Cold running problem - 79 SC

[ixxified]

Hey there,

got a cold running problem, not necessarily a cold start problem. Here's what it does and what I did:

When I start the car with the engine cold:
1. attempt: car starts immediately, revs to 2000rpm, dies
2. attempt: car starts immediately, revs to 2000rpm, dies
3. attempt: car starts immediately, revs to 2000rpm, stays at 2000rpm. I can drive away, stays at 2000rpm for about 3 minutes with the engine sputtering and judding every now and then for the next 5 minutes, then everything works fine after that.

Here's what I did:
Checked the vacuum hoses, replaced them, no leaks (I guess, since opening the oil cap changes the rpm)
I've replaced the WUR with several others, no changes.
I've checked the timing cold and warm, low and high rpm (as it should be)
I've checked the CO value, it's at 1,7%, changed it into both directions +- 0.5%, no changes.

Whats the next thing to do?
AAV, AAR or CSV?
What makes the most sense in which order?!

Thanks!

[ossiblue]

Originally Posted by ixxified

Hey there,

got a cold running problem, not necessarily a cold start problem. Here's what it does and what I did:

When I start the car with the engine cold:
1. attempt: car starts immediately, revs to 2000rpm, dies
2. attempt: car starts immediately, revs to 2000rpm, dies
3. attempt: car starts immediately, revs to 2000rpm, stays at 2000rpm. I can drive away, stays at 2000rpm for about 3 minutes with the engine sputtering and judding every now and then for the next 5 minutes, then everything works fine after that.

Here's what I did:
Checked the vacuum hoses, replaced them, no leaks (I guess, since opening the oil cap changes the rpm)
I've replaced the WUR with several others, no changes.
I've checked the timing cold and warm, low and high rpm (as it should be)
I've checked the CO value, it's at 1,7%, changed it into both directions +- 0.5%, no changes.

Whats the next thing to do?
AAV, AAR or CSV?
What makes the most sense in which order?!

Thanks!

The fact that you get an immediate start indicates that the CSV is likely working correctly.

Guessing the vacuum leak is fixed is not necessarily good enough, IMO. You should run a simple air leak test to see if you have gotten to all the problem areas. There are vacuum hoses on the front of the engine (facing the firewall) that you may have missed. Your symptoms do show an air leak issue.

If you are certain there are no air leaks, then I'd check the AAR first. It is heat activated and if the element doesn't work, the regulator closes due to engine heat--at a much slower pace. Here's a description of the regulator in failure mode:

"Failure mode: May remain partially open in cold ambient conditions due to open resistance element. Idle speed stays high after warm up. If it stays closed due to mechanical malfunction, the car may be hard to start." 911 CIS Primer - Components

This sounds much like your issue. However, you still may have another problem. Your engine should start on the first try and continue running, not die immediately. I would also run a fuel pressure test on your WUR as an out of spec cold pressure will result in the start/die symptom you describe.

[T77911S]

engine RPM goes to 2k then drops down when warm, doubt anything wrong with AAR.

what is your cold CP if you don't know the status of the spare WUR's.

sounds lean.
air leaks.
if you have a CO meter, richen it up, not by the CO meter but richen it until either it hunts at idle or when you let off the gas the RPM's drop down then back up to normal idle, then lean it out until both conditions stop. the reason I say since you have a CO meter is you can always set it back to where it was.

I would still verify CCP.
do you have a pop off valve, is it closed
intake bolts tight
spray a little water around the injectors
rubber boots on intake runners


I prefer AFR's but I was thinking 3% is more correct. don't hold me to the CO numbers.

you can push up on the sensor plate with the first start to richen it without making adjustments.

[gomezoneill]

Like the others said sound like a good sized air leak. Check your pop off valve for a good tight seal.

[ixxified]

Well I've recently had the CIS of the engine, teared it apart, cleaned anything, checked for leaks, and put it back together. So rubber boots (and bolts) are tight, pulled the injectors and added new gaskets for the injectors (and this plastic thing), the pop off closes and there is no leak. WUR reads 13 ohms.

So when it runs great at warm but lean on cold, what else could that be?

[T77911S]

bad cold control pressure.

[boyt911sc]

Originally Posted by ixxified

Well I've recently had the CIS of the engine, teared it apart, cleaned anything, checked for leaks, and put it back together. So rubber boots (and bolts) are tight, pulled the injectors and added new gaskets for the injectors (and this plastic thing), the pop off closes and there is no leak. WUR reads 13 ohms.

So when it runs great at warm but lean on cold, what else could that be?

Martin,

What WUR do you have now? It is only reading 1/2 the value it should have at room temperature. It is important to monitor the cold control fuel pressure versus time as your baseline data. Without knowing your cold, warm, and system fuel pressures, you are doing a lot of guess-work troubleshooting.

I test almost every CIS components before installation and been very successful in starting engines with CIS. With only 13 Ohms, the engine will always have erratic cold idle and as the weather gets colder, the problem gets more noticeable. Keep us posted.

Tony

[ixxified]

I've replaced the WUR (045) with one from my other cars - tadaaaa - it works perfectly well.

Now I need another WUR or someone who can fix my old one ..

[boyt911sc]

Originally Posted by ixxified

I've replaced the WUR (045) with one from my other cars - tadaaaa - it works perfectly well.

Now I need another WUR or someone who can fix my old one ..

Martin,

I have a fellow from Germany whose WUR and AAR I am now testing and evaluating at the moment for FREE. He has access to a mailing system that costs him about 20% of the commercial rates. PM me and contact him. Then I could send back your WUR-045 back to him in Germany.

Tony