911 SC cold start problem

[medarwin]

Hello, Have been fighting this one for over a year. 82 911 with CIS. Car will not readily start when the engine is not warm or at operating temp. Stumbles, won't take fuel. Seems to be a lean condition. Once it get to temp it smooths out and idles and runs well. It is an occasional self-healer but always reverts. So far I have replaced the WUR and the cold start valve, the intake boot and eliminated vacuum leaks as the culprit (I think).
The fact that the car runs fine when warm would seem to eliminate a fuel mix problem as well as a fuel pressure problem.

My question is, what functions does the ECU under the seat perform? I am suspicious as I cleaned and sprayed the contacts on the plug recently and the car worked flawlessly for about two weeks before reverting to prior behavior. There is not an apparent difference with the ECU plugged in or unplugged. I would think that the ECU is there for a reason other than CC or such.

I am somewhat convinced that the CSV or the WUR is not functioning possibly because there is a communications breakdown between components. The fact that they were both replaced with new ones would seem to indicate that the fault lies elsewhere. I've searched tech articles and various forums but so far no luck.

Any help would be greatly appreciated and likely to earn privileges in your afterlife.

many thanks, darwin

[boyt911sc]

Darwin,

As a protocol, new members posting for the first time are required to post pictures of their car/s. Otherwise, replies would not come as quickly as expected. Why did you replace the WUR & CSV in the first place? Did you test and confirm they were both defective before buying new parts? Keep us posted.

Tony

[medarwin]

OK, pic of car posted. A mechanic, who I no longer take advice from, suggested that the culprit was first the CSV and then the WUR. My big question is, does the ECU control the CSV and/or the WUR?

[schumicat]

check aux air regulator, it is on right side of engine. very easy to check (search here for procedure).

the ecu under seat controls the frequency valve. non working FV can definitely cause lean condition. unplug the 02 relay under seat. if no change your relay or ecu or FV may be dead. the FV makes a distinct buzzing sound when working.

[tom1975]

It's happened to me two weeks ago ,99% it's the o2 relay ,Replace the o2 relay under the passenger seat , 10$
And you solve the problem and the car will run like a Missile
You must bosche relay no :
0332019150
Look and read Carefully this thread :
81 SC Oxygen Sensor Relay
Good luck

[Bob Kontak]

Originally Posted by tom1975

Replace the o2 relay under the passenger seat , 10$

Replace the O2 relay because your car is old and replacing this part alone, even if functioning, will provide a mini tune up. They get tired.

I doubt it is your problem, though. Your car will run like crap all the time if it is not working. Like CRAP. No warm smooth out.

As noted, the car will transition from cold to warm running with the assist of the Aux air regulator and aux air device. The decel valve will, by design, allow "false air" to bypass the throttle when decelerating. Plug that stinker.

Since you can't start easily cold, I think you have a CSV issue. the CSV will overcome a host of cold start issues with a typhoon of gasoline laden vapor. Without it you are not going to start first time.

Since you can't start easily warm you have a residual pressure issue. Meaning you have an internal gas leak allowing pressure to drop. A fuel injector, fuel regulator, blah blah

Get some CIS gauges. Not a universal set at Harbor Freight, a set of CIS pressure gauges. If the freight has then, fine.

The CSV works when the starter is engaged and that is it. No ECU interface.

The WUR pressure is controlled by the bi-metallic strip warm up and engine temp (across time) No ECU input.

However, the 12 pin (I think) connector on the rail between the two rear shock towers - more on the left than the right - is a good connector to split apart and check out. It is suspect as the FV signal goes thru there.

Also, wait for boyt911sc's input. Do get the pressure gauges when $ allows.

[Newfie911s]

On Sale now

CIS Fuel Pressure Test

The only thing to help with CIS Systems.

[tom1975]

I had a problem to srart the engine when its cold, the engine started and shut down immediately and I had to start several times and hold the gas pedal until it warms up, and i have alot of backfire from the air box
Driving performance of the engine were poor,
I replaced the relay and the problem was solved and the vehicle drive like a rocket !!! Yes old 1983 sc
you think the car drive good when the engine is hot, wait you'll see the difference on the road after replacing the relay.
Before you buy anything and get
Into expenses replace the relay.
Anyway after disconnection of the unit under the seat (not the relay ) you must To adjust the mixture Again.

[Bob Kontak]

Originally Posted by Newfie911s

On Sale now

CIS Fuel Pressure Test

The only thing to help with CIS Systems.

I would recommend the specific to CIS set of gauges for simplicity unless you work on lots of cars.

911 CIS Primer - Testing: Pressures

Pelican Parts.com - C.I.S. K-Jetronic Fuel Injection Tester with Case

[boyt911sc]

Darwin,

There are several things that could cause your cold start problem. Check these:
1). Cold control fuel pressure.
2). WUR is delivering the specified fuel pressure at x temp.
3). CSV is working during cold start phase.
4). No significant source of unmetered air.
5). Check if the FV is vibrating or pulsating when FP is running.

At this point, you have no idea how these basic requirements are met or not. So checking and verifying are mandatory for a systematic troubleshooting. You could get all the answers for the above without even running the engine.

The WUR and CSV are not controlled by the ECU. They are in a different circuit. What did you mean by ECU connected or unplug? The main ECU harness unplugged? Keep us posted.

Tony

[medarwin]

I have pulled the O2 Relay. HAve found the Bosch part (0332019150) at ******** AZ that was referenced in the '07 thread as the correct relay which connects the (2) 87 legs. The diagram on the relay matches the one in the old thread but I cannot make sense of the diagram on the original VW/Audi relay I pulled.If no luck then I will be in the market for a CIS fuel pressure test gauge. In the meantime I am trying to keep my 87 930 and 72 911 going with their various issues. My biggest problem is that I do not drive my cars enough, hence they tend to disintegrate

[fireant911]

Originally Posted by Bob Kontak

Replace the O2 relay because your car is old and replacing this part alone, even if functioning, will provide a mini tune up. They get tired.

I would have never believed this if I, too, had not experienced exactly the same thing. The O2 relay is either off or on and no in between... however, when I replaced this my car performed much, much better than before. Earlier, I had discovered that the previous owner had plugged one of the auxiliary air valve hoses which was causing my issue. It took three deep cranks before the engine would stay running after a cold crank. after removing the 'plug', it cranked great! replacing the O2 relay made a huge difference.

[tom1975]

0332019150 Is the relay you need for sure, leave what you had before, who knows what was Previous owners do on your car, change the relay and update us

[medarwin]

Thanks Tom, the relay that was in appears to be the original VW/Audi relay, PN 821951253. Seems to make sense that it might be the culprit since the car performed exactly the same whether the ECU was connected or not. Of course, the ECU itself could be bad and not functioning with the O2 relay.

[tom1975]

Yes, I hope for you that it's just the relay, in any case the original 821951253 is very difficult to achieve and is also very expensive, buy the relay I told you, it functions great and does the same job

[Iceguy]

Did the O2 relay replacement solve your cold start problem? This forum thread stops without any resolution.

I had the same problem in my 1980 SC -- wouldn't start easily when cold, seemed to run fine when warm, started fine when warm -- until yesterday.

Yesterday, I received the new O2 relay (Bosch 332019150) from Amazon, plugged it in, and the cold car fired up like a dream. This morning at 45-50 deg F, it started perfectly.

Just as tom1975 said, seems to run better warm, too.

Recommendations you got to pressure test everything weren't necessary, I bet. Would have been difficult to understand how the O2 relay was causing whatever pressure problem you turned up.

Moral of the story? If someone tells you a cheap and easy part replacement will fix your problem, try that first, I guess.


Iceguy