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Running worse at altitude

7K views 73 replies 10 participants last post by  aglinks 
#1 ·
Hey all, my truck (2006 mega cab) stumbles on cold starts and blows black smoke when I accelerate at home in Flagstaff (around 7000ft elevation) regardless of outside temp. When I’m in Phoenix (1500fy elevation) it never stumbles on a cold start and never smokes, even on a WOT run I can’t see a trail of gross smoke. Is that normal? I would assume the computer adjusts the tune for altitude.
 
#10 ·
check your baro/ambient air temp sensor on the airbox with a scan tool at both low and higher altitude. at sea level it should read 14.4~14.8 psi, 5k ft ~12.2 psi & at 10k ~10.1 psi. If not you could attempt to clean it but its easier to swap it. That sensor feeds the ECU with pressure & air temp info to help calculate fuel & timing and it sounds like yours is off.

I use the android app torque with a scantool.net MX bluetooth module to monitor things daily and can spot things pretty quick if something is not right.
 
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#13 ·
I live at about 6,200ft. I've never had any issues with stumbling on cold starts, and on stock programming it was pretty much impossible to get more than a haze of smoke. Even running on a 90hp tune, I have to miss a shift or really lug the motor to get much smoke. I'd do some investigating.
 
#18 ·
the chart I have for baro vs altitude says that sensor is dead on. leave it alone.

edit: what are your mods, if any?
 
#24 ·
The truck is a stock rebuild with 30k miles. New stock injectors and turbo were installed at the same time as the engine. No aftermarket programming or anything. I installed gauges, additional filtration, and an ATS Stage 1 trans.
look at the map sensor next & compare it to what the boost gauge says.... should be = baro + boost, meaning if the baro sensor is 10.0 psi and boost on the gauge is = 15 psi then it should read 25psi. If not then should be compensated and = the boost gauge.
It needs an external boost gauge to verify that.
The BOOST reading from OBDII would be wrong when the MAP reading or the IAT pressure reading is wrong.:wink2:
Agreed... and he has gauges which is why I said what I did... On my setup, there is a gauge that contains uncorrected MAP readings, meaning if at idle MAP should be approx. equal to baro. I dont use it but I know its there. OBD data is converted A to D data and should be uncompensated by the ECU.
 
#20 ·
look at the map sensor next & compare it to what the boost gauge says.... should be = baro + boost, meaning if the baro sensor is 10.0 psi and boost on the gauge is = 15 psi then it should read 25psi. If not then should be compensated and = the boost gauge.
 
#21 ·
look at the map sensor next & compare it to what the boost gauge says.... should be = baro + boost,
It needs an external boost gauge to verify that.
The BOOST reading from OBDII would be wrong when the MAP reading or the IAT pressure reading is wrong.:wink2:
 
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#22 ·
The stumbling would concern me at first. But I took my truck 06 crew cab from Stuart Fl to Colorado Estes park and it was smoking the whole time. I’d be cursing up an incline at 50 and shed smoke. And I thought I broke something coming down pikes peak 14000+ feet. But it’s just the air is thinner. Not as dense. I wouldn’t sweat it at all. As soon as I got down to Texas in my drive back she was fine.
 
#23 ·
On another note for you bud. There’s a huge difference between 8000 feet and sea level. Honestly 4500 feet isn’t a huge difference in air density. But 8000-14000 is a great deal. A lot of guys n here make things a bigger deal than needed. Your truck sounds like mine. Mine is bone stock and was smoking and lagging st 8500-14000 feet. I really wouldn’t sweat it.
 
#27 ·
I bought this truck from my dad right after the engine and trans work. It lived its life at low altitude the entire time prior to me buying it so I have no idea if it ever acted up at higher elevations. He ran a Predator "chip" for the 200k miles that is lasted before he blew it up. I think the Predator was a boost-fooler, it plugged into the harness and stayed there. When the new motor went in, I insisted that the truck not be chipped or programmed.
 
#28 ·
Just re-read your first post and am I clear this is only happening on cold starts at altitude? When its warmed up then no issues?

Do you know if your grid heater is working correctly? <- you can check this by cycling the key and watching the IAT/MAP sensor vs the Ambient air sensor. IAT should be +15~20 over ambient before even starting it up.

There is a contractor I know of with a motorhome (non cummins motor, a CAT IIRC) that has almost the exact same thing however he has trouble getting his to fire up at all. It was suggested that his intake heater was not working. He has not worked on it yet so no idea if that was it or not.

What is happening from what I can tell is your injection event is not lighting off soon enough which could cause the cold start issues. Either that or it has an aftermarket tune in it that stinks.
 
#29 ·
You are correct, this only happens on a cold start at elevation. The grid heater is definitely pulling power because in the morning I can watch the voltage gauge drop and rise as the heater cycles. I will check in the morning and see if the IAT rises before I start it. If the truck is warm it will fire like it’s brand new.
 
#30 ·
Cycle the grid heater a couple of times before you fire it up. I forget what year yours is, on the 2005 & older trucks there are 2 elements along with 2 relays IIRC. If one is bad it may not be so happy starting. I had a relay fry on me and in 0~10*f temps I had lots of white smoke and a not so happy motor till it warmed up. Different symptoms than yours but still worth it to have a look.
 
#32 ·
I'd start with compression tests. If low, won't develop sufficient dynamic running compression at high altitudes thin air to combust atomized diesel properly, black smoke out the exhaust. Rebuilds often leave something to be desired quality wise on ring selection, end gapping, ring gap placement, cylinder wall roundness top to bottom, cylinder wall spec finish per Cummins.

Time to take it to a Dodge Diesel dealer and have stock firmware prog'd in. May be corrupted, who knows what shops have done to the ECU.

If that doesn't solve it, get 2 EFILive tunes, high altitude and lowlander.
 
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