1970 911 s pop on decel

[denson]

The car runs great, but after a 50 mile ride today, she popped real loud on two separate occasions. The car never does this, so is this a sign something is up, or does this just happen sometimes? Maybe gas related, or is it time to call Gus Phister?

Thanks,

John

[Flieger]

Do you have the speed switch (rpm transducer fuel shutoff on overrun) enabled?

[denson]

Ok, so far so good. I took the S out today for another 50 miles. No pops today! Thank God, MFI can be a bit tough sometimes.

[boxster03]

If the MFI is dialed in and the micro switch cut off is working then your throttle bodies might be starting to wear. How is your idle ?

[denson]

Funny that you ask that. The idle seems a touch lower than is normal. As a matter of fact when going into neutral after higher revs, I found the red battery light came on, but went off once I gave the car a bit of gas.

Hmmm!

Any thoughts?

John

[edmayo]

When was the point gap and ignition timing last checked?

[boxster03]

with worn throttle bodies idle will actually rise above the 900rpm norm

[304065]

99% of the time we think the pump needs to be rebuilt, it does not.

Start the car and make sure you are not wearing anything that can catch in the fan, no rings, neckties, etc.

Raise the rpm by moving the throttle crossbar, to about 2400 rpm. OK, now with the engine held there, actuate the throttle microswitch with your other hand.

The RPM should instantly fall to below 1300 rpm, then rise to 1500, then fall to 1300, then rise etc. With a properly working overrun cutoff circuit that is the correct mode of operation.

[denson]

okay, it happend again. Time to get it in the shop. Thanks for all these ideas and things to check. I will make sure the mechanic looks at all of them.

[Mr9146]

Did it pop in the intake or out the exhaust?