Temperature switch circuit 2000 Johnson 150hp

[Jose67]

When the temperature switch is activated and shows that the engine is hot is this just a visual warning or does it cause the engine to go in "safe mode" of operation and reduce fuel or spark? My engine overheated and I had no choice but to continue to run it until I got to an area where I could be seen and towed in. The next day when I went to restart it still shows "hot". Compression test shows all six cylinders at 92-94psi. Replaced starboard temp switch (port side switch is no longer available) still showing "hot" light. Motor is now hard to start and I have to continually hold choke for it to start and runs momentarily then turns off, seems to have fuel delivery issue now. Any thoughts on what overheating may have done to the fuel system?

 

[Chris1956]

What is engine model number? A lot of Johnson outboard motors go into SLOW mode when they overheat. They often have a horn that signals overheat.

 

[Jose67]

What is engine model number? A lot of Johnson outboard motors go into SLOW mode when they overheat. They often have a horn that signals overheat.

J150vxsss.

 

[tphoyt]

compression numbers sound low to me but at least they are even so maybe it’s just the head gaskets that got cooked. If it were me I think it would be worth pulling the heads and having a peek at what you have.

 

[Chris1956]

OK, looks to be a 60* V6 2 cycle motor. It should have the SLOW mode, activated by either temp sender.

Where does your motor show "hot"? On the System Check gauge? I would disconnect the 2 wire sensor and see that the warning goes away. The ignition must be turned off to reset the hot indicator.

The 2 wire temp sender activates the QuickStart system to help the motor warm up. You can simulate the Quickstart mode by using the throttle only button (and choke as necessary) to run the motor at about 1000 RPM until she is warm. She should then idle properly.

You might check to see if Sierra makes the temp sender that is NLA. Otherwise, buy another 1 wire sender and jumper the wiring harness to connect it, and use the cold start procedure I outlined. At least then you will have overheat warning on both heads.

 

[Jose67]

OK, looks to be a 60* V6 2 cycle motor. It should have the SLOW mode, activated by either temp sender.

Where does your motor show "hot"? On the System Check gauge? I would disconnect the 2 wire sensor and see that the warning goes away. The ignition must be turned off to reset the hot indicator.

The 2 wire temp sender activates the QuickStart system to help the motor warm up. You can simulate the Quickstart mode by using the throttle only button (and choke as necessary) to run the motor at about 1000 RPM until she is warm. She should then idle properly.

You might check to see if Sierra makes the temp sender that is NLA. Otherwise, buy another 1 wire sender and jumper the wiring harness to connect it, and use the cold start procedure I outlined. At least then you will have overheat warning on both heads.

It shows hot on the system check gauge, I can unplug the two wire sensor and goes away. Something definitely happened to the fuel system when it overheated, I can manually choke it pump primer bulb until I get fuel into the manifolds and it starts fine but I have no fuel pressure ( verified by a gauge going to starboard side carbs). When in SLOW mode what is affected, fuel or spark? I was thinking a bad fuel pump but $500 for a new pump is a lot to spend without knowing for sure if it's bad.

 

[Crosbyman]

I can manually choke it, pump primer bulb until I get fuel into the manifolds and it starts fine....

anything wrong with the lift pump ?? feeding the vst
no expert on these big engines but....
Carbs look like regular old style float valved carbs. Strange that no fuel reaches them .... any chance that VRO pump needs a look at ..? is it restricting fuel flow to the carb bowls ?

not being an injector type engine what fuel pressure were you expecting into the carbs ? ....should it be more than a few psi's (2-3??)

 

[dingbat]

What caused the over temp?

It’s possible that the over temp was the result of lean condition.

Don’t leave the malfunctioning temp sensor circuit open. Jump it out to make sure the controller is getting the appropriate feedback.

The OEM manual has a procedure to test the fuel pump off the motor.

https://www.outboardmarine.co.nz/catalogues/VRO-pump-tests.pdf

 

[Jose67]

I can manually choke it, pump primer bulb until I get fuel into the manifolds and it starts fine....

anything wrong with the lift pump ?? feeding the vst
no expert on these big engines but....
Carbs look like regular old style float valved carbs. Strange that no fuel reaches them .... any chance that VRO pump needs a look at ..? is it restricting fuel flow to the carb bowls ?

not being an injector type engine what fuel pressure were you expecting into the carbs ? ....should it be more than a few psi's (2-3??)

I checked fuel pressure on this engine a couple years ago and it had about 5psi. If my compression readings are indeed low at 92-94psi would this not be enough to pulse the fuel pump causing it not to pump fuel? In addition to checking the fuel pressure I also removed drain plug on 2 carbs and no fuel came out. Is there a way to check if fuel pump is receiving pulses?

 

[Jose67]

What caused the over temp?

It’s possible that the over temp was the result of lean condition.

Don’t leave the malfunctioning temp sensor circuit open. Jump it out to make sure the controller is getting the appropriate feedback.

The OEM manual has a procedure to test the fuel pump off the motor.

https://www.outboardmarine.co.nz/catalogues/VRO-pump-tests.pdf

I am sure it is a worn impeller as the stream from pee hole is weak at low rpm.

 

[Chris1956]

SLOW limits the spark advance and keeps the engine RPM down. A healthy waterpump will pump at 30PSI plus. Of course, there is no way to check this without a water pressure gauge, which I do recommend. Obviously you need to repair/replace waterpump before using boat. I recommend a full kit.

Your compression numbers, if all even across all cylinders are fine. That should not be the low fuel pump pressure cause.

Clean/replace the Pulse Limiter. That controls the pulse strength to the fuel pump. Check/rebuild the vapor pump. The vapor pump helps the fuel pump. Check the vapor separator cover for leaks. That must be sealed for fuel pump to pump correctly. Obviously check the vacuum lines that power vapor pump and fuel pump.

Your two overheat sensors are connected together. There is therefore no way for system check to tell what cylinder head is overheating. Leaving the defective one unconnected for test purposes is therefore acceptable. I do recommend you have both overheat sensors working before using the boat.

 

[Jose67]

Since the two wire sensor is no longer available, to replace it with a one wire sensor do I tie the 2 wires coming from the harness together and connect to 1 wire coming from sensor?

 

[Crosbyman]

If my compression readings are indeed low at 92-94psi would this not be enough to pulse the fuel pump causing it not to pump fuel?

Actually compression#s inside cylinders have nothing to do with the vacum (crankcase pressure loss during the piston up stroke) inside the crankcase.

the fuel pump works with alternating peaks and drops of pressure in the crankcase as pistons move up and down causing the diaphragm to pull and push fuel using check valves .

you should try to measure engine surface temperature variances with an infrared (cheap $$ ) gun to confirm overheat problem versus faulty temp. probes.

 

[Jose67]

I performed the fuel pump test per the Johnson service manual 3 times, results say air motor diaphragm and/or vacuum rectifier leaking- replace air motor diaphragm. Would this be just a rebuild kit for the fuel pump? Also the two wire temp sensor seems to bad, "hot" light displays when key is turned to run position on a cold motor, I can unplug it and light turns off, the one wire sensor has been replaced. Since the two wire sensor is NLA can it be replaced with a one wire sensor by connecting the two wires coming from harness together and splicing to the wire on the one wire sensor?

 

[Chris1956]

OK, D/C the two wire sensor. Connect a 1 wire sensor to the tan wire for overheat warning.

Have you checked the pulse limiter, vapor pump, vapor separator cover?

 

[Jose67]

OK, D/C the two wire sensor. Connect a 1 wire sensor to the tan wire for overheat warning.

Have you checked the pulse limiter, vapor pump, vapor separator cover?

Pulse limiter looks clean inside, vapor pump looks good externally but may have to disassemble to inspect it internally.

 

[Chris1956]

Vapor separator cover must make a seal as well.

 

[racerone]

Pulse limiter is a ----Flow fuse----For the VRO-----Prevents damage from too much airflow or pressure spike to the pump.