Diagnosing CIS Components from Pressure Test

[JoeyD1005]

Hey Everyone,

First off thank you for any help in advance, I've been doing quite a bit of reading and I'd like to try and provide as much information as possible for what I'm hoping is an easy diagnosis.

Car: 1978 Porsche 911SC

Background : First nice day rolled around in Michigan and I was going to try and take my car out for a drive. Unfortunately, I was having some trouble starting it. For the first few attempts, the car cranked but wouldn't start. After cranking for some time, it would kind of have a very weak burp type of a fire after I stopped cranking. With no luck after a few tries, I gave my starter a break and said I'll come back to it. After about 30 mins, the car reluctantly started and I let it warm up. Pulled out of the garage, seemed to be running a little rough but thought it could just be because it was stored all winter on bad gas so I ran to the sation up the street for some 93. On the way there, the car died twice at a light and I had to keep revs up with the car in neutral at lights and breaking. Got it home and started doing some research.

What I've Done So Far: Upon some general reading I decided to perform some general vacuum leaks. To do this, I uninstalled some of the heater piping so that I could spray some carb cleaner around the injectors and airbox. No change in idle.

Once the car has warmed up for some, I removed the oil cap and the idles dropped 1-200 ish RPM and the idle became a bit rougher.

Took out the airbox and tried to see if there was any sign of mixture related issues by doing the field test with the air plate. Seemed generally to be right in the middle of rich surge and lean. Decided not to even mess with mixture to keep variables in check. On to the CIS pressure test.

CIS Pressure Test Procedure:

1)Connected Fuel Guage between Fuel Distributor and WUR (Ball Valve on WUR Side of T Fitting)
2)Jumped FP Relay Socket
3) With Ball Valve Closed, ran Fuel Pump : System Pressure read 75 PSI (5.17Bar)
4) Opened Ball Valve w/ WUR Unplugged : Cold Control Pressure read 12 PSI (0.69Bar)
5) Kept Ball Valve open and plugged WUR connector back in:
- 1 Min Reading : 12 PSI (0.82Bar)
- 2 Min Reading : 18 PSI (1.24 Bar)
- 3 Min Reading : 22 PSI (1.52 Bar)
- 4 Min Reading : 25.5 PSI (1.76 Bar)
6) Kept Ball Valve Open and Shut off Fuel Pump:
- 0 Min Reading : 28 PSI (1.93 Bar)
- 10 Min Reading : 24.5 PSI (1.69 Bar)
- 20 Min Reading : 23 PSI (1.59 Bar)
- 30 Min Reading : 22 PSI (1.52 Bar)



Notes: I ran this test with NO vacuum to the WUR. I am not sure if that is something that is required on this year. I unfortunately am not able to see from where I looked any sort of part number designation for the WUR from where I checked. Between the top vacuum line and the electrical connector I only see the word BOSCH. I did however see that there is a vacuum line off the drivers side of the WUR (away from center of engine) that does not have any vacuum cap or line that has fallen off.

From what I have read on the CIS Primer site, it looks as though my WUR control pressures are lower than what is expected by the engine. Am I correct in suspecting that this is my main problem?

Please let me know if there is any more info needed for the discussion, I will try to get it asap.

Thank you again!
-Joe

[JoeyD1005]

After some more digging around int he engine bay, I was able to determine that the part number for my WUR is 033

Hope this provides a bit more info for diagnosis.

[pmax]

Nice work.

0438140033 is a 76-77 WUR.

I would also run the same tests with vacuum applied on the port to see if the WUR is adjusting the fuel pressure accordingly.

[JoeyD1005]

Thanks for the feedback, I can redo the test again tonight with vacuum. I unfortunately do not have any electric vacuum pumps. I do however have a mighty vac that I use for brake bleeding. What is the appropriate amount of vac to put on these lines, also do I pull vac on both fittings? On the 033 regulator, it looks like there is one on top and one on the left hand side.

If the test still shows low control pressure, is it time to make it an adjustable WUR? and tune with the CIS guages for control pressures?

I also saw today that I can do a resistance check on the electrical points so I can do that at the same time. Is 18-22 Ohms the expected reading?

Last question, is the mentioned startup and running problems inline for what we would expect for lower control pressure or do you think there might be another issue at hand?

Thanks for any advice.
-Joe

[pmax]

Vacuum applied from a manual pump should do, to the lower vacuum port. The port on the top is to "atmosphere". Another CIS elf which might be malfunctioning is the thermovalve, in line with the WUR vacuum prot, which controls the application of vacuum in your 78.

Yeah, it could. Adjustable is great for tuning your WUR. These are hardly precision devices given the >20% slop in the acceptable operational band.

[JoeyD1005]

Sure, I can run it again with vacuum on the side port. Any thought as to how much vacuum is on it?

[JoeyD1005]

Quick resistance check at the plug shows about 26.5 ohm. Out of spec on the diagram I saw, but it looks like another post says between 20 and 30 is fine. Hoping metal strip is functioning as expected and just takes a bit more time to heat up.

Any thoughts?

[pmax]

Around 7-8 psi I believe.
CIS Troubleshooting for Dummies

Yeah, the strip is working given the rising pressure vs heating time in your test. As you surmised, just takes more or less time to warm up ... in minutes, no big deal.

[boyt911sc]

Originally Posted by pmax

Vacuum applied from a manual pump should do, to the lower vacuum port.The port on the top is to "atmosphere". Another CIS elf which might be malfunctioning is the thermovalve, in line with the WUR vacuum prot, which controls the application of vacuum in your 78.

Yeah, it could. Adjustable is great for tuning your WUR. These are hardly precision devices given the >20% slop in the acceptable operational band.

WUR-033 has the vacuum port on top. You must be thinking on WUR-045/-069/-089. The early CIS WUR’s up to ‘77 (WUR-033) was the last group of WUR’s for 911 using the top post for enrichment. ‘78~’83 RoW (without lambda) are all using the side nipples for vacuum enrichment. ‘80~’83 (with lambda) do no use vacuum assisted WUR’s.

Lastly, you could use WUR-033 in your 3.0 engine provided you use the correct vacuum connection from top instead of side nipple. However, these WUR-033’s are not as robust and steady as the later WUR’s (-045/-069/-089) as far as enrichment is concerned.

Post some pictures of your engine and see what you have there. Where does the vacuum line to WUR-033 in your motor connected? Picture will help. Thanks.

Tony

[JoeyD1005]

Originally Posted by boyt911sc

WUR-033 has the vacuum port on top. You must be thinking on WUR-045/-069/-089. The early CIS WUR’s up to ‘77 (WUR-033) was the last group of WUR’s for 911 using the top post for enrichment. ‘78~’83 RoW (without lambda) are all using the side nipples for vacuum enrichment. ‘80~’83 (with lambda) do no use vacuum assisted WUR’s.

Lastly, you could use WUR-033 in your 3.0 engine provided you use the correct vacuum connection from top instead of side nipple. However, these WUR-033’s are not as robust and steady as the later WUR’s (-045/-069/-089) as far as enrichment is concerned.

Post some pictures of your engine and see what you have there. Where does the vacuum line to WUR-033 in your motor connected? Picture will help. Thanks.

Tony

Hey Tony,

I'll run out and grab some pictures after dinner.

From memory of about 20 mins ago, the vac line from the top of the port goes to a T fitting and feed of that vacuum line goes into somewhere near the throttle body.

Should the 033 model have vac on both top and side ports?

-Joe

[boyt911sc]

Originally Posted by JoeyD1005

Hey Tony,

I'll run out and grab some pictures after dinner.

From memory of about 20 mins ago, the vac line from the top of the port goes to a T fitting and feed of that vacuum line goes into somewhere near the throttle body.

Should the 033 model have vac on both top and side ports?

-Joe

Joe,

If you have a hand held vacuum pump like a Mity vac use it to measure your WCP (warm control pressure) @ 16” Hg. From the initial data I saw from your early posts, the WUR-033 needs some calibration. BTW, you got the wrong WUR for your ‘78 SC. You could make it to work. I actually used a WUR-033 in my ‘78 SC for a while till I found a -045 three (3) decades ago. And that’s a long time ago.

To answer your question:
WUR-033............vac @ top post/atmospheric @ side nipple. For WUR-045/-069/-089 it is the reverse or opposite. Be aware of this difference between these WUR’s.

Tony

[JoeyD1005]

Originally Posted by boyt911sc

Joe,

If you have a hand held vacuum pump like a Mity vac use it to measure your WCP (warm control pressure) @ 16” Hg. From the initial data I saw from your early posts, the WUR-033 needs some calibration. BTW, you got the wrong WUR for your ‘78 SC. You could make it to work. I actually used a WUR-033 in my ‘78 SC for a while till I found a -045 three (3) decades ago. And that’s a long time ago.

To answer your question:
WUR-033............vac @ top post/atmospheric @ side nipple. For WUR-045/-069/-089 it is the reverse or opposite. Be aware of this difference between these WUR’s.

Tony

You're the man Tony, much appreciated.

I'll run out and re-perform the checks and be back with the results.

-Joe

[JoeyD1005]

So a lot different results now that there was vacuum on the top port:
Temp = 40F

System = 75 PSI
CCP = 12PSI
1Min CP = 16PSI
2Min CP = 22PSI
3Min CP = 29PSI
4Min CP = 34PSI
5Min CP = 36PSI
6Min CP = 39PSI
6Min CP = 41PSI

Vacuum on Port = 16" Hg

[JoeyD1005]

Uploading some pictures of the engine bay:

1) Shows the Vac T Fitting (1 port to throttle body, 1 port to WUR, 1 port to vac cap


2) Shows the vac source from throttle body (Dark Blue line, Red line goes to spark distributor)


3) Shows this hack of a vacuum cap (will be fixing asap)

[T77911S]

41(2.7bar) is still too low. you should be around 3.6bar and have about a .8bar drop when you have no vacuum.
.7bar could be low depending on your outside temp and if you have the TV. the TV will block vacuum when cold dropping the CP even more for cold starts when it is really cold out.
BUT, if that is where the CP was when someone set your mixture then just leave it for now and get it running how it was before.

check for vac on the line going to the WUR at idle. this line should goto a thermo time valve (TV) (you may not have it and that is ok. ) then it should goto the decel valve (DV) with a "T" and then to the TB. it needs to goto manifold vacuum, its one of the ports below the throttle plate. (i may be wrong, too many years now, but i am thinking it was on the back, but could be wrong).

check your pop off valve and make sure it is seated properly.

my 033 would be .8bar when really cold, then 1.8bar once vac applied when cold then it would warm up to 3.6bar with vac and 2.8 without.
you may get away with adjusting your pressures.
tony can even check your WUR for you if you send it to him

top port is vac, side port is a vent that goes to the intake (no vacuum). it there in case of fuel leak inside the WUR

[boyt911sc]

Gilbert,

What is this mystery line? Where does the line connect to? Never seen one before and curious to know. Keep us posted. Thanks.



Tony

[JoeyD1005]

Originally Posted by boyt911sc

Gilbert,

What is this mystery line? Where does the line connect to? Never seen one before and curious to know. Keep us posted. Thanks.



Tony

Tony, that is sort of some weird brass adapter that goes from the small vacuum line from the T junction to a larger hose to fit over the vacuum port on the top of the WUR.

-Joe

[JoeyD1005]

Originally Posted by T77911S

41(2.7bar) is still too low. you should be around 3.6bar and have about a .8bar drop when you have no vacuum.
.7bar could be low depending on your outside temp and if you have the TV. the TV will block vacuum when cold dropping the CP even more for cold starts when it is really cold out.
BUT, if that is where the CP was when someone set your mixture then just leave it for now and get it running how it was before.

check for vac on the line going to the WUR at idle. this line should goto a thermo time valve (TV) (you may not have it and that is ok. ) then it should goto the decel valve (DV) with a "T" and then to the TB. it needs to goto manifold vacuum, its one of the ports below the throttle plate. (i may be wrong, too many years now, but i am thinking it was on the back, but could be wrong).

check your pop off valve and make sure it is seated properly.

my 033 would be .8bar when really cold, then 1.8bar once vac applied when cold then it would warm up to 3.6bar with vac and 2.8 without.
you may get away with adjusting your pressures.
tony can even check your WUR for you if you send it to him

top port is vac, side port is a vent that goes to the intake (no vacuum). it there in case of fuel leak inside the WUR

So I can tell you right now that the vac routing that you posted is not what is in my car. Since one of the lines coming off of the T fitting has a freakin golf tee in it, the routing is effectively going directly from the WUR to the throttle body (the dark black vac line I showed) it is on the drivers side of the throttle body. Not sure if that is correct or not - I'm guessing it is not.

So I will go check for a thermovalve and decel valve when I get home and see if the vac routing is just completely borked.

Car ran and drove fine for the last two years until this spring. I'm guessing that it wasnt running at peak but unfortunately I didn't know due to it being my first 911. Ill be happy to get all of this sorted out.

[SkiVT]

I believe if you envision the blue line coming off the top of your WUR (ignore the yellow line), the rest of the vacuum routing through TV and DV is accurate.

[JoeyD1005]

Originally Posted by SkiVT

I believe if you envision the blue line coming off the top of your WUR (ignore the yellow line), the rest of the vacuum routing through TV and DV is accurate.

Correct, except I have a 033 wur so the ports are flipped on part 5 of the diagram. Ill take a look at it when I get home.