Video diagnosis: Is my WUR faulty?

[universeman]

Team,
I published a video to ensure that I'm doing things right when I check my cold control pressure.

It's 36degF outside right now and I have 1/2 bar or so of control pressure. Seems too low. Voltage to the connector, next I need to check the resistance on the element (which I'll post in an update.)

Video here: would you guys make sure I'm doing this right?

http://www.youtube.com/watch?v=YOmTLryWQ6E

You can hear the idle start surging a little bit. I think I'm running really rich based on this. My thoughts on next step to fix are to remove and clean the WUR, and check the element. Any other ideas welcome, thanks!

[universeman]

Update: I was unable to detect any resistance between the two male spades of the WUR, meaning broken element? I don't know - my understanding of electrics is a little light.

Ground side of connector on WUR has continuity with ground, so I know that is good.

[tirwin]

Valve closed will give you system pressure. You got that right.

Open the valve and that will give you cold control pressure and the electrical connection on the WUR disconnected starting with a cold engine. You got that right.

For warm control pressure, you don't have to start the car. You can do it that way, but then you will get the effect of the ambient heat from the engine. If you're looking to see that the WUR is actually working, don't run the engine. All you have to do is start the test with the electrical connection on the WUR disconnected and then plug it in. If the control pressure doesn't change at all, this would confirm your electrical test result that something inside the WUR isn't working.

As far as the electrical test, clip your meter to the two small male spades and then set to Ohms on the meter. You should get some resistance value. Any other reading is cockpit error or there is an air gap in the WUR internals.

Let the engine cool off again and then repeat the WCP test without running the engine.

[tirwin]

Also remember that as control pressure increases, the mixture leans out. So if the WUR is not working correctly (CP never increases) and you start with a relatively low control pressure (which is normal*), you will have a good cold start and then an overly rich mixture for normal (warm) operation.

* see the chart in the Bentley

[universeman]

Thanks Tim. I'll try this a bit later. Bentley does say to do the CCP test on running engine and gives values at cold and warm. It's odd though because the hookup instructions say to run FP without running engine.

Even with no running engine (tried yesterday), CCP is exceptionally low and does not change. I think I need to focus in on the WUR ohm test.

Thanks again.

[tirwin]

Here's the difference on running, not running during the test.

The bimetallic strip in the WUR will heat up eventually from the ambient heat of the engine. If you run the car for long enough, you should see the control pressure rise. Won't be as fast as the electrical connection, but it will eventually happen. If it never, ever rises that would indicate something is wrong with the bimetallic strip or the pin.

If you do the test with the engine cold that should tell you if the WUR electrical connection works or not. Now if the strip (arm) doesn't work, the electrical portion will never make a difference.

[javadog]

The first thing you need to do is get a fuel pressure chart for your WUR and see if your cold control pressure is too low or not. Yes, it sounds low, but nobody does the test at that low a temperature, so you might be surprised to find it's within specs.

The heating element sounds like it's bad, so replacing the WUR seems to be in your future.

JR

[universeman]

Thanks tirwin

Javadog I am not too good at C-to-F calculations so I realized that my reading was "off the chart" once I tried to look it up.

However, considering that the chart *starts* at 1bar at the lowest temperature (10C ambient), and my pressure was .5bar at ~3C ambient, I think it's safe to say that pressure is too low. Message received however, am trying both tests later this afternoon when it warms up and will post back.

[javadog]

Extrapolate the pressure minimum and maximum lines to 2C and see where you are. Just a guess, since I don't know what WUR you are testing, but a little under 1 bar may be the minimum. Your system pressure is on the low side, as well. Might be worth bringing that up a bit.

You still have the problem with the heater element, so it may be a moot point.

JR

[universeman]

I did this again at 55F / 13C ambient just now.

With the engine off, the control pressure never raised off of .8 bar, even after 3-4 minutes of letting the FP run with the WUR connected.

I started the engine on a lark, and let it run. After a while, lo and behold, control pressure started to raise. After 5 minutes or more, it got up to around 2.1 bar. Not as high as it's supposed to be, but up there. It raised fast as soon as it started moving - 3-4 minutes of nothing, then all of a sudden, boom, needle went up in 5 seconds or less to the 2.1 bar range.

I'm thinking that has to do with engine temperature causing the bimetallic action.

Since I have 12v at the plug, and ground continuity (though I couldn't replicate ground continuity this afternoon ,but I did have it this morning), I'm thinking something is wrong with the electric portion of the WUR, but that arm is there and does work, as long as engine does the heating. Does this seem to follow logic? Is there a further way to test/troubleshoot the electric circuit of the WUR specifically? thanks for all the help thus far.

[tirwin]

That sounds to me like the control pressure may be low but I'm speculating a bit because I'm not looking at a chart and I don't know which WUR model we're talking about. Also sounds like the bimetallic strip does work at least somewhat with ambient engine heat, so that's good.

You could be right that there is a problem with the electrical element. If you do a continuity test between the two male terminals on the WUR electrical connector, do you have continuity? If you did the test correctly earlier, it sounds like the answer is going to be no.

If both of these assumptions are true, then it sounds like a WUR tune-up is needed.

[scarceller]

That arm with the heating element is only for cold start, once that element fully warms the arm the arm no longer makes contact with the control shaft. Meaning, once the arm fully deflects from the heat via the element it's as if the arm is no longer involved.

So the simple test tirwin outlined to apply power to the connector with engine off and observe pressure is a really good suggestion. If the pressure does not change (increase) with power applied you have an issue with the arm or the heater on the arm.

This may be helpful:
http://www.jtresto.com/e21/WURServicing.pdf

[boyt911sc]

Originally Posted by universeman

Team,
I published a video to ensure that I'm doing things right when I check my cold control pressure.

It's 36degF outside right now and I have 1/2 bar or so of control pressure. Seems too low. Voltage to the connector, next I need to check the resistance on the element (which I'll post in an update.)

Video here: would you guys make sure I'm doing this right?

http://www.youtube.com/watch?v=YOmTLryWQ6E

You can hear the idle start surging a little bit. I think I'm running really rich based on this. My thoughts on next step to fix are to remove and clean the WUR, and check the element. Any other ideas welcome, thanks!

Jason,

What is the Bosch ID number on your WUR? Is your car a US or RoW model? If you have a US model, you should have WUR-090 same as Tim's. Based from the video you provided, the cold control and warm fuel pressures were both out of spec. This WUR will be always problematic until it is rebuilt and calibrated. What is the resistance value (Ohms) at 55 deg. F? What problem/s are you having now? Keep us posted.

Tony

[universeman]

I've got a US model and it's an 090. Tomorrow morning I think I'll do one more test and adjust the fuel pressure into spec. But the control pressure is most definitely too low. Thanks all, really appreciate the support!

[tkmoore]

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[universeman]

Have determined that my WUR is faulty; probably a burned up heating element. Getting a loaner from boyt911sc to try while it's still cold out.


One thing I learned is that the wiring of a WUR is not reversible; the 12v power needs to go to the spade that is farthest from the WU lR fuel inlet/exit, or it will fry the heater. It's possible a PO rewires the plug and does it backward.

Will update...