4.3L won't shut off with key, fuel pump runs constantly

[RyanSS]

Good news there. I would still modify the wiring at the 90A block on the starter. An alt should only blow the alt fuse and not affect the ships power.

So you would separate the orange ALT output wire and the red system wire into different connectors and run the orange wire to the positive solenoid post on the BAT side of the fuse and leave the red ignition system wire on in the "engine" side of the fuse?

So if that fuse blows again, the ALT is still connected to the battery but the ignition system is not and therefore still protected. Correct?

 

[Bt Doctur]

No, the orange wire from the alt to the battery lug is protected by the 90A link.that you leave. You remove the red wire by cutting it away from the block, piece it out to make it longer if necessary with #6 crimp connector and some #6 wire. crimp a ring connector that fits over the battery lug on the starter .The red wire is protected by the 50 A circuit breaker and the 50 A breaker protects the engine and ships wiring. Should you develop an alt burnout, /failure/ excess voltage the 90A should blow but you still will have ships power to run the engine ,

 

[Bt Doctur]

 

[RyanSS]

Ah, got it. Any idea why mercruiser has the orange and red wire connected on the same ring terminal?

 

[Bt Doctur]

3 more inches of wire $.15 cents and a ring connector cost more
forgot what manual I got the pic from but it shows the red wire to the starter. later production has both wires crimped to the same terminal that bolts to to 90A block.

 

[RyanSS]

Update: Replaced the alternator....i now have 14.1x volts at the battery at 1k rpms. BUT....motor still runs with key off and fuel pump still runs with motor off and battery switch on. Pulled the TKS diode and have continuity both directions. So...shorted TKS diode. With the diode removed, the motor starts and shuts off normally. The weird thing is, the TKS system seems to be functioning normally too. With the diode removed, the motor starts, idles arouns 800-900ish rpms with the tell-tale TKS hissing sound. After a few minutes of warming up, the hissing lessens and then stops completely while the rpms drop to normal warm idle speed. If the TKS system works without the diode, and the motor starts, runs, and shuts off normally without the diode....then why is it there and should i bother replacing it? The 20amp fuse for the TKS module is good.

I'll replace it next anyway. Anything else i should test while i wait for it? So far, I've replaced the blown 90amp fuse at the starter solenoid, replaced the alternator, and fixed the orange power wire going from the alt to the starter solenoid.

 

[RyanSS]

Ok experts....check my logic here:

part of the TKS system is a temp switch. If the TKS diode is missing, the only way for the TKS module to get power is via the temp switch. If it's warm enough for the temp switch to be "closed", then the TKS module will function normally. But if the engine is completely cold, then the temp switch will be "open" and therefore the TKS module gets its power from the fuel pump/oil pressure/circuit breaker circuit. Correct? Could this be why the TKS system seemed to work correctly for me even with the TKS diode removed? When I did that, the motor was "warm". I'm going to let it cool down completely cold and see if the TKS system still works.

 

[Fun Times]

Merc service bulletin 2006-04

Situation
A blocking diode is used in the electrical system of MerCruiser V6 and V8 engines with TKS (Turn Key Start) carburetors. When the engine is warm but is not running, a temperature switch allows positive current to flow to the TKS heater module, while the diode prevents the positive current from reaching the electric fuel pump and the ignition system. This prevents the carburetor from returning to cold start mode when the engine is turned off but still warm. Under some conditions the blocking diode in the electrical system can fail. Two failure modes for the diode are possible. One is that the diode is shorted internally and will pass current both ways, and the other is that the diode is open internally and will not pass current through either way. ? If the diode is shorted internally, the engine will continue to run after the key is turned off. If this condition is found, removing the diode from its connector will shut the engine off. ? If the diode is open internally, the TKS module will not have positive current when the engine is warm and the key is off. The engine will be hard to start when it is warm.
Correction
If an engine will not turn off or becomes hard to start when warm, check the blocking diode with an ohmmeter to determine if the diode is the problem. If the diode has continuity both ways, it is shorted. If the diode does not have continuity either way, the diode is open. If either condition is found, the diode needs to be replaced for the engine to operate properly. Replace the diode and test the engine to verify: 1. The engine turns off with the key switch and the lanyard switch.
2. Both positive and negative current are supplied to the TKS module connector after the engine reaches operating temperature and the engine is turned off (Refer to "Testing for Voltage at the TKS Module" ) .

http://ww2.justanswer.com/uploads/ROCKETBOAT/2008-12-09_042450_TKS.pdf

 

[RyanSS]

Bingo. Fixed. Replaced the diode, all is right with the world again.