CIS experts - help please....
 

Hey all...

Subject is a 1983 911SC Cabriolet.

Over this past winter, I performed an oil cooler upgrade, exhaust replacement with a catalytic converter bypass, new O2 sensor, various vac hoses replaced, a tensioner upgrade, and a couple other minor items. I also had to replace the CIS airbox - with pop-off valve installed in BOTH old and new.

When I tried to start the car a couple weeks ago, it would run almost perfectly until it warmed up. Once warm - it'd buck, hesitate, and stall unless I kept it over 2500rpms when driving. First gear stinks!!!

I did have to play with the mixture a bit to get it to start in the first place - as the cat that was on there was nice and plugged and I'm sure that the Previous Owner had it set with the bad cat.

I've since -

Set the timing, checked the plug wires, replaced the dist cap and rotor. I've also set the idle speed when the car is nice and hot.

Problem is - that last year the car ran fine, when it started cold it'd run at a higher RPM till it warmed up - and now it barely hits 800 rpm cold when I had it at 950 when warm.

I've taken system pressure (5.0bar), control pressure cold (1.6 bar) and control pressure warm (3.6 bar) readings, and from what I can tell those are dead on spec. I removed the Auxiliary Air Regulator today, it was open. I hooked it up to 12V and within a couple minutes - it closed totally. I couldn't blow air through it. So - back in the car it went.

When I remove the oil tank cap - vacuum is affected -- so I don't think I have any major vac leaks in that circuit.

I just came back upstairs from replacing the fuel filter, though I haven't run the car yet. With my luck - it'll still have issues.

Does anyone have any other ideas on where to go from here - I'm about to give up and make an appointment at a dealer. Perhaps the mixture is still way off? I don't know enough about CIS - but am learning - manuals on the way in fact - but with the O2 sensor disconnected (as it is now) you'd think that'd it run almost ok...

Thanks!

Jay

the lambda relay may be bad, or not getting power from the fuse. same fuse as the dome lights. unplug the lambda relay which is under the front of the passenger seat, next to the lambda computer. if nothing changes, that may be the culprit. if the idle drops off, then it was working. it controls the frequency valve, which has to work, whether the oxy sensor is unplugged or not. if the freq valve is not working, it feels like you're dragging an anchor, and the engine runs way rich.

John -

I did in fact set a duty cycle meter to the frequency valve - and got 50% duty cycle with the O2 sensor disconnected. I can feel it buzzing too..

thanks for the idea though!

Jay

I would set the mixture with a CO meter to eliminate that. I have one if you want to swing by and use it. E-mail me if you are interested