skidrdan

Hi, New here, Hoping to get some help. I have a 1985 911 that runs perfect till it get all warmed up. Once it gets warmed up or hot it will start missing mostly at lower RPM's. Very frustrating. I have changed the coil thinking it might get hot and miss. Not better. A friend mentioned a head heat sensor might be bad. I'm not sure wear that is located. Any and all advice would be appreciated. Thanks

My991

I’d start by adding sea foam to some high octane gas, replacing spark plugs, then distributor cap and wires. If that doesn’t do it find a good mechanic

theiceman

there is a much simpler aproach to this problem.


when it starts misfiring, stop it and open the engine bay, you will see 3 white connectors to the left. the top one is the CHT sensor, do not disconnect it but short it out across the posts with a paper clip. restart engine.. if it stops misfiring and runs fine it is the CT sensor that is bad.

( jumpering it out simulates a hot engine and leans out the mixture )

My991

“simple” if that’s the problem and will add that the op should start cold and then short the CT sensor. ;-)

theiceman

exactly, start with simple stuff, your tips are good for any new owner to get a baseline.

I've never used seafoam though, But we have pretty good gas here..

skidrdan

Thanks so much, I will give that a try.

skidrdan

Thanks, I have done all that and didn't fix the problem. I would like to learn to fix it myself with advice from others.

skidrdan

I have located the plug you are talking about but not sure how to insert the paper clip. Can I insert it while plugged in threw the outside back of the plug and make the contact? Very frustrating dealing with this kind of intermittent problem. Thanks again for the advice.

oldskewel

Just an alternative idea to consider - the AFM, Air Flow Meter, in these cars are known to get flaky. Basically they contain a wiper on a resistive element to make a potentiometer as air flow changes. The contact between the wiper and resistive element can be flaky (giving intermittent performance), and tracks wear in the element as well. Fairly common problem. Very hard to find if you don't know about it. Some good troubleshooting steps if you can catch it when it occurs. I'd search on here and Pelican for details on troubleshooting. Good luck.

You might consider just replacing the CHT sensor, even if your testing shows it as good. They do fail, and are pretty cheap.

Hopefully the advice you're getting in this thread will point you in the right directions to investigate, but you'll probably need to do your own googling to get detailed procedures and write-ups. They're out there.

skidrdan

Thanks, Any and all advice is welcome. This has been very frustrating. I will see what I can figure out . Thanks again.

SARGEPUG

Here's a post of mine, that might be helpful to you / help troubleshoot...
https://rennlist.com/forums/911-foru...d-startup.html