ground wire and the ignition cannot be shorted to ground. I believe the other wire (white with green) goes to the ignition module wire harness and short ignition there. On some TB IV and older ignitions it went to coil - where tach leads connects.

I have seen new pick ups fail after a few engine rotations.................kind of leaves you dumb founded for a bit...........
 
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gotten

New member
Thanks Jack - I bypassed the kill switch joining the two wires. I get 12 volts at the ignition coil. I'm probably going to just try another ignition sensor, assuming my new one died after the first crank. Before shelling at $500.00 for a new ICM, I'll probably go for the Delco EST complete change out. What a pain. This boat has been trouble free for the last five years since I purchased it. Oh well.
 

kghost

Silver Medal Contributor
You did get the correct coil didn't you?

People install the wrong ones all the time.

The correct coil is one that has a internal resister. If it is one for external resistor it can fail......

I have come across a few............quick $20 fix
 

gotten

New member
Yea, I've got the correct coil. The problem actually started after replacing only the distributor cap, rotor, and ignition sensor. The boat started immediately after that but hasn't started since. I replaced the coil the next day and still don't get any spark. Makes me wonder if the ignition sensor fried after that first crank.
 

gotten

New member
Thanks to all who responded to my problem. A new distributor sensor solved the problem. The first sensor I installed failed after the first crank. Second one worked.
 

Beaverlaker

New member
I am new to this forum, but just received great benefits from post #7 above on this thread. I am sharing my story here hoping that may help others.
To prepare for the 20th season with my 1998 Maxum, Mercruiser4.3 Thunderbolt V, two years ago I replaced the electronic components : plugs, distributor, ignition sensor, plug wires, and coil. All of these parts are made by Sierra, because having had much luck with Sierra parts in the past, I stayed with Sierra. Especially, the Sierra coil, PN 18-5438, was even more expensive than the Mercruiser one PN 805570A2. We had very good time with the boat performance for the 2017, and 2018 seasons. The 2019 season started out well as expected, the first 30 min ride was responsive and peppy performance, then all of a sudden engine ran rough. Engine was turned off for inspection, and would not restart again. Boat got towed to slip, and an hour later engine would start easily as if there never was an issue. The problem can easily be recreated: driving the boat hard for about 20 min, turned off engine, while the engine was still hot it would crank but not started. A spark tester inserted between the coil and distributor will show no spark, but once cooled down, couple hours later engine will start to the first turn of the key. A comparison of the Sierra coil and the original 20 year old Mercruiser coil (I've saved ) showed 1.2 ohm for Sierra and 0.8 ohm for the original coil. After reading this post, and cross reference to few others, my understanding is that the Sierra coil using external resistor is not compatible with Thunderbolt V ignition. Having no luck finding a new Mercruiser coil locally due to the holiday activities, the original 20 year old coil has to go back replacing the Sierra, Boat runs well now and starts easily hot or cold. Also noticed that engine responses solid to throttle, not peppy as with the Sierra coil, and it seems all gauges register normal, not fluctuating or a little on the high side while with Sierra coil. Also wondered if the Sierra coil may have caused other damages to the electrical system. I appreciated the information posted on this forum. Kghost saved my July 4th, thanks!
 
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kghost

Silver Medal Contributor
Fyi, 99% of all electronic ignitions use a INTERNAL RESISTER coil.

Only point ignitions used a External resister coil.

Another FYI, any automotive coil internal or external is exactly the same as marine.

So you can go to any auto parts store to purchase the correct coil....
 

markic

New member
Fyi, 99% of all electronic ignitions use a INTERNAL RESISTER coil.

Only point ignitions used a External resister coil.

Another FYI, any automotive coil internal or external is exactly the same as marine.

So you can go to any auto parts store to purchase the correct coil....
thanks for all your input solving this issue, I have similar on a 4.3 220mpi and will work through your test method/s
 
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