need some diagnostic help

[Rob Gold]

The background info: I own a 1983 911sc cab; it has 43,000 original miles. The car is used once in a while, and virtually not at all during summer (I live in Las Vegas).

The original problem that I had was a rough running engine after the car sat without being driven. The engine missed at 3000 rpm and less, but once I got the revs up it seemed to smooth out especially on the freeway. I was advised by forum members to try techron and drive the car for at least 50 miles. I did that and I noticed that the car showed some definite improvement, but it is still running rough at low rpm.

What I noticed tonight which has never happened before was a loss of power when I stepped on it coupled with a "rattling" or a "pinging" sound, again only when I accelerated. This symptom will also occur when I shift from 1st to 2nd, and it happens until the rpm gets above at least 3000 rpm.

Is it time to visit the mechanic or is there something I could try first?

Thanks for your help and advice.

Rob

[SCWDP911]

Is your clock working? domelight? Sounds very similar to the conditions I experienced when my dome light shorted and blew the fuse - which is also the fuse for the clock and the lambda brain I believe, which gives the rough lower rpm conditions.

[Rob Gold]

checked the fuses, dome light and clock all working, but thanks for your suggestion

[billybek]

Does this seem to happen when it is hot?
My 83 ran a rough after being run on the highway. When passing through a town and trying to keep the car at aprox. 26-30k rpm it would misfire and buck a little bit.
Changed out the platinum plugs and went with the standard Bosch plugs and that seemed to help a lot. Otherwise car is stock.

[mhackney]

Don't overlook all of the simple things:

• spark plugs clean and gapped properly
• new rotor and cap
• spark plug wires - when was the last time these were replaced? Frequently the culprit of these types of symptoms
• fuel filter - when was the last time this was changed?

I just got my 83 Cab 2 weeks ago and replaced all of the above plus the air filter. Runs like a top. The fuel filter I cut apart and it was fugly inside. Surprising that any fuel got through at all!

Cheers,
Michael

[T77911S]

think about what makes a car "ping". too lean or timing is advanced.
how could either of these be affected by a car that is not driven very much.
bad gas?
lean- gunked up injection system? lack of fuel, fuel filter as mentioned above
vacuum leak. but not likely caused from sitting unless some hose has dried up. (car inside or ouside)
timing? broken spring on advance? i dont know what type of advance your car has.
just some ideas. good luck

[DaddyGlenn]

Originally Posted by T77911S

think about what makes a car "ping". too lean or timing is advanced.
how could either of these be affected by a car that is not driven very much.
bad gas?
lean- gunked up injection system? lack of fuel, fuel filter as mentioned above
vacuum leak. but not likely caused from sitting unless some hose has dried up. (car inside or ouside)
timing? broken spring on advance? i dont know what type of advance your car has.
just some ideas. good luck

Good logical thinking. I'd go with a fuel problem. Run another bottle of Techron through it and then change the fuel filter. (make sure you get the right one)

The long term solution is to drive it year round. But I'm guessing it doesn't have A/C, correct? That's okay, we can help withthat, too.

P.S. How about a picture?

[scarceller]

If you can hear the car ping STOP!!! More than likely you have a lean mixture as already mentioned. When these engines run lean they detonate and I'll tell you first hand you WILL destroy that motor. This happened to my 75 CIS 911, turned out to be a faulty warm up regulator that caused fuel pressure to drop and thus leaned out the mixture.

Do not guess here! Have the AirFuelRatio checked with a WideBandO2 device it's the best way to know what's going on.

Having destroyed a 2.7L in the past I'd hate to see the same happen to you.

[Rob Gold]

I would like to try and check the fuel filter first, it has never been changed in several years, I searched the forum but could not find the basic steps to do so, I am eembarrassed to admit that I do not even know where the filter is located. By the way is there a good manual for a beginner that I could purchase that would help me to perform the suggestions that have been made to me?

I am not very experienced but I am not afraid to try as long as it is not too technical.

thanks again

Rob

P.s. will post some pictures tonight.

[mhackney]

Rob, a good manual for your car is the Bentley "Porsche 911 SC Service Manual". Our host sells it. The factory workshop manuals are also great but much more $$. "101 Projects for Your Porsche 911" by Wayne our host is also very, very helpful.

The fuel filter is located in the engine bay in the front left corner under the cowl. It is straightforward to replace but the fuel may be under pressure so wear glasses and proceed carefully when removing it. Work on a cold engine to because gas will spill.

Here is a recent link: Fuel Filter Installation on 83 SC

cheers,
Michael

[T77911S]

i was hoping someone would chime in as to the bad gas and if draining the tank was in order.