911 cuts when hot

[EuroAirHead]

Hi all,
I have a Euro 911 3.2, standard, in the UK. Had it 6 months only, so I don't completely know it yet, but I love it (boyhood dream).
After 1800 faultless miles through France, it cut out. Tried the DME relay. While waiting for recovery I tried to start occasionally - cranked but no fire. Fuel was getting through, & breakdown chap said it was sparking, but never a hint of life.
Two days later at home, started first time. Fuel pressure good, big fat spark. Took for a run, started to run rough as it warmed. Got it home, but idles and revs fine!
Any thoughts?

[OsoMoore]

Congrats on the new car! Can you post some specifics about the model year, and any engine modifications from stock?

[EuroAirHead]

It is registered 1987, for 1988 model year I think (it is 25 year 'celebration' model). Cabriolet, 65k miles. I believe completely standard engine, Euro spec of course. Always starts first time - it's only vice has been a little hunting at idle when cold, and a slightly high idle speed (1,000 rpm).
I deliberately didn't fiddle with anything before taking it to France as it was running just fine, although its history suggests it has not been driven too far in recent years...
Thanks for your interest!

[twistoffat]

Hunting Idle is usually the idle Control Valve on the top of the Motor. It may be just dirty and sticking. Give it a tap to see if it effects the Idle. Ideally a few minutes after starting the Idle revs should drop to 900rpm

As for the cutting out when it was warm you may want to check your cylinder head sensor. Its this part here.

http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=930-606-915-00-M14&catalog_description=Cylinder%20Head%20Temperature% 20Sensor,%20911%20(1984-89)%20

[EuroAirHead]

Thanks for that - I've seen a few comments refer to the temp sensor.
Can it really have that effect? I know it works to some extent because if I unplug it then I get clouds of black smoke: open circuit = DME thinks engine is very cold. Can it give a short when hot which confuses the DME?

[twistoffat]

This article should bring you up to scratch on the Sensor
Pelican Technical Article: Cylinder Head Temperature Sensor - Upgrade for 84-89 Carrera

[kidrock]

I've never tried it myself (yet), but I've read here several times that you can disconnect the cylinder head temp sensor at the harness (white connector) and use a paper clip to "jump" the portion of the connector that runs back to the DME. Apparently, if your car continues to run when jumpered, then you have found the source of the problem.

[EuroAirHead]

Thanks all - I am now 90% convinced the temp sensor is the problem: if I warm the engine then pull the connection, the engine can stall, and - crucially - will not re-start (flooded). So confident was I that I took the car out armed with some pliers and a 140 Ohm resistor so if the problem manifested I could bypass the sensor and have definitive proof. However, the car is behaving perfectly. But I will replace the part (which has the one wire only - further proof perhaps).

[hcoles]

+1 CHT, I had your symptom, replaced and problem gone