I think I've diagnosed my WUR as faulty, with a "left field" method...?

[dino_jr]

Ok so I repeated step 2 above. I measured "cold pressure" 15 psi again at key on, then connected the WUR electrical plug after about 30 sec. Then I waited a further 4 minutes... the "warm" pressure increased to 40psi. Unconnecting the electrical plug again I can see the pressure then starts to drop off.

So now I think the WUR is OK. I measured my warm pressure too quickly before. How fast should the pressure increase... Seconds or minutes?

I think I am mainly confused by the car starts fine if I block the WUR Return line. That implies the air/fuel/electrics are all good... buy a new WUR

[boyt911sc]

Originally Posted by dino_jr

Ok so I repeated step 2 above. I measured "cold pressure" 15 psi again at key on, then connected the WUR electrical plug after about 30 sec. Then I waited a further 4 minutes... the "warm" pressure increased to 40psi. Unconnecting the electrical plug again I can see the pressure then starts to drop off.

So now I think the WUR is OK. I measured my warm pressure too quickly before. How fast should the pressure increase... Seconds or minutes?

I think I am mainly confused by the car starts fine if I block the WUR Return line. That implies the air/fuel/electrics are all good... buy a new WUR

Dino,

How did you run the FP? By just turning the ignition switch to ON position? Did you remove the FP relay and use a jumper wire? Keep us posted. Thanks.

Tony

[dino_jr]

Yep, jumper harness bypassing the FP Relay...

[boyt911sc]

Dino,

First, identify your WUR and FD. I believe you have '80 Euro/ RoW? This is how I test and evaluate a WUR;
1). Measure and record the cold control fuel pressures every 30 sec. intervals. The initial value @ zero sec. with the plug disconnected. Connect the electrical plug and start the time. Read the gauge at 30 sec. intervals.
2). Do the measurements until the cold control pressure stopped rising and becomes WCP (warm control pressure).
3). The duration of the test would be between 3 mins.~ 4 mins. (5 mins. max.)
4). Connect a hand held vacuum pump to the WUR and apply 15"Hg vac. and read the pressure gauge. This would be your WCP with vac. Record this value.
5). Check the system pressure by closing the shut off valve. Record this value.
End of test.

The data you have collected will show the characteristics of your WUR. Make sure you have a fully charged battery. Keep us posted.

Tony

[RarlyL8]

Sorry to step on your morally self righteous toes but baseline pressure of the fuel system is 100%. If the flow is 100% occluded (you really had to look that up?) at the fuel distributor then return pressure and flow back to the tank remains 100%. This occurs every time the pump(s) are running but the injectors are not firing.
At this point we need to know the part numbers of the FD and WUR. Factory repair manual lists the spec system/warm control pressures and cold control pressure per ambient temperature. Warm up baseline pressure and raising rate is dependent on ambient temperature and WUR part number. Euro models have a less aggressive curve.

[boyt911sc]

Originally Posted by boyt911sc

Brian,

I hate to disagree with your post (highlighted above in bold letters). Since this is a Technical Forum, I feel many would be mislead by your statements. You are a Bosch authorized rebuilder as you mentioned before and people would believe whatever you say regardless if it is true or not. As an avid CIS troubleshooter and no formal training from Bosch Technical School I should never question the 'experts'. But I have a moral responsibility to the community to differentiate a myth from fact.

The 'Return line pressure is not and will never be the System Pressure. And the return volume is not a good indicator for WUR to be occluded. BTW, I learned something today from your post. Never knew what 'occlude' meant until I looked at the dictionary. Definition: (1). To cause to become closed; obstruct. (2). To prevent the passage of. And other definitions.

At this point, I would consider you statement/s as a typo unless you want to discuss this subject with facts and data.

Tony

Part of first PM:

return pressure is system pressure.............WRONG!!!!!! Strike One.

.............(editted).

[B]if you connect a gauge to the return line to the tank and CLOSE the valve, it should read system pressure. after all that is basically what you are doing when you measure system pressure the correct way..........Wrong again!!!!!! Strike two!!!

I have never done this but I am sure you will now do it.
let me know......................................I've done these tests before many times over already.

..................(editted )



Second PM:

I don't think you understand the test............I do. It is you I am worried.

the valve on the gages needs to be CLOSED on the return line. IE, no fuel is making it back to the tank. its just like doing system pressure at the WUR, close the valve.
if you plug the return line I would think you would see system pressure.....................Wrong again!!!! Strike three.


My Dear Friend,

I am slightly disappointed of all people because I was expecting more from you. Anyway, when you closed the valve to measure the system pressure, the excess fuel goes back to the tank. Are you aware of this? System fuel pressure is set and controlled by the Primary Valve inside the FD and not by the return flow.

And your suggestion to close the return line to mimick the system pressure test is simply WRONG. If not STUPID (excuse my language) because you are going to build pressure in the system more than the system pressure (70 psi.) to over 100 psi. and if you are working on your 930 with 2 FP's and with system pressure of 100 psi., the build up pressure would be sky high.

If I am wrong and you're correct, I will make a public apology for not trusting your found knowledge. Including one to Brian, but only time will tell.

Tony

[theiceman]

ie you want to see system pressure with return line in operation . The fuel pump can put out way more than 70 PSI . it is not correct to test against a " dead head" all you are doing is measuring the highest possible output from a fuel pump.

But all that said , might be useful as a good test on an aging pump . But certainly not in troubleshooting CIS starting issues .

[dino_jr]

Hello, I am back. Various work commitments have kept me from the car, but I had a chance to look again yesterday. I randomly decided to fit everything back to spec... WUR, fuel lines etc... And the car started 1st time?!? It hasn't run until yesterday, for 2 months

However I now find when the car warms up for ~5 mins, the idle begins to hunt and then engine dies. I tried driving around the block but the car died every time I come off the throttle.

So I put the car back in the garage last night and re-did my pressure check:

* System pressure at fuel pump on: 4.6 bar and stays constant.
* My control pressure looks like this:



* Fuel pump on at zero, WUR (Cold) measured for 1st minute: 1.1 bar max
* WUR Electrical connector in after 2 minutes / green arrow: (Warm) 2.7 bar max
* Fuel pump off at 8 minutes / blue arrow.

So my new questions are:
1. Is the pressure drop off from 8 minutes my residual pressure? Is the rate of dropping correct?
2. If not, is this likely to be a drop off consistent with an air leak, failed FP check valve etc?
3. My cold and warm value are approx 0.5 bar too low, in reference to others I have seen. What could be the issue here or are they actually OK for now?