964 INTERMITENT POWER

Ok buddies, who ever could figure this one out deserves very high recogniton and should be mechanic of the century. Good Luck!

I have a 89 964 c4. I will start from the begging; I bought the car and it seemed to have no problems but every once in a while (+ - month) it will have a sudden urge of power as if the car was not dragging something anymore. Keep in mind if you were to drive the car you will think the car is running fine so you must always be driving to feel the power kick in. I did not pay attention to it; later I decided to do a complete rebuild of the engine, plus other parts: hi performance cams, hi compression orings, mass air flow, light weight flywheel, chip, exhaust, new DME, rebuilt dist., knock sensors, new ignition parts except coils, checked fuel pressure on stand still(may have to hook up a temporary gauge in my car),plus other little things that I can not think of now, and all have been done by professional mechanics. They also hooked up to hammer and other exspensive tools and still could not find anything.(several mechanic shops)After all of that I still have the same intermitent problem for 1 year after the rebuild now. Nobody can figure this out!! Help!
Thank you for any suggestions; it will be of great help.

Bad O2 sensor? Just a guess.

is this car a turbo?

JH:

Have your mechanics actually experienced this problem? How many miles are on the car?

One thing you can count on is that it's probably not related to anything you've changed. The problem *SOUNDS* like a fuel pressure problem. Does the surge in power occur after a fill up, and get progressively worse? On older cars, the pistons in the brake calipers can stick as they age. You might want to get the car up to a reasonable speed, apply the brakes heavilly to bring the car to a complete stop, and then VERY quickly get out of the car and touch the rotors quickly (they should be HOT). Get back in the car and bring it up to speed and let it slow to a stop with little or no braking(like up a hill) and then quickly touch all the rotors again...they should all be cool...if you have a hot one, you've got a sticking caliper. Sticking calipers can be erratic...sometimes they'll free themselves for some reason and then go back to sticking.

These are shots in the dark, but relatively easy to check.

Good Luck,

Bill Wagner

I which I had a turbo, but people tell me that after all of the modifications I did that I should be faster then a single turbo, but I don't think so!

Bill Wagner:

Nobody has ever heard of this problem that is why I am writting in this board hoping someone has experienced something like this and my mechanics are just taking vague gueses;moreover, rebulit at a 100k and now has 8k.

I have to say that for not even looking at the car you hit the spot with your highly educated gueses(wish my mechanics could gues like that)I agree with the fuel problem and am in the middle of trouble shooting, but it comes randomly out of nowhere. I already checked the brakes recently, but that is exactly how it feels like(something holding it back)which is making me think; that it can have something to do with the 4 wheel drive maybe. Some mechanics told me that all 4 wheels should not spin; other mechanics told me they should(ha!) mine all spin, but I think that is normal.

Thanks for your advice, and those were some good shots in the dark!

There was an article in Excellence a while back on a 964 C4 that they called the "traction master." Anyway, they were talking about tire size differences because the one in the article wanted to use smaller fronts than rears - total circumference that is. They had to use a different gear ratio in the front diff. to "fool" the computer to thinking the fronts and backs spun at the same rate. Long story - er - long guess short - are your front and rear tires the same size in circumference. If not, I've heard that the computer will think there is slippage and "drag" things down to equalize.

...but that probably wouldn't be intermittent - more of a constant "drag."

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Brian Smith
'91 C2

[This message has been edited by ServerDude (edited 04-28-2001).]

JH:

About 4 years ago I bought a trashed Toyota MR-2 as a project car. The fuel pump was in the process of dieing. The symptoms sound strikingly familiar. In my case, the car wouldn't have a sudden surge of power, it had good power most of the time, but occasionally it would go into a mode where it would act like I was driving with the parking brake on, and sometimes even flat out die. This would typically clear up if I stopped the car and let it cool down for an hour. The saving grace (that identified the problem) was that when this occurred the fuel pump would get extremely noisy. Eventually the car just flat out died, and I knew why. I pulled the fuel pump out and the pump filters and intake to the pump were covered with rust and other debris that accumulated over the cars 100K life. The pump would overheat trying to suck fuel in as it got clogged, get noisy, and then die. I had an independent mechanic look at it after one of the power reduction episodes. He let it idle for about 3 hours and I think he concluded that I was an automotive hypochondriac!

Your car uses a plastic tank, so rust entering the fuel pump shouldn't be an issue, but you'd be surprised how much other garbage accumulated at the filter to the pump to my MR2. In addition, with 100K on the car, you shouldn't be surprised if the fuel pump is beginning to show signs of failure...they won't last forever.

I wouldn't expect the Porsche to exhibit the exact same behaviour as the MR2 did...they're two totally different cars and manufacturers. When I turn the key on my '91 C4 I can hear the fuel pump come on line. Assuming your car is the same, maybe you could detect a difference in the levels of noise coming from it during a power loss vs. full power episode by bringing the car to a stop, cutting the power, and then turn the key just as if you were getting ready to start the car. If you notice a significant difference in the noise (should sound like a hum coming from the front) then it could point to the fuel pump being the problem.

Another shot in the dark, but hey, no one else has solved it!

Good Luck,

Bill Wagner

make sure both of your ignition systems are working. perhaps only one coil/dist works all the time and the other cuts in occas. a long shot, but possible.