240efi gen1 - temperature sensors

[ripcuda]

The starboard head temperature switch (as labeled in the service manual wiring diagram) is the top sensor in the pic with only the single wire connector. This is an overheat "switch" in that at the set designed temperature, the sender grounds the single wire connector. This Tan/LtBlu wire then gives the grounded signal to the Ignition Control module and to the dash where I think it triggers a warning light (and buzzer?).

Q1: What is the temperature this triggers at?
-- I put the sensor in a pot of water and took it all the way to boiling 210-ish degrees F. It never triggered.

Q2: Does the Ignition Control module limit revs or go into a limp mode when this is triggered?



Cheers!

 

[Shortrun]

I have spent quite a bit of time studying the wiring diagram looking for a problem and in the process followed the overheat sensor connection. My understanding it ground when too hot. It is in the same circuit as the key and kill switch up on the dash. They also ground the TAN/LTBLU to shut the engine off.
So it just shuts the engine off.

I would hope it triggers before the boiling point of water.

Can you measure the ohms of your intake air sensor and let me know? (the middle one in your picture ) Also what temperature it is.
thanks

The manual mentions 2 water temperature sensors on page 4B-3. But only discusses the port side sensor used by the ECU to adjust fuel enrichment. No mention of the over heat sensor at all.

 

[ripcuda]

I hope to have my engine running for the first time this weekend. Bought my Challenger as a "project".

I'll have to test grounding the Tan/LtBlu wire and see what it does. Thinking warning light+buzzer?

My read on the service manual (Merc and SD)... is the Blk/Yel wire is what stops spark and stops the engine. It is the wire grounded when the safety lanyard is pulled. It also connects to the Rev box... which sounds logical... although I'm not sure exactly what the Rev box does.

The Air Temp sensor reads 8.8K ohms at ~66deg F on the bench.

Cheers!

 

[Shortrun]

Thanks for the Air Temp sensor reading. Yours is good, mine is bad.
I did not follow the Blk/Yel wire up to the key but what you say makes sense.
The Tan/LTBLU goes to the Control Module as well, that could shut the fuel off. Maybe

 

[ripcuda]

I got my Challenger running and in the lake today. It's still got some bugs... won't rev beyond 4k... but in my troubleshooting I did test a couple sensors.

Grounding the starboard temperature switch (simulating an overheat) triggers a constant beep... but no warning light on the dash. It also does not limit revs... I could rev up normally... nor does it kill the engine.

Tripping the low oil switch (my tanks are removed, premixing) triggers a repeating beep and the oil light on the dash. But like the temp switch... there is no rev limiting.

Cheers!

 

[Tim75]

I got my Challenger running and in the lake today. It's still got some bugs... won't rev beyond 4k... but in my troubleshooting I did test a couple sensors.

Grounding the starboard temperature switch (simulating an overheat) triggers a constant beep... but no warning light on the dash. It also does not limit revs... I could rev up normally... nor does it kill the engine.

Tripping the low oil switch (my tanks are removed, premixing) triggers a repeating beep and the oil light on the dash. But like the temp switch... there is no rev limiting.

Cheers!

If your engine only revs to 4000rpm, you still have an issue. Or 6. Have you done a compression test? All plugs out, WOT. Ideally, 140psi. You may have ignition issues. Do you have 6 spark testers that you can install and test run on the water? How do the spark plugs look? All the same? Some black, some white? You may have injector issues. If you have injector problems, one or more may not be spraying. If no spray, then that cylinder or cylinders are NOT GETTING ANY OIL. Stop running until all this can be corrected. You may be in for a piston meltdown. One of the best things I ever did was have my injectors serviced. About $25 each.

Have you ever checked the resistance of each pair from the trigger? Have you ever looked at the wires of the trigger? Early OEM units had really crappy wire.

 

[ripcuda]

Thank you Tim75 for lending some advice.
Yes, I am in a running but not 100% quite right state. I am still diagnosing my troubles.
I will start another thread (and copy your post there) to better document/troubleshoot my issues.
Cheers!