3.0L hard starting when warm

[alldodge]

I would try disconnect the plug from the Temp switch. As before one side will have power until the motor starts, then it will be ground and go to zero. You could pierce the insulation but that can cause issues later if not sealed up

If after the motor starts the lead goes to zero, you know the TKS module is turned ON

 

[Dremmick1985]

I would try disconnect the plug from the Temp switch. As before one side will have power until the motor starts, then it will be ground and go to zero. You could pierce the insulation but that can cause issues later if not sealed up

If after the motor starts the lead goes to zero, you know the TKS module is turned ON

I verified the tks works. I hear the “hissing” and the back of the module gets hot. When the engine is running the module has 12v power. The issue is that when I turn off the engine hot there is no voltage being sent to the TKS module. Im assuming the sensor is bad and replace it. What are the 2 sensors for shown below? The gauge is not working either it’s stuck on 150 all the time when the key is on. The one on the left appears to be for an audible alarm and the run on the right for gauge? Can the gauge one be tested?

 

[tank1949]

I have a 2005 mercrusier 3.0L with TKS carb. The boat starts instantly when cold but starts really hard when warm seems like its flooding itself.

I replaced the dist cap , rotor, spark plugs, spark plug wires, and fuel filter.

I have only been exposed to carbureted MCs, but most of the time when they were hard to start (crank) after getting hot, was due to too much "advanced" timing. If it turns over but will not "ignite" I after heating up, suspect perhaps a wire from coil is leaching current? Buy some GOOD rubber gloves and wiggle wires on motor at night. If leaching, you will find it. Trust me.

 

[alldodge]

I verified the tks works. I hear the “hissing” and the back of the module gets hot. When the engine is running the module has 12v power. The issue is that when I turn off the engine hot there is no voltage being sent to the TKS module. Im assuming the sensor is bad and replace it. What are the 2 sensors for shown below? The gauge is not working either it’s stuck on 150 all the time when the key is on. The one on the left appears to be for an audible alarm and the run on the right for gauge? Can the gauge one be tested?

The one on the left is alarm - Tan/Blue wire
The one on the right is the gauge sensor - Tan wire

Test gauge sensor but putting in a pan of water. Connect ohm meter and heat it up

 

[Dremmick1985]

The one on the left is alarm - Tan/Blue wire
The one on the right is the gauge sensor - Tan wire

Test gauge sensor but putting in a pan of water. Connect ohm meter and heat it up

Definitely a bad sensor. Is the ring terminal near to starter solenoid supposed to be hooked up to something?

 

[alldodge]

The ring terminal is most likely used for something else that could be installed but wasn't like a Mercathode. Being black it should be a ground

 

[Dremmick1985]

Sorry for the confusion but I wanted to know how test the TKS temp sensor. The TKS module seems to work since I hear the hissing sound during startup when cold and goes away after about 8 mins. The back of the module is hot to the touch. When I turn the engine off hot there is no longer 12V being supplied to the the TKS module so I suspect its a bad tks temp sensor.

 

[alldodge]

The temp sensor is a switch on/off. Put in water and heat it up. Manual shows
If the coolant temperature is above 43º ± 3º C (110º ±8º F) the switch should be closed

 

[alldodge]

Switch is item 32

Electrical Components

Electrical Components

www.mercruiserparts.com

 

[Dremmick1985]

Switch is item 32

Electrical Components

Electrical Components

www.mercruiserparts.com

This manual shows you should not have continuity at 110F and should have continuity at 130F. I get no continuity from 70F to 150F. I’m guessing the sensor is bad since it never closes the circuit and provides a ground

 

[alldodge]

Agree its bad, but it list 110 +/- 8 which means it should be open between 102* to 118*

If it closed at 110 but was open at 111* I wouldn't replace it

Edit: agree I misspoke at first

 

[Dremmick1985]

Agree its bad, but it list 110 +/- 8 which means it should be open between 102* to 118*

If it closed at 110 but was open at 111* I wouldn't replace it

Edit: agree I misspoke at first

Which seems weird because when you start a engine cold <90F you would want it to remain open so you are not sending voltage to the Tks module

 

[alldodge]

Less then 90* it is open, it's open at 118 and closes at 119. My comment was if it closed at 110 I wouldn't replace the switch

 

[Dremmick1985]

Less then 90* it is open, it's open at 118 and closes at 119. My comment was if it closed at 110 I wouldn't replace the switch

I replaced the tks temp switch and still don’t get 12 volts to the tks when engine is warm. I’m at a loss

 

[alldodge]

Something isn't right. TKS is working when motor is first started. This says that the oil pressure switch works.

Once warm temp switch is not applying a ground. The ground wire is not grounded, the wire going to ground side of TKS is broken or there is another bad connection. Check continuity between TKS and oil switch and temp switch

 

[Dremmick1985]

If I put a jumper wire on the tks temp sensor input into the harness I get 12 volts to the tks module. Maybe my thermostat is stuck open? It’s a bear cat to restart when warm. I replaced my temp sensor for the gauge and it just reads 175

 

[Dremmick1985]

If I put a jumper wire on the tks temp sensor input into the harness I get 12 volts to the tks module. Maybe my thermostat is stuck open? It’s a bear cat to restart when warm. I replaced my temp sensor for the gauge and it just reads 175

Got got to mention I tested the tks temp switch in hot water and it closed the circuit at 135F

 

[alldodge]

If I put a jumper wire on the tks temp sensor input into the harness I get 12 volts to the tks module. Maybe my thermostat is stuck open? It’s a bear cat to restart when warm. I replaced my temp sensor for the gauge and it just reads 175

You should have 12V on one lead of the TKS module full time, doesn't matter if the key is ON or OFF. It comes from a 20 amp fuse which is connected to the red/purple wire coming from the 50 amp breaker

 

[Dremmick1985]

Test with a positive lead on one of the leads and the other grounded to the block? I found out my thermostat was partially stuck up which would explain why the engine temp never got hot enough to provide the ground from the TKS temp sensor.

 

[nola mike]

Test with a positive lead on one of the leads and the other grounded to the block? I found out my thermostat was partially stuck up which would explain why the engine temp never got hot enough to provide the ground from the TKS temp sensor.

Ok, I'll take a stab, but I don't have the actual wiring diagram to look at (@alldodge ?), so making a few assumptions, correct me if those are wrong. Also, one of the assumptions is that the 3.0 still has a mechanical fuel pump and doesn't need the diode and fuel pump connections?

1. You should only have 1 12v input into the module. It should be hot all the time--measure this by grounding to engine block.
2. There's one 2 wire plug into the module, one constant hot 12v and one switched ground from the OP switch and temp switch
3. So that means you can disconnect the connector from the module to do the testing. With it disconnected, you should get 12v between the terminals if the OP switch is closed (while running) OR the temp switch is closed (running warm/off warm). Alternatively, you can check for resistance between the plug negative and engine ground--should be 0 when either of the switches are closed. If you get 0 ohms/12v between terminals when running but not off, the problem with the wiring in the temp switch (since you already replaced it and verified that it's good presumably). Either the input from wherever it connects to engine/battery ground or from the switch to wherever it ties into the TKS/OP switch ground. So you'd start by checking the ground wire resistance to battery neg in both of those legs (but depending on how much current is going through the circuit that may not be a definitive test, you'd want to measure voltage drop)

I replaced the tks temp switch and still don’t get 12 volts to the tks when engine is warm. I’m at a loss

Also note that you should *always* get 12v to the module when measured between TKS + lead and engine ground. You should only get 12v when measured between the plug terminals when the OP/temp switch is closed (ie engine running or warm). Doesn't matter if the plug is connected or not.