81 Vanagon, signs of running lean at ~3100-3500 rpm

[Kubelwagen]

So, had a weird weekend with the Vanagon. For the most part she ran great, good power. Up and down hills, fine.

But - starting with heading out camping (of course) she ran a little rough for the first time since I got my new-to-me AFM just before Maupin. Light to light she just ran rough. It was warm out, I really wanted to go camping, I got to the freeway and it all smoothed out and off we went.

Had a few times of very slight bucking going up to Clackamas, but over all ran good, but not super smooth, on down to Detroit lake. Certainly not as smooth at the trip to Maupin, but we strolled up some impressive forest service inclines (what with getting lost and everything). A few times up hill felt like she was 'hunting' for power across the rev range, but if we were going up a hill all steady like she did fine. Most in third, a couple steep ones in second, one or two truly scary sections of road were crawled in first.

On the way home this evening I was able to almost always reproduce the following.

Gradual increase from 2000rpm up to 3000 there would be a clear increase in power at 2500. Engine sounds good throughout.

Could cruise at high 2000's up to about 3100 even up grades, no problem. 3100-3500 engine seems to run lean, rough, moderate bucking. Back off to 2900 alls well. All gears seem to be the same but it is easiest to examine in 3 or 4.

But, wait, there's more. Sometimes run right up through the trouble zone without the least sign of problem, though that became more common as we came into town or my stress level was causing me to notice it more.

Didn't delve into the engine when we got home as it's dark out already. But, in the AM plan to look for vacuum leaks.

Thoughts? Tomorrow is supposed to be our laundry day so we can head out camping again on Tuesday. So, obviously, I'd like to sort this nonsense out. In retrospect I think my "rough" periods on the way out were probably the same as what I'm calling "lean" on the way back. But going out I was mostly bopping along slow like in 4th not trying to cruise over rolling hills at highway speeds.

Note: the tach is a dangly add on by the PO and I don't guarantee it's calibration. I was doing 55 mph (per GPS) at just under an indicated 3000rpm and could go up freeway hills as smooth as could be. Move up to 58-59 and 3100rpm it was rough and almost missing. Back off and its fine.

[Westy78]

That really sounds like a bad spot in the track on the potentiometer. Since it happens at a relatively common spot in the rpm. Is this AFM rebuilt or just a "new" one you picked up? I'd be popping the cover off of it and checking for worn areas in the track and also checking the resistance on the pins per Bentley. Don't let a rebuilt unit make you think that's not the case. I had a two year old rebuild by Fuel Injection Corp. give me random bucking to the point I couldn't get over 35mph that I chased for a year before I figured it out.

[Randy in Maine]

You may find this sort of interesting....

http://www.thesamba.com/vw/forum/viewto ... hlight=afm

[airkooledchris]

my aircooled Vanagon had a similar issue that also ended up being a bad spot on the AFM track.

I loosened the screws that held the board in place and nudged it up just a few MM, which put the wiper on a better/clean section of the board to slide across and the stuttering/slight bucking went away.

[Kubelwagen]

Hmmm - that is more or less what I was visualizing the problem to be while I was driving, confirmation that it's a possibility is good.. The Samba link looks very helpful, thanks! I think that, once the coffee is down, I'm going to go listen for leaks, check the fuel filter and then take a look at the wiper.

I have to admit a certain degree of timidness about the AFM, but once more into the breach!

[Kubelwagen]

Cleaned the strip, tried moving the wiper board - it doesn't seem to move much even with the screws loose. Maybe a little. Symptoms seem improved but still rough under a load in second. I'm not sure that at this point I'm not just being picky and expecting too much across too big of range of rpms and load. Cause I can shift and move out of the "rough" patch.

At this point I'd say she's drivable and that I can continue to troubleshoot after tomorrow's 120 mile round trip camping trip. Thoughts? I don't want to drive through something that is going to cause damage....

[Gypsie]

Stop by the Lab tonight and we can grok this over a pint....

[Kubelwagen]

Enriched dynamic mixture with the help of Jason and Stephan in the Lab parking lot. Much, much improved. Plan to do more examination soon, but hopefully after camping.

[Kubelwagen]

Ran much, much better on this last camping trip. I still wonder, however, if I don't need to play with the dynamic adjustment in the AFM.

Plan to do some more searching for vacuum leaks this weekend and then seek the learned ears at the Lab again on Monday.

Mike

[Amskeptic]

Ran much, much better on this last camping trip. I still wonder, however, if I don't need to play with the dynamic adjustment in the AFM.

Plan to do some more searching for vacuum leaks this weekend and then seek the learned ears at the Lab again on Monday.

Mike

Catch me in the parking lot.
Colin

[Gypsie]

the adjustment made in the lab parking lot was in fact the dynamic adjustment (the cog was clicked 8 times CCW as I recall...). This allowed the spring that pushes against the 'flapper'(?) in the afm to push a little less, thereby allowing more fuel to be delivered. A little less 'more' at lower rpms and a little more 'more' at higher rpms.

This is a must read for greater understanding:
viewtopic.php?f=50&t=7761

Perhaps what is needed is a static enrichment (say a cog or two on the static adjuster), with a reset to original position on the dynamic cog.

But first....

Thorough vac leak check. As I recall you said that things were running great with the 'new to you AFM' on your trip to maupin and then it started acting up...?

Eliminate the basic faults first...

I am curious about the decel valve issue. My understanding is that when the vac line is connected to the decel the engine begins a steady rpm climb? to almost redline?

Lab Lot tutorial with Colin?. Don't forget to let me know when you go out to the lot...I'll try to remember the lm1...

[Kubelwagen]

I'm looking for vac leaks - Other than the 'knob' issue which is clearly a potential I've not found anything so far. I put a layer of the outside of that crack we found in the boot, but have not had a chance to take everything apart. I really need a garage tall enough for the Adventurewagen. I hate working in the rain.

Yep, that's what happened with the decel valve. Hooked it back up and the engine stepped - that is, rev up, pause, rev up, pause, rev up,- right on up towards red line. Gunning the throttle would bring it part way down and then it would step back up.

I have to say it ran pretty well on our camping trip though. Seemed to run out of go in the low 60's on the freeway, but we cruised at 55 just fine. Seemed a little rough the last few blocks, but I may very well have just been dumb with the tired.

[Amskeptic]

decel valve. Hooked up and the engine stepped right on up towards red line.

That is crazy and unacceptable behavior. I say take the decel valve out of the program here.
Colin

[Kubelwagen]

So - an update. Colin looked around my engine at the Lab, looks like #3 isn't contributing to the party as it should.

I'm a bit over my head here. Where "a bit" means totally. But, I'm going in on Sunday. At least I'll see if I can figure out how to do a compression test. If someone can point me to a 'adjust your valves - a guide for the uninformed' I'll look at that too. I suspect that I'm looking at more work here than I'm going to be able to 1) do and 2) afford. I work for the state so am looking at yet-another-pay-cut so the afford is a bit grim.

M

[Kubelwagen]

Putting out another call for a its-got-pictures link to valve adjustment. I've done some Googling and, well, they all seem to make the assumption that I *know where the valves are* which is less helpful.