CIS Gurus, seeking second opinion

[Rockafella]

Fellow Pelicans, I am seeking a second opinion on a low rpm stumble I am working on. There is a stumble from idle to about 3500 rpm, then runs fine above that. On a cold start, a few cranks are required, then it has a "stumbly" idle. It used to start immediately. No hot start problems.

Car: USA 81SC, bone stock engine with a Permatune (about 5 years old), euro pre-muffler, and bursch sport exhaust. The cap/rotor/plugs have about 3k miles on them and the fuel filter is new. Distributor recently rebuilt by Jerry Woods.

Control pressure is a little high at 80. Not too sure why that is or how to fix it. No notable false air (as determined by the brake can test). O2 is connected and the frequency value does work.

I am thinking that I have a lazy WUR, slow thermo-time switch, or the control pressure is creating drivability probs. The car ran great 6 mos ago and I did not change any adjustments from then.

Any help is appreciated. This includes diagnostic steps .

[Rockafella]

Was told off-board that the mixture is over rich. Thoughts on this?

[Superman]

If you can measure control pressure, then you can measure it at different temperatures to see if the WUR is doing its job.

The first step would be to make sure your ignition system is working flawlessly. Measure resistance in each ignition wire, for example.

Then.....follow the CIS troubleshooting steps.

[Gunter]

Permatune?
Consider going back to Bosch CDI.
Thermo-timer works only while engine is cranking on cold-start, has no effect on idle.
WUR, AAR and AAV are the CIS-components affecting cold-starts; read up on how each is suppost to function. (Bentley, Tech. Articles, Jim Williams thread)
Timing and mixture setting is important.
If you think it's rich, set it according to factory specs after a thorough check for vac. leaks.
Checking for vacuum leaks with a can is not really effective; an acetylene torch with a small nozzle can pin-point the areas that are the usual suspects.

[john walker's workshop]

unplug the oxygen sensor relay, next to the computer under the right seat and see if the idle gets noticeably rougher. it should, if the system is working. it feels like you're dragging an anchor if it isn't.

[914efi]

If control pressure is high, it will be lean not rich. There are lots of internal tweaks you can do to the WUR to get it in spec if you have the patience. I would chase and eliminate possible ignition issues if your are using Permacrap.

[Rockafella]

Originally posted by john walker's workshop
unplug the oxygen sensor relay, next to the computer under the right seat and see if the idle gets noticeably rougher. it should, if the system is working. it feels like you're dragging an anchor if it isn't.

John, I lost the dome light circuit and the car ran so bad it was undrivable. That's how I "discovered" the frequency valve, lambda, and O2 are working.

When that happened, it turned my plugs a powdery white. I'll need to check again to see if we are starting to get that golden caramel.

I will start back at ignition, then go to mixture. Thanks for everyone's input!

[Paulporsche]

Your control pressures should be : cold (@15C) about 30 psi, @20C about 40 psi. Warm running engine should be about 50-55psi.

If you search WUR and knocking the plug you will see how to get the pressures down so the mixture is correct. Your fuel pressure should be about 75 0r 80 psi.