CIS troubles - any ideas?

[lagoon]

Current status: car stalls upon cold start up - does not go into a fast idle AND after getting idle speed to stablize enough to drive, car bucks like a bronco in 1st gear from a stand still. After car is warm, everything seems to be ok. I verified the AAR is functioning. Is the CO set too rich maybe? I have a new WUR but it might be set too rich. Any ideas guys? 81'SC

[wckrause]

A quick way to tell. Reach into the airbox (with the filter off), and gently lift up on the sensor plate, while the engine is idling. If this improves the idle, then you are too lean. If the idle gets worse or it stalls, then you're too rich.



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Bill Krause
'79 911SC Euro
MY PELICAN GALLERY

[Superman]

I believe this is an instance where measuring fuel pressures is just about absolutely necessary. You will probably spend a lot of time trying to track down this problem, that you could perhaps avoid with a pressure testing unit (kits are available from JC Whitney among others. I agree that the AAR can cause similar problems, but I am far more suspicious of the WUR. And if your fuel pressures are not correct, you will not be able to make the car run properly by simply adjusting the mixture.

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'83 SC

[rstoll]

Does your '81 have thermo-time switch on left chain cover? Might check that.

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Robert Stoll
83 SC
83 944

[lagoon]

yes, it's a new one.

Originally posted by rstoll:
Does your '81 have thermo-time switch on left chain cover? Might check that.

[Obin Robinson]

Originally posted by lagoon:
Current status: car stalls upon cold start up - does not go into a fast idle AND after getting idle speed to stablize enough to drive, car bucks like a bronco in 1st gear from a stand still. After car is warm, everything seems to be ok. I verified the AAR is functioning. Is the CO set too rich maybe? I have a new WUR but it might be set too rich. Any ideas guys? 81'SC

if there's one thing i have grown intimately familiar with... it's the K-Jetronic fuel injection system. there's a few things that can be doing this:

1) a vacuum leak... check all your vacuum hoses. there even might be a few PINHOLE leaks that you can't see, or tell until you take a really close look at all the hoses. do you have a way to test the vacuum hoses for leaks? if not i can tell you a few ways.

2) dirty or worn fuel injectors can do this, but my experience has been that your symptoms don't point to that. it may be possible, but i'm not betting the farm on it.

3) the AAR may be functioning, but is it even slightly leaking, or faulty? i once changed my AAR and the EXACT situation you described went away. i got a brand new AAR, and when i tested it, it looked and acted like my old one.

4) the control plunger in the air intake boot could be sticking. this was the case in my friend's car. we hosed the plunger out with hrottle body cleaner, and we checked to make sure it was moving up and down correctly.. and that fixed his cold start issues. check to make sure the air flow sensor plate is moving properly.

5) you could have a faulty cold-start valve. when these things leak, or don't work right, they cause similar problems to what you are experiencing. also MAKE SURE to check that the cold start valve is getting the proper voltage. i once replaced a cold start valve only to find out that the wires leading to it were what was causing the problem. do you have a multimeter to test the circuit?

6) check your fuel pressure. get a fuel pressure test kit if none of the above tests do you justice.

if your problem is really bad... e-mail me. i have a friend who is a BOSCH engineer and he knows that system like the back of his hand.

good luck! keep us informed!

obin

[Obin Robinson]

one thing i forgot to mention is that you really should check the electrical connections to all of the above mentioned components. there's a lot of gremlins in the 1970s-mid 1980s Porsches from the 924 to the 911 turbo. these gremlins usually ahve to do with a corroded, loose, or frayed ground wire. check the electrical operation of all of your fuel injection parts that have harnesses on them.

good luck!

obin

[lagoon]

Obin, how do I test the AAR and the AAV for proper operation? The fact that I get no cold fast idle leads to this. let me know. thanks

Originally posted by Obin Robinson:
one thing i forgot to mention is that you really should check the electrical connections to all of the above mentioned components. there's a lot of gremlins in the 1970s-mid 1980s Porsches from the 924 to the 911 turbo. these gremlins usually ahve to do with a corroded, loose, or frayed ground wire. check the electrical operation of all of your fuel injection parts that have harnesses on them.

good luck!

obin

[Obin Robinson]

Originally posted by lagoon:
Obin, how do I test the AAR and the AAV for proper operation? The fact that I get no cold fast idle leads to this. let me know. thanks

lagoon. there's another thing that i wanted to note and that's your car is a K-Jetronic with the Lambda sensor. i don't think that a bad lambda sensor could cause this, but just wanted to make sure i mentioned everything possible.

how to test the Auxiliary Air Regulator:

1) start your car up after the engine has cooled overnight. squeeze the hose that leads from the back of the auxiliary air valve. if the idle drops low then your AAR is good.

2) if the engine RPMs don't drop when the engine is cold, remove the AAR from then engine.

3) if you look through the AAR, when it is cold there should be a little slot open that lets air in. when the engine warms up this little slot is closed, and the engine does not let in extra air.

4) the AAR slowly closes when 12 volts from the car's electrical system goes through it. check to make sure that there's 12 volts at the electrical harness that plugs into the AAR. if there isn't 12 volts or so, then you may have a break in the wiring. this was what caused a cold start problem in my car a while ago.

remember, the AAR is letting in a little bit of extra air while the engine is warming up. if it's blocked then that air isn't getting in. this is why you test the hose by seeing if the idle drops.

the test should only take about 10 minutes. go give it a shot. worst case, remove the AAR and make sure that there's nothing blocking it. i hosed mine out with some throttle body cleaner, before i bought a new one. that seemed to help.

good luck!

obin

[wckrause]

Obin -- he's not getting a fast idle, how will pinching the bypass hose reduce his idle when it's not idling properly anyway?

You need two things to have a fast idle. The right mixture, and bypass air. Do what I recommended with raising the sensor plate to rule out a mixture problem, it only takes a second.

An electrical problem won't cause a cold start problem with the AAR or WUR because if they don't get power, they will just stay in the cold start mode longer until the engine temps warm them up.

The fact that you just replaced the WUR sort of points in that direction. Why did you replace the WUR? Did you replace it with the correct one?

------------------
Bill Krause
'79 911SC Euro
MY PELICAN GALLERY

[This message has been edited by wckrause (edited 08-15-2001).]

[Obin Robinson]

Originally posted by wckrause:
Obin -- he's not getting a fast idle, how will pinching the bypass hose reduce his idle when it's not idling properly anyway?

i've done it and it drops the idle even further. the car chokes and tries to stall.

i agree that the Warm up regulator can be a culprit, but he said he had a new one.

obin

[lagoon]

Obin, just to follow up - problem solved! It was the WUR set too low a control pressure causing a rich condition upon start up. thanks!

Originally posted by Obin Robinson:
i've done it and it drops the idle even further. the car chokes and tries to stall.

i agree that the Warm up regulator can be a culprit, but he said he had a new one.

obin

[lagoon]

Superman - problem solved! Checked the cold control pressure on the WUR and it was LOW causing a too rich condition upon start up. Thanks for your ideas.

Originally posted by Superman:
I believe this is an instance where measuring fuel pressures is just about absolutely necessary. You will probably spend a lot of time trying to track down this problem, that you could perhaps avoid with a pressure testing unit (kits are available from JC Whitney among others. I agree that the AAR can cause similar problems, but I am far more suspicious of the WUR. And if your fuel pressures are not correct, you will not be able to make the car run properly by simply adjusting the mixture.

[Obin Robinson]

glad to see that things worked out! i thought that it could be fuel pressure too, but it's always worth going down the list. it's much easier to eliminate the cheap and simple items before going out and buying $30 or $40 guages.. just to verify that it WAS something cheap and simple.
i'd hang on to that fuel pressure guage though, you never know when you'll need it in the future. CIS can be a pain to understand at first, but once you keep it clean and tuned, it works like a charm.



obin

[cabman]

hello

[speeder]

Lagoon, glad to hear you solved it, but I would hope that you possess at least a Bentley Manual. When trouble-shooting CIS, fuel pressure is first thing to check. God knows I've wasted $ and time in the past barking up wrong tree or even buying unneccesary parts without book. I consider the experience of others on this board extremely helpful,(including this thread), but a good mechanic always systematically goes through the TS steps even when having a hunch at the outset. I cuss a lot less since buying that book.

[wckrause]

Lagoon? Why was the WUR out of spec? Was it a new one, or rebuilt, or what? Why did you replace the old one? Just curious.


Along with the Bentley manual, I'd recommend a book on Bosch fuel injection by Probst. It goes into how all of the Bosch fuel injection systems work, how to troubleshoot them, and mentions (briefly) performance upgrades. It's not specific to 911's (a slight fault).

Any 911 owner with CIS that wants to do their own maintenance (or second guess their mechanic) should own a CIS pressure tester. $50 at JCWhitney is all it takes. Check your system and control pressures, and verify pressure retention. Also buy a handfull of those crush washers for putting it all back together.

------------------
Bill Krause
'79 911SC Euro
MY PELICAN GALLERY



[This message has been edited by wckrause (edited 08-19-2001).]

[lagoon]

Bill, my WUR was a rebuilt. I should have checked the pressures after installing. Thinking that it should have been set to spec. Now I know. My original WUR was most likely ok, but out of spec.

Originally posted by wckrause:
Lagoon? Why was the WUR out of spec? Was it a new one, or rebuilt, or what? Why did you replace the old one? Just curious.


Along with the Bentley manual, I'd recommend a book on Bosch fuel injection by Probst. It goes into how all of the Bosch fuel injection systems work, how to troubleshoot them, and mentions (briefly) performance upgrades. It's not specific to 911's (a slight fault).

Any 911 owner with CIS that wants to do their own maintenance (or second guess their mechanic) should own a CIS pressure tester. $50 at JCWhitney is all it takes. Check your system and control pressures, and verify pressure retention. Also buy a handfull of those crush washers for putting it all back together.

[lagoon]

Yor are rignt. I have wasted money on what I thought were bad parts. Goes to show, you should check the basics first and go from there.

Originally posted by speeder:
Lagoon, glad to hear you solved it, but I would hope that you possess at least a Bentley Manual. When trouble-shooting CIS, fuel pressure is first thing to check. God knows I've wasted $ and time in the past barking up wrong tree or even buying unneccesary parts without book. I consider the experience of others on this board extremely helpful,(including this thread), but a good mechanic always systematically goes through the TS steps even when having a hunch at the outset. I cuss a lot less since buying that book.