1981 SC CIS - low idle - wrong WUR?

[wreckah]

Hi guys,

i've got this 1981 911 Targa with some cold running issues, and i would love some input from you lot, i've done lots of research but i'm reaching a ceiling on my knowledge...

the car is mostly stock, and in pretty good condition, inside and out, original california car, so US spec. Weinrot.
I know i need to post a pic, so here goes :


I just did some pressure testing and here are my results (all with non running engine, bridged the FP relay, so non vacuum):
cold control: 1.6bar (around 5 to 10°C here in Belgium at the moment)
warm control: 3.4bar (reaches after 3-4 minutes when i plug it in)
system pressure: 4.5bar
(fuel pump sound good, also no fuel leaks whatsoever)
i haven't got any residual figures because the fuel pressure tester is leaking a tiny bit in one of the connections. (i don't think it has influenced the numbers too much)

Worth mentioning: the car has no O2 sensor attached, and is running a 072 WUR,
the AAR is working good, and i did not find any vacuum leaks so far...

Issues: cold start is not great: it will start relatively easily, but never reaches high rpm...it idles (barely) at 500rpm and is very temperamental the first couple of minutes. It will stall too if i give it some throttle and then let go of the throttle. After a while, stumbles go away, and the car feels quite good once warmed up. Warm idle is rock steady at 950rpm.

It seems that warm and cold control pressures are a bit on the high side. Although it smells very rich, which is strange? It should be too lean when cold with these numbers, right?
I made the WUR adjustable for CCP, so that will be a reasonably easy fix, push it in a little bit and measure again. I opened it as well, and it looks brand new in there. Is it also adjustable for WCP? Is this WUR correct for this car?

I wonder why it keeps this low rpm when cold...any other things i should check?

cheers for the input,
Jan

[wreckah]

warm starts are great by the way.
Airbox looks fine, new stock airfilter.
Stock exhaust as far as i can tell. Very quiet.

[OsoMoore]

Same color as my '79 Targa! I had a lot of CIS adventures this past summer. My car also has the "wrong" WUR, a Euro on a California car, but with proper setup it works fine.

There are some differences between '79 and '81, but I believe the issue could also arise from the Auxiliary Air Regulator. It allows more air when cold, and slowly closes as the engine heats up. If it is sticking closed, the engine will be choked on air while cold.

In the end, there are a lot of "knobs" to turn for a CIS system. It isn't too hard to take off the top of the system (throttle body and tubes) and clean them out, and put back on. You don't have to alter the settings of anything to do this, and you can clean out lots of gunk and possibly find vacuum leaks.

[OsoMoore]

911 CIS Primer - Introduction is a great resource for such things.

[wreckah]

thanks guys, the AAR works well, so i ruled that one out. it's nicely open when cold and closes after ca. 5 minutes.

[wreckah]

hmm...it looks like i have a 1980 WUR in my 1981. so do i go for the 072 pressures? Then i need a little bit more CCP, which means leaner running when cold...? warm is not far off then...

Year model System Pressure Cold pressure Warm pressure Vac conn Info Source

'80 .072 4.5 to 5.2 1.8 @ 10 3.5 @ 40 None F.M.

'81 - 83* .089 4.5 to 5.2 1.2 @10 3.0 @ 40 3.6 @ 40 S.B.

[psalt]

Jan

Is this a USA car with a cat and disconnected O2sensor , or a ROW car ? On USA models, the cold start, stumble and stalling is usually caused by a combination of the vacuum retard. a lean mixture and sometimes the wrong spark plugs. If your distributor has two vacuum lines, disconnect and plug the rear grey hose and reset the idle speed to 950 rpm with the thumb screw on the throttle body. Ignition timing should be 5 degrees BTDC with both hoses disconnected and plugged. The engine was calibrated with BOSCH Normal spark plugs and others can cause this symptom. Retest the cold start overnight. If it still stumbles and stalls, look for vacuum leaks at the injector sleeves and Orings and around the airbox with an unlit propane torch. Almost all 911SCs at this age will have leaks at the injector sleeves that will alter idle mixture due to the method Porsche choice to mount the injectors. Fix the leaks before resetting the mixture and you can usually tune these cars to instantly fire and immediately run at a 1500 rpm fast idle regardless of temperature. There is a lot about this problem in the archives.

[wreckah]

Hi Paul,

thanks for your insights,
it's a US car, with 02 sensor deleted...edit: cat is still there.

Will try your suggestions in the morning, i will let you know what happens.
Will check spark plugs as well,

cheers, Jan

[psalt]

Jan,

The O2 sensor is irrelevant to cold starting, however CIS lambda requires a pulsing FV for the mixture to be anywhere near correct. You need to confirm the dome light fuse is OK, the lambda relay is OK and the FV is buzzing. If you reconnect the 02 sensor, this engine will talk to you though the test port and a dwell meter. Much better info than web posts. Search for CIS Lambda.

[Bob Kontak]

Originally Posted by wreckah

'81 - 83* .089 4.5 to 5.2 1.2 @10 3.0 @ 40 3.6 @ 40 S.B.

Pretty sure the US 81 uses the 090 WUR. Don't know if there is a California variant.

Believe the 089 is the WUR for the non-US versions through the early 80's. Perhaps the whole run of ROW SC's?

Here is the 090 chart. Your readings actually look pretty good.

[groovydude]

While you pressure readings look good for a 090, I had the exact same symptoms, and they were fully cured by replacing the WUR (with a rebuilt one from CIS Flowtech). Not sure what could be going on. Is it possible that the fuel line from the WUR to the FD is clogged?

Btw, I like your bumper/valence, do you know who makes it? Nice color too.

[boyt911sc]

Originally Posted by wreckah

hmm...it looks like i have a 1980 WUR in my 1981. so do i go for the 072 pressures? Then i need a little bit more CCP, which means leaner running when cold...? warm is not far off then...

Year model System Pressure Cold pressure Warm pressure Vac conn Info Source

'80 .072 4.5 to 5.2 1.8 @ 10 3.5 @ 40 None F.M.

'81 - 83* .089 4.5 to 5.2 1.2 @10 3.0 @ 40 3.6 @ 40 S.B.

Wreckah,

WUR-089 is for Euro/RoW and vacuum assisted. You can not use this WUR-089 without modifying your CIS. Your problems are having a different WUR-072, O2 disabled, and your WCP & SP at the very low end of the range values. If your decision is to omit or by-pass the lambda, it would take some serious tinkering to get your engine to run well. First, could you post the fuel distributor ID number? I expect it to be -077 but who knows. Thanks.

Tony

[wreckah]

Hi Tony,

yepp, it's a 077 FD.

i'll check the easier things first, and then move on to bigger things.

cheers, Jan

[T77911S]

how was the O2 sensor deleted? was it just removed
do you still have the frequency valve and does it vibrate when engine is running.

mixture is way off when cold. the CCP is not far off enough to make a difference based on a stock car, but depending on the O2 sensore delete mods it could be

when cold, lift up and pull down on the aif flow sensor plate behind the air filter, just to see if it needs to be richer or leaner.

copper plugs.

[wreckah]

ok, took off the blue dizzy vacuum line, plugged it,

set the WUR to 1.8bar CCP, as per 072 specs,

starts ok, runs 800rpm instead of 500ish, so a bit better, but still lots of backfires through the exhaust when i give a slight bit of throttle.

sprayed lots of carb cleaner around the injectors and no change in rpm to be noticed.

gonna source a FV relay this afternoon, and maybe a mirror too, because i don't know where to feel exactly for buzzyness.

groovydude: the bumpers are RUF or RUF lookalike/style (you know, yellowbird mid-eighties). They look rather nice, not cheap.

[wreckah]

the O2 is replaced by a plug, i haven't got a clue where to wiring went or where it's supposed to be...need to look into that. PO did this.

spark plugs are Bosch W3CC

[wreckah]

dome light, dashboard light works, pulled the relay under the seat, no difference in running.

[boyt911sc]

Originally Posted by wreckah

Hi Tony,

yepp, it's a 077 FD.

i'll check the easier things first, and then move on to bigger things.

cheers, Jan

Jan,

Do you still have the ECU (lambda brain/electronics) under the passenger (right) side? You need a good working ECU plus FV relay, OXS, and WUR-090 to get your engine to run and idle correctly. An appropriate dwell meter or an oscilloscope could verify if the ECU, relay, OXS, and FV work in tandem. FD-077 is designed to run leaner than the FD intended for Euro/RoW. WUR-090 keeps the cold idle richer and longer than WUR-089 does. As you can see, it is a balancing act of the different CIS components to achieve what Bosch designed for a particular CIS unit.

Any particular reason why you want the lambda engine to run without OXS? Are you trying to make this motor to run similarly as a Euro version? Keep us posted.

Tony

[psalt]

spark plugs are Bosch W3CC

Jan,

Correct spark plugs for a 81 US 911SC are WR5DC.

If you pulled the OXS relay on a hot running engine with no change, you have found the problem, now determine if it is just the relay, ECU or FV. Search for Lambda CIS and you will find everything you need on this site. If the FV is not operating, chances are the PO used other bodges and posh wannbe hairdresser techniques to make it almost run properly.

[82 SC]

Good post, I bought my 82 with the cat and 02 sensor missing. I have a bit of idle issues as in high idle but I think its mostly vac issues. Still wonder how my car is set up without cat and sensor. Pulls great thru 1 and 2nd, when in traffic and I give it some gas at high speeds it kind if shudders a bit. I am waiting on working on my 911 till after my shop is ready.
later