Classic Audi Technical Mech/Tech Engine » MB hesitation when warm

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Old 05-02-18, 10:17 AM   #1
AdrianH
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Default MB hesitation when warm

After about eight years of progressive work (over when I got the car) my MB is now running - in general - very sweetly. There's just one last nagging glitch. When the engine is cold throttle response is smooth throughout the rev range and under all load conditions. However, once it's warm there is what I can only describe as a sharp hesitation when I come back on the throttle at about 1500rpm under load. This doesn't happen while the engine is warming up. Normally I can drive around this but in town it's a bit of a PITA and it doesn't feel good for the car *it would be nice to get it sorted. BTW the car has a new ISV and the picture is all set up correctly according to Phil Payne's instructions. Th only slight question mark in that is that I'm not sure when the gas analyser I used was last calibrated.

Anyone any ideas?
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Old 05-02-18, 10:45 AM   #2
vagdream
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Presume you have checked that the WUR or control pressure regulator is working correctly and allowing the required increase in fuel control pressure when warmed up?
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Old 05-02-18, 10:53 AM   #3
AdrianH
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That was my initial suspicion *unfortunately I don't have the gear/knowhow to correctly diagnose, or how to adjust.
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Old 06-02-18, 09:10 AM   #4
AdrianH
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OK looks like I'm going to be taking some readings. Couple of questions what size connectors am I looking for on the fuel pressure gauge I'll be buying, and can anyone point me in the direction of the various pressures I should be looking for (i.e. system pressure, control pressure cold, control pressure hot etc).

Thanks again!
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Old 06-02-18, 07:57 PM   #5
vagdream
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This might provide a few clues;
http://audifans.com/mirror/www.isham.../pressure.html
extracted from the last few pages of Phil Payne's quattro bible.
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