3rd Update: Odd "Vanagon Syndrom" FIXED

[DrDarby]

A little background 1st. I bought this '87 Vanagon 7 passenger about 2 weeks ago from the 2nd owner. He had been having drivability issues with it and he had replaced the plugs, wires cap & rotor with Bosch items. The grounds look like someone recently cleaned then, replaced the eyelets and used new bolts to re-secure.
I haven't driven it more than about 50 miles back & forth to the shop and have begun fixing, replacing items as I see the need.
I've cleaned the battery terminals while checking the battery, repaired the broken exhaust collector, replaced the collector to car pipe including temporarily deleting the cat converter and added a new muffler. I replaced the oxygen sensor as the old one looks like the wires melted on the exhaust and were taped up. Timing is set to 6' at idle and 44' at 3000 rpm, no ping.
I also added a used "Vanagon Syndrome" pigtail / connector just because when the P/O said drivability issue that's the first think I thought of. Lastly I changed the fuel filter which was marked Feb 2012 and did get some crap out of it when emptying the input side. (New tank here ready to go in). It has a replacement fuel pump that I feel has a little too much whine when running but the noise never changes.

OK, enough background....

Last night I left the shop and it felt a little sluggish on acceleration. About 5 miles into my trip I realized that if I gave it heavy throttle it would really go to hell, sputtering, loosing power and even backfiring out the tailpipe. If I'd upshift and begin acceleration at a lower RPM it wasn't as bad.
So while it was still driving down the road I put in the clutch, shut it off for 5 seconds then turned it back on and let out the clutch....problem solved ran great.

This isn't typical vanagon syndrome as it happened within a block of my leaving.

I had to leave it at home today as my Wife's beetle needs some TLC today but tomorrow was going to check the air flow meter swipe and re-do the grounds.

I'm open to ideas and prev experience. Thanks
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Midwest Autosavers, Inc. Woodstock, IL

[cookrw]

[comet42]

Comprehensive thread on the many causes of bucking, hesitation, etc:

http://www.vanagain.com/bucking1.htm

It sounds like you have a good start already with newly cleaned grounds, fuel filter, dist cap, cat converter, etc.. may as well go through the rest of the list and have a perfectly running Vanagon.

Also, just a thought, since your problem has the appearance of being related to hard acceleration - have you checked the throttle for excess play, or the adjustment of the throttle position switch?

Good hunting to you!
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86 Doka (Suby 2.2)
02 Eurovan Weekender (sold)
73 Squareback (sold)
79 Bus - Champagne Edition (sold)

[jberger]

Throttle Switch... Check it out.

[cookrw]

[boof1306]

Check AFM and Coolant temp sensor.

[DrDarby]

I had a lift open and a spare set of hands this afternoon and thought I'd get the fuel tank replacement out of the way. I drove the van earlier to power loss and some bucking. Fuel gauge read 1/2 full and after I pulled the main fuel line exactly 1/2 gallon came out. But the tank still felt like it had quite a bit of gas and thunked solidly. I pulled the return and gas would have run out of it forever so I just removed the tank. It was a little less than 1/2 full and nothing more would come out of it! Guess Im lucky it was running at all!

Anyway thats all I have to report on, new tank, lines and hoses in place but thats as far as I got. Monday I'll fill it with gas, change the gear oil and try to get my wife out for a ride.

I also noticed that although all the grounds look recently repaired, Im pretty sure there should be a ground strap from the left head to the body under the coil that I dont have.
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Midwest Autosavers, Inc. Woodstock, IL

[DrDarby]

Ok here's what I've accomplished so far. Replaced fuel tank, had 2" rust at the bottom, actually had to drill a hole to drain it as nothing more would come out the fuel pickup. Removed all engine grounds, cleaned, added new connectors, new bolts and installed new 4ga ground wire from block to body under coil (braided ground was missing). Throttle switch was not working at idle, removed throttle body, cleaned it, repaired switch (arm bent) and adjusted. Found positive wire loose at starter (cured the funky cranking).

Drove it around the block and noticed a huge improvement in acceleration then about 5 minutes of driving time problem came right back. No acceleration, actually wont accelerate at all, severe bucking and backfire out the exhaust when bucking. At this time I moved the circuit board in the air flow meter so the wiper runs on a new path, problem still there.

Fuel filter I replaced BEFORE replacing the tank so I'm going to replace the fuel filter again since the tank was so bad and am also going to replace the fuel pump as well as it whines pretty loudly.

Ordered a Temp Sensor II also for good measure especially since it looks original.
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Midwest Autosavers, Inc. Woodstock, IL

[D-roc]

try disconnecting the o2 sensor. it will run rich but will not have the syndrome. it takes about 5 min of driving with a warm engine for the o2 reading to lean out the ecu to cause the bucking. shutting off engine usually resets it and is good for a few minutes.

[insyncro]

A digitool would diagnose the issue in short order.

[DrDarby]

[DrDarby]

[denwood]

Is it always running great when cold now, then issues warm? Very often problems are stacked, particularly neglected vehicles. You really should step through the digifant pro training manual PDF, particularly as this vehicle was purchased with issues. Example, some adjusts AFM to "fix" what is actually a grounded o2 sensor wire. You replace o2 sensor, it still runs like crap...AFM issue.

If it runs great when cold, consistently, then some shortcuts can be attempted. I've chimed in a few issues like this where after weeks of frustration the owner finally does a leak down test and finds out a stuck lifter was the issue. Just saying...assume nothing.
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Cheers,
Dennis Wood
The Grape

[DrDarby]

I replaced the fuel pump and the week old fuel filter. Van now runs very well cold and warm.
Here's my take on the problem, same as cookrw noted first post. There was so much crap in the fuel pump inlet from the old fuel tank that after the van ran for a few minutes it would partially starve for fuel. The fuel pump made noise but not extreme matter of fact the new one is louder still.

I've put 100 miles on it this evening and it runs like a Vanagon should.

I'd like to adjust the mixture a little at the air flow meter but and fighting removing the still there factory plug over the allen screw.
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Midwest Autosavers, Inc. Woodstock, IL

[vanonimous]

My Vanagon syndrome turned out to be high resistance (9K Ohms)in Bosch wire from the coil to the cap. After a while when hot the resistance would build up and engine would cut out.
I hate the idea of two 1K Ohm resistors in that Bosch wire so I always make custom wire and solder beemer wire connectors and no resistors. I leave the 5k Ohm resistors in caps for radio interference. My vans love it and they idle perfect cold or hot.
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If happiness is being a mechanic, owning a Vanagon is nirvana.

Lighting upgrades: https://www.thesamba.com/vw/forum/viewtopic.php?t=578291

[August978]

I had a similar problem which was fixed by removing the resistor I had put on the fuel pump ground wire. The purpose of the resistor was to quiet the fuel pump whine and it did that for 3000 miles then the bucking &c started. I removed the resistor (along the side of the road) and ta-da! the 1985 Westy runs smooth.

Recently I bought a more expensive Bosch 69469 fuel pump but that one still buzzes.

[Wasted youth]

Your thoughts about a fouled fuel pump remind me of a pain in the ass I once experienced. I will tell you a story about a 1972 1-ton Ford F-350 stake bed truck I bought from a service company about ten years ago. They told me it had a bad carb, had been rebuilt twice, and it still ran horribly sometimes, usually when they were headed for a dump run, but never on the way back. They did not use the truck very often, about once or twice a month and were upgrading their fleet.

I also suffered through it, exactly the same. It would putter around fine, but load the hell out of it and get on the freeway, and it got weak and sputtered. I too rebuilt the carb, because the fuel pump tested fine. It was obvious the carb had been rebuilt several times.

After racking my brain and giving up in disgust, I decided to pull the tank thinking maybe the fuel pump was sucking in big crap under heavy loads, and then the crap would drift away from the suction tube at idle, or light demand. I found nine beads of solder of varying sizes inside the split-seamed gas tank. I can only speculate they had been there since the tank was made at the Ford plant. Maybe the truck had been a pain in the ass its whole life.

The truck ran like a raped ape after I shook out all the solder beads. I carried them around with me for quite awhile as show and tell. How does this relate to you? You found a bunch of rust and crap in your tank, and I think some of it got sucked into your fuel pump. Maybe not enough to stop you, but once you got the high demand going, that stuff drifted into the suction stream and then fouled the pump pick up tube, starving your system for fuel, and likely harming your pump by overworking it with crap inside.

[Paddyw]

Expercing bucking and loss of power. Cleaned elec connections and ran great for a week. Total loss of power and coasted home. Replaced syndrome cable and now it wont even idle. Disconect syndrome cable and it will idle but no power. Any suggestions.