911 SC Cold Running Problem
 

Hi,

I'm new here and I just wanted to get some views from the forum members about a problem I am having with my Porsche. I have a 1971 911T model with a turbo body conversion and a 3.0 Euro Spec SC motor fitted (CIS). I have a problem with cold running in that I can start the car, it starts easily and on first crank, and then runs at approx 950 rpm for a few minutes. I take off straight away and at the first set of lights the RPM dies down to the point where it stalls. It then starts again (easily), but will stall at the next intersection (all within a few minutes) if I don't catch it with the accelerator. After about 10 minutes, the idling is then fine and it sits nicely at 950 rpm. I am thinking that the mixture is not rich for long enough during warm up hence it is stalling before the engine temperature is up to normal levels. As this if my first 911 would appreciate any help on where I can start troubleshooting

thanks and love the forum

Matt

That can be anything to do with fuel....I would pressure test the lines first since it's the cheapest thing to do first, make sure your fuel pump is giving out the right fuel pressure, do a search on cis fuel pressure ....good luck..

Cold control fuel pressure........
 

Matt,

Check your cold control fuel pressure. It will tell you a lot about your cold running problem. You need a fuel pressure gauge to do the measurement. Keep us posted.

Tony

Thanks for the suggestions guys. Just ordered my pressure test kit today and will report back

cheers!

start with control pressures, cold and warm, as tony said.
also look into the aux air regulator (AAR), sounds like it may not be working.

CIS troubleshooting.......
 

Matt,

After you get the new fuel pressure gauge, hook it up and measure your cold control and system pressure. Don't touch the accelerator pedal during start-up or try to assist the motor's RPM. You have a fuel injected system not a carb!!!! Once you get it running from a cold start take note of the following:
---- cold control pressure after start-up.
---- engine RPM (speed).
---- observe and record the control fuel pressure as the engine starts to get warm-up. Example: initial, after 30 sec., after 60 sec., 90 sec........up to where it stabilizes. This will be your baseline data for your WUR. What's the number on your WUR?

Your engine should rev up high (cold) between 1500 - 1800 rpm. If not, there is something wrong with the set-up. For what ever reason, do not alter the mixture screw setting at this point!!!!! You will make a bad situation worst. Save it later.

Another test you could perform for us is to remove the oil cap when the engine is completely warm-up. Take note of the idle speed with oil cap installed and compare it with oil cap removed. There should be an RPM change!!!! Keep us posted.

Tony

before control pressures..i would get someone to check the mixture.

I have been in the same boat with my SC. Tony has some good points. If you are going to keep a CIS car, its good to keep a pressure tester in the tool box.

I have had the same issues on two different SC's. My first issue involved a faulty cold start thermo-switch thingy and my second car had a faulty AAR.

I never liked the idea of just replacing parts to see if that fixes it. I made some expensive mistakes, like replacing a perfectly good Warm Up Regulator. Its good that you are getting the correct tools to diagnose the issue. Believe it or not, once you get the CIS sorted out, its a pretty solid system.

I'm going agree with T77911S. I would guess the AAR is frozen and an adjustment to the idle screw was made, after the engine was warm, to get a solid 950RPM.

Tony,

I know the original poster has a euro spec motor so this doesn't apply to him ... but I noticed that there won't be an RPM change when removing the oil cap if the 02 sensor is connected.

After 6 years of ownership I finally connected my sensor again. I did my monthly oil level check and noticed that my RPMs didn't drop. Just thought I'd throw that out.

Craig

the mixture can be right even though the prssure/s are not. in all fairness pressures and mixture should really go hand in hand, but never adjust the mixture until the pressure are verified, especially with his symptoms.

craig,
sorry i missed your call, i tried to call you back.
did u get the LM2?

they do go hand in hand. but mixture is a quick check..if it is off and getting it set right doesnt help, you then go and find the culprit. which is to check control pressures.

Fuel injection............
 

Vash,

First and foremost in any fuel injection troubleshooting is to determine the integrity of the fuel pressures. Go visit your medical doctor and find out what they do first to you. They don't ask how you feel or what's wrong with you. They take your blood pressure reading and let you wait for the doctor to see you.

Remember that we are talking about a fuel injection system. And in most cases, the mixture problem is commonly caused by unmetered air and I strongly advise not to tinker the mixture screw at this early stage.

For the sake of discussion (technical), what would you do if you found out that the fuel mixture was LEAN or RICH? What would you do next? Adjust the mixture screw? Let us know. We could all benefit from this discussion. Thanks.

Tony

Follow-up........
 

vash,

Would you care to share with us why adjusting the air mixture is a prudent course of action for the above condition? Thanks.

Tony

Interesting enough, yesterday, I put some street tires on my track whore for the yearly inspection. I hadnt driven the car since early December, about 1.5 months. I started the car but it ran really rough and my AFR indicated 11.2 or so and I was hoping that the car would eventually pull out of it after it warmed up. After about 15 min of driving, the car was at full temp but the AFR was still at 11.2. Prior to this, the AFRs were set at ~13.3. In any event, I reluctantly adjusted the screw to get the AFR back to 13.3 or so and took it for a spin. Within 5 min of driving, the AFR went to 14.5. I adjusted to 13.3 and it climbed again to about 13.8. I just let it idle for another 10 min or so and did a final adjustment and checked the timing. I dont know what to think about this. this is the first time I have had to tinker with this in about a year since I had the engine out. Maybe I just had to heat the engine up real good and run it hard to blow the winter cobwebs out. Im wondering if this engine just needs a good kick in the flat-six with a heavy right foot ;)

you do not think a car's air/fuel mixture can simply be off?

I also have a Euro 3.0SC (81) engine in a 1970 911T.... similar problems with cold weather cold starting and surging on tickover ... cold engine straight into a traffic jam was a real pain. Problem was that the 911T wiring loom does not have the cabling for powering the WUR and AAR on the CIS for regulating the fuel system and managing cold starts - particularly when the engine was cold in winter temps.
The solution was dead easy and involved getting power to pin 10 on the 14 pin engine connector (red/white cable on engine side). It's easy to check if power is getting to this circuit.

(other post: http://forums.pelicanparts.com/porsche-911-technical-forum/580866-idle-bounce-between-200-2000-help.html)

Useful info source: Auto-Solve Diagnostic Assistance