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These sensors are very reliable. I've only replaced a temp sensor once. The sensor hadn't failed but the bracket that it was attached to had. The sensor had fused to the bracket so I replace both during my engine rebuild.
I tested the CHT sensor at its plug in the engine bay today (not at the DME).
At aprrox 10c ambient I saw 15.5k ohm which is about three times what is called for stone cold 0deg.
However at running temperature (oil near first mark) I'm spot on, 155ohms.
This tracks exactly with my symptoms - very hard cold starts which are god awful in freezing temps and not so terrible in summer.
A-okay in all conditions from idle to redline once she's warmed up.
So the sensor isn't dead but its either on the fritz or out of spec.
Does anyone have the 993 factory manual on hand to check if these specs are the same?
Does anyone have a CHT on a (preferably freezing cold) bench they can check resistance on for me?
When I had my problem with the CHT I also tested it at the plug and it was within spec according to the 964 manual (I dont have the 993 manual but given that the factory list the 993 part as a substitute, Ive assumed the output would be identical). The fault with mine was that it intermittently had no continuity ie a break in a wire/weld. This would only appear sometimes (but often) on a cold engine. I assume as the sensor/wires heated up the expansion bridged any continuity gap. I only could prove this once I got the sensor out and bench tested it.
Well its no-cost for me to take advantage of FCP's lifetime warranty so I have done just that. I'll bench test the replacement Bosch (not "Porsche") sensor when it arrives, including jiggling its wiring to look for intermittent faults. It's not all that easy to find a 14mm open socket so I thought I'd share this well priced set which includes other sizes useful to me as well. The 17mm in particular will be useful for the fuel line connections on the Alfa MFI pump.
If you had a scan tool that could read data your air temp sensor and head temp sensor should read the same cold. that tool set was cheaper than I paid for the one socket.
I do have the scan tool from Tores site. I cant recall if the software let me read the actual values or not. maybe that was only the tester that Rob loaned me. Ill try hooking it up when Im home later today.
Well it looks like the sensor is working from the scan tool. I'll have to try it again after a drive and on a colder day. Which aren't in short supply.
I received a new Bosch sensor from FCP today. I also got a set of difficult access sockets. This test fit shows the issue with this particular sensor the strain relief is quite long so the fit is not great into the socket. The good news is I tested the resistance and found it to be dead on when cold.
I too am having cold start issues. No other problems aside from that first start of the day, or when the car has cooled down (i.e. started in the morning and then again at night)
I'm not the most electronically versed - but would love to see how you adapt the 993 plug to the 964.
I have a feeling I may have pinched the wire somehow when I was putting back my refinished engine tins. Will need to pop off the wheel when I get a chance to take a look.
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