911 SC 1983 warm running issue

[Hyllski]

Hello

I have an issue with my 911 SC 1983. Itīs a european car sold new in Germany and exported to Norway in 1986. The engine is original, except for a completely new exhaust system (Dansk) so any lamda or oxygen injectors that might have been there once is not present anymore but the car has been working perfectly with this setup for a long time. So I dont think this is an issue. Problems started last summer...

So this is my problem: Engine starts up easy and runs perfect when cold. Start driving and everything works perfect for approximately 10-15 minutes. Now the problem starts appearing. The engine surges from time to time when driving straight forward and the throttle is activated. At full acceleration the car is fine. When I brake to turn or brake for a speed bump the problem increases. The engine surges like crazy and itīs no power at all. I have to give it plenty of rpmīs to avoid the engine from stopping. Car idles almost fine when warm after driving. Itīs a bit uneven but it does not stop. The problem is when the engine is loaded.

This is what I have tried so far:
-New fuel filter.
-New spark plugs, cables and coil. (rotor and distributor cap was pretty new so I have not changed).
-New ECU (Bosch module placed on the left handside of the engineroom).
-New WUR.
-Checked that AUX air reg. closes the gate when engine gets warm. Seems fine.
-Checked for any false air with starter gas. Cant find any. All vacuum hoses looks fine.

Next step is to measure fuel pressure.

Any other ideas?

Regards Steinar

[AndrewCologne]

If your car is an European version than it did not leave the factory with a lambda system.
The BOSCH module in the left engine compartment is a "HKZ" or in englisch called CIS.
An ECU is the module for driving the lambda system and is present under the passengers seat on 911 SC US models from 1980-1983.

So even if you got a new WUR, you should definitely check – beside system fuel pressure – the control pressure at cold an warm states. Ive read so many times of problems with "new" or overhauled WURs as these where sold being not calibrated accurately.

[Hyllski]

Thanks for info about ECU/CIS. So itīs the CIS I have changed then...

The WUR came from a car that ran perfect when removed, but I will check more around this for sure. Could there be an electrical or vacuum issue around the WUR?

Will work on making a setup for fuel pressure testing the coming days.

[boyt911sc]

Originally Posted by Hyllski

Thanks for info about ECU/CIS. So itīs the CIS I have changed then...

The WUR came from a car that ran perfect when removed, but I will check more around this for sure. Could there be an electrical or vacuum issue around the WUR?

Will work on making a setup for fuel pressure testing the coming days.

Not ECU.
Not CIS.
It is referred as CDI.

What is the Bosch ID on top of the WUR? It should read like 0 438 140 xxx. The last 3 digits will identify your WUR. You need a pressure gauge kit to test and measure your fuel pressures (system, control, and residual).

Post a picture of your WUR showing the top side. Other test to perform is air leak test using a smoke generator. Keep us posted.

Tony

[Hyllski]

Thanks for input on ECU/CIS/CDI. So it's the CDI
I have changed then...

Bosch ID is 089 on both the old and the new WUR.

Working on building a pressure gauge kit. Will post results...

[AndrewCologne]

Originally Posted by boyt911sc

Not ECU.
Not CIS.
It is referred as CDI.
Tony

yezzz :-)
i mixed up ...

CIS is simply the k-jet

[Hyllski]

I got my pressure test kit finished today and I connected it to the tickest line on the WUR (the one with the hose). I also connected the 87A and 30 pin on the fuel pump relay to do the testing without the engine actually running. 5 degrees Celsius today or 41 degrees Fahrenheit.

First issue: Ignition on. Fuel pump running. Electric connection on WUR disconnected. As good as no reaction on the pressure gauge! Disconnected hose and put it in a bottle. There is fuel flow but not very strong (that being said, I dont know whats normal).
Continued with test anyways. Connected the electric connection on WUR. Pressure starts to rise.After 5 minutes 23 PSI. After 10 minutes 28 PSI. Now it came to my head that I was supposed to disconnect something behind the airfilter? Stopped the test/fuel pump. After 20 minutes pressure is 21 PSI.
Possible to do some conclusions after this first test or do I need to do this again with the connection behind the airlifted disconnected?

[boyt911sc]

Originally Posted by Hyllski

I got my pressure test kit finished today and I connected it to the tickest line on the WUR (the one with the hose). I also connected the 87A and 30 pin on the fuel pump relay to do the testing without the engine actually running. 5 degrees Celsius today or 41 degrees Fahrenheit.

First issue: Ignition on. Fuel pump running. Electric connection on WUR disconnected. As good as no reaction on the pressure gauge! Disconnected hose and put it in a bottle. There is fuel flow but not very strong (that being said, I dont know whats normal).
Continued with test anyways. Connected the electric connection on WUR. Pressure starts to rise.After 5 minutes 23 PSI. After 10 minutes 28 PSI. Now it came to my head that I was supposed to disconnect something behind the airfilter? Stopped the test/fuel pump. After 20 minutes pressure is 21 PSI.
Possible to do some conclusions after this first test or do I need to do this again with the connection behind the airlifted disconnected?

Steinar,

Since you know how to test run the FP using the FP relay (87A & 30), no need to disconnect the AFS switch. Both CCP & WCP are too low. Once the motor starts to warm up, the problem would be more noticeable due to too RICH or low WCP. To correct this problem, you need to calibrate the WUR to deliver the correct fuel pressures.

The residual pressure is good. How about the system pressure? Could you post the ID # on your WUR? Thanks.

Tony

[Hyllski]

Tony

Number on WUR is 0 438 140 089

Is it not strange that 2 WURīs have the same issue. I have tried to switch to another WUR also ending on the number 089 and the problem is the same.

Will check system pressure later today.

How do you calibrate the WUR?

Steinar

[boyt911sc]

Originally Posted by Hyllski

Tony

Number on WUR is 0 438 140 089

Is it not strange that 2 WURīs have the same issue. I have tried to switch to another WUR also ending on the number 089 and the problem is the same.

Will check system pressure later today.

How do you calibrate the WUR?

Steinar

Steinar,

Unless your pressure gauge is defective, your pressure data would be questionable. So using a properly working instrument is critical for diagnosing your problem/s. Since I am relying on your information, my suggestions and observations are all based from your feedback.

I have four (4) sets of CIS gauges that I test periodically to verify their calibration. You only need one and a good one. It does not have to be super accurate. As long as it could read 5% (+/-), your data will be acceptable. CIS is very forgiving and tolerates broad margin of errors.

Tony

[Hyllski]

Tony

I changed to another pressure gauge and checked the system pressure. It reads 65 psi or 4,5 bar.

I also noticed a tiiiny fuel leak on the connection where my pressure measure kit connects to the WUR. This should have no impact on the system pressure check as the line down to the WUR then was blocked. But it may impact the rest of the test maybe? However the residual pressure was good and indicates that the small fuel leak does not impact much. Did the warm up test again with the new gauge and result is the same.

Really appreciate the help here

Steinar

[Hyllski]

I fixed the minor fuel leak and did a new test today.

6 degr. celsius or 42,8 degr. Fahrenheit today.

System pressure 65 psi or 4,5 bar

Cold control pressure 3 psi
Plugged in electric connection on WUR
1 minute 7 psi
2 minutes 12 psi
3 minutes 16 psi
4 minutes 19 psi
5 minutes 22 psi
6 minutes 24 psi
7 minutes 24 psi
8 minutes 25 psi
9 minutes 26 psi
10 minutes 27 psi
20 minutes 28 psi
Warm control pressure 28 psi or 1,93 bar

Residual pressure (turned of ignition and fuel pump)

1 minute 25 psi
2 minutes 22 psi
3 minutes 20 psi
4 minutes 20 psi
5 minutes 20 psi
10 minutes 19 psi
15 minutes 18 psi
20 minutes 18 psi

So I guess I need to learn how to adjust my WUR now?

[gomezoneill]

You tube is your friend.

[Hyllski]

Hereīs a little update on my WUR project:

Opened up the WUR and knocked the screw/pin that holds the bi-metallic spring further out of the WUR housing. Put back on car. Now both cold and warm pressure is 37 psi (2,5 bar) no matter what. I think I probably destroyed something/missed something when opening/closing the WUR. Opened it 3-4 times now, but can't find anything wrong...
Anyways... With these pressures (that is a to high cold control pressure and to low warm control pressure) I decided to try the car. In theory the car should idle worse/badly when cold and run better than before when warm. And guess what... It actually did! Still not happy, but on to something...

[boyt911sc]

What is the heater resistance value (Ohms) when the engine is cold? The fact that you are getting pressure changes up to 20 mins.+, is an indication that the bimetallic spring is some what lethargic or “tired”. Did you have a fully charged battery?

After the last adjustment, how long before you get the WCP to maxed out and stabilized? Keep us posted.

Tony

[Hyllski]

I will have to wait until tomorrow when the engine has cooled down to check the resistance. Have checked it earlier and found it OK, but not after my latest opening/adjustment on the WUR. I drove the car really nice and warm (30 minutes) today and then measured the control pressure. Still stuck on 37 psi. A warm engine should do the same as the heater element with the bimetallic spring if I understand it correctly?

Steinar

[boyt911sc]

Originally Posted by Hyllski

I will have to wait until tomorrow when the engine has cooled down to check the resistance. Have checked it earlier and found it OK, but not after my latest opening/adjustment on the WUR. I drove the car really nice and warm (30 minutes) today and then measured the control pressure. Still stuck on 37 psi. A warm engine should do the same as the heater element with the bimetallic spring if I understand it correctly?

Steinar

Steinar,

Are you getting the same WCP with motor not running (FP only) and when it is running? Just making sure we are on the same page. Thanks.

Tony

[Hyllski]

First I checked WCP with FP only and got no reaction as the CCP was also 37 psi. Then I removed the pressure gauge (did not want to drive the car with that installed) and drove the car for app. 30 minutes. Connected the pressure gauge again. Engine nice and warm and ran FP and electric connection connected on the WUR and got the same reading, 37 psi.
Steinar

[boyt911sc]

Originally Posted by Hyllski

Yes, same WCP with FP only and after 30 minutes driving. 37 psi.

Steinar

Are you aware that WCP is measured in two (2) different conditions?
1). WCP without vacuum.
2). WCP with vacuum.

Could you post a picture of your motor showing the 1-2-3 intake runner side and the decel valve? Thanks.

Tony

[Hyllski]

Ok, now I got what you meant. Engine was not running when I checked WCP after driving. So no vacuum on both tests.