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Mercruiser 4.3L TKS blowing 15A fuse when cranking

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Brandon1326

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I have a 2007 Crownline 19ss with a Mercruiser 4.3l TKS Mercarb engine serial # OW670023. The problem that I am having started when I couldn't kill the engine after running for about 2 hours. The engine would continue to run after turning the key off and removing it along with flipping the kill switch. Finally stopped the engine by tripping the 50a circuit breaker. Then after resetting the breaker the fuel pump would continue to run. I then turned the battery switch off and of course everything shut down. When it was time to head back to the ramp, turned the battery back on and the fuel pump started again even with the key off. Started the boat and returned to the ramp.

The next day I began to locate the problem and found that the purple and yellow stripe wire attached to the starter solenoid had a small nic so I wrapped it with electrical tape and started the boat to see if that was the problem. Since then the fuel pump doesn't continually run and the motor will turn over a few times before a 15a fuse in the wiring harness (red/purple stripe & pink/purple stripe wires) on the rear of the engine blows, which then kills all power to the ignition switch and audible alarm. My trim, blower and lights all still have power along with power to both sides of the circuit breaker. After replacing the fuse, power is restored to everything and the key works in aux and on without blowing the fuse. The fuse only blows when you turn to start. So far I have replaced the TKS diode, oil pressure switch and a relay that's tied into the harness without any luck. It should also be noted that when I unplug the purple and purple with yellow stripe wires from the oil pressure switch, the engine will turn over and over and sometimes crank and run for a few seconds without the fuse blowing.

Any ideas or suggestions of what this may be. Thanks in advance
 
the ign if it is fused should be a 20A Nothing should be added to the ign circuit under the dash , like stereos and amps. The motor and fuel pump issue could be a alt going bad and backfeeding the engine harness keeping the engine running.
 
Thanks for the reply Bt Doctur. That's correct the ign fuse is a 20A but it's not the fuse that is blowing. The fuse that is blowing is a 15A fuse that is located in the engine wiring harness and is located between the engine pin plug and the 50A circuit breaker. There is a red and purple striped wire running to the fuse that stays hot after the fuse blows and a pink with purple striped wire on the dead side of the blown fuse that runs to the harness pin. I just had the alternator, starter and starter solenoid tested and they are fine. I've tried to locate a slave solenoid on my engine but haven't been able to locate one. The wiring diagrams for this 4.3L TKS engine shows a relay in it's place. So far I have replaced that relay along with the TKS diode and oil pressure switch and still having the problem. Very frustrating to say the least. The pictures below are of the fuse and the relay. Thanks.

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Thanks, Ill give it a try. I replaced that diode but it could be the TKS module it self as noted in the bulletin. Will update my findings.
 
Brandon1326 said:
The problem that I am having started when I couldn't kill the engine after running for about 2 hours. The engine would continue to run after turning the key off and removing it along with flipping the kill switch.
Click to expand...

This is caused by the diode. If the Module is shorted it would burn the fuse and the diode. I would test you Module and your new Diode.
 
I ordered a new TKS enrichment solenoid module and when it arrived in the mail this past Monday, it looked like a fork lift ran over it, so I sent it back and waiting on the replacement to arrive. Just my luck!! Will update when installed
 
Sorry for the delay, I received the new part and had a chance to install the new TKS enrichment solenoid module yesterday. I also replaced the engine harness and TKS diode . After hooking everything back up and starting the boat on the hose, she started right up and ran fine for a minute or two. I then heard a pop sound and looked back to see that the TKS diode had exploded and smoking! Immediately I killed power to the boat. Any suggestions, I've read were the thermal switch can go bad or short out. How would I test it? Thanks
 
After changing the thermal switch (part # 866089) my problem seems to be fixed while on the hose. Hope to river test it soon! Thanks for all the advice and suggestions!
 
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