cold start runs great. warmup runs like crap

[kokenm]

When I turn over my 82 911 sc and the idle goes up from the warm up regulator I can take her down the street and she moves like a dream. once she warms up and the idle starts to drop she stumbles and pops on acceleration.
I was thinking mixture but adjustments there don't seem to have to much of an impact. now I am thinking vacuum.

Thoughts?

[ossiblue]

Originally Posted by kokenm

When I turn over my 82 911 sc and the idle goes up from the warm up regulator I can take her down the street and she moves like a dream. once she warms up and the idle starts to drop she stumbles and pops on acceleration.
I was thinking mixture but adjustments there don't seem to have to much of an impact. now I am thinking vacuum.

Thoughts?

Whatever you do, do not fool with the small mixture adjustment screw in the fuel distributor. At least not yet. If you have turned it, return it to its original setting.

Your symptoms sound like you have a vacuum/air leak. The overly rich setting in cold start mode probably masks the lean condition caused by a leak but as the engine warms and the fuel mixture leans out, you get the problem you describe. When the engine is warm, remove the oil fill cap. Do you notice a drop in idle? If not, you likely have a leak. This is not a definitive test, but a good indicator of a leak if the idle doesn't change. Do a search on "air leaks" and you'll find lots of threads on how to track them down. There are several devices and hoses that may be causing your problem. I would still suggest you do a test of your fuel pressures, just to be sure everything is up to spec.

[kokenm]

I am on it. lets get her warmed up and start looking.

[Paulporsche]

The main reason for getting your fuel pressures checked is, even if you find no vacuum leaks and all ignition components up to scratch, it's possible your WUR is out of spec and, while your cold control pressure may be fine for cold starts, the warm control pressure may not be correct.

Also make sure your O2 sensor/Lambda system is working correctly.

[kokenm]

oil cap removed and RPMs drop. Good sign.
The O2 sensor is not hooked up at this point.
Background info. I just put this engine back together. I did not crack the case but I did pull the heads. they are tightened to specs and the rest done to spec in putting it back together.

[Nickshu]

Originally Posted by Paulporsche

The main reason for getting your fuel pressures checked is, even if you find no vacuum leaks and all ignition components up to scratch, it's possible your WUR is out of spec and, while your cold control pressure may be fine for cold starts, the warm control pressure may not be correct.

Also make sure your O2 sensor/Lambda system is working correctly.

I agree with all above, but remeber the O2 sensor on CIS lambda does not kick in until the engine reaches a warm temperature (controlled by the thermo-time switch on one of the cam covers (can't recall if it's right or left).

Many problems are vacuum leaks, that's the place to start. Read old posts here on the forum, there are TONS of posts on CIS cold start issues.

Also be cautious rev-ing the engine when it's cold on a CIS car. This is when backfires occur which can crack your airbox (even with a pop-off valve).

[Paulporsche]

Let us know when you get your fuel and control pressures checked.

A very common occurrence (maybe the most common) w/ these engines is the cold control pressure is too high while the warm is correct. Since the cold is too high, the mixture becomes too lean, and then someone sets the mixture back too rich to make up for it. Then when the engine warms up the mixture is too rich.

I may be getting a little ahead of things right now, but if you want to study up while doing your tests, there are a lot of threads on this, including how to reset the WUR (knocking the plug) and make it easily adjustable.

[kokenm]

enrichened the mixture. and it seems to have smoothed out.
I have not driven it.
Raining and pretty cold here in good old Alabama.
tomorrow is suppose to be a much better day.
I am going to go check the valves on 4,5, and 6 tonight.
Thanks for all the help so far.

[ClickClickBoom]

Originally Posted by kokenm

enrichened the mixture. and it seems to have smoothed out.
I have not driven it.
Raining and pretty cold here in good old Alabama.
tomorrow is suppose to be a much better day.
I am going to go check the valves on 4,5, and 6 tonight.
Thanks for all the help so far.

You have just compensated for the vacuum leak.
Stupid Vacuum leaks!

[kokenm]

Next project is door pockets and since everyone likes photos I am attaching two

[ossiblue]

Originally Posted by kokenm

enrichened the mixture. and it seems to have smoothed out.
I have not driven it.
Raining and pretty cold here in good old Alabama.
tomorrow is suppose to be a much better day.
I am going to go check the valves on 4,5, and 6 tonight.
Thanks for all the help so far.

Originally Posted by ClickClickBoom

You have just compensated for the vacuum leak.
Stupid Vacuum leaks!

With all due respect, you have not figured it out and ClickClickBoom has made that clear. There was a reason I put my advice in bold print in my first post. Fuel mixtures do not change by themselves, something causes it. You appear to have a lean running engine and when you adjusted the fuel mixture screw, it smoothed out because you made it richer but you did not fix the issue which caused it to run lean to begin with. There is a reason why Porsche put a cap on the mixture screw in most models as well--it is a setting that is seldom adjusted except when all other components are verified to be in spec. Your car may be running smoother but the CIS is not is spec and will, eventually, deteriorate once again.

Your O2 sensor is not attached, you have not checked your fuel pressure specs, and you have not checked for unmetered air. All of these should be checked for proper function before setting the fuel mixture.

[ClickClickBoom]

Originally Posted by ossiblue

With all due respect, you have not figured it out and ClickClickBoom has made that clear. There was a reason I put my advice in bold print in my first post. Fuel mixtures do not change by themselves, something causes it. You appear to have a lean running engine and when you adjusted the fuel mixture screw, it smoothed out because you made it richer but you did not fix the issue which caused it to run lean to begin with. There is a reason why Porsche put a cap on the mixture screw in most models as well--it is a setting that is seldom adjusted except when all other components are verified to be in spec. Your car may be running smoother but the CIS is not is spec and will, eventually, deteriorate once again.

Your O2 sensor is not attached, you have not checked your fuel pressure specs, and you have not checked for unmetered air. All of these should be checked for proper function before setting the fuel mixture.

It's OK, when the leak finally gets too bad it won't start, or it runs really good right up to the point a valve melts, he will be back asking what's wrong, at least he will have really nice door pockets!

[kokenm]

Wow those are interesting comments.
I do not doubt that anything that you have said is true. In fact I would like to get the mixture set back to the factory spec if for nothing else to find out how far off I am now.

[kokenm]

when I did remove intake I know that there were many leaks as everything was fairly loose. I know that the mixture has been adjusted before and I don't know what the original setting was. So here is the question that I can pose back to CLICKCLICKBOOM: what did you do to reset everything back to the truth?

[timmy2]

Use a CO meter to adjust your mixture once you have confirmed your fuel pressures are in spec.
If you get the pressures in spec and it still runs the same, you probably have a vacuum leak.

[kokenm]

Just happen to have a CO Meter and will get a reading and check the pressures.

[ClickClickBoom]

Here is some more of my CIS experiences:
Idle bounce/hunting
The CIS system is a little mysterious, once you dive in it all comes together. System integrity is paramount. Fix every vacuum leak first, then worry about the CO and control pressures.
First things first.

[ossiblue]

Originally Posted by ClickClickBoom

Here is some more of my CIS experiences:
Idle bounce/hunting
The CIS system is a little mysterious, once you dive in it all comes together. System integrity is paramount. Fix every vacuum leak first, then worry about the CO and control pressures.
First things first.

I agree with everything mentioned. To the OP, when working on CIS issues such as yours, think of the fuel pressure tests as like taking your temperature when visiting the doctor--it's a routine check to see if a basic element of proper health is within the normal range. Personally, I check pressures first for that very reason. If they check out, I know they weren't the issue. If they are abnormal, I fix it and move on, if necessary. Just a variation of the same theme. First things first, one step at a time.

Whatever course you take, keep us updated on results.

[zacharyminot]

FWIW, I had the exact same symptoms. Started fine, warmed up, and completely started stumbling & popping. It was 100% vacuum leak, had a hairline crack in the air box that we couldn't really see. Fixed the crack & car runs perfectly.

[kokenm]

haven't gone away. life is getting in the way of working on the car.
same problem / no time.