rdurff

Hi Folks,

I'm new to 993s, having just traded in my practical daily driver for a lovely guard's red '96 Carrera. I'm a longtime Porsche owner though (still have a '75 911s as well) and am very slowly getting used to all the differences in the newer car. This forum has been of great help and I just purchased a membership.

Anyhow, I need help identifying a mysterious pinging noise and am hoping someone here has seen something similar.

• Pinging only occurs under significant load, for example when cruising leisurely in 5th and then downshifting to 3rd and really getting on the throttle
• Pinging is not constant, but just a few pings during said hard acceleration
• Confirmed that both ignition systems are working correctly and that this is not a distributor connecting belt issue
• Have driven the car with a Bosch hammer hooked up, timing appears to be adjusting correctly and knock sensors show no unusual behavior
• Running the car on the best Seattle has to offer, i.e. 91 octane Shell and Chevron
• Have run at least 1 tank through the car with an extra dose of Techron
• Car has 48k miles on it and is in great shape overall, no leaks or smoke
• Had new plugs, caps, rotors, filters, and fluids done at the time of purchase

I've been working with a great local independent mechanic to identify the root cause, and we haven't found anything definitive yet. He did discover that the resistor for the low fan speed on the oil cooler is dead, so I'm having that replaced. Pinging is certainly increased when the car is hotter, but I've looked at other posts here and don't think it runs that hot generally (pretty cool in Seattle).

Just wanted to throw it out there and see if anyone else has solved similar pinging issues and has something to add.

Thanks!
-Robert

Robin 993DX

I think your issue is the 91 octane. Based on your description your car is functioning as it was designed to, engine pings and goes away right away, as the knock sensor sense the ping and retards the timing.

I have noticed that my 993 even when it was new did occasionally ping for a split second on very hot summer days when the engine is under full load, normal driving it never pings. The ping is so slight that you really need golden ears to hear it, if you even had your radio on there is no way you can hear it.

Recently with very corroded distributor cap and rotor I was getting more ping under full load with the 91 octane california gas, but again it is just for a spluit second.

AOW162435

Robert,
PM sent.

Andreas

TheOtherEric

So if you've driven with a Hammer hooked up, I assume you monitored whether or not it was knocking. I know that "knock yes/no" is a measured parameter, but I'm not sure if you can be certain or not of knocking activity using the Hammer. Are you sure it's not knocking? Becuase like Robin, that would be my first guess.

Blaine S

Maybe plug wires? Under load you will get the highest voltage and most likely chance to arc. I'd take a close look at all of the exposed insulation and check for small cracks.

Steve Weiner-Rennsport Systems

Robert:

I think Robin has thrown some illumination on part of the problem.

You should have 92 octane fuel in Seattle; at least there was when I was there several months ago at all the Chevron stations I visited.

Detonation issues under load at low-to-mid RPM are usually caused by several factors after all the engine's external components have been checked and/or replaced.

1) Heavy carbon buildups on the pistons and chambers that raises the static CR.

2) Cam timing variations that create high cylinder pressures at lower engine speeds (advanced).

3) Variations in cylinder height groups: some Mahle sets come out a tad higher than others.

All three of these items, combined with marginal fuels, can trigger slight transitory detonation between 2000 & 4000 RPM in warm weather. I would use the Porsche PST-2 and see what the knocks-per-minute counts are to determine if this is acceptable or not.

I've seen enough heavily carboned engines at your mileage to know that this is usually the biggest offender and its caused by the valve guide issue allowing excess oil into the engine to be burned. I'd love to know what your oil consumption is, but I suspect that a valve job and piston cleanup (soaking them in carb cleaner) will aleviate your problem.

Before I spent that kind of money, I'd suggest removing your fuel injectors and sending them off to be professionally tested and cleaned. That really helps,....

rdurff

Guys,

Thanks so much for the replies!

Plug wires: These have not been checked, nor am I aware that they have ever been replaced. I'll look into how worn they are.

Carbon buildups, etc.: Steve, your post was very interesting. Are there any good solutions for reducing carbon buildup without resorting to tearing the engine apart? I've read some threads here with very creative solutions (pouring various chemicals and lubricants into the intake), but they all seem pretty scary. (Maybe I'm not informed though!) I have also heard about the "Motorvac" treatment. Any thoughts on any of those?

Fuel injectors: Good call. Do any places offer these on a core exchange basis? The 993 is my daily driver, so having it out of commission for a week is a challenge (but not impossible).

Again, thanks for the advice folks.

Cheers,
-Robert

Steve Weiner-Rennsport Systems

Robert:

993 plug wires last about 30K. After that, the insulating jackets break down (from heat) and cause misfires.

If one has enough carbon buildups to raise the CR a bit or create small glowing hot spots, Techron and similiar products, will not do a thing to help. Motorvac is a very good process and may help you. Beyond that, the only effective way to remove the buildups on the chmaber surfaces and piston crowns is by pulling things apart and cleaning them with soda blasting and chemical means. Have you tracked your oil consumption? Do you use more than a quart in 900 miles?

We use RC Engineering to do our injector work. Its about a week turnaround, so if you need faster service, you might be ahead by installing new ones. They do not stock Bosch OEM injectors.

rdurff

Thanks again, Steve!

Plug wires: If 30k is the general replacement time on the wires, I'll need to do it anyhow. Good palce to start!

Motorvac: Does anyone have a recommendation for where I can get this done in the Pacific Northwest, preferably Seattle?

Davies

I had the same issue several years ago. It was arcing plug wires.