Hi everyone...this is my first posting. Very exciting.
(I checked previous postings for this problem, but none of them
addressed my car's specific issue...)

My '96 C2 Tiptronic (80,000 miles) is knocking/rattling at around 4000 RPM and If I really
push it, (which I have stopped doing) sometimes the check engine light will come
on. But otherwise the car is running fine, though is very slightly rough at idle. and strangely, sometimes there's no knocking at all.

The diagnostic says Cylinder's #1 & #5 are the issue.

(I should also preface this with the fact that I use 94 octane gas, the car has
good oil pressure, still runs cool, consumes approx. one quart per 2,600 miles
and - according to Porsche - is not a part of the wiring harness recall).

So far the #1 & 5 plug wires have been replaced, ignition/timing belts checked
and we swapped out the ECU (heck, You never know) and it's still knocking.

I know the common theory for a host of "check engine light" 993 maladies is carbon build-up/valve wear, but I had that problem with my old '89 Carrera and the symptoms were different (copious oil consumption & valve noise, but definitely no knocking).

Just wondering if anybody has encountered this or has any ideas/suggestions before I drop the car off for further diagno$i$...

Thanks!

 

Welcome, Matt! Maybe Steve Weiner can pop his head into this thread.

<edit> I wish I could leave my posts at the "917" count forever.



<<<<<<<<<<

 

Thanks, Steve.
And I couldn't stand it that my posts only numbered one. (no longer)!

 

Some say that the distributor belt inside the distributor will break and cause this. Keep us posted.

 

You use the words "ignition/timing belts" if by this you are referring to the distributor belt, then ignore the following advice: otherwise....

Check the belt between the two distributors. this can be broken and the secondary distributor will then spark to the wrong cylinder at the wrong time. because the rotor is not moving. It is hard to visually inspect this.

Easiest way to test is to pull the lead from the coil to the primary distributor cap. Car should start/run with this disconnected. If it wont start with only the secondary distributor connected. then the belt is broken.

If you can't figure out which distributor is which, then pull each lead in turn, should run with just one connected.

 

Hi Matt:

My first inclination is that the little belt inside the distributor has broken. Its not uncommon at that mileage.

Just pull off the distributor caps and see if the lower rotor turns freely, if so that your problem.

If its broken, you can either:

1) Replace the belt yourself

2) Buy a rebuilt dist from Porsche ($ 800)

3) I can rebuild it for $ 170.

Let me know what you find.

 

Thanks guys. Give me a few days....& I'll let you know!!!

The car is my daily driver and My 20 mile commute/prelude to the office
(timed for minimal traffic) is on a twisty and freshly paved parkway here
in Connecticut.

I'm going OUT OF MY MIND keeping the car below 4000 rpm.

 

Oh...And sorry Mark. I just noticed I called you Steve earlier.
I have a three-month-old at home and I'm a tad sleep deprived....

 

Unfortunately(!) the distributor belts are fine.
I'm wondering if it could be fuel injector related or
a bad knock-sensor.(?).

 

Hi Matt:

I would have all of your injectors checked for pattern and flow rates.

I've never seen a bad knock sensor and a scan of the ECU with a PST-2 will tell if they are working or not.

I would also look very carefully at your spark plugs. A small bit of carbon on the threads will glow and can cause knocking. I do not use the Beru plugs; only the FR5DTC's in these.

 

No problem at all, Matt.

Good luck with troubleshooting your car.