2.4L "S" engine misbehaving

Greetings all......the Goddess Porsche hath claimed the soul of yet another mortal being!

Tony here from the Seattle area - proud owner of a newly purchased light yellow ‘73S coupe. It wasn’t long into my search for an early “S” coupe that I buckled and made a purchase. Actually, it was the first car that I was able to make contact with its owner. Lucky for me, the owner just happens to be very deeply rooted in vintage Porsches and Porsche racing, not to mention he now runs a Porsche service facility just half an hour away. The car was gorgeous…the price was fair…it came with its own mechanic…how could I NOT buy it?

Anyway, the car has been outstanding. I don’t know what I enjoy more…the excitement that comes with driving an early 911 at speed, or the almost sensual process of hand washing the car’s exterior. However, I am experiencing what I assume is a problem with the engine’s performance at just above idle to about 50% throttle. When driving just about anywhere within this range, the car tends to hesitate under acceleration and pops and even backfires under deceleration. Accelerating at 60% and above, the engine operates absolutely flawlessly. Never skips a beat…Never!

The engine was completely overhauled by the previous owner approximately 2,000 miles ago, balanced and blueprinted. It’s due for a valve adjustment in about 500 miles, but is otherwise totally serviced.

If anyone can lend some valuable insight into what I’m experiencing, it would be greatly appreciated. Despite looking through numerous forums and tech boards for similar complaints, I haven’t been able to find any other mention of this problem.

Thanks and very best!

Tony

Tony,
This is what I suggest: Take your car to the seller/Porsche shop owner ( If have absolute confidence and trust in him.. if not, then a reputable Porsche shop that comes with references) and have them do a 'major service' sometimes called a 'big service’: Which should consist of an oil change, oil and fuel fillers, electric tune (points, plugs, condenser, and setting the timing) compression test and valve adjust. They should also check and adjust the clutch and breaks. They will also check all fluids and systems. Buddy, you should have fresh window washer fluid and newly greased door hinges if the service is done right.

If your problem still occurs, now you have a good base line to start a diagnosis from.

The problem could be one of several things.

When your service is done we can give you much more intelligent answers to your questions.

Hope this helps Tony, and congratulations!
Chuck

I had a similar problem when I first got my 2.2 S. It turned out that the timing on the MFI was off. Whoever timed it set it off the #4 cyl and not #1 or visa versa I can't remember. However, the symptoms were very similar. The belt that drives the MFI also can "set" itself sometimes especially if the rear cam seal is leaking oil at the pulley.

Just a thought.

I will have my $1 on the MFI system. I have had and still are having similar but worse symptoms which after much searching and replacing still point towards the pump in one way or another. Get a copy of the Ten Commandments as published by Porsche and follow them religiously. They will eliminate many of the possibilities as Chuck has suggested and then you may be better placed to hone in on the problem.

Thanks everyone for the insight. I'm taking the car in next week for service...hopefully the problem will be easy to diagnose.

I'm not familar with the "Ten Commandments" published by Porsche.....any advice on where I might locate this?

Very best,
Tony

Hope this will help, this is the publication you need.
PORSCHE Mechanical Fuel Injection
Check Measure Adjust
This is the PORSCHE factory manual for mechanical fuel injection. Part # WKD453220 and can be ordered by any
PORSCHE dealers parts department. I've had my copy almost twenty years and I think it was about $15.00 when I bought it. If you have difficulty getting a copy let me know, I can one ordered for you or I'll make a copy for you. It's a MUST if you have MFI.
Best regards, Roger Grago
RG73RST@AOL.COM