Well, I'm not quite sure what to make of this. Here's the Cliff's Notes version.

SYMPTOMS:
Under hard (more than 65% or so) throttle, there is DEFINITE pinging from the engine. Seems worse at higher RPMs. Also, there is sometimes hesitation upon normal acceleration...the powerband isn't totally smooth across the board all the time. The hesitation isn't bad, but I can feel it.

CAR HISTORY:
Car is an '88 N/A, ~130k miles. Has been sitting and driven little in the past year. Plugs needed replacing, and the air filter was FILTHY (almost brown in color, with a lot of debris in it). I replaced with NGK Iridium and a K&N, car became smoother. Then I had the engine, cooling system, and fuel injection all flushed/cleaned yesterday, refilled w/ Mobil1. Car is even smoother now, VERY smooth in fact, but the pinging didn't go away (it did seem to help a little though). Cap and rotor were replaced a year ago. NO idea on the fuel filter.

POSSIBLE CAUSES:
I have no idea. Here's the first things that came to mind:
- Knock sensor?
- Fuel filter?
- Coolant temp sender?
- Bad DME?
- Fuel pump going out?

One random observation...something makes an audible whining sound, sounds like a CIS fuel pump from a VW. Dunno if that's normal, haven't noticed where it's coming from.

So any ideas here? I'm all ears!

 

Maybe the tps, or perhaps you need to clean the Air Flow Meter (AFM) tracks. Check out frwilks site for info. http://www.frwilk.com/944dme/afm.htm the same info can befound at http://clarks-garage.com/

 

****ty gas? have you drained the tank and put fresh gas in? Might try getting mid grades gas too, '88 was 10.2 CR IIRC.

 

I have no idea what was in it before, but I only put genuine Grade-A California **** water (91 Oct) in her.

I was going to buy a couple gallons of Toluene today (I've used it many many times) but Sherwin-Williams wanted $13/gal, which is twice what I usually pay @ Vista Paint. Forget that!

EDIT: Found the version on Clark's (AFM procedure). I'll try that this weekend, along with sunroof gears and a fuel filter, and probably some toluene.

Thanks guys! I'll keep you posted!

 

You didn't mention whether the DME has a performance chip and whether you have
turbo, & 944S. If it's not either the turbo or S, then you don't have knock sensors.

Possible problem sources:

1. too advanced ignition timing (chip)
2. engine running way too hot
3. poor quality of gas (low octane)
4. mixture way too lean (fuel pressure too low, O2 sensor shorted to a plus voltage,
AFM mis-adjusted

 

91 should be okay unless it's the first tank you put in there and there was still a considerable amount of P.O. crap gas (like 87 or something) in there. Were the chips changed or something? Timing might be too aggressively advanced.

 

Sounds like bad gas to me too! Run a few tanks of high test through it and see what happens. I know many cars ping when they have bad gas in it they don't like. Best wishes - Jay

 

Have no idea about a chip, car is all stock otherwise so I have no reason to believe there's a chip. The N/A has no knock sensor?! That's odd. All my old VW's did, I assumed this did too! How does it control the timing if it can't detect knock?? Weird man!

I'm gonna try boosting the octane and cleaning/adjusting the AFM this weekend if I can find a dry place to work on the car (friggin rain in the forecast...arrgh). I'd also like to do a fuel filter and the sunroof gears if I have time.

 

Sean,
I know my 924 S sat for years and when I first got it going again I noticed a PING as well. After a few tanks of 93 and it cleared right up. Good luck!

 

"How does it control the timing if it can't detect knock?"

It just uses the ignition map to control the timing based on water temp, engine load,
and RPMs. The early Bosch systems didn't have knock control.

 

Make sure the plugs are of the proper heat range, you may have to go to a colder plug. Better yet check the owners manual and buy the original spec plug.

I had the same problem when I switched to Bosche Platinums, so I sourced out the original spec plugs and the car has been good since.