Possible Altitude Issuew

harrywt

harrywt

Member
I am now in Carbondale CO. Drove from LA, to Lake Mead then Richfield UT before arriving in Carbondale. I am towing a pop up camper that is 1500 or so lbs.

Scout had surprising struggles up hills (mountains?) I changed the sparkplugs in Utah and also the wire set, cap and rotor. I have been changing plugs every few months as they were fouling alot. I had been at 10 BTDC and have been backing this off over the past year. I finally got rid of all pinging and this past change showed no plugs fouled. The timing had been 4 BTDC. I dont have a timing light here, trying to borrow one

I noticed that the dist. clamp bolt was somewhat loose so I decided to play with the timing. I tried advancing the timing first. I was never able to get any pinging but the engine is missing quite a bit. It misses more as timing is advanced more and more. I backed off the timing until I was reasonably happy with the acceleration and driving from Richfield to Carbondale was better than the previous legs.

Since I live in LA I had the carb (Holley 2300) jetted for sea level. Carbondale is at 6000 ft. Would high altitude tend to explain the missing and lack of pinging at advanced timing? Maybe I was too shy when advancing? The truck has a more pronounced gasoline smell which would be consistent with running rich with sea level jetting at high altitude
 
If your truck was fouling plugs in LA, and it wasn't oil, then it was already running rich near sea level. Now at 6k ft elevation it will be really rich. And as you've observed it doesn't ping at altitude, that's because cylinder pressures are lower.

I used my Scout to tow a 2500# RV trailer on the most difficult pull in the US, from Death Valley to Lone Pine on 395. We could only get regular gas at the last station in Death Valley and it pinged like crazy until about 2500' in altitude and then you couldn't make it ping. The Scout was in 2nd gear almost floored for about 45 min doing 35MPH. I think the summit was 7500'. Wow what a ride and the Scout didn't miss a beat.
 
So ping or detonation is related to cylinder pressure. Sea level you have 14.7 psi ambient pressure filling the cylinders with air that is then compressed. At 6000 feet you only have 12.5 psi. That reduction in cylinder pressure effectively lowers the compression pressure to a level that is very detonation resistant. Your mixture also goes rich lowering temperatures in the combustion process further lowering the propensity to ping.
Run it hard for a few minutes and check a plug. Will likely be dark at the center electrode insulator and down a ways if rich and at altitude.
 
Sorry that I didn't notice your replies earlier. In the past, I have received an email notifying me of replies. Your points are very helpful, thanks, rounding out the picture of I was making to explain all of the behaviors I was observing.

I am embarrassed to admit that I didn't realize the pressure differential sea level to 6000 ft, explains how my tires went from 18 to 22 psi. We were up as high as 10 000 ft on trails in colorado. I've always known that Scouts are the best off road vehicles. I grew up 4 wheeling on beaches. This trip was my first time doing serious mountain trails. My Scout was an absolute monster. It is very gratifying to get compliments from so many off roaders (who never say nice bronco!). I have now a truetrac in the front and the rear gets its truetrac this week. I was constantly amazed at the obstacles we overcame and my Scout was just saying to me, what's the worry, damn it was fun.

we climbed a couple of hills from 2000-8000 ft, I was able to go to 3rd gear, 3000rpm, 45mph, engine likes 3000rpm was surprised actually. It only has 30k on the rebuild and I try to take good care of it.

BTW, during the past 2 years once I settled on 4 BTDC the plugs stopped fouling. But now having gone through this trip I do notice that there is still a gasoline smell, might be time to change jets.

Although, I think FI is got to happen
 
how does one become aq "Well Known Member"?

FDChappie said:
If your truck was fouling plugs in LA, and it wasn't oil, then it was already running rich near sea level. Now at 6k ft elevation it will be really rich. And as you've observed it doesn't ping at altitude, that's because cylinder pressures are lower.

I used my Scout to tow a 2500# RV trailer on the most difficult pull in the US, from Death Valley to Lone Pine on 395. We could only get regular gas at the last station in Death Valley and it pinged like crazy until about 2500' in altitude and then you couldn't make it ping. The Scout was in 2nd gear almost floored for about 45 min doing 35MPH. I think the summit was 7500'. Wow what a ride and the Scout didn't miss a beat.
Click to expand...
 
BTW, I am about to post in engine tech, developed a tapping noise that is driving me nuts. going to take off valve covers this weekend
 
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