911 sc poor idle when cold/ gas given

[ckakoliris]

Hello
I've got a 911 sc 1981

Firstly: It takes about 5-7 seconds to start when cold (starts right away when warm)

Secondly: It idles at 800 comfortably for about 1-2 minutes (when cold) until it you give it some gas. when coming to the end of the street it idles at about 500(in neutral) and stays there until it the car warms up. The car nearly dies when in 1st idling at about 100-200 at stop.

I have recently changed the fuel filter, sprayed carb cleaner into the auxiliary air valve, (has 1/2 moon shape when cold). checked vacuum lines on the warm up regulator (fuel lines to this might blocked?). I have tightened vacuum connections and can't see any leaks. I recently changed the air filter.


What else? any suggestions?

cheers chris

[Joe Bob]

CIS requires good fuel pressure for start up. Have access to a set of CIS diagnostic gauges?

[ossiblue]

Originally Posted by Joe Bob

CIS requires good fuel pressure for start up. Have access to a set of CIS diagnostic gauges?

+1! If you're planning any DIY with CIS, a fuel pressure gauge set is a must.

Properly adjusted, on a cold start your car should start immediately and idle high--approximately between 1200-1500 or so rpms--until the wur and aar begin to warm. From your post, cold idle of 800 is way to low.

Begin by testing your fuel pressures and report the findings. It's really all speculative until you can give us some data as to the pressure readings.

[Jdub]

What happens when you unscrew the oil cap? Does the idle change? I suspect a vacuum leak - how is your brake booster hose as an example?

[ckakoliris]

I haven't had the chance to get any gauges as yet. when i take the oil cap off the idle goes down slightly but not much, which has made me think there is a vacuum leak. Recently it has been taking me about 8-10 seconds to start the car, with very poor idle being at the first black line...200? It does this untill the car heats up for 5-10 min. Idle will gradually reach 800 when the car temp is at the second black mark (usual running temp).

When the car is heating up at idle in the first 5-10 min, if i try to give it some gas it really struggles BAD untill i pass 2000rpm (occasionally backfires).

I was thinking hard starting is check valve (fuel pump)? or accumulator ( i will try and get some pressures). I opened the warm up regulator everything seems to be clean and in working order. Mine doesn't have a mesh filter on the input/output line...

Could it be the mesh filter in the fuel tank blocked with sludge (i've got the original tank form 81)


HELP!

[ossiblue]

Originally Posted by ckakoliris

I haven't had the chance to get any gauges as yet. when i take the oil cap off the idle goes down slightly but not much, which has made me think there is a vacuum leak. Recently it has been taking me about 8-10 seconds to start the car, with very poor idle being at the first black line...200? It does this untill the car heats up for 5-10 min. Idle will gradually reach 800 when the car temp is at the second black mark (usual running temp).

When the car is heating up at idle in the first 5-10 min, if i try to give it some gas it really struggles BAD untill i pass 2000rpm (occasionally backfires).

I was thinking hard starting is check valve (fuel pump)? or accumulator ( i will try and get some pressures). I opened the warm up regulator everything seems to be clean and in working order. Mine doesn't have a mesh filter on the input/output line...

Could it be the mesh filter in the fuel tank blocked with sludge (i've got the original tank form 81)


HELP!

Don't get frustrated--be patient but persistent. First and foremost, get the fuel pressures tested. You are speculating on many possible causes but you have to start with systematic diagnosis and eliminate each possibility one by one. Invest in a gauge set or take your car to a shop that will test your pressures. There is no sense jumping into other areas until you can confirm the new areas are still likely suspects.

The fact your WUR doesn't have a screen is important and you should find a screen to insert. Fuel pressure tests will let you know if you may have blockages as well as if the cold and running pressures are in spec--await the results and post them. Meanwhile, don't worry about vacuum leaks until your pressures are confirmed. You quite possibly have more than one cause for your symptoms, but you need to attack them one at a time.

[ckakoliris]

I have discovered that when i unplug the vacuum line(on the side) into the warm up regulator the car runs and starts up fine from dead cold. idles at 1200 then down to 1000 then gradually down to 800. as soon as i plug it back in back down to 200 etc...

is it worth while changing it? something wrong with the spring/heating coil unit maybe?

[boyt911sc]

Originally Posted by ckakoliris

I have discovered that when i unplug the vacuum line(on the side) into the warm up regulator the car runs and starts up fine from dead cold. idles at 1200 then down to 1000 then gradually down to 800. as soon as i plug it back in back down to 200 etc...

is it worth while changing it? something wrong with the spring/heating coil unit maybe?

ckakoliris,

What's the number (0-438-140-xxx) on your WUR? The last three (3) are important to know. Does the car run good with vac line from WUR totally disconnected and plugged? Without knowing your control and system fuel pressures, your guess is good as anybody could offer. If you don't have a CIS fuel gauge kit, don't bother to do fuel injection diagnostic. You're doing a lot of guesswork in fixing your problem. Which could be time consuming and probably expensive (parts & time).

Tony

[ckakoliris]

The part number of the WUR is 0438140-089. The car will run fine when i UNPLUG the vacuum line during warmup.

[ckakoliris]

should the round cap be pushed/ dented in?

[makaio]

As others have stated, without testing the fuel pressure with a proper gauge you're just guessing. Take it from me, I have played the CIS shotgun parts game and it's a good way to throw money at your car and still not have it run right.

[ckakoliris]

New Update-
I have changed rotor, distributor cap, and ignition wires all brand new!
I have noticed it starts strait away most times now.. although still does the stupid low idle after a minute or 2.
i received a cis test kit. i installed it and these are my readings
start pressure WUR plugged in = 2bar
when hot = 3.5bar
system pressure = 5bar
Leakdown
0minute= 2.4bar
1minute= 2.0bar
10 minute= 1.5bar
30min= 1.3bar

[ckakoliris]

ps: fuel distributor has been reconditioned as well as lines and injectors... all vacuum lines also checked no leaks to be found.

HELP!

[ckakoliris]

pps: WUR reconditioned to spec also

[Porscher]

Bringing this thread to life again. How did it go? Having the exact same symptoms.