On my 97 4.6 I have known for a few months that my CHS is reading 392 temp. Read the temp on my Snapon brick scanner and my OTC Nemysis to double check. I know that this is part of the 'Fail-Safe Cooling Strategy' and I know how it works, but shouldn't I be experiencing some injector shut down problems because of this constant max reading of this sensor. No codes or drive problems.

 

I haven't ever tried to read the CHT with either of those scanners, but the PCM has a peculiar strategy built in. It steps the CHT reading when it passes a threshhold, so it's possible that the scanners are reading the raw signal, which would be misleading.

Does yours read 392 when the engine is stone-cold?



As you can see by that graph, 392°F uses the same voltage as 175. So your scanners are probably just misinterpreting it, and that's why the PCM isn't setting any codes. If the PCM was seeing 392, it would turn on the FSC light on the dash, peg the temp gauge, & drop injectors to cool the engine down. Axe me how I know...

 

Yes it does read 392 stone cold [after sitting over 8 hrs.] How do you know this?

 

I swapped a '00 engine/trans/PCM into my '94 CV & didn't notice the slow leak from the heater core until it ran dry on a long trip. The FSC kicked in exactly the way it should & I was able to drive to a gas station to get water. Part of the FSC strategy is to peg the temp gauge hot, regardless of what it was showing. FSC strategy is based entirely on the CHT signal, so I don't think the PCM is seeing the same thing that your scanners are.

 

Thanks, Steve. You have saved me from changing a sensor and still seeing the same problem. I thought there was something I was missing.

 

I'd still get it scanned with a WDS or NGS to find out what the CHT is really doing, and what that PID shows. That's the only way to know for sure if your scanners just aren't reading it right, or if there's really a problem.

 

Got a friend/ FORD tech who has a NGS. I'll get it checked out, thanks again.

 

Mr. Steve. My Edge reads cylinder head temp and Engine temp. They almost always show exactly the same temp, but temp changes reveal a 1/2 second delay. Where are the two sensors located? Thanks.

 

Wish I had one of those tools... Some of my friends are tools, but that's about as close as I get.

 

Both values are from the CHT, there is no ECT.

The time lag is due to PCM/Edge processing and communications overhead.

steve

 

Interesting. If you note my "choice of language" I said "almost always". Occasionally they show different temperatures, and stay that way for a while. Sometimes, one will change, and the other will stay steady. What gives?

 

Since ECT is inferred from CHT, and due to the aformentioned overhead, there will be some lag, and some degree of imprecision - s/w algorithm is not perfect.

 

MGDfan
A '97 does have a separate ECT, so it can show something different from the CHT. It was later when they dropped the ECT & used only the CHT.

It's also worth noting that the PCM doesn't just spray all this info out continuously. It only sends data after the scanner has sent a request for a specific PID to be transmitted. So if the scanner doesn't request an update, it will continue to show old data. And if the scanner is requesting MANY updates, each one will take a while; especially if it's connected thru a slow bus.

 

Using LiveLink & an Xcal2 I can & have datalogged the PID labelled as 'ECT' (inferred value from the CHT sensor), from the list of all PID's & DMR's listed for my particular calibration code which leads me to believe an ECT PID exists

 

Yeah, I know the "ECT" PID exists. But I said "Engine Temp" because that was his "choice of language". And I know it's NOT inferred on chester's '97.