High Altitude Performance Problem?

[TylerDurden]

From the Bosch VE Injection Pump doc:

Atmospheric-pressure compensation

At high altitudes, the lower air density reduces the mass of the inducted air, and the injected full-load fuel quantity cannot burn completely. Smoke results and engine temperature rises. To prevent this, an altitude-pressure compensator is used to adjust the full-load quantity as a function of atmospheric pressure.

Altitude-pressure compensator (ADA) Design and construction
The construction of the ADA is identical to that of the LDA. The only difference being that the ADA is equipped with an aneroid capsule which is connected to a vacuum system somewhere in the vehicle (e.g., the power-assisted brake system). The aneroid provides a constant reference pressure of 700mbar (absolute).



Method of operation
Atmospheric pressure is applied to the upper side of the ADA diaphragm. The reference pressure (held constant by the aneroid capsule) is applied to the diaphragm’s underside. If the atmospheric pressure drops (for instance when the vehicle is driven in the mountains), the sliding bolt shifts vertically away from the lower stop and, similar to the LDA, the reverse lever causes the injected fuel quantity to be reduced.

[vwzzuk]

So, according to the diagram info on this turbo pump, those of us who do not have an altitude compensator (Naturally aspirated engine and pump) should reduce the amount of fuel to compensate for extra soot and perhaps the symptoms of "missing" that two of us have experienced.

Anyone going to Cheyenne? How about a little adjustment to the fuel screw to see if that may resolve the problem? Shoot, less power will result for sure. I can't image doing that with 1,100 pounds in the back.

Moral of experience/story....get a turbo...like wolf_walker said.

[TylerDurden]

So, according to the diagram info on this turbo pump, those of us who do not have an altitude compensator (Naturally aspirated engine and pump) should reduce the amount of fuel to compensate for extra soot and perhaps the symptoms of "missing" that two of us have experienced.

Anyone going to Cheyenne? How about a little adjustment to the fuel screw to see if that may resolve the problem? Shoot, less power will result for sure. I can't image doing that with 1,100 pounds in the back.

Moral of experience/story....get a turbo...like wolf_walker said.

The turbo will probably solve the problem, but some members report no issues with standard kit. They may have engines tuned beyond the "average-joe's".

It seems if everything is at optimum tune, a bit less fuel should do the trick - the ADA pump only reduces fueling (maybe*). That ADA pump & control module  (on the fender) are not a small increment in design change, so it may be that VW was getting flack from owners and/or needing to meet emission regulations.

*The control module on the fender also activates the electric valve on the timing cover of the IP - it may change timing and/or change pressure in the governor control sleeve (I haven't determined the function yet, no literature I have found describes it).

[wolf_walker]

I did 6 or 7K feet I know of recently going through Flagstaff when I moved to CA and it was the same as usual, little more smoke, on the floor in 5th running 60 with the NA AAZ, no alt compensation module on NA pump, two people and three or four hundred pounds of load.  A lot of otherwise healthy diesels will overheat under such use, mine didn't but I attribute that to the huge oil cooler as much as anything else.  On the smoke/fuel issue I think you can get about the same effect in steady state driving by just backing off the throttle some.  It's hard to do but it's there.  Overfueling would have to be insane to make a motor miss though, I think it would melt something before it got to that point.
There has to be something more complex going on than just thin air.

As an aside, my old tired 1.6 that was a reliable daily for 40 or 50K miles before I left it back east, and did 42mpg average, etc, etc, would never have made it.  It would have been crawling in 4th and probably overheated.  Nothing exactly wrong with the cooling system, but the low compression from age (half mil on motor) and worn pump with lazy timing would have done it in I'm sure.  It's one of the reasons I brought the 82 out here instead of the 81.  If you made it up that kinda grade carrying a load without anything dramatic going on I'd say your motor and pump are OK in general.

We need a diesel x-files for weird stuff like this.

[TylerDurden]

On the smoke/fuel issue I think you can get about the same effect in steady state driving by just backing off the throttle some.  It's hard to do but it's there.  Overfueling would have to be insane to make a motor miss though, I think it would melt something before it got to that point.
There has to be something more complex going on than just thin air....

We need a diesel x-files for weird stuff like this.

Agree.

[vwzzuk]

The hills on I80 in Wyoming are high elevation, of course, long and gradual compared to say...Montana coming from Great Falls on 15/12 South to the Garrison area. One of those roads has a wicked climbs to a summit where I spit out a long cloud of black pulling my load in 3rd gear...barely. I expected it to overheat but it never did it. I was amazed. I think that pass was over 8,000 feet. I rarely noticed a small hesitation on that trip but it only did it up high.

[wolf_walker]

Pretty weird man.

I have been driving VW diesels, more NA than turbo, for fifteen years or so I guess, many many hundreds of thousands of miles all over the midwest and eastern part of the country and I've never felt one actually miss, ever, other than cracking an injector line open enough that the pressure was not enough to open the injector and make it spray.  Seen a lot of other weirdness on the road, but not that.  For it to miss, the mixture in the chamber either has way too much fuel, way too little fuel, way too little air, or way too little compression, or some combo of. 
I'd be freaked out enough that I would adjust the valves if not hydraulic, check the lifters if hydraulic, check the cam lobes for wear, check the cam and pump timing, pull the glow plugs and look for signs of erosion, replace/test the injectors, and replace the pump, probably in that order more or less.  If there was a better way to test the pump, or if you had a friendly pump guy with a pump dyno I'd be more inclined to do that first.  My knee jerk reaction says a weak cylinder is showing itself at altitude, but that's not based on any science.  I'd comp test it for sure.
Or just leave it alone and try and avoid elevation if it's OK around home.  The fresher and healthier the motor is/supposed to be the more freaked out I'd be.  I make allowances for old tires ones.  Most of mine have been.  So weird.

[vwzzuk]

UPDATE: Problem solved without a turbo or turbo pump.

I continue to go on the trips from Portland to Colorado Springs (through Wyoming) and I no longer have the symptoms previously stated. What I experimented with was putting a hose from my air box tube to the front grill so that it created a basic "ram air" affect. As soon as I did that, the issues disappeared. So, a little ram air fixed my rich fuel hesitation problem at higher elevations such as 7000 feet.

Thanks to all for your help in this process.

--dave

[wolf_walker]

Trippy, but cool.  What airbox were you running to start with?

[vwzzuk]

Stock diesel Air box, filter and plastic insert.

[fatmobile]

 Did you change your fuel filter too?
  Since it's been stated high altutude won't cause bucking, and fuel supply is the most common problem.
 I suspect partially gelled fuel combined with a high fuel demand.
 Or a funky ignition switch like mine.

[vwzzuk]

Yes, the trips from Portland to Colorado Springs were made twice with the same "missing" results on a rebuilt engine, rebuilt injection pump, head, etc.... When I pulled into Denver, I replaced the fuel filter, ran a can of purge, cleared the lines to the tank, and then returned home with my load. Still had the same "missing" results in Wyoming.

Did some more research here on the forum and at home and discovered that the engine could be running too rich at higher altitudes without an aneroid on the pump. I  experimented with forcing a little more air into the air box at higher speeds. Been on three more trips since then (after putting on the hose from grill to the air box) and it has not "missed" at any point above 7000 feet anywhere in Wyoming. COOL!

[wolf_walker]

Which stock airbox, just out of curiosity.  The oval center inlet from the early rabbit with the narrow offset inlet pipe a foot or so long?
A2's had a slightly better looking side inlet, I've used those for awhile.

[vwzzuk]

I have the square air box with the oval center inlet with the plastic tube that comes out just over the timing cover.

[jhax]

I live in steamboat springs, CO and just moved up here from Tempe, AZ. My intake tube (A2) finally fell apart while in Tempe so I just left the flex pipe off and the hard plastic tube starting from the front of the engine to the air box. I noticed lack of already little power up in CO so I took some black plumbing pipe and re-made the missing intake section from the side of the fender to the stock air intake and noticed a difference. If you do use the pluming piping make sure to avoid sharp 90* turns because it screws up air flow and 2" diameter pipe worked well for me.