60 mph, manual, rpm' drops very low in a flash and back up, huh?

[dsdunbar]

Hi All,
My westy has been super awesome to me but I have noticed some issues and I am unsure how related they are to each other. I have a stock 2.1 WBX w/ approx 140k mi on it with a manual trans (original).

over the last 6 mos every now and then when driving down the highway i will get a "jerk" that I have associated with the trans slipping/disengaging (I am not mechanically inclined but this idea of the trans disengaging seems right). I do know, that my Circ(sp) clips (maybe C - clips?) have broken in my trans and as a result my transmission has fore/aft movement potential (Peace Vans found pieces of the circ clips when they changed my gear oil). As such, knowing the C clip issue, I assume my hiccup/jerk that sometimes occurs is a slip in the trans (this happens maybe once every 5th time i drive the van).

Yesterday, I was driving the van looking for a parking spot, was in 2nd gear pushed in the clutch to take a sharp turn, pushed on the gas pedal when coming out of the turn and had no engine response. (engine stayed at idle), I touched the gas pedal a couple more times and reached down to ensure it was connected (had it pop off before), and then I touched the pedal again and it had a response. No more hiccups there.

I drove the van in today to see if any more issues would occur, and as I am driving up I-5 at about 60 mph, I feel the similar phenomenon as before (jerk/hiccup) but I am able to see my tachometer and I swear it drops to zero and then comes right back up to normal rpm.

I know that the RPM's are measured at the engine, so a clutch slip wouldnt make sense for RPM's to fall off suddenly then come back (this fall off was like a split second, barely saw it happen). If RPMs were to drop like that, it would indicate the engine stopped turning (but it couldnt have because I am going 60 mph and can't imagine I was reactive enough to push in the clutch in the split second).

I dont know what of the above is related or not related, I suspect there are different things going on, but...does this sound familiar or plausible? Am I crazy and I just dont remember the events right? If not crazy, how could RPMs drop to zero (or 800, again split second just saw the need spike low and come back up)?

Thought I would ask here before calling a local shop. Any input is appreciated.

cheers,
DSD
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'89 2WD Westy "Grey Goose" - Manual 4spd
Crozet VA
Vanaru EJ25, Peloquin

[SCM]

I'm not the best with diagnosis but here's my 2c until someone else chimes in...

I had a similar problem with my van and after some research was starting to suspect the Hall Effect Sensor or it's wiring in my distributer. Then I read a troubleshooting procedure (maybe at GoWesty's site) that stated that the first step of any intermittent issue should start with replacing the common tune-up items (cap/rotor, air filter, etc.).

I had some of that stuff lying around so I replaced the old with the new and viola', no more problems.

I suspect my cap and rotor were bad. Maybe that's worth looking at as a first step.
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'91 Westfalia GL Automatic (GTA "Turbo" Rebuild w/Peloquin) and 2.3L GoWesty Engine

[mustard675]

When I experienced stumble at highway speeds it turned out to be "Vanagon Syndrome" and was fixed with the harness which has a built in capacitor to smooth out the reading coming from the air flow sensor to the ECU.

Some reading:
http://www.benplace.com/vanagon_intermittent_syndrome.htm

https://www.vanagain.com/troubleshoot-your-vanagon-loss-of-power-syndrome/

Van-cafe sells the harness but they're not cheap:
http://www.van-cafe.com/air-flow-meter-harness
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1987 VW Vanagon Westfalia
@peanutbutterwestytime

[Howesight]

As SCM has identified above, the tachometer needle bouncing violently between actual RPM and zero is a very telling clue. It ONLY results from one of two causes:

1. As SCM pointed out above, a faulty Hall Sensor or related Hall Sensor wiring;
2. A crack in the Printed Circuit Board(PCB) on your Engine Control Unit (ECU).

If you inspect the Hall Sensor and test it (see the test in the link below at pp 103 and 119) and it passes the test, then see if you can borrow a known-good ECU from someone to test.

http://www.google.ca/url?sa=t&rct=j&q=&...Fe9Gm0tn1I
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'86 Syncro Westy SVX

[riceye]

Possibly ignition switch.
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'87 Westy Weekender - daily driver on salt-free roads

There's gonna be some changes made.

“I find that things usually go well right up until the moment they don't.” - Ahwahnee

"Quality isn't method. It's the goal toward which the method is aimed." - Socrates, later quoted by R.M. Pirsig

[0to60in6min]

all the above.. plus

- check all the connectors on the 2 black boxes on the driver side of the engine bay - remove, apply some dielectric grease, replug.

- replace fuel filter and fuel pump relay if it's too old.

- check the harness to the AFM so it's NOT too tight, unplug, dielectric grease, replug and make sure there is NO tension on the wires.

[mikemtnbike]

Frayed hall sensor ground for me on this symptom. Bumps on the road would cause jumping tach.
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1991 Vanagon GL 2.1 AT Westfauxlia. "Frankie" Totaled https://www.thesamba.com/vw/forum/viewtopic.php?t=764510&highlight=carnage
1995 Eurovan Camper "Marzivan"
2020 GTI SE manual

[dsdunbar]

Thanks all for the responses! I’ll start looking into it! Cheers.
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'89 2WD Westy "Grey Goose" - Manual 4spd
Crozet VA
Vanaru EJ25, Peloquin

[djkeev]

Mine was an odd misfire/stumble after pausing to refuel hot.

It would clear up and then be fine until the next hot restart.

A replacement ECU fixed that completely.

Dave
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Stop Dead Photo Links how to post photos

Ghia
http://www.thesamba.com/vw/forum/viewtopic.php?t=392473

Vanagon
http://www.thesamba.com/vw/forum/viewtopic.php?p=6315537#6315537

Beetle
https://www.thesamba.com/vw/forum/viewtopic.php?t=482968&highlight=74+super+vert

[the joker]

check all the grounds

[pdm777]

I had similar symptoms -- tach dropping to zero, like it was shorted--

Check your spark plug connections, the boot that snaps onto the top
of the sparkplug.

I had one loose plug wire, and no problems since.
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1990 Westy Full Camper

[dsdunbar]

I had my van in for R134a conversion at Eions Automotive in seattle, and I mentioned to Eion my issue and he said he noticed it seemed to bog down at the start and then run fine, and based on his experience with my van and the symptoms I described, he thought the Air Flow Meter was acting up.

As such, I bought a new AFM from van cafe, installed it, and havent had the issue reemerge, so hopefully that is all that was needed.

Thanks all for the help.

-Dana
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'89 2WD Westy "Grey Goose" - Manual 4spd
Crozet VA
Vanaru EJ25, Peloquin

[jberger]

[Wildthings]

Bus Depot had a special on Hall senders a month or so back, don't know if it is going on today or not. The harness for the Hall sender also goes bad, but I don't know of a source off hand.

[dart330]

I just had this happen after installing a re-manufactured AFM to try and diagnose another issue. I ended up sending it back as defective. Plugged the old AFM back in and everything ran normally.

I also have a rebuilt distributor with new hall sensor and harness.

[dsdunbar]

Yeah....I am concerned about the transmission, but I am not taking a proactive approach (shame on me).

PeaceVans was the shop that identified the circ clip was broken based on the parts attached to the plug. I spoke with them at length about it and came away with, "it could go at anytime, or it could last a while". I asked what symptoms I should be watching for and they indicated difficulty in shifting.

Right now my van shifts easily. I've been driving it with this issue since 2016. I do not put a lot of miles on my van each year (probably 3000 - 6000 depending on our camping schedule).

I plan to buy a german transaxle transmission, but I am waiting as everything is working really well.

[dsdunbar]

Good to know.
I had my distributor cap and rotor replaced in 2015. I didnt do anything with the hall sensor.

I havent returned my AFM core yet (debating if it is worth keeping at the cost of $80.00).

[jberger]

[Wildthings]

A bad AFM isn't going to cause the tach to drop to zero or bounce around suddenly. Something needs to be killing the ignition to do that.

[dsdunbar]

I do not have a picture of the magnet. These are the shop notes:

Check gear oil.
Found gear oil level ~ 1 qt low.
Drained fluid & found piece of retaining clip for mainshaft on magnetic drain plug. Without clip mainshaft can migrate rearward eventually making contact w/ shift rod gradually increasing difficulty in shifting. Rebuild on transaxle would be required to repair.