Thoughts on effects of altitude on cold starting

[TWeatherford]

I moved this summer from Kentucky, elevation 547 ft, to Colorado, elevation 9,000 ft, finally to Arizona, elevation 7,000 ft. It seems to me my diesels (truck and TDI Jetta) were harder to start in CO and here as well. It wasn't as noticeable in the summer, as the difference between 2-3 revolutions and maybe 3-5 is pretty minimal. But we've been getting below zero here lately, and the difference seems bigger to me. I know atmospheric pressure is about 4 psi lower here, which is certainly noticeable in power and black smoke. I'm wondering if anyone else has had an opportunity to cold start at drastically different altitudes, and noticed the difference I have?

The Jetta has all the same parts between last winter in KY vs this winter in AZ. So they are a year older and more worn out certainly. Nothing is showing signs of failing, and the battery was replaced just before the 1st winter in KY.

The 94 Ford, in KY, started at -2 F (coldest it ever got) in just a few revolutions with a 16 second manual glow. This was with 4 year old group 65 batteries, corroded battery cables, and the starter that it came with. As soon as I moved to AZ, the alternator died and took the batteries with it. So it has a new alternator, I swapped in group 31 intersate batteries, new battery cables from custombatterycables.com including a 3/0 starter lead, and threw a brand new starter (can't remember what it is, it was recommended here), and it most recently has a new injection pump. I've checked that the glow plug system is in good shape, and it still starts, but not nearly as well. I'm going to blame altitude until someone tells me I'm wrong.

 

[RLDSL]

Yup, its the altitude. The VW is automatically compensated for the altitude to a certain extent, it will adjust itself to lean out and advance the timing above roughly 3800-4000 ft, but when you start approaching double that in altitude, the automatic stuff really isnt equipped to deal with it and if you are going to be up there all the time you need to change your base settings, i.e. go in and increase the base injection timing a tad and lean the fuel out.

Same goes for your truck, and even then, expect some extra cranking that high remember you have to compress a certain amount of air to generate a certain amount of heat for the fuel to ignite, and up there at cranking speed, there isnt a whole lot of air to begin with so it takes a couple of rounds to pre heat the cylinder. I remember being up in Leadville Co and around there at 11,000 up to around 13,000 ft in some places we were exploring, and I had pre tuned for it, but it still took a little extra wind up with the air that thin ( heck, I sure couldnt blame the old girl, it took me two days for my head to stop spinning at that altitude... At least I know why my late Grandmother was such a tough old bird... she was born up there in around 1887