Manager Forum

Got a customer with a 10/95 VW Passat with tdi 1.9L diesel and 127,000 on the clock. Problem is at 40-50 mph it has a bucking especially noticeable in 4th and 5th gears only under load. Engine starts fine, otherwise runs good. Vehicle is maintained well. No codes in pcm memory. Does this with egr hooked or unhooked. Replaced injection pump with other one and same problem. Ideas anybody? Mitchel info is somewhat scant.

I should also mention that anytime we tried to increase fuel to the engine such as a power box or larger delivery valves it makes the bucking worse. I am out driving the car now (stopped to post this) and the bucking starts at 40 mph and is at its worst then and as mph increases the bucking slowly goes away. By 50 mph it is totally gone. Rather a strange one. This vehicle has been at several shops already with no success. One shop advised new injectors.

check pm. for wiring diagram information. if i were to guess on the surging i would lean towards a waste gate issue on the turbo. personally, i haven't seen any of these but it sure sounds like bucking issues i've had in the past on other vehicles where the waste gate or dump have been faulty. again i haven't seen one of these cars but check to see if there is a diaphragm assembly on the exhaust side of the turbo that looks like an exhaust pressure control.

Check for carbon restrictions in the intake.

charles4741 wrote:Check for carbon restrictions in the intake.

Will I have to remove the intake manifold to do this?

i use a snappy camera probe. well worth the investment since it has so many uses including seeing on top of gas tanks so they aren't dropped needlessly. please don't spray solvents into intake for an overnight soak. it's a dsl not gas and can have a run away acceleration issue.

Well, I followed my gut feeling on this one. Further diagnosis was pointing to an injector issue. So, I removed all 4 injectors, took them to an injector/pump facility and got them tested. We found that not only was there 2 leakers but the pop off pressures were lower than expected. So, we got injectors that need to be rebuilt or replaced. Once that is done, we'll see if there are any further issues with this toy.

thanks for the update.

Well, we installed new injectors and now we got a real bucking issue at most engine rpms above 1200. So, I guess we need to look further. Or is there something else we should be checking?

Isn't there an anti shudder valve of some sort on these? I hate to admit it, but I own a New Beetle TDI and know very little about it because it is so trouble free. (I'm about to make another thread about one that belongs to a customer) Check out TDI club forums. What little bit I know comes from there. Haven't had much luck posting there, but I have gotten alot by searching.

Gonna get it back in soon an take the injector pump off an take it apart.

does the turbo have a waste gate on it?

steven kiser wrote:does the turbo have a waste gate on it?

Sure does.

ok, is it working? i've seen waste gates malfunction causing a bucking issue.

Yea, the wastegate is working fine. And, yes they can and do at times give problems. We put a clear line between fuel filter and injection pump and there is air bubbles going through which we suppose could be an issue. We need to check it out more.

it would have to be a lot of air. but then again after you replaced the injectors and bettered the fuel flow the issue became more prominent. i'm wondering..............................................

An electric Air Dog lift pump was installed and this vehicle runs like never before. The bucking issue is gone and has more power than can be imagined.