'86 Vanagon (2.1L MV) Altitude Adjustment ?

[reiney]

Greetings!

I've just completed a 2000+ mile trip from the East Coast to Santa Fe, NM. The van ran great for the whole trip but now that it's at 7000 ft. it's a dog! It is extremely difficult to start whereas before it would immediately fire right up. Once I get it running, sometimes w/ the help of some ether, it will run and idle smooth and I can drive it but it has noticibly less power and a very "spongy" accelerator pedal feel. Here's what I've done so far:

1. Fuel filter is NOS Bosch, installed b4 trip
2. Checked temp. sens I & II, airflow sensor vane resistance, air temp sens.
3. Verified that above sensor readings appeared at ECU connector
4. Compression test; somewhat low but all above 110 and within 12% range
5. Checked fuel pressure reg. and replaced vac. hose to manifold
6. Checked fuel pressure
7. Swapped in a known working ECU
8. Checked all ground pins on ECU connector

The plugs, wires, cap & rotor are all fairly new. The idle stabiliser unit was removed long ago and replaced with a simple PWM circuit that lets me adjust the valve manually from the dash.

I'm stumped! Any ideas?

Thanks in advance ..

Reiney

[Wildthings]

I have had mine that high, and am sure it lost some power. Can't compare it to your's though. In the olden days of motoring it was pretty common to bump the timing up a few degrees once you got over 6000 feet, don't know that it would hurt anything so it might be worth a try. If you are running anything more expensive than regular gas that can cut your power slightly as well. These things don't have a MAP sensor to automatically correct for elevation so mixture correction would be totally up to the O2 sensor. Make sure yours is working right.

[tencentlife]

You're in my neck of the woods. Most of the power loss is due to there being 20% lower atmospheric pressure in Santa Fe than at sea level. It's that pressure that fills the cylinders on intake, so there is less charge mass to be burned per cycle, and lower compression to boot. Sorry, but you won't get most of that back as long as you're up at altitude unless you fit a turbo to 'er.

But you can compensate somewhat. Timing can be advanced 3 degrees, but it won't have as much effect with the Digifant as it can have with conventional ignitions. There's no reason to run premium gas, with the lower compression detonation is a long way off. I'm running 9.3:1 and drive hard on regular gas.

The main thing is to get your basic mixture reset. Counterintuitively, you need to enrich the mixture in order to recover some power since combustion has become less efficient. Turn your mixture screw in several turns to enrich the base setting. And make sure your O2 sensor is working.

[Wildthings]

A clean air filter will make more difference as you go up in elevations as well.

[reiney]

Thanks so much for the tips! I screwed in the mixture adjustment a few turns and it does seem to help. Can't quite figure out if the hard starting issue is also related. Will probably buy it a new O2 sensor since I don't have the proper test gear to check exhaust CO. Turbo sounds like fun! but I'm hoping to put in a diesel motor soon. This is the last vehicle in the "fleet" that's still a gasser ...


Take care,

Reiney

[tencentlife]

Disconnect the O2 sensor with ignition off. Put your voltmeter between the O2 sensor connector and ground and see if there's a small voltage, varying between 0.1-1.0v. If it's putting out in that range it's probably working fine, no need to get a new one. Disconnecting it will also reset your ECU memory, which may have a positive effect (it can't hurt) after the big altitude change.