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Thread: Engine misses, surges or bucking (FI related only)

  1. #1
    Join Date
    Jun 2000
    Sault Ste. Marie, MI, USA

    Default Engine misses, surges or bucking (FI related only)

    I have 78 westy with a new engine and at about half throttle and in the midrange of rpm's I get an intermitant skip. I've check the airflow meter, timing, and all my vaccum lines, am I missing something obvious. (It did sit for a while so I just got a good fuel system cleaner and hope that will do the fix.) If I stay hard on the gas it does not do it. It isn't stalling or really losing power just kind of hiccups at that perfect rpm/throttle position. Thanks for the help...

    [ 07-23-2001: Message edited by: Capt. Mike ]
    Sean Woodworth
    White Lightnin(78 westy)
    Jerry(86 Jetta t-diesel)

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  3. #2
    Join Date
    May 2000
    Raleigh, NC USA


    There is a good Type II troubleshooting chart for fuel injection posted on my pic site linked from the home page. Look in the technical diagrams folder. That will check out the FI with nothing more than a volt-ohmeter.

    You symptom sound like the air-flow meter may have a burned spot in it's control "switch" section as it works on the principle of constantly changing voltage. Something like a rheostat that has a burned section. But isolate everything else out first; they're expensive compared to other sensors & components.

  4. #3
    Join Date
    May 2000
    Raleigh, NC USA


    Car bucks & stalls. Turning off and restarting solves the problem.

    Has anyone else experienced this? I don't want the mechanic to replace the fuel injection system part by part, hoping he'll eventually stumble on the cause. No one in this area has any real expertise in vanagons. There aren't many!

    By the way, we did get a tune-up last week too.

    Capt. Mike Moderator Member # 11 posted 05-20-2001 10:18 PM

    Have you done the full FI system check-out with a volt-ohmmeter per the Bentley? Replacing parts until one works is not the way to test! I can sympathize if you can't find a good mechanic, but the troubleshooting is far more complex sounding than in practice.

    A shot in the dark would suggest you see the post on Vanagon Syndrome. Although the usual symptom of Vanagon Syndrom is working only at start or full throttle, the CAUSE is incorrect voltage through the air-flow meter. If the voltage does not change with deceleration, the air-flow would stay on.

    An '88 should have the fix harness; and you'll note in that post that a fix harness is not forever. We have found the harness cures some mighty weird FI problems that aren't anything like the tech bulletin description.

    Serious wet weather grief with my van

    miket Member # 430 posted 06-05-2001 07:20 PM

    I’m having some serious wet weather grief with my van. It is a 1988 VW Vanagon Syncro, manual transmission, 195,000 Kms.
    During rainy weather (some accumulation of water on road), the van will gradually lose power (in 10-15 sec.) until it either idles roughly (below 500 RPM) or stalls. Will re-start easily, accelerate, then repeat the power loss. This cycle continue until road is less wet, then runs normally. This problem used to be more intermittent, but now consistently happens on rainy days.

    One other thing: When the van starts to lose power, an initial regain of power can be had by flooring the accelerator or switching the ignition off and on again.

    In dry weather, no problems. Van idles steadily at 800 RPM, steady engine power thru RPM range.

    Recent new parts:

    1. Distributor assembly with Hall sender unit
    2. distributor cap (with shield) and rotor
    3. ignition wires
    4. ignition coil
    5. fuel filter
    6. air filter
    7. spark plugs
    8. ground strap from engine block to chassis
    9. muffler and oxygen sensor connection pipe


    Cleaned and packed with lithium grease all accessible connectors inside engine compartment, including:

    1. Fuel injector connectors
    2. Fuel pump connectors
    3. Air flow meter and auxiliary inline wiring harness connectors
    4. Ignition coil primary connectors
    5. Idle stabilizer connectors
    6. Sensor connectors
    7. Ground wire connectors on left side of engine compartment


    Cleaned airflow meter (AFM) internal copper spring contacts. Added some spring load to contact

    Checked function of AFM according to Bentley manual - ok

    Cleaned and checked throttle valve switch according to Bentley manual - ok

    Even wrapped and taped a plastic bag around the distributor. I'm getting desperate!!

    I have done most of what I believe can do to fix this, but I don't want to replace the entire FI system! Any suggestions as to next steps?

    Capt. Mike Moderator Member # 11 posted 06-06-2001 10:03 AM

    Your condition brings to mind two items. First is Vanagon Syndrome. See the post on that subject elsewhere, as at your mileage and age, a failure of the harness module is a possibility. Since it functions as a signal stabilizer & rerouter, it could be beginning to become moisture sensative. That's easiest to check, just borrow a good harness upgrade from another Vanagon for a test run under the condition you describe.
    2nd is the throttle valve switch. They seem to be susceptible to water and moisture. Last I checked, P/N 025 906 011A. They are in an area that also seems to trap moisture. That one happened to me; a new switch cured the problem.

    A way-out possibility, your fuel breather system through the charcoal cannister. If the cannister is old and the media breaking down, it might not allow full breathing in soggy conditions. Cannsiters are basically a service item and fuel overfills can eventually cause them to break down & clog. Thus your tank is getting airbound.

    I realize both of these can give temporary test OK's but the moisture relationship may only come into play under the wet driving conditions. Please let us know the results so I can then move this post to its correct topic.
    miket Member # 430 posted 06-28-2001 04:28 PM

    I confirmed yesterday that the oxygen sensor was causing my wet weather problems. Here's the sequence of what I did:

    1) Installed a lawn sprinkler underneath the van, to simulate water splashing around during driving in the rain. Ran all tests with sprinkler on.

    2) Ran the engine at 2800 RPM, with oxy sensor disconnected for several minutes. No problem.

    3) Ran the engine at 2800 RPM, with oxy sensor re-connected for several minutes. Engine stalled out

    4) Ran the engine at 2800 RPM, with oxy sensor disconnected for several minutes. No problem.

    So, based on these results, I figure the oxy sensor was getting wet, or water was getting drawn into the exhaust and screwing up the signal to the FI computer, causing my engine to stall. Until I get a new exhaust system, I'm leaving the oxy sensor disconnected.

    Buck or bolt at 2800 rpm

    dwolterd Junior Member # 47 posted 08-26-2000 08:37 PM

    I want to thank everyone for helping me solve significant problems (dialogue is now archived).

    One problem remains with my 1985 Westfalia camper. When 2800 rpm is sustained for any length of time, the engine bolts. We got around this by trying to quickly pass through this speed on a recent trip through Ontario. But I know the times when we were unable to avoid this rpm, and the engine has bolted, have not done the engine's longevity any good. When viewed from behind (from another vehicle) it looks like the muffler and tail pipe are shaking loose for a moment. What really is happening is that the whole engine is bolting for a moment. Any ideas will be appreciated. Third engine was installed earlier this year. Ecu and throttle pos sensor/switch were recently replaced.

    Doug Wolterding, Woodbridge, Virginia

    jpquick Member # 121 posted 07-03-2001 10:13 AM

    MY 85 WESTY bucks at approximately, 1800 to 2100 RPM. It drives me crazy. I Just down shift and tach up to avoid the bucking bronco. This usually happens when in a parking lot, otherwise ,I just tack it up, CASTROL style.

    I have tried fuel injection cleaner, to no help.

    I once had an 83.5 water cooled 1.9 liter that bucked all the time after a fillup at a not so great gas station (Pilot). I received plenty of water which, I combated with heet, cured the problem 5 bottles later through two fill-ups.

    I think the airflow meter section contains
    info. related to this problem.

    Hey, If I learn about a fix, I'll post.
    Let's hope we get some attenion of the
    others out there.


    Capt. Mike Moderator Member # 11 posted 07-04-2001 05:50 AM

    That your throttle valve/deceleration/idle switch assembly was replaced does NOT mean it was properly adjusted. The full throttle enrichment switch (Bentley 24.34) requires adjusting and could give your symptom.
    The pressure regulator could also give similar symptoms if you are not getting the normal increased pressure above idle vacuum. It could be enough to get you to 2800 RPM, but not enough for more until you pass through with the full throttle enrichment phase.

    This presumes you have already checked for proper CO levels and temperature sensor I specifications.

  5. #4
    Join Date
    May 2000
    Raleigh, NC USA


    Transferred from another post to consolidate similar topics.

    Water related Vanagon Syndrome

    Earthlinkmike Junior Member # 1209 posted 09-09-2001 10:27 PM

    I just got another new 1991 Westy and its going to be the final one (4th so far). After reading the info on the ignition board regarding rain and the syndrome, I felt right at home. I've had this van about 3 months and every time I wash it for the next 30-40 minutes or several miles it looses power until I reset the ignition switch. I have heard a bit about a harness and not sure if mine has it opr not. I'm not nearly as knowledgeable as most and probably not able to troubleshoot beyond the basic level. Any clue where to start for a novice?

  6. #5
    Join Date
    May 2000
    Raleigh, NC USA


    As to whether you have the Vanagon Syndrome fix is well covered in the Vanagon Syndrome topic. All you have to do is look for the harness as described there. That doesn't mean the harness hasn't failed; that possibility is also covered there, along with references to a picture of the harness module.

    First, your symptom is not typical Vanagon Syndrome -- and Vanagon Syndrome isn't usually water related. Reread that thread.

    Two questions. If you immediately shut down and restart, does the symptom go away? If not, it's not "reset" related.

    And second, what are you doing when you wash the car that would get water into a FI system component? Does the problem happen in just ordinary rain? Although the water-cooled Vanagons can easily get wet, there is very little of the FI system that gets wet following a normal wash job. (I am presuming you are NOT sending it through one of those infernal automatic washes whose sole purpose is to ruin paint, & every external accessory in the shortest possible time!) About the only places that get routinely wet in a normal wash would be the O² sensor and the wiring harness that runs from front to back.

    The possibility of an O² sensor getting wet is already covered in this post along with miket's excellent and methodical efforts to track it down. That's a good place to start.

    Elsewhere on the site is a post about how Vanagons are subject to harness damage from extended driving on gravel or dirt roads. Forget where it's posted at the moment, but the net result is there are a couple of places where the harness runs side-to-side on the 'front' side of frame members and spray and gravel from the wheels will eventually abrade the harnesses. Get underneath and thoroughly inspect your wiring as it runs from to rear and up into the engine compartment. The one I had to protect was at the left rear just in front of the LR wheel about the area of the fuel pump. The harness went up to feed the rear seat heater fan and the FI system brain.

    I'd suspect if your problem occurs for just the first 30-40 minutes, it's a matter of it drying out. But that also raises another possibility -- water in the intake systems.

    Vangans get their engine intake air from the RR quarter panel grill. Are you running a lot of water into that area? And have you checked your air filter system after a wash? If you are getting your filter wet, it will severly restrict flow (with resultant loss of power) until it dries out.

  7. #6
    Join Date
    Apr 2001
    Bethlehem, PA USA


    fuel. We manually made the connection for the relay and she started right up and ran fine all the way home (300 miles).

    I bought a new relay once we got home and the car wouldn't start. We checked as many connections and grounds as we could and they seemed fine. So off to the VW mechanic we went. He said it was the computer. There were some burnt areas on the board itself. He had a used one that he charged me $200 for, he put it in, she started right up, and he called me to say that she was fine and we could pick it up tomorrow. The next morning he calls, he took it for a test drive and she was not fine. She would stall at lights, when she ran the RPMs would go from 3000 to 0, 3000 to zero. It would get worse as she warmed up. He checked all of the grounds, they were fine, he checked sensors, found the idle stabilizer control unit was fried. One of the little parts had actually melted a bit. That little bugger was 249 dollars! So that goes in. No improvement whatso ever. He had a working Vanagon in the shop so he swiched the temperature sensor and the airflow meter. No improvement. After 3 grueling weeks in the shop (he wasn't just working on my car) my husband and I drove her home. She barely made the 1/2 hour ride.

    We did check the AFM by prying off the lid and cleaning it and checking the arm. We bought the syndome fix harness for $150 dollars. She doesn't stall at lights anymore but those RPM are still dropping and rising while we drive. When we put her in park the RPMs will often rise to 2000, we tap the gas and she returns to normal. Now pre-problem she would hesitate a bit when she was cold (like at the first light I'd stop at but that was it). She did do the RPM dropping once, a week before our trip, I was pulling away from a stop light and she almost stalled.

    Sorry to ramble on a bit, I'm just hoping some tid bit of info may help. Do you think it could have anything to do with the used computer?

  8. #7
    Join Date
    May 2000
    Raleigh, NC USA


    What year?

    The mechanic is checking first hand what we can only guess at second hand. When there is surging or fluctuation with idle, it's often related to the O² sensor system. Remember that's its function -- to adjust FI back & forth as exhaust characteristics change. See the O² sensor topic for further info.

    Your indication that a blip of the throttle will let it idle back down is more closely related to idle stabilizer, or the throttle valve/idle switch system which will depend on which model you have.

    I know it's frustrating, but every part of the FI system can be checked by other than the 'parts changer' method. Since you have a new air flow meter & CPU, chances are now that its down to a sensor or adjustment.

  9. #8
    Join Date
    Aug 2001
    Portland, Oregon


    My 87 Westy is hesitating until RPMs reach 3000+. It ran great and wasn't doing this until after we did a tune up (new plugs, distributor cap & rotor, fuel filter) and added the "vanagon syndrome" harness fix. The timing has been adjusted and we reconnected a hose which was disconnected from the front opening of the pressure regulator. It seems that when the pressure regulator hose is disconnected, it idles more smoothly at 1000 RPM (instead of about 900) and the hesitation is reduced or negligible. Does this mean the pressure regulator is in need of replacement? Also, with the hose connected, the OXS and battery light on the dashboard stays on when the engine is started until I rev it up a bit. When the hose is disconnected...lights don't stay on. What's going on?? Any input would be helpful. Also, for a little background, prior to the tune-up we had experienced the Vanagon syndrome twice randomly on long trips in the form of surging while in 4th gear while driving along the highway. Each time, stopped van, restarted and no problem thereafter. Other than those instances, we had no hesitation problems. Actually, the installation of the "fix" is what prompted the whole tune-up idea, "while we were at it." Thanks for all the info provided on this forum...it has been invaluable.

  10. #9
    Join Date
    May 2000
    Raleigh, NC USA


    You need to isolate several concurrent problems. Easiest first; the O² sensor. Testing is in the Bentely 24.54 but the light in the dash is controlled by a speedometer activated elaspsed mileage trip. You'll see more info on that in the O² sensor topic.

    The battery light is a function of the voltage so a low idle will cause it to flicker; revving up will increase voltage to stop the light. That normally doesn't activate the O² light, but I'll never say never.

    The pressure regulator adjustes fuel pressure in relation to the intake manifold pressure. This is engine speed related and could cause your symptoms. Testing is per 24.55. Note that the specs show a lower pressure connected and higher disconnected. Regulators typically throttle DOWN the pressure, indicating yours is throttling it down too much, thus the bad idle when connected. Also, as engine speed increases, you get into the higher pressure requirement range so the engine smooths out -- it's now getting the appropriate pressure.

    Other parts of the FI system that can cause similar symptoms are the throttle valve switch & adjustment, and the idle stabilizer. Note 24.59 specifically says if the throttle is imporperly adjusted, the engine will surge under light throttle.

    Often fixing one part of an interrelated system like the FI will show up other defects. The Vanagon Syndrome fix has taken away one problem and allowed the others to become apparent.

  11. #10
    Join Date
    Jul 2001
    hamilton, ontario


    I'm having a terrible time with a too rich idle. It blows black smoke terribly.

    It is a 90 Westy and this is what I have done so far, all with no improvement:
    (1) Changed Temp II Sensor.
    (1A) Plus checked wiring to ECU and resistence per Bentley graph.
    (2) Changed the AFM.
    (2A) Plus checked Temp I sensor per Bentley.
    (2B) Plus changed the Aux AFM wire (Vanagon Syndrome).
    (3) Changed the ECU.
    (4) Disconected the Q2 sensor.
    (5) Changed the Idle Stabilizer Control.
    (6) Disconnected and reconnected the Idle Stabilizer Valve.
    (7) Changed the ignition wiring.
    (8) Resoldered every ground wire I could find and replaced the ground eyelets. Even changed the battery ground and engine ground.
    (9) Checked timing.
    (10) Checked air filter and air intake.

    All of the above did not work.

    The engine starts fine when cold. As it warms up the revs drop as expected and then it starts to stumble as it blows black smoke. Too rich.

    If I disconnect the Temp II sensor, the revs go up as expected and the problem is gone.

    The Temp II sensor provides the correct resistence throughout the temp range. This was done at the ECU.

    With the Temp II reconnected, it spews black smoke again. If I shut down the engine for about 60 seconds, and then start up, the engine runs fine - no smoke for about 60 seconds, then the black stuff starts.

    The O2 sensor connected or disconnected makes no difference.

    Okay, so now I'm thinking about the Pressure Regulator. My local parts place will sell me a fuel pressure tester for $110 but I am reluctant to throw more money at this problem. So here's my question: How prevalant is a Pressure Regulator malfunction? Does a malfunction of this regulator make any sense regarding my problem?

    I'm tired! Someone tell me what to do.

    Laurence Smith

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