Could my tranny be going.....

[nacradriver]

Driving around today I had notice a bucking with my van that only happens in third and fourth gear above 3K RPM.

I had just filled up with gas and figured maybe a I gotten some bad gas as this is the season for all the crap they put in it... but first and second work fine when putting on the power, and when in neutral reeving the engine above 3K there are no sputters...

Anyone ever experience something like this?
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Güdrun -1989 Westfalia - 2013 - 2018
Petra - 1985 Vanagon - 1985 to 1991
Zisa - 1974 VW Van "Bus" - 1974 to 1985

[borninabus]

doesn't sound like a trans problem to me.
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88 Van WBX, A/T - 13 JSW TDI 6M/T - 2012 Touareg TDI Sport

[Syncro Jael]

When was the last time you changed gear oil and checked the magnet?

It could give you a "VISUAL" of the condition of your gearbox.
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1987 Syncro Westfalia Hightop - NAHT
Subaru EJ25 Forged Frankenmotor, Triple Knob.
Jael = (Mountain Goat)

[nacradriver]

[levi]

Yeah not the trans.
Could be fuel delivery.
Could be a bad spot on the wiper in the afm.
1st and 2nd you just drive right through it.
4th you hold rpm longer on the bad spot and it "bucks".... just one of the possibilities
_________________
One of these days I'm gonna settle down,
but till I do I won't be hangin round.
Going down that long lonesome highway,
gonna see life my way

https://youtu.be/cSrL0BXsO40

[Howesight]

Is the van in question the 1985 (1.9 digijet) or the 1989 (2.1 digifant)?

1. You might be experiencing "vanagon syndrome". In that scenario, what happens is that an oscillation in the signal from the AFM causes the ECU to react with bucking. If you shut off the engine and re-start, the symptoms disappear. If this is happening, then you have "Vanagon syndrome". The cure is to install a tantalum capacitor in the AFM circuitry. To me, the symptoms you described did not seem consistent with this.

2. When the "bucking" occurred, was it as though the engine lost all power for a moment, or as though it just lost some power. If it seemed to have lost all power momentarily, then you might have a problem with the ECU where a crack in the printed circuit board in the ECU causes the ECU to momentarily shut down completely. The hallmark of this problem is that in addition to the "bucking", the tach needle bounces violently. There is also another potential problem with the same symptoms (bucking and bouncing tach needle) that occurs when the wiring to the Hall Sender unit on the distributor is compromised.

3. Finally, bucking can be caused by compromised electrical grounds in the engine compartment. Ground terminals need to be thoroughly cleaned and then electrically tested with a VOM. The reason for checking is that sometimes the fault is in the wire itself, just upstream of the terminal. What happens is that salt, water, etc, cause corrosion in the strands of wire upstream of the terminal and cause enough resistance to affect the signals of the various sensors that are resistance-based. When you find such a wire, you will need to cut it back, add wire as needed and solder the repaired wire and shrink wrap it. Occasionally, you can fix this by stripping the insulation from the affected part of the wire and dipping the wire in mild acid, twisting and untwisting the wire to allow the acid to remove copper oxides. Then clean off the acid and apply shrink wrap.
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'86 Syncro Westy SVX

[nacradriver]

[IdahoDoug]

Doesn't sound like a transmission. In a manual transmission the sudden vehicle movement that creates bucking would require quick loss/gain of gear engagement that would have other symptoms. Like horrible metallic crunching and gears stripping teeth. No other way a manual transmission could have on/off thrust like that. I agree it will be fuel/air/spark.
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1993 Toyota LandCruiser, 2002 BMW 325iX, 1982 Toyota Sunrader

[nacradriver]

[nacradriver]

This morning I replaced the AFM with the one I originally had along with the patch cord that came from VW... so we can rule out Vanagon Syndrome.

Same problem... It only happens in third gear and when above 3K.... I ran it in 2nd and kept it pegged a 3500 RPM... no issue.

Will be checking all grounds later today as well replace the relay... $10 @ NAPA, and testing as per Bentley 20.29

Will report back and what happens...
_________________
Güdrun -1989 Westfalia - 2013 - 2018
Petra - 1985 Vanagon - 1985 to 1991
Zisa - 1974 VW Van "Bus" - 1974 to 1985

[Wildthings]

Sounds like fuel delivery or possibly a vacuum leaks between the throttle body and the AFM. You are demanding more torque out of your engine for longer when in the higher gears so a lean mixture may be more evident than in lower gears.

[nacradriver]

[Tom Powell]

Somewhat similar problem with my '69 camper and a clogged fuel filter.

Would run fine on the fuel in the carburetor bowl and accelerate up to 48mph and then lose power. Could maintain a constant power at 42mph and fill up the bowl. Accelerate to 52mph, lose power and speed and regain it as I slowed and the bowl filled up again. New filter and cruise at 58mph all day and night.

My carburetor scenario is maybe a slow motion of FI clogged filter symptoms.

Aloha
tp

[nacradriver]

[Tom Powell]