I think it's my CHT sensor....how 'bout you?

[silvercar00]

Here are the symptoms: It stalls out like a rev limiter....but only when warm and only at RPM's above 4K. Cold, it runs perfectly.
After stalling out, the difficulty restarting depends on how warm it was and how much over 4k I revved it, and under how much of a load ( i.e. winding 3rd gear up to about 70mph). The car can be driven for extended periods of time regardless of temp IF I keep the rpms extremely low ( below 2800 RPM) without stalling. I was disappointed to find that there were no photos in the tech article....people keep saying that the R&R on this sensor is a real beaaatch...any tips in case I might go DIY in the face of mechanic's shop backups ( I'd have to wait until late next week to get this changed).

[WydRyd]

Sounds like it. When it stalls again, quickly put a ohm meter on the loom going to the CHT sensor and measure the resistance. It should not be short curcuit, or open circuit. It should be reading anywhere between 100-300 ohms or so. I think the Bentley manual shows typical ohmage values for various temp ranges. Good luck!

[stlrj]

Or you could jumper the head temp sensor connector and see of it makes any difference. That way you could eliminate the sensor if no change.

Joe

[wcc]

It might be your impulse sensors. Here is a good link with other links in it worth reading.

89 Carerra Hot Start Problem

[UK Carrera]

Bill

IMHO I think you're on the right track there.

The flywheel sensors corrode and 'grow' reducing their operating gap. Expansion due to heat further compounds the problem. The fact that the problem is above a certain rev limit also points to this area.

[KCPSG]

It sounds somewhat like mine did when the sensor went out. I happened to be making a LM-1 logfile @ the time and had just completed the 1st run to redline, and as soon as I let off of the pedel the engine died. Then all kinds of white smoke came pouring out of the tail pipe. It almost smelled like an electrical fire. But a few minutes later the engine cranked right up and died a few more times before I could limp home.

As far as the R&R of the sensor it was harder than I thought it would be, but in hindsight I could have done it much quicker if I had gone w/my 1st instinct which was to remove the shock and the drivers side SSI. w/those gone it was only a few minutes later that the new one was installed and replacing the shock and SSI.

[KCPSG]

The whole job (including removing SSI and shock) took approx 4 - 5 hrs. but 2-3 hrs were trying to get the CHT sensor to thread in, before I finally gave up and took the other items off and finally installed the CHT.

[silvercar00]

What's SSI?

[silvercar00]

Oh, BTW, my mechanic is about ready to throw a CHT sensor at it, he's so conviced that that's my problem. I've seen on this board that the original sensor is prone to failure and that an improved, 2-wire sensor replaces it, Should I just be replacing this as a preventative measure anyway ( along w/ DME relay, which also can spontaeously strand you).

[KCPSG]

SSI's are the heat exchangers

And as far as replacing it as preventative maintenence. I would be more inclined to do that if I were a Do it Yourselfer (which I am) I wouldn't even consider it if I had to pay someone to do it.

[wcc]

It doesn't sound like the CHT to me, but it very well could be. I'd be more inclined to test the CHT with the resistor setup in my previous post with links. If it fixes your problem then sure replace the CHT. If not, why waste the money by throwing parts/money at your car for no reason. At least rule it out with a simple test.

It's more likely your IMPULSE SENSORS. If your CHT checks out ok, which I'm pretty sure it will, these would be next on the list.

Tell us what you find out....

[greglepore]

Regardless of whether its CHT or not, I'd start there as if its the original cht its due. It's not that hard, more tedious than difficult. When I did mine, I cut the wires off of the old unit and used a standard socket to remove it, then used a cheap (14mm I believe) box wrench, cut a slot in the box to clear the wire, and tightened with that. You could do the same with a deep socket, use a whizzer or dremel to slot it like an O2 sensor socket is slotted.

[KCPSG]

Strangely I agree w/both Greg and Bill...you should test it to see what the results say...however I had just a few weeks before, tested my CHT and the results were as Bently's said it should be, Hot and cold. So take that into consideration...my CHT never gave any sign that it was going out. I also tested it when I the car shut down..or shortly later on that day..and the results were nearly the same as before. The only sign that I had, was that the car ran good cold. And like crap when it warmed up just idleing.

[JeremyD]

Originally posted by greglepore
Regardless of whether its CHT or not, I'd start there as if its the original cht its due. It's not that hard, more tedious than difficult. When I did mine, I cut the wires off of the old unit and used a standard socket to remove it, then used a cheap (14mm I believe) box wrench, cut a slot in the box to clear the wire, and tightened with that. You could do the same with a deep socket, use a whizzer or dremel to slot it like an O2 sensor socket is slotted.

Yes, that is usually the best way to start - although when I R & R'd my engine all three sensors were in poor condition.

[silvercar00]

Originally posted by KCPSG
It sounds somewhat like mine did when the sensor went out. I happened to be making a LM-1 logfile @ the time and had just completed the 1st run to redline, and as soon as I let off of the pedel the engine died. Then all kinds of white smoke came pouring out of the tail pipe. It almost smelled like an electrical fire. But a few minutes later the engine cranked right up and died a few more times before I could limp home.

As far as the R&R of the sensor it was harder than I thought it would be, but in hindsight I could have done it much quicker if I had gone w/my 1st instinct which was to remove the shock and the drivers side SSI. w/those gone it was only a few minutes later that the new one was installed and replacing the shock and SSI.

The "electrical fire" smell was just what I recall the first time this happened. I popped the hood looking for a fire...nothing. It started right up....unitil I revved it up, and then it died. Drove it home below 2500 rpm.

[JeremyD]

Originally posted by silvercar00
Should I just be replacing this as a preventative measure anyway ( along w/ DME relay, which also can spontaeously strand you).

Just buy a spare DME relay and keep in your glovebox - cheap insurance.

[ChrisBennet]

See my post in this thread for a way to eliminate the CHT as the cause without replacing the it or using a meter (which doesn't prove anything BTW) - Engine cuts out
-Chris