turbojames

Recently bought a 1995 Carrera with 100k. Great shape, great leakdown. But it pings and is definitely down on power. It has one of Steve Weiner's GIAC chips, but even when I swap for a bone stock DME, the problems remain.

-Pulled a spark plug, definitely lean
-Plug wires are in great shape (recently done)
-Distributor belt not broken
-No error codes
-New air filter

Yesterday, I took my first reasonably long drive (~25 mins) in the 45 degree weather. Pinging was much worse (credit the denser air here most likely) - power too. Toward the end of the drive, I could smell fuel (unburned) in the cabin. I should note that the engine runs incredibly smoothly, which prompts me to believe it's not a one-off thing, like one injector or one plug, etc.

I will appreciate any and all suggestions/advice on where to proceed from here. Fuel? MAF? Timing? All of the above?

Thanks in advance.

CalvinC4S

Distributor belt missing teeth?

Steve Weiner-Rennsport Systems

Call me on Saturday AM to discuss.

Dwane

When was the last time the belt was changed? Just because it is intact doesn't mean it is fine.

johnsjmc

Sounds like belt issues to me too. A tooth missing will allow one half to be out of time from spec. Does the engine run the same on either distributor equally well? Unplug one coil wire at a time and test by running it. You don,t need to drive it to tell because it should idle smoothly on either half.. You might also have mixed up the firing order on one set of wires. The engine will run but one side might be igniting one or two cylinders way early.

Deadeye

Vacuum leak?

turbojames

Interesting. Will try the above next week. Thanks greatly for all replies.

Steve: talk to you Sat, and thanks again for all of your help.

turbojames

wouldn't vacuum leak make the idle screwy too?

Davies

I'm surprised you aren't getting a CEL/code. Definitely sounds like an ignition issue, though. Dual-distributor-belt-missing-teeth theory sounds plausible. @Johnsjmc suggestion of mixed up plug wires is good too.
You say the plug wires were changed recently. How recently, and who did it?

geolab

if all mechanicals are good
1- carbon deposits or
2- cam - chain expansion- timing adjustment slightly off or
3- Oil overfill (some)
Some 993 engines ping like hell when oil tank is over-filled
oil vapor thrown in inlet. miniscule particles of oil in cylinder provoke knock
oil level at midrange on manual gauge is good alternative

matt777

Accidentally filled with regular/low octane / service station got its premium tank filled with regular. The ECU can only retard the timing so far.

turbojames

I should have mentioned that this is my third tank of gas (93). Also I don't know how I forgot to mention it, but I did run one tank with half 93 and half 100, and the car stopped pinging (still could have been faster, though).

Well, I know it's not 3, thanks to my lower VC gaskets . Let's hope it's not 1 or 2.

Plug wires were changed about 16,000 miles ago - no mention of where. (Though that was 2003!) I just had them inspected locally (Taylor Chapman), and they are supposedly fine. If they are indeed in mixed up order, wouldn't I be able to tell? The car is glass smooth, though the exhaust sounds weird to me (Fister III, seems to "putter" at idle)...

deekay911

I had two plug leads mixed up after a service on my 964 and it pinked like crazy. I didn't go back to that shop again

FisterD

Hmmm.....interesting

deekay911

lol - we call premature ignition pinking in the UK....