CIS issues, please help!
 

Hey all -

Hope someone can point me in the right direction here.

This past winter, I did all sorts of maintenence to my 83 911 SC Cabriolet. Tried to start her up as it's warming up here a bit in Southern NH, and I had a wierd problem, even though she ran like a champ last year.

What I did was replace the cat converter, as it was plugged. I also did a hydraulic tensioner upgrade, and oil cooler upgrade. I do have a pop off valve, though I found my airbox cracked in half and just finished that job yest.

When I put her to sleep for winter, she ran great. Now, as it warms up, my idle gets worse and worse. I hear a slight poping sound now too as it sits and idles. I've checked timing, and also replaced a whole mess of the vacuum lines while the old airbox was off.

I tried adjusting the CIS mixture, and it gets a bit better, but I don't know if I have gotten it dead on yet. I don't have access to a gas tester (yet) but do have access to a digital dwell meter. I have to borrow that tool once more to try to set the mixture again, now that the cracked airbox is fixed.

What's the potential that the mixture is now the only problem left I have? Does the mixture itself (CO setting I guess) cause that noticeable of issues? I have also replaced my O2 sensor - so that part shouldn't be bad. All of the other parts are there, though the AAV isn't... I guess someone removed it. Also - when I bought the car, the decel valve was there but the vac line to it was plugged. I've re-hooked that line up to the valve.

Looking for some direction - as I'm new to the SC world.

Thanks!

I would say that you might have hooked something up wrong. Because the mixture doesn't go bad just sitting there. So get a manual and make sure all the lines are hooked up correctly. The WUR could be messed up so you could also get some pressure gauges and diagnoss the problem

Dean -

Thanks for the idea, but the car developed the issues after I replaced the Cat (with a test pipe - shoulda mentioned that) and did the other jobs. I think the mixture may have been set with things wrong in the engine bay, and not that the engine bay is squared away (I think) - the old settings are no longer valid. Initially, the car wouldn't even start, but turning the mixture screw got me to at least run...

Thanks!

It could be the mixture. I think it is hard to diagnos a CIS problem with out gauges. It is also hard to set the mixture without a tester. You can get it close but not perfect.

If you had a blown air box when the car was running well before, then the mixture would certainly by out of adjustment. You really need to just follow the steps. You need a FI book. They provide a step-by-step CIS troubleshooting procedure. You'll need a fuel pressure tester. Without following the troubleshooting steps, you'll just be guessing.

Hey all -

I borrowed a pressure tester, and a bentley manual. I'll post pressures tomorrow, assuming the couple vacuum leaks I fixed don't fix the problem.

Thanks!

With the pressure tester, and a dwell meter, assuming the ignition systems is up to snuff, you should have a nice-running car. If not, and if you are confident there are no air leaks, then you can get suspicious of FI parts. At temperature, if the mixture is set (dwell meter fluctuating around 45 or a little less) then it should run fine. Let us know what you find.

Superman -

I have a digital dwell meter, in fact a duty cycle meter too, so hopefully it's just the mixture that's messing me up.

I'm going to take a cold pressure first, then a warm one, assuming the car doesn't stall out. Is there a specific idle speed to take the pressure readings at?

Thanks!

Get out the carb cleaner and start spraying everywhere until you find where the idle goes up. There, you found your vacuum leak.

Cheers,

Joe