Classic Audi Ľ Technical Ľ Mech/Tech Ľ Engine » Treser UR rough running

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Old 03-04-21, 08:43 PM   #1
Treser UR
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Default Treser UR rough running

Can you guys offer any reasons for jerky handling on my WR.Acceleration and deceleration is fine but in traffic or just maintaining any constant speed itís not happy and hunts all the time.Maybe a fuel/air mix problem? What other possibilities are there from you wise guys?
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Old 04-04-21, 01:49 AM   #2
Hanuman
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Is his sudden, or gradual?
This sort of thing plagued my WR for a while until I got a grip with keeping it fettled, and it wasn’t anything major as such.

First few things worth checking, before getting into the more technical stuff.
Induction system- no air leaks. One of the most common causes of poor tune being the mixture at idle adjusted to compensate for an air leak. The engine should stall if the oil cap is removed. If it doesn’t, and some don’t even stumble when the cap is removed, then there is unmetered air being overcompensated for,
The various small bore vacuum hoses around the system need to be in good shape.
The idle screw needs to have a good o-ring seal, and the throttle body needs to be clean. The induction system does build up oil residue over time, which messes with the idle bleed.
Fuel system- pump delivery, mainly.
But also worth establishing that the cold start injector isn’t feeding extra fuel.

The above being for a standard WR. On the tresser, I’ve little idea what else goes on.
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Old 04-04-21, 07:57 AM   #3
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Thanks for your views which seem very sensible.Curious to know what action cured your problem.The cold start injector was replaced recently and whilst it starts first time now,at lease when itís a cold start,maybe it throws in fuel when it warms up.Is that a sensor issue?

The jerkyness starts from start up and when itís warmed up it still does it.Slow traffic travel involves a lot of clutch work so it doesnít kangaroo so a right pain.

The Treser has Mercedes v8 fuel distributor,a higher lift cam and bigger valves and bigger inter cooler but otherwise the set up is as standard.

Could the problem be an injector seal or a stuck injector that sprays inconsistently?

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Old 04-04-21, 08:24 AM   #4
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In the UK youíll find a significant number of Urs (especially as theyíre not used as a daily/winter car now) have the cold start injector disconnected as it hampers warm starts with flooding.

That said, Iíd go with Mark and the induction system, theyíre pretty sensitive. Try the Ďstumbleí test.

Also, have a quick check of the wiring to the air flow sensor on the front of the inlet manifold.
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Old 05-04-21, 01:53 PM   #5
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Quote:
Originally Posted by Hanuman View Post
Is this sudden, or gradual?
I may have been a little unclear. Did this situation develop very quickly, 1-2 days, or something that became gradually worse over a longer period?

In any event, Iíd suggest all those things that I mentioned should be checked first. I would say that the biggest and lasting improvement that I had was ensuring that the system had no air leaks, idle screw and port were clean (it does gunk up to the point that you run out of idle adjustment completely.) and then mixture set right.
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Old 06-04-21, 06:53 PM   #6
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Thanks for that.Itís been occurring for a while but havenít been using the car much during the winter months so havenít done anything about it.

Now the sun is out it needs fixing.
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Old 07-04-21, 03:48 PM   #7
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As itís something thatís developed over time, it doesnít sound like anything has broken completely, suddenly. So Iím inclined to think itís a slow degradation, that has been compensated for over time. But now has reached the point that it needs sorting. As such, Iíd go with the basics, making sure those are right.
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Old 11-04-21, 12:50 PM   #8
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Hunting is a sign of fuel/mixture problems....If it were mine I would do a complete fuel pressure test, check the AFM flap for smooth operation, check injector flow and the main fuel plunger in the distributor....(handle it with care).
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