possible WUR problem.
 

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:

http://i1263.photobucket.com/albums/...pspoqoinjp.jpg

http://i1263.photobucket.com/albums/...ps7uhfsnu5.jpg


Mystery plug 2:

http://i1263.photobucket.com/albums/...psv1irbfgq.jpg

http://i1263.photobucket.com/albums/...psjt49qprz.jpg

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

SC mystery plugs.........
 

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

Review the pictures of theplugs.......
 

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

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)

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.

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


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

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

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

Buy this model..........
 

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

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!

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?

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.

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.

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

CIS type indetification.........
 

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

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.

My 81 SC is a USA spec with lambda.

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

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.

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..?

Additional information.........
 

Since you have confirmed that you have an ‘81 SC with lambda (OXS) and WUR-090, could you measure the heater resistance (Ohms) of the WUR when the engine is cold? Keep us posted. Thanks.

Tony

Your 090 wur should match up to an 077 FD. Tony will get you over the finish line on this one. Alsways critical to be sure all the cis parts match before too much trounleshooting.

Okay will check the resistance in the AM. Along with engine number etc.
Just to help me understand the way a WUR works, if I tap down on the plug to lower the cold pressure, does that also effect the warm pressure?
I am not planning to do this unless it is determined it is nessisary, but I am trying to understand the inner workings a bit more.

Just checked, the FD is 077 will have to check resistance in the morning since engine is now hot.

Control pressures chart........
 

With the engine cold, measure the cold control fuel pressures versus time (30 sec. intervals) no more than 5 mins. and don’t forget to measure the WUR heater resistance (do this before running the FP).

0 sec. (initial) elec. plug to WUR disconnected. This is CCP (cold control pressure).
30 sec. Connect the elec. plug to WUR and start the count.
60 sec.
90 sec.
etc.
5 mins. max. (This is WCP, warm control pressure).

Please post your data. Thanks.

Tony

I think I either have a bad multimeter or a bad wur, or I'm doing something wrong.
Multimeter set to 200ohms
G to ground is reading 0.7
W to ground is reading 0.94
G to W is reading 10

I will perform the test for cold control pressure at intervals and post shortly.

Okay here are the values

Cold 2.75 bar
Plugged in;
30 seconds, 3.2 bar
1:00 - 3.6 bar
1:30 - 3.6 bar and stayed there all the way up to 5 minutes

I just tested the resistance again with a much better quality tester, and the values above are correct. So it looks to me like the WUR is not functioning correctly.
Any insights into those number?

Heater resistance value (Ohms)........WUR.
 

Alk,

From the above post, you seemed to me checking the TTS (thermotime switch). Why? What is the WUR heater resistance (Ohms) value of the WUR at room temp.? Your WUR is working except the CCP is out of calibration. I like to know the WUR’s heater resistance to help me understand more about its performance. Keep us posted.

Tony

Okay, I think I don't know how to check the resistance than.. can you walk me through that process?
I was measuring the resistance across each terminal in the wur plug, and then the resistance to ground from each leg of that terminal.. is that not correct?
Sorry, I am new to this, and am eager to learn but may be missing some of the subtleties of these tests.

Here is the Wur with the connection showing



http://i1263.photobucket.com/albums/...ps0nghz2qr.jpg

Here is the terminal I am testing. Putting a lead onto each of these connections.

http://i1263.photobucket.com/albums/...pstcar2yc6.jpg


Here is the reading, and my multimeter settings.

http://i1263.photobucket.com/albums/...ps1vaiunvz.jpg

Alk-3,

This is what I suspected about your WUR-090. Your current WUR will not prevent the engine from starting but will always experience erratic cold idle. There is nothing you could do to correct this nagging problem except find a good working and calibrated WUR.

I like to lend you one of my WUR’s (tested and calibrated) but you live outside USA. Shipping to Canada is not convenient and expensive plus you pay for import tax. However, if you have a US address to ship the WUR, I would be more than happy to accommodate your needs. PM me if you need help.

Tony

Update;

Tony was kind enough to send me a calibrated WUR and I had a chance this evening to install it.
It made a huge difference, car started right up and ran well, but still a slight backfire when the throttle is blipped while the car is still warming up. Particularly when I blip the throttle while the rpms are dropping from a previous blip.
When the car is first started the idle is a bit low, and slowly comes up to speed over several minutes.
I decided to take the car out and get it warmed up well, when I got back I disconnected the o2 sensor and re adjusted the mixture and set the ideal.
The idle was set too fast and the mixture was a bit rich. Now it's set properly, so I'll have to wait for the car to cool down over night and then try the cold start with all the new settings.
There doesn't seem to be too much of a vacuum leak because the idle drops off when I remove the oil cap.
It's running much better, but I will post again tomorrow once I re try the cold start.