guznax

Hi Guy's,

My twinbrother and I bought a US SC (O2 sensor). It is a Florida car which is brought to France in 2015 and we brought in to Holland last summer.
(I re-glued the mirror by the way )

We seem to have a CIS problem. When we adjust AFR the engine runs well cold and warm. The O2 is about 3% and after warm-up the idle is solid 900 RPM.

The problem occurs when the car is restarted when warm after is has ben shut off (1, 5 of 10 minutes does not matter). When the car is restarted warm it is harder to start and surges like this SC:
https://rennlist.com/forums/911-foru...-engine-2.html

The difference between the Car of this topic and ours is that our SC runs fine warm after adjustment so I'm not sure the WUR causes the problem.

We checked the Vacuum (cracked hoses replaced)
O2 sensor is still from 82. We had to heat it up to loosen it for 74 heat exchangers and sport exhaust.

What is the next step we should take solving the problem?

thank you guys in advance,

Xander

stlrj

Try leaning the mix and see if it helps.

guznax

Thanks,

Leaning out as well as enrichment don't help.
system pressure and vacuum are ok by the way.

After readjustment it runs fine no matter how long I drive, but the problem occurs after the restart,
Somehow after the warm restart the AFR seems to change. The thing I can think of that is activated at e warm start is the Air Auxiliary Valve. Is that a possible explanation?

I dont have experience with CIS combined with a O2 sensor.
Should I adjust first with the O2 loop closed or open?

cheers,

Xander

stlrj

3% CO is a bit rich considering factory specs call for a 0.4 to 0.8% range. On my 82, too rich would result in warm hunting which is why my suggestion.

Cheers,

Joe

guznax

I got it Joe
ill try to lean it out and let you know the results

guznax

Leaned it out today after readjustment at about 0,5-1%.

After restart surging again :-( . Because of the surging no good measurement possible (stalls after 2-3 times)

09mageec

I have had surging on a cold start, after the car warms up and idle rests. Surges from 1000k-1100k. I am rebuilding the pedal cluster, so I'm not sure what happens after the cars drives around. I've had the car for 2 months now, prior to that, it sat for 4 years. I have started the car and let it run about 8 times now.

I tried adjusting the mixture a bit, and then the Idle Screw. It only seemed to make it worse (to the point that it would stall out after opening the throttle, and settling back down to idle). This is just one of those things that I don't have the proper tools to gauge and measure. Not to mention that this is my first Porsche. After talking with some folks at Auto Associates up here in Canton, CT, I was told it sounds like the mixture may be too lean, or that there is an Intake Air leak. This air leak could be from a number of sources, so I think I'm going to let this one go and bring the car in to get it done right. I would hate to screw anything up on this car before I get the chance to drive it for the first time.

That being said, I definitely wouldn't rule out a vacuum, or an "intake air leak". How extensive was your system pressure and vacuum test?

guznax

I realize you are right.
thanking about it I haven't tested control- and systempressure after the restart.
and that's quite essential of course

guznax

Hi,

Problem solved.

It was the oxygen sensor (I feel very stupid :-( ).
Pressures were ok.
System: 4,7
Control cold: 1,7
Control warm: 3,2 (a bit low, should be at least 3.4 but is not cause surging)

Runs fantastic now with the 70's heat exchangers and sport exhaust. The oxygen sensor measures the left 3 cylinders. Power in the whole RPM range feels better.

CO = 1,25%
HC = 75 ppm

thanks for the response,

Xander