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 Misunderstanding WUR warm pressure calibr?
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raueda1

USA
37 Posts

Posted - 08/06/2017 :  16:00:40  Show Profile  Reply with Quote
After reading everything I could find on WUR calibration, troubleshooting etc it eventually dawned on me that I may have totally misunderstood the calibration method.

My original understanding was that both hot AND cold pressure are set by finding the sweet spot of the post with the bimetallic arm. Pretty much all the procedures out there talk about tapping the post in/out.

It finally occurred to me that warm pressure is set by driving the entire valve body (the steel cylinder about 3 cm diameter) in/out. Then, when that's set properly, the cold pressure is set by adjusting the post.

Is this correct? If so it's surprising that there's so much emphasis on tapping the post, modding the post for easier adjustment, etc. yet almost no corresponding references (that I can find) to tapping the valve body in/out to set warm pressure. Any insights would be of great interest. Thanks much,

Dave

1977 450SEL 6.9, No.923

Ron B

Australia
11545 Posts

Posted - 08/31/2017 :  22:38:41  Show Profile  Visit Ron B's Homepage  Reply with Quote
I dont understand why people mess with the WUR .The pressures are fixed at set limit by the bimettalic strip and no amount of belting them is going to alter them. The best way to really check them is to fit a pressure gauge, remove the fuel pump relay shut off lead, the blue one on the air meter, turn on the ignition and note the pressure variations as it the bimettalic strip warms and alters the fuel flow >if it doesn't perform to specs , check the bimettalic strip by freezing the WUR in the fridge, then check the shape of the stip . it should be bent in one direction. Apply 12 volts to the two point plug (with a ground so you have a circuit ) the strip should bend in the opposite direction. If it doesn't, the pin is jammed or the strip has broken off. Finally, make sure you have the correct part . Quite a few 6.9 owners have discovered things like Porsche 928 or other strange WUR's have been substituted.
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S class

South Africa
943 Posts

Posted - 09/05/2017 :  05:58:15  Show Profile  Reply with Quote
Dave you are correct about how to adjust warm control pressure. But as Ron says, it shouldn't be necessary unless someone has previously messed around with it.



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raueda1

USA
37 Posts

Posted - 09/14/2017 :  13:33:02  Show Profile  Reply with Quote
quote:
Originally posted by S class

Dave you are correct about how to adjust warm control pressure. But as Ron says, it shouldn't be necessary unless someone has previously messed around with it.




Thanks for the clarification. It seems incredible that with all the stuff out there about WUR settings that this point isn't clearer. Cheers,

Dave

1977 450SEL 6.9, No.923
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