possible WUR problem.

[alk-3]

Hey All, I have a cold start issue i was hoping i could run by some people with more experience.
I found my (new to me) 1981 911sc to be running quite rich, i knew this right from the start so this past weekend i did some diagnostics and adjusted the air fuel mixture using the guid here.
immediately my car stopped bucking at low rpm, throttle response was much less touchy at low rpm and the rpms dropped off when the oil cap was removed which all were issues before the adjustment.
Once i had that adjusted, i adjusted idle, then double checked everything. I still plan to get the system tested with an 02 meter, but will wait till the end of the driving season.

I think someone in the past set the mix so rich in order to get the car to cold start well.
now that everyone is adjusted properly (or at least much better) the car with have very low rpms, sometimes even stalling for the first 30 seconds to a minute or so after a cold start. If i try to give it any throttle is backfires and pops (i have a pop off valve, thankfully).

My thinking is the car is running lean at startup, and once it begins to warm up settles out.

Does this sound like a WUR issue to you? Any other possibilities?

I am purchasing a test kit to check fuel pressure but wondering if I am on the right track.

Once the car is warmed up it performs perfectly.. rock solid idle at 950rpm, doesn't surge, drives perfectly, cannot complain at all. just this cold start issue to deal with.

(EDITE to add: my voltage regulator is on its way out, so could that be causing problems for the WUR? will be replacing that next weekend.)

Also, there are 2 plugs i found in the engine bay that were unplugged.. any idea what these are? The first one goes into the harness where the WUR plug also terminates, so is it possible they are related? could either plug be part pot this problem?

Maybe i should make a separate threat for the mystery plugs..

mystery plug 1:






Mystery plug 2:

[timmy2]

Mystery plug questions answered in other thread.
Only way to know about the WUR is to pressure test.

[boyt911sc]

Plug #1 with brown and brown/green wires..........???? (can’t remember this one).

Plug #2 with brown and red/white wires............For TTV or N43.

Plus #3 with three-wire plug............................For external voltage regulator. This is not utilized for late SC’s alternator with integrated VR.

Dennis (Timmy2) would surely know plug #1.

Is your engine a US/CAN or a RoW spec? What Bosch ID number is on your WUR? If you have -090, check the heater resistance value (Ohms) when the engine is cold. Keep us posted.

Tony

[boyt911sc]

Originally Posted by timmy2

Mystery plug questions answered in other thread.
Only way to know about the WUR is to pressure test.

Dennis,

Please take a good look at the pictures posted above. The first picture shows brown-green wire and the 2nd. picture shows red-white wire. Unless my eyesight is really going bad, these are two different plugs and are not the same. You are the electrical wire guru. Please tell me if my vision is impaired. I know I am old but I could still distinguished between brown-green and red-white. Please advise. Thanks.

Tony

[timmy2]

Tony, it is the same photo of the same connector in both, just zoomed in on the first one with distorted colors.
Hopefully the OP will confirm.
There is no reason for 2 of those unused connectors to be there and especially with wire colors that shouldn’t be there... (brown/green)

[Paulporsche]

It certainly sounds like someone has richened the mix to make up for an out of spec WUR, especially its cold control pressure setting. However, as others have mentioned, the only way to confirm this is by getting hold of a gauge and testing. The gauge must have fittings for CIS.

Check the number on the WUR and post it here. Tony or someone else can verify if it is correct for your car. You can then check your findings against a chart for your WUR.

Always make sure your plugs, wires and cap are up to spec first. Since your revs drop when the oil cap is removed, you are probably good re vac leaks. Again however, the only way to verify is by testing. Tony has posted some test procedures and I have seen some on YouTube.

[alk-3]

can anyone tell me if this gauge will work for testing?


https://www.amazon.ca/dp/B008FJXA3M/ref=pe_3034960_233709270_TE_item

[timmy2]

Lol, Can’t view from US without changing countries....

[LIRS6]

Originally Posted by alk-3

can anyone tell me if this gauge will work for testing?


https://www.amazon.ca/dp/B008FJXA3M/ref=pe_3034960_233709270_TE_item

I'm not sure that I would be a fan of a quick-release system when it comes to fuel.

I have the S & G Tool Aid 33800 - about $90 here is US

[boyt911sc]

Originally Posted by LIRS6

I'm not sure that I would be a fan of a quick-release system when it comes to fuel.

I have the S & G Tool Aid 33800 - about $90 here is US

Alk,

I would recommend the above S & G CIS pressure gauge kit. I have three (3) of them and the first one was purchased more than 25 years ago and still very reliable. I am not a fan of quick disconnect fittings for flammable fluid application.

Tony

[alk-3]

Originally Posted by Paulporsche

It certainly sounds like someone has richened the mix to make up for an out of spec WUR, especially its cold control pressure setting. However, as others have mentioned, the only way to confirm this is by getting hold of a gauge and testing. The gauge must have fittings for CIS.

Check the number on the WUR and post it here. Tony or someone else can verify if it is correct for your car. You can then check your findings against a chart for your WUR.

Always make sure your plugs, wires and cap are up to spec first. Since your revs drop when the oil cap is removed, you are probably good re vac leaks. Again however, the only way to verify is by testing. Tony has posted some test procedures and I have seen some on YouTube.

Yes, that's what I was thinking, someone has set it up to start well, but there are obvious compromises.
I inspected the wires and cap, and all seems fine, but I do have a replacement cap and plugs if I need them.
I will test it this weekend and get some real numbers to work with. Unfortunately, I only get to see the car on weekends (it is not at my home) so I try to prepare for the work during the week, arming myself with as much information as I can, and then try to apply it on the weekend with the limited time I have - making guesses as to what I need, and ordering parts etc.
This help is invaluable, so thank you all!

[alk-3]

hey guys. I got some numbers.

system pressure 4.7bar
cold pressure 2.5bar
warm pressure 3.5bar

i think the system seems fine, cold seems high and warm seems a tad high..

what do I do now?

WUR has 086 stamped on the top along with BOSCH and 482

is that WUR incorrect for this car?

[SkiVT]

Your wur number should be 438140090, or 089, I believe. The last 3 number are the key. Look along the top, oposite side from the electrical plug.

[alk-3]

I'll look again but I wrote in the above post all I could see stamped on the top surface of the wur. I can look with a mirror to try to find other stampings on the far side of the wur, but I wonder if mine is the 086 version.

EDIT just looked again, pulled the vac line and found the following: 0438140090

What do you think of my pressure readings? The cold pressure seems suspect to me.

[alk-3]

According to this the 090 version doesn't have a vac connection, but mine does..

[boyt911sc]

Originally Posted by alk-3

I'll look again but I wrote in the above post all I could see stamped on the top surface of the wur. I can look with a mirror to try to find other stampings on the far side of the wur, but I wonder if mine is the 086 version.

EDIT just looked again, pulled the vac line and found the following: 0438140090

What do you think of my pressure readings? The cold pressure seems suspect to me.

alk-3,

Do you have an ‘81 US/Can spec with lambda (OXS) or a RoW engine? What is the Bosch ID number on your FD? Keep us posted. Thanks.

Tony

[SkiVT]

Post a picture of your wur and find the engine number (by the oil pressure sensing unit and fan belt). The 089 wur is tied to the 930/10 engine. The 090 is tied to the 930/16 engine, I believe. The 090 has no vacuum but may have a vent to atmosphere. The frequency vavle controls the wur instead of vacuum. The frequency valve is tied to an O2 sensor in the exhaust and a lamda brain under the seat in your car. Lots of other members know how to troubleshoot this 090 wur.

[alk-3]

Originally Posted by boyt911sc

alk-3,

Do you have an ‘81 US/Can spec with lambda (OXS) or a RoW engine? What is the Bosch ID number on your FD? Keep us posted. Thanks.

Tony

My 81 SC is a USA spec with lambda.

Does FD stand for Fuel Distributer? If so, I'll check on that.

[alk-3]

Originally Posted by SkiVT

Post a picture of your wur and find the engine number (by the oil pressure sensing unit and fan belt). The 089 wur is tied to the 930/10 engine. The 090 is tied to the 930/16 engine, I believe. The 090 has no vacuum but may have a vent to atmosphere. The frequency vavle controls the wur instead of vacuum. The frequency valve is tied to an O2 sensor in the exhaust and a lamda brain under the seat in your car. Lots of other members know how to troubleshoot this 090 wur.

Okay, that vac connection very well might be a vent to atmosphere, that would make more sense.
Will get the engine number.
I just replaced the o2 sensor, thinking that might be the problem, I also just replaced the relay under the passenger seat. No change with either of those.

[alk-3]

I just performed a test that might be valid.. or not..
I jumpered the fuel pump with the WUR plugged in, and watched the pressure on the gauge go up until it stopped at 3.5bar. I think this means the WUR is at normal operating tempurture. I then started that car. It did the same backfire and stutter for about 2 or 3 minutes before settling into a good idle and acted normal.
Would this test bypass the wur as being the problem, since it was warmed up before I even started the car? Or is this actually creating more of a problem..?