Possible WUR issues with new to me 911
 

I have a 79 911 that I am having issues with the car as it warms. It starts fine and idles at approx. 1100 RPM, which drops to 900 or so within a few minutes. The car then starts to search for RPM after driving a short while and coming to a stop. Sometimes it will stubbled to the point of stalling. Once the cars is completely warmed the RPM search gradually diminishes. Here are my fuel pressure numbers. I ran the test with the WUR vacuum hose disconnected.

System pressure : 4.8 B @ 31c
Cold Control Pressure 1.6B

I ran a 10 minutes test with the WUR Connected

1M 2.2B
2M 2.4B
3M 2.5B

The pressure does not increase after 4M

Residual Pressure
@0= 2.9
@15M =1.6
@30M = 1.35

Any advice is appreciated!

If you post your WUR number - stamped on the WUR, the specs will be known.
But it may abe a simple idle mix adjustment.
Alan

The number on the WUR is 0-438-140-089

Thanks!

Your SP is good and your RP measurements are good. Your cold CP is probably within spec, but the chart depends on the temp when you ran the test. At 20C, the graph shows 1.6-2.0 bar. Your warm CP is too low, should be 2.7-3.1 with vacuum disconnected.

HOWEVR, I don't think the WUR is causing the idle to "hunt" during warmup. IME, timing is an important influence, so make sure your timing is set correctly and increases to 25 or a bit more at full advance. Too much timing at idle tends to increase hunting. Are the vacuum hoses connected correctly? Have you oiled or disassembled and cleaned the dizzy yet? Does the vacuum advance can have two vacuum hose ports, one for advance and one for retard?

Also see the parallel thread about "Higher rev when at stoplight or stop."

Thanks, no I haven’t done anything else. I am just learning about this car and didn’t want to monkey around with too many things at once. I have a smoke test on my list next and will look at timing, dizzy etc as mentioned. Thanks for your time!

My order for drivability would be 1) check for and fix vacuum leaks, 2) confirm fuel pressures are in line with the WUR specs, 3) confirm timing, 4) adjust fuel ratio and 5) adjust idle.

Agree with Ltanderso ...

First and foremost introduce yourself with good literature and the right videos onto CIS on 911 cars:
1. https://p914-6info.net/PDFs/K%20Jetronic%20Workshop%20Manual.pdf (access with Firefox e.g)
2. https://files.bmwclassic.nl/E21/K-Jet/Bosch_K-Jetronic_web.pdf

In 1. you'll find also the WUR curve foryour car and all other relevant settings incl. procedures on how to make adjustments and repairs...

Also I recommend the Porsche 911 Workshop Manual to study:
https://www.turbosition.com/_files/documents/Porsche_911_Workshop_Manual_1972-1981_EN.pdf

Also I always recommend Curts fabulous YT channel "KlassikATS" with it's video series about the 2.7 CIS 911 (there are a lot more videos about 911 there). Here you find almost everything you need to know about CIS. It's the perfect addition to the literature which is also still needed for details:
https://www.youtube.com/playlist?list=PLkWFofpgz2OgF9FdliKnlzuY0pygqRkMj

Also his website klassikats.com.

So you're busy until X-mas :D

Thomas

CIS Troubleshooting……….
 

Jay,

Follow the above suggestions. One of the best recommendations I’ve seen recently for CIS troubleshooting. And have the following tools available

• Smoke generator.
• Inductive Timing Light.
• Hand vacuum pump.
• A copy of the Control Pressure Chart for Bosch 0-438-140-089 WUR.

The control fuel pressures of your WUR-089 is out of spec and needs some calibration work. Confirm the absence of unmetered air going into the system before attempting to adjust your fuel mixture. This is the last thing you want to tinker if your motor is starting and running. Otherwise, you will be making a bad situation worse. Keep us posted.

Tony

WUR 0438140089 chart in this post ...

https://forums.pelicanparts.com/porsche-911-technical-forum/758788-cis-troubleshooting-dummies-5.html#post9693566

Thanks, yes went ahead and ordered a new intake boot, after attempting to remove, it was apparent that the old one would likely not come off in good shape. Also, the pop off valve install looks a bit suspect and I am betting it will leak. Will post findings once I have everything tested for vacuum leaks.