No Power in Reverse at Elevation

[blackglasspirate]

I've had a weird issue happen to me a few times and I'm wondering if someone could shed some light on why.

Last night I camped pretty high in the mountains (10,500ft). When I went to back out of the spot this morning it just wouldn't go. I put it in reverse, floored it, and it essentially did nothing. It wasn't really revving at all. The RPMs may have gone up slightly with the pedal to the floor, but the wheels weren't moving, and the RPMs would drop way low briefly when I let off the gas. What's weird is that I could go forward no problem. The only thing that was affected was reverse. I let it idle for 10 minutes or so but same problem.

I had something similar happen a few days ago at 6500ft but the engine was completely cold and it only took a minute before it kicked in. I've also had some issues recently with hesitation and sluggishness. I more or less fixed that, although the sluggishness started to creep back at elevation and I haven't been able to determine if it's just the result of the elevation, or I still don't have it right.

Either way, I was just curious what would cause a zero power condition in reverse but going forward was just fine. I've never had this problem before and have spent considerable time at elevation while traveling in South America (over 16,000ft). Any takers?



Side-notes:
Going in reverse was just slightly uphill, but just barely.
This is an automatic transmission, newly rebuilt by GTA.
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'87 Vanagon GL Westfalia
IG: @holidayatsee
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[dobryan]

Not engaging reverse? Revving but not engaging?
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Dave O
'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD

"To travel hopefully is a better thing than to arrive." Robert Louis Stevenson

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[blackglasspirate]

Not even revving. I can feel it engage reverse, but when I floor it the rpm remains roughly the same and it just doesn’t move.
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'87 Vanagon GL Westfalia
IG: @holidayatsee
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[dobryan]

And if it was in first it moves? Sorry to be obtuse but that seems like a trans issue not an engine/altitude issue?
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Dave O
'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD

"To travel hopefully is a better thing than to arrive." Robert Louis Stevenson

MD>Canada>AK>WA>OR>CA>AZ>UT>WY>SD
https://www.thesamba.com/vw/forum/viewtopic.php?t=620646

Building a bus for travel in Europe (euroBus)
https://www.thesamba.com/vw/forum/viewtopic.php?t=695371

The Western Syncro build
https://www.thesamba.com/vw/forum/viewtopic.php?t=746794

[jimf909]

Are there conditions where the trans operates in reverse as expected?

I'd call Kateka at GTA in the morning.
_________________
- Jim

[blackglasspirate]

Yes, in first in moves. In reverse it just sits there, doesn't rev, and the engine stumbles when I let off the gas but doesn't die. After driving it for a mile or so, reverse works fine.

The reason I thought it might be engine related and not trans is because it always works fine when not at elevation and also works fine at elevation as long as it is warmed up. I can feel it engage reverse, it just has zero power to move the wheels.

I wasn't sure if there was something else in play when putting it in reverse that I'm forgetting. Like, does reverse put more load on the engine than 1st and maybe the engine is having such a hard time at altitude that the extra little bit of load is too much? It also doesn't do it every time, which is confusing. I'm down at 8,500ft now and will test it on a cold engine when I leave this spot.

I'm trying to cover all my bases before contacting GTA. I was there so many times last year I'm pretty sure they never want to see me again (wasn't my fault, to be fair).
_________________
'87 Vanagon GL Westfalia
IG: @holidayatsee
FB: https://www.facebook.com/holidayatsee

[blackglasspirate]

Oh, I forgot to mention - yesterday it briefly did the same thing in 1st AFTER moving from the camp spot. So it when like this:

1. Start the engine, no power in reverse (very small incline).
2. Had power in 1st, and was able to drive another way out of the spot about 100m to a turn around.
3. At the turn around I still had no power in reverse for the first few tries and then slowly the engine started to rev up and I got power to reverse.
4. Put it back into 1st to go forward (uphill) and briefly had the same no power issue (no revving, just no power), but in a few seconds it took and I was fine.


The rest of the day I had no issues with reverse. I did have one time going up a rocky hill in 1st where the van had almost no power. I was flooring it in 1st and it was barely crawling. I thought I was going to have to back up the hill. It was at 11,000ft, so could have just been because of that - who knows.
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'87 Vanagon GL Westfalia
IG: @holidayatsee
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[kourt]

Troubleshooting guide.

My first thought on this is a linkage issue. I would be looking at the linkage at the transmission, plus the shift lever linkage where it enters the transmission body.

Also be sure to look at the accelerator pedal itself for any changes in the hardware.

Keep us posted. Interesting problem.

kourt

[4Gears4Tires]

Does it rev in neutral just fine at all times?
_________________
'87 Syncro
Ferric Oxyhydroxide Superleggera Edition

[0to60in6min]

bad Temp2 sensor or maybe bad/sporadic connection at Temp2 sensor?

[Wildthings]

Do you have a tach so you can quantify what "doesn't rev" means? Sounds like a cold running issue combined with altitude, so I would guess you are running overly rich until the engine gets hot enough the ECU goes closed loop.

Read the resistance of the TSII sensor at different temperatures and compare that to the charts given in the Bentley. You could also try just shorting between the terminals in the plug for the TSII and see what that does for you.

If you engine was running rich at cold startup at sea level it would be very rich at 10,000 feet.

[blackglasspirate]

Thanks for the responses - I'll try to answer all the questions.

I haven't checked the linkage, though I would have thought that since it works fine at sea level and I can feel it engage reverse that that isn't the problem? I could certainly be wrong though and will add that to the list of things to check.

It does rev fine in neutral at all times. It idles fine too in neutral/park, though maybe at slightly lower RPMs at altitude.

Temp2 sensor was replaced recently as part of some general maintenance and I tested the wiring as well. Hopefully that's not it!

I do have a tach, so when I say it doesn't rev I mean there's virtually no change in the RPMs between pedal to the floor in reverse and no gas idling.

It could definitely be a running rich issue. As mentioned, I did have some running issues recently and did a lot of work, including adjusting the AFM. I'd like to put a rebuilt AFM in here to test it but it seems like GoWesty and VanCafe are sold out. What confuses me though is even if I'm running rich, why would forward gears work fine but reverse wouldn't?

It's really a strange issue and it does it infrequently enough for it to be very hard to troubleshoot. Maybe I'll just have to drive back up to 10,000+ft for a few days to see what I can do
When I leave this spot I will chock the wheels in front and behind to simulate the slight uphill and see if it affects both forward and reverse.
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'87 Vanagon GL Westfalia
IG: @holidayatsee
FB: https://www.facebook.com/holidayatsee

[Yota-toy]

Sometimes depending on the layout of an intake on FI engines a difference in forward and reverse travel power issues could simply be a tear in the intake boot between the MAF or MAP sensor and the intake manifold.
The engine torques up in forward and down in reverse (or the opposite) opening the tear and reducing or eliminating the air flow one way closing the tear in the other way.
Fixed this on a Range Rover once with a pringles tube. They thought I was crazy, I wasn't!!

Hope it's an easy fix!!!

[Yota-toy]

this would make a lot more sense especially at high altitude if close to or beyond your ECU's map.

[jimf909]

[Wildthings]

[djkeev]

[Abscate]

[Jake de Villiers]

[Zeitgeist 13]

I'm wondering if the engine or trans mounts are either failing or loose. This seems like a shifter/accelerator linkage issue
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Casey--

'89 Bluestar ALH w/12mm Waldo pump, PP764 and GT2052
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