924Board.org

[Maybe924]

Finally was able to get my 931 running problems fixed... almost. It ran perfect, a nice change after months and months of troubleshooting.

Replaced my DITC (thank you Ideola!) and my 3 aggravating symptoms have disappeared. No more dropping idle, glowing exhaust, bad misfire and poor performance. It seems that for some reason the old DITC was significantly retarding ignition.

During my previous troubleshooting I had disconnected my O2 sensor, thinking it may have been part of the problem. It ran a bit better at the time but the improvement was slight at best.

So despite the fact that the replacement DITC has apparently been the solution to my issues I still needed to re-hookup the O2 sensor and give it another test drive.

Unfortunately with the O2 sensor plugged-in I get a very slight misfire on part throttle/cruise.

The obvious solution would be to replace the O2 sensor but I'm wondering what the theory would be for a bad O2 sensor being the cause of the slight misfire.

Also, will a universal O2 sensor work instead of the pricey OEM unit?
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1981 931 GT (CGT Intercooled)
1985 911 Targa Carrera (Sold)

[tbramich]

bot sure about your misfire but i recently read an article saying you need to clean up the ditc module with electrical parts cleaner. that might help you outor might not

[Smoothie]

[Smoothie]

More on A:F and the o2 sensor system ("lambda system") -
As I found after much aggravation trying to get my car through emissions testing a few years ago.. The lambda system can/will overcompensate for an incorrect A:F setting. Sooo, turning the mixture screw too far rich (clockwise) can actually result in a too-lean mix as lambda overcompensates. + the flip side...setting it too lean can result in a too rich mix. So you need to set A:F with the o2 sensor unplugged. I do it by nose now, or of course do it with an emissions tester if you have access. Try it by nose only if you're already familliar with the scent difference between too-rich and too-lean, and can do it quickly. (NOx on the lean side "eats lung tissue" and we all know what CO on the rich side can do..)
Once the A:F is correct, re-attach the o2 sensor or splice in and attach a new one. The old one is most likely due for replacement, and you'll want to get the A:F correct before installing a new one to avoid damaging it.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[stevekat]

John, use the Bosch universal. As Smoothie said, they are the same sans the wire connector. But I'd go with the Bosch. They are typically $18 to $20.

I do my AF with the oxygen sensor connected and sometimes taking whatever steps the book says regarding some of the connectors (and sometimes not Also, make sure your frequency valve is operating. This was a problem I had. If you hear it not clicking, or clicking furiously, that is a sign you are at one end or the other of the lambda capability. Also no clicking at all could mean it has failed if you are not at one end of the range.

I believe the idea is to have the frequency valve operate at 50% so it has the greatest range to the rich and lean side, as necessary, to correct mixture based on the oxygen sensor signal.

I use a Dwell meter and/or frequency meter to set this baseline. 45 degree dwell when set to 4cyl or 50% frequency. There are some posts around about what pin to connect to on the three pin connector on the fender well for attaching the dwell meter.

I used to use smell like Smoothie, or a CO meter at times, but now if I do not have the equipment, I listen to the frequency valve and try to get it into some perceived middle ground.
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"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

[Maybe924]

Thx guys,
I will be looking into the AF mixture with the O2 senors unplugged and will replace with a Bosch universal.
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1981 931 GT (CGT Intercooled)
1985 911 Targa Carrera (Sold)