1988 930 Mixture Adjust

[pbennett]

Just picked up an 88 930 and trying to get it to pass smog. Need to make a small adjustment to fuel mixture. Can I get some help finding the mixture adjustment and adjusting it just a tad richer. Much appreciated

[Rich76_911s]

Use a 3mm allen wrench in the circled adjustment screw.

You have to push the spring-loaded arm down and make small adjustments a 1/8 - 1/4 clockwise turn should richen the mixture a little.

[Rich76_911s]

Hopefully, the image loads this time

[mark houghton]

Originally Posted by Rich76_911s

Use a 3mm allen wrench in the circled adjustment screw.

You have to push the spring loaded arm down and make small adjustments a 1/4 turn to the right should richen the mixture a little.

My experience is that 1/4 turn is like....wow....a whole bunch of love, unless the car is already so lean that it's hardly idling at all. A couple degrees make quite an impact on AFR's.
Push the spring loaded adjustment post down until it you feel contact, then holding it there you should feel resistance when trying to turn it CW or CCW, as it engages the adjustment thingy. Do this while the engine is running. Pushing down on the adjuster until contact....and then just a little bit more will cause a richer condition. If your rpm drops at that point, it was either right on or a bit too rich to start with. Conversely, if the rpm's increase then it was too lean to start with. Just rough "tune by ear" stuff but gets you in the ball park.

[pbennett]

Can I access it without removing the airbox?

[908/930]

Yes,

Does your car still have a O2 sensor?

[pbennett]

I'll have to check. It's got exhaust with high flow cat, K27, cams etc on it. Just trying to get it past smog. Passes everything but NOX with lots of margin. Fiddled a little with the timing but that just made it worse, so next stop is making it a little richer.

[flightlead404]

FWIW in case you don't know, this only affects mixture at idle. Above about 1,500 it has little to no effect.

With the narrow band O2 sensor and a working CIS "brain" (and other components), you set the idle mix to the target spec with the "brain" disconnected, and then when connected the brain can use the O2 sensor and lambda valve to hold the idle mix at probably right around stoich.

[RarlyL8]

If I were in your shoes I'd put the OEM cat/muffler back on for the test and $hit-can the high flow cat in place of a bypass pipe or straight through muffler. Any cat at all will hurt performance.

[dannobee]

A/F ratio will affect HC and CO. NOX, not so much so. Check base timing and retard it a couple of degrees from stock spec. And yes, put the stock cat back on.