Diesel stumbling above 70 mph while climbing

Discussion in 'VW Mk3 Jetta, Passat TDI and other/older diesels' started by eghaley, Aug 6, 2007.

  1. eghaley

    eghaley New Member

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    Aug 6, 2007
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    I have a 96 Passat TDi with 140k miles on it. It runs flawlessly at speeds up to 85 mph. If speed is 65 to 70 and the road begins a gentle climb, the engine rpm slows down 5 - 10 mph even tough I try to give it a little more fuel. What could cause this?

    I've been consistently getting 46 - 47 mpg up till now. Any ideas???
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  2. diesel guy

    diesel guy Guest

    There are lots of things it might be.

    It could be worn vacuum lines, faulty solenoids, clogged fuel filter, limp mode.

    These won't affect mileage but sometimes it saps power. Does the engine feel like it slowly loses power or does it feel like it suddenly loses power?
  3. tokendog

    tokendog New Member

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    This happend to me not to long ago.

    Take a look through the FAQ linked at the top. There is a tiny hose that splits in teh ecu. In my case, it had a pinhole in it and was putting me into limp mode. I had never heard of a hose in a ecu, but there it was. Replaced it and no prob
    http://www.myturbodiesel.com/1000q_how_to/a3 b4/ecuhosechip.htm

    also, take your car to autozone, they can do free code scans for you and it will help figure out what the problem is
  4. chittychittybangbang

    chittychittybangbang Administrator

    Joined:
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    21,783
    Car:
    2006 Jetta TDI
    Location:
    CT
    This could also be related to a bad n75 valve. See this picture? It's right above the coolant tank w/red hose coming out the top and black hoses on the sides. It controls the turbo boost. If it gets stuck or loses air pressure, it will not work right.

    From your description, it sounds like you might be in limp mode all the time. Your car should be able to go faster than 85 mph without a problem. I don't know the top speed, but an unmodified car should be able to get to at least 100mph I'm guessing. Not sure exactly,but definitely faster than 85 mph.

    It's the lack of power that causes you to slow down while going up a small hill. Your car should have about 90 hp stock, if you are in limp mode, you only have about 50 hp.

    Because of the mileage of the car, I would also suggest replacing all the vacuum hoses that look even slightly worn. These are the colored or black 3-4mm hoses with braided covers. If they crack and leak due to age the car will run, but you will lose power.

    Lastly, you need to figure out what the codes are, if any, on your car. Take it to autozone and they will scan it for free. Post it here and it will tell you what the possible problem is.

    Attached Files:

  5. eghaley

    eghaley New Member

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    TDi stumbling

    I'm heading to AutoZone and ses if they can analyze a problem.

    I'm sure I can exceed 85 mph but that's where the stumbling occurs. It occurs sooner if I going uphill. The greater the slope the sooner the stumbling. And it occurs suddenly without a gradual reduction. It's like a governor is attached.

    I took the microclimate filter off and cleaned it but I wasn't sure what the ecu unit is so I can look at the hose. Is it the silver metal box (6"x4"x1") to the right of the filter? I wanted to take it to AutoZone before I look at anything like that.

    I'm pretty good mechanically but have never worked on my TDi. I sure want to because of the VW labor charges. At any rate, I thank you for the helpful responses. If I find out anything, I'll post it here.
  6. eghaley

    eghaley New Member

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    AutoZone unsucessful ....

    in establishing a connection with the diagnostic circuit. In a dozen attempts to access the circuitry, the screen always came up with an error message that indicated no connection.

    Next, I'll try to replace the hose in the ecu, carefully to see if there's a difference. I'll get back to you in a few days.
  7. chittychittybangbang

    chittychittybangbang Administrator

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    Car:
    2006 Jetta TDI
    Location:
    CT
    That makes me strongly think that...you have a control problem with the turbo system.

    Somewhere, a vacuum hose or solenoid is not working right. When you go uphill, the turbo has to make more pressure. There is a vacuum line that goes all the way to inside the ecu, lines all over the place. The how to had a pic of the diagrams. There are also vacuum lines going to the wastegate solenoid, the N75 valve. The leak is probably in one of these.

    Going up a hill makes more boost, and a bigger leak suddendly puts you into limp mode. Does the pickup at low speeds return if you shut the ignition off and back on? If so, that is 100% the problem. You are also supposed to drain the fuel filter every 10,000 miles, and replace every 20,000 miles. This could also cause high speed shuddering. This symptom could also be caused by a clogged intake but this doesn't sound like the problem.
  8. eghaley

    eghaley New Member

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    Pickup returns ....

    as soon as the incline levels off. Then it seems normal.

    I had the fuel filter changed recently.

    Under normal driving conditions, the car feels peppy and smooth. I filled the fuel tank today and I'm down 4 mpg at 42+.

    All in all this is a minor problem but it's nervewracking in the sense that I'm not sure where the problem is. Could it be the MAP?
  9. diesel guy

    diesel guy Guest

    Figure out what it isn't.

    It's not the fuel filter. It's probably not a clogged intake. To make sure, open the intake hose before the EGR and take a peek inside. It should only have a little build up and soot. If it's not, then it'll be VERY dirty after the EGR. It could be the air flow sensor, but it rarely fails on these cars, it's the mk4 cars which have deective sensors. It isn't a timing or timing belt related issue. It will have nothing to do with the alternator (spark because there's no spark) or glow plugs.

    The most important thing you can do is get the codes instead of guessing. At this point, I am thinking vacuum hose leak. If you get 00575 Intake manifold pressure control difference, this is the hose that goes from the intake hose to the ecu or the hose inside the ecu.

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