SimonH

Bill,
No I didn't think you meant that the crank sensor is disabled during knocking, it was this bit:

>>the fault will likely NEVER even be reported until the engine is pushed to the point that knock appears and the DME attempts to reference the position of the distributor wipers only to realize that the reference isn't there.<<

that I was on about. I reckon that it's unlikely that the dizzy sensor is only checked for faults during a knock event, I would have thought that it's checked more often than that, that's all.

GMS,
Yes you're right. Misinformation from the manufacturers is helping no-one, especially as auto electronics get ever more complex. How are we going to deal with the current cars in ten years time? Multiplex wiring anyone?

Jon,
I don't want to guess at your problem in case I'm incorrect and send you off in the wrong direction, but I can give you my thoughts:
If the aftermarket chip is somehow falsely triggering the dizzy sensor diagnostic - a stray byte written somewhere ? - then the system may go into a failsafe knock detection mode as it can no longer rely on knowing which cylinder is knocking. Loren stated this above:

>>4. The knock system can operate w/o the Hall
because it can effect all cylinders at once,
i.e. a common retard value.<<

So it might be forced into this mode. Now, as the chip has much increased base spark advance - that's how they get the performance increase, - then the limited funcionality knock control doesn't have enough authority to stop pinking in hot weather. Maybe.
As a footnote, I have seen aftermarket chips do also sorts of dodgy tricks - including setting both the high octane and low octane spark maps to the same increased levels. Effectively disabling the knock control! And putting your engine at serious risk. Be careful out there.

Cheers
Simon

Adrian

Another thing with after market chips is the rev limiter. I have seen them go up to 7200 rpm and there was one which allowed 8000 rpm. Not good.
With aftermarket chips I have a little rule. If the aftermarket chip fires up fault codes 1141 or 1241 on a 9288 Bosch hammer, 9268 flashing led tester or on the check engine light system (USA only or DIY installations) then remove it and send it back.
Other key issues are the variant jumper plugs. If you are set to ROW and use low octane fuel you are going to have problems.
The knock sensors can only retard the timing to all cylinders to a maximum of 6 degrees on the crank. Therefore if your new aftermarket chip is one of these cheaper advance timing only modified codes jobs in the hot weather you may well run into the knocking problem mentioned because the knock sensors can only retard from the new aftermarket chip´s maximum advance position. If this is say 3 degrees higher you have effectively lost 3 degrees of timing retard. This may not be enough to stop the knocking. Maybe one solution would be a fuel cooling system.
Ciao,
Adrian
911C4

jonfkaminsky

Dear Adrian-
I think that makes some sense - In other words, if the system is only capable of 6 degrees retardation, and one is staying withing the original Porsche specs for fuel, one should expect the system to catch the knock and there would be enough margin left to retard to a non-knock producing setting. But if you are "artifically" set to a higher than expected spark advance setting above orginal Porsche specs, than how can you ever get back down to the "safe" level Porsche originally designed into the system, if you only had 6 degrees or retardation to work with.

This makes even more sense to me, because my car has never entered limp mode. Despite the knocking, it always ran strong. During hot conditiona, I would just have to feather the acceleration through the knocking rpm range and hitting it hard after that would produce good performance and strong pulling in any gear. Seems like from about 3000 to 4000 RPM.

Instead of fuel cooling, I may just try to get ahold of some race fuel and see what effect that may have. Those aftermarket additives don't do much. The best solution at the moment, however, is the action I already took to protect the engine- removing the chip.

BTW, this condition never triggered the check engine light per se. I just decided to check whether any fault codes were present after I detected knocking, and discovered the hall signal code.

Adrian

Dear Jon,
I think the fault codes are due to the programming technology used in the DME. I have said many times that it is 1980s technology with many removed features compared with other brands of car of the same vintage. Inotherwards the faulr detection system is rather dumb. You are getting the hall sensor fault code because such a failure is "plausible". I will not explain this too much but this was a Porsche requirement for fault finding. The DME is supposed to work out what might be wrong if it cannot work out what is actually wrong. If the knock sensors retard the system 6 degrees because of an aftermarket chip and the knocking but the knock sensors are still recording a knock on both sensors then the DME says to itself, well I am getting a knock signal from both sensors so they must be alright, what else could it be, ah yes I know, the hall sensor.
This plausibility detection system has since been removed because it fires up many false fault codes. This problem by the way is not exclusive to Porsche. Aircraft self diagnostic systems are even worse. Very few tell the truth the whole truth and nothing but the truth. I have a healthy disrespect of these systems based on experience and wasted time. Funnily enough I can glean more information from these systems by what they do not say rather than what they say.
Ciao,
Adrian
911C4

johnfm

SimonH

I have e-mailed you.

Adrian

Guys there was something I forgot to add with the aftermarket chips business. Many aftermarket chip suppliers have in their very small fine print that you have to run high octane fuel. I have seen them up as high as 104 octane. I recommend that you read the fine print or contact the supplier for the correct information. I had a quick look through one of my German catalogues and the lowest octance required was 98 RON which I think is 95 in the USA.
Ciao,
Adrian
911C4

PCar SBA

some info and one open question & thanks to all who answered

- The hall signal (or its absense) gets noticed by the DME (after a reset) even before you start the engine. It can be flashed out as fault code 1134. Ask me how I know...

- What still bothers me is that I would have never noticed the missing hall signal without flashing out fault codes. The check engine light did NOT come on. How would Jonny Doe notice that there is something wrong with his engine?

- Once I activate the aftermarket chip my check engine light stays on all the time. With this particular chip (RUF) I am not able to flash out fault codes at all. Since I don't own a hammer I wasn't able to check what fault code is triggererd. Adrian's comment makes sense in that the DME senses the aftermarket chip and lets the world know that is has been tampered with.

The open question is: Where would I get a hall sensor in case it really would go bad? Nothing in PET or the factory WS manual.

Ingo