Randall G.

I don't know why this is, but knock-sensors don't always prevent audible pinging. If you look through the 993 (and likely the 964) archives, lots of examples of people with unmodified cars, working knock-sensors, intact distributor belts, getting audible pinging anyway. In most of these cases, raising the gas's octane has gotten rid of the pinging. Also, apparently, a seasonal thing with gas additives.

There are also the notorious "east-coast" chips that have caused such horrible pinging in west-coast cars. I seem to recall that the horrible pinging has even lead to turbo engine damage.

I've asked a few mechanics, and haven't gotten any good explanations for why the knock sensors don't provide perfect knock protection. Perhaps Loren can answer this question?

Some interesting threads on the this subject from the 993 archives:

<a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic;f=3;t=001208#000001" target="_blank">Ping Link1</a>

<a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic;f=3;t=003092#000000" target="_blank">Ping Link 2</a>

<a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic;f=3;t=006582#000000" target="_blank">Ping Link 3</a>

Lorenfb

There's really two issues here:

1. Do some performance chips cause additional
problems? The answer appears to be yes for this
recent thread. The owner claims that the pinging
has abated with the stock chip.

2. Yes, the knock sensor system is not perfect
for these "early" cars. Bosch probably has better
DSP (digital signal processing) approaches now
in 2004 vs 1990.

Who knows what's in those performance chips? As I
mentioned before, only Andial who is tied into
Porsche can really do chip mods reliably. I don't
think they have a 964 one, do they?

I've converted three "boxes" to stock in the last
month because of pinging or poor running.

Good luck guys
Loren
Systemsc.com

jonfkaminsky

Randall- very illuminating links. I think unfortunately, the chip is the culprit and probably exacerbated by some carbon buildup or some such crap. I am still going to try to chase the Hall sensor issue nonetheless.

Thanks
Jon

jonfkaminsky

I left the car with the local Porsche dealer for diagnostics while I went on vacation (and so he gets to deal with storing and protecting while I am gone).

They found nothing awry - which isn't surprising considering I removed the aftermarket chip. The Hall sensor fault code they found they attributed to the K&N filter I am using. They claim that the filter design allows unmetered air flow which triggers the hall sensor fault code. This didn't sound correct to me as a possible cause. They performed a system readaption and I replaced the fuel filter. Dist. belts and rotor, etc. all looked okay.

SimonH

Jon,

Sounds like the dealer was clutching at straws blaming your air filter for a phase sensor fault code. How can a sensor mounted in your distributor be affected by the air filter?!
Have you checked the output of the sensor at all?
If you can get your hands on an oscilloscope it's not difficult to see if it's working properly.

Cheers
Simon

Colin 90 C2

Hi All,
Please forgive me if this question had been answered before. I am a newbie 90 C2 owner.

What is the diagnostic procedure that is being referred to? Is there a link to the procedure?

I am getting some unstable idling and sometimes the car just cuts out when returning to idle, usually when the car is warmed up. Also, if I catch the cut-out, the car stumbles for a few seconds and then returns to normal.

The car is completely stock with 138,000 miles.

Thanks,
Colin

jonfkaminsky

Colin-
The diagnostic procedure I think you are asking about is the system readaption. This basically clears the ECU and when the car is fired up again the fuel maps, etc., are re-downloaded from the EPROM to generate "best guesses" as to current environmental and engine operation to allow the system to operate at best performance. There are many threads that speak to this issue.

You can do this yourself by disconnecting the battery from the circuitty for about 30 mins. After reattaching the battery, the advice is to take the car on a "spirited drive" to re-adapt the car to the most current conditions of operation.

You may of course, have other problems beyond which a simple re-adaption may address. These may include faulty O2 sensor, faulty head temp sensor, faulty idle control, valve adjustment, crappy fuel, broken dist. belt, clogged fuel filter, etc. I would check with Adrian, Jeff, or Bill for more info.

You may have fault codes stored in the ECU that may aid in diagnostics- but if my memory serves me, you do not have a way to get at those codes with the Bosch dianostic tool (the "hammer") because of the model year of your car. I believe only US models 1991 and later years allowed the checking of fault codes though a procedure outlined here in the 964 FAQ:

<a href="http://members.rennlist.com/jfk964/bw_faultcodes.htm" target="_blank">http://members.rennlist.com/jfk964/bw_faultcodes.htm</a>

As discussed, some California-equipped models prior to 1991 may allow this. YMMV. Again, best check with Adrian, Bill or Jeff.

Dave R.

Jon,

Are you are still interested in checking your cylinder head temperature sensor?

You can measure resistance across the sensor by putting an ohmmeter across pins 30 and 45 of the DME plug.

To access, move the driver's seat all the way back, unbolt the DME box (4 bolts), then remove the cable from the box and do the check. Reconnect and run the car to vary the temperature.

I did not bother to rebolt the box until I was all through, but as a precaution I did ground the box using a jumper between the box casing and one of the bolts/studs. I made sure the ignition was always OFF when connecting/disconnecting the cable.

jonfkaminsky

Dave-
Yes I would be interested. A question or two though. Why must one unbolt the DME box? I recall being able to remove the cable without removing the metal box. Second, are there some values I am looking for, or am I just looking for different values of resistance at different cyl head temps. Seems to me without some sort of an idea of where those values should fall, there is no way to determine whether its operating out of spec or not.

Dave R.

Jon,

I mentioned unbolting the DME box first because I cannot safely disconnect the DME cable without doing so, I don't have enough play with the cable.

In your 06-06-2003 post in this thread, I thought you said you had a chart of resistances and temperatures?

I used the chart in the factory shop manual to check and see that the values were "in the ballpark". For example, I first tested sensor resistance with the engine "cold" at ambient temperature. That's the only point at which you know precisely the temperature of the cylinder head. Then I ran the engine a few times to warm it up to different levels and checked to see that the resistance values changed as the oil temperature changed. Since there is a loose correlation between oil temp and cylinder head temp, that helped give me a rough idea of what was going on. From experience with aircooled airplane engines I also guessed that after a few minutes of running after cold startup in shirtsleeve weather, the cylinder heads would be near 200F-250F with the oil still cool near 150F. In other words I got a firm reading at the ambient temperature, and then checked to see that the sensor readings changed as the oil temperature rose, and finally checked to see that the sensor reading (resistance) topped out near the high mark of the chart with the engine warm enough to keep the oil thermostat open, or warm enough to open the oil thermostat.

If I remember tonight I'll check the shop manual for the highest temperature on the chart. My recollection is it seemed to me to be a midrange temperature (warm, but not the hottest the cylinder would see). This is consistent with the idea that the CHT sensor is intended to tell the DME whether the engine is cold or warm for fuel enrichment -smooth running purposes, not whether it is warm or hot.

Trivia: I don't know how hot the Porsche air-cooled cylinder heads run. I'm not sure I want to know: I suspect by the time the oil cooler fan kicks on they are way hot. I've a little experience with aircooled Lycoming airplane engines (flat 4s). Although Lycoming specifies a redline CHT of 450F, that's way too hot; its best to keep them always below 400F, and better yet at or below 375F. Several reasons cooler is better, among them a) the strength of the aluminum alloy in the heads drops off sharply with temperature, and b) valve temperatures generally track or correlate with cylinder head temperatures (oil splash on the valve stems cools them a bit, but as I understand it most of the heat transfer is from the valve to the head through the valve seat while the valve is closed, so a cooler head means a cooler valve).

-Dave
90C2

jonfkaminsky

Hi Dave-
Yes you are right, I do have a table of values- I do not know the source of the data. The ranges of resistance given for the temperatures are also seemingly broad, so I'm not sure how useful these data are. It would also seem that if the values of resistance are allowed to be broad for any given temperature, this sensor could not provide data to the ECU for any significant decision making. Seems to me its a more or less "engine is cold, engine is at operating temps, engine is too hot" criteria.

I'd much rather go with something I know is from Porsche. Somewhere also, I've seen a correlation between the oil temp gage and actual temperature. I may be able to extrapolate from that somewhat.

Thanks for the help.

Jon

Dave R.

Valid CHT sensor readings across pins 30, 45 of the DME plug per the Porsche shop manual (page D 24/28 - 12):

0 degrees Centigrade (C), 6.8 kilohms - 4.4 kilohms
15C - 30C, 3.6 kilohms - 1.4 kilohms
40C, 1.3 kilohms - 1.0 kilohms
80C, 390 ohms - 250 ohms
100C, 210 ohms - 160 ohms

jonfkaminsky

Thanks Dave.

Now today coming into work, I got the check engine light on for the first time ever (the aforementioned Hall Signal error was observed while performing a routine check). I extracted the error code and this time it was 1134, which indicates again the Hall Signal, but this time its not intermittant. Because the dealer had performed a re-adaption, I take it that the car is trying to tell me something :-(. First intermittant Hall Signal, now check engine light and constant Hall Signal.

Now I hate call bullsh*t on a Porsche dealer, but I just don't buy the unmetered airflow story.

any other recommendations, I'd love to hear 'em.

thanks,
jon

jonfkaminsky

Does the check engine light stay on between engine startups? When I got back in the car to go home, there was no check engine light? In other words, does the light only come on the first time the fault code is recorded, and until the engine is first shut off after the fault code is recorded?

jonfkaminsky

Sorry to bring this up to the fore-front again, but now today for awhile, ALL the warning lights went on. I stopped the car, checked the engine, restarted, now just the check engine light went on. Later on, this went out and all appeared normal. ANyone have this kind of behavior? Its getting annoying. Dealer can't find anything!!!