MarkD

Thanks for the info on the FQS...

Worries me a bit that the instructions with this chip state it is for a 964 and really emphasizes the need to set the FQS to Zero. I am sure there must be some reason... but I can't see why.

LeRoux Strydom

N51: see here:

https://rennlist.com/forums/showthre...quality+switch

Heirsh

Whether it is called a fuel quality switch or not, it is probably still prudent to put it in the default position of 0 when using his chip. Hopefully he will chime in with an answer.

Perhaps he can answer another. Will these fuel and timing adjustments still do what they are supposed to do with your chip? I guess I'm wondering if the program has to look at this switch and then look up different tables or if its done seperate to the timing and fueling maps (sort of a post processing function where it alters the result)?

N51

Thanks for the link, LS. My confusion.

Lorenfb

"The potentiometer that is accessible in the 964 DME adjusts the fuel/air ratio on the AFM, and should be left alone."

Not correct! It's the timing retard & fuel trim switch selector.
The microcontroller always reads the switch unless:

1. no switch or,
2. the microcode has been altered.

MarkD

Loren, does changing this switch setting any effect on the knock control?
I am guessing not based on all of the other stuff I've read.

Also this statement: "2. the microcode has been altered" refers to the code on the chip, correct?

Thanks!

Lorenfb

"Loren, does changing this switch setting any effect on the knock control?
I am guessing not based on all of the other stuff I've read."

Correct

"Also this statement: "2. the microcode has been altered" refers to the code on the ship, correct?"

Yes, that (microcode) refers to the operational code versus the actual maps.

MarkD

Corrected my post above to read "chip" (not ship!) though you figured that out. Thanks again Loren.

So, this makes me wonder why changing the FQS setting would matter if the code on the chip has been altered. Perhaps the specific changes to the microcode would determine that?

I thought I understood what I was doing... now I am not so sure.
I suppose my biggest worry is fuel quality here in California and it appears that is not a concern.

JasonAndreas

One possibility might be if you push the ignition timing far enough you can "trigger" the knock sensors and the ECU will kill performance to save the engine, negating any benefits from the chip. I seriously doubt they changed any "microcode" on the chip, I've looked at several aftermarket chips and nobody else has, they only alter the data maps. More likely I think the request to set the switch to zero might be more of a quality control issue. The chip programmer set the ignition timing and fueling based on the 0% starting value and anything else might be untested, etc. Your MY92 ECU does not have a FQS so don't worry too much...


Every european tuner has had problems with fuel quality variability in the USA. Even today, well established aftermarket performance chip producers have had problems with the newer models (996TT for one).

MarkD

I thought there was a FQS in mine.. no worries then. Well, except for the open question: Does it all really matter since the chip may make no difference whatsoever? We'll see!
Excellent info, thanks Jason.

Heirsh

A little plastic cover on the left side of the dme (as it sits under the seat on a lhd car) can be removed to gain access to it, if you do have it. You can feel it with the seat all the way back and your carpet pushed forward. I made a little 3 sided screwdriver to adjust mine.

JasonAndreas

Anything built after March 1990 should have the updated DME control unit (with the 964 part number) without the FQS.


If anyone decides to dynotest this chip could you remove the negative terminal from the battery for 10 seconds before you perform the first test with the stock chip? That way the test conditions will be the same with the performance chip!

Lorenfb

"One possibility might be if you push the ignition timing far enough you can "trigger" the knock sensors and the ECU will kill performance to save the engine, negating any benefits from the chip. I seriously doubt they changed any "microcode" on the chip, I've looked at several aftermarket chips and nobody else has, they only alter the datamaps. More likely I think the request to set the switch to zero might be more of a quality control issue. The chip programmer set the ignition timing and fueling based on the 0% starting value and anything else might be untested, etc. Your MY92 ECU does not have a FQS so don't worry too much..."

- Jason -

Jason is totally correct on the above statements, and was very comprehensive on
the issues discussed.

Changing of the microcode, e.g. modifying when & how the knock
sensor signals affect the timing, as I mentioned is WAY beyond
what most tuners are capable of, but was only mentioned as a
very small possibility. As an eample, an east coast chip guy claimed
he had modified the O2 system in a 959 chip to make it fully
functional for emissions, but upon fully testing (bench & in car)
it didn't function.

Marc Shaw

Huh?

You'd disconnect the battery before swapping chips so why not allow each chip to work under optimized conditions?

It should only take a short drive to re-map the new performance chip before the second test, yes?

Marc

Heirsh

Marc,

The couple shops I looked into for dyno runs (never did any, just curious) charged by the time, not the run. So if you can quickly pull the chip, put the new one in, and retest it would be a lot cheaper than going to drive around and come back.

Of course if the shop charges per run, or you have free access that changes things significantly.