Avalanche gets hot and dies while long distance towing.

I?m in need of some advice. On two long family vacation trips in my 05 Avalanche (5.3, Z71, 3.42 gears, tow package). After about 2.5 hours or so driving in 80+ degree heat or when going up mountains (Appalachian), my Avalanche will stall out and die like it is running out of gas regardless of fuel level. This has only happened while towing my 19 foot travel trailer (roughly 5200 lbs loaded). And after mechanics have reset the codes and the truck has cooled off it starts and runs fine and they can?t get it to replicate the stall and die. The codes that came up the first time it happened were p0300 and p0455. I have replaced the evap system components except the canister and that has solved those codes. The most recent time I noticed the temp creeping up to 3/4 (I think around 235 degrees) and when it died the codes were p0171 and p0174. I know those are lean codes and have checked for vacuum and intake leaks (the choke cleaner trick) and nothing seems to be leaking. Once again, the mechanics can?t find anything either and it is running as it should without towing. I?ll also mention I am towing in tow haul mode.

This is a mystery and I?m sorry to say has me considering trading my Avalanche for a bigger truck (2500 Avalanche or duramax Silverado) despite my loving it. Has anyone else experienced this and if so what was the problem?

Thanks in advance.

Sounds like a fuel pump going out to me.  Apparently yours is sensitive to temperature of the fuel in the tank.  After 2.5 hours of pulling your trailer, the extra heat generated in the engine by towing with either a raised ambient temperature or an increased load due to mountains has elevated the temp of the (recirculated) gasoline in the tank enough to make the fuel pump give up.  Cool it down and all works again.  At least that's my theory!

How to tell?  Get loaner fuel pressure gauge from parts store and keep it in the truck for when it happens next time and won't start.  Either that or just replace it (but that's a pretty expensive repair to have done without good reason).  Another thing would be to check the dead-ended fuel pressure (max the pump will put out without going through the fuel pressure regulator).  This should be well over 100 psi, even though the engine uses only around 60 psi regulated pressure.  This requires some custom fittings to adapt the exit of your fuel filter to the Schrader valve fitting on the pressure gauge, but could be illuminating as to the problems you are experiencing.  Just barely making normal PSI is not a good thing.  Don't block the return line to the tank to do this or you can blow the fuel pressure regulator.

According to two of my mechanics the fuel pump was fine but I see what you mean and it being temperature sensitive. The two instances of this happening were about 4 months apart and the temp was lower the first time than the second, which logically seems backwards, at least to me. I?ll have the fuel pump pressure checked again though to make sure.

I read on a Silverado forum that the increased engine temp caused the air in the combustion chamber and exiting the engine to expand and that caused the lean codes. I was wondering if changing to a 160 thermostat from the stock might help it run cooler or if it would be trouble in the long run. I also can?t find a consistent opinion as the to normal operating temp to compare mine to in order to see it the thermostat is going bad. Mind is currently running between the half way and the last tick mark before half not towing and right at 210 or just above while towing.

I appreciate the response and will check it out over the weekend.

YOU need to run it with soem scanner or data logger so when it gets hot and dies you can see what is happening.
might die too quick to throw a code and a sensor on engine does not like this added heat ..

thinking crank sensor or similar.

Would the crank shaft sensor act like the engine wasn?t getting enough fuel?

One other thing I forgot to mention in my original post is that the truck had 99k the first time it happened and 104k the second (currently at 105k). Would mileage matter? And is there a test other than leaving a scan tool connected all the time?

I guess the only I may have to do what I was thinking as a test and hook the camper up a and pull it back and forth over a mountain until it does it again. Thanks.

I think the heated fuel pump theory is a real long shot.

I'd be curious to know what your oil pressure was at the time of shut-down. I can't say for certain about the Avy, but the older Tahoes and Suburbans (in fact, many GMs) will shut down the fuel pump on loss of oil pressure to save the engine. Is it possible that the oil thinned out enough to drop the oil pressure below the threshold (usually ~5 psi)?

My scan tool can stay connected while driving and show real data.

Read this guys thread about his similar troubles:.

http://www.chevyavalanchefanclub.com/cafcna/index.php?topic=153867.0

MAke sure you Read post 15
Did not throw a code and died but had it hooked up to see what happened just before it died.

I AM NOT saying yours has same issue -
What I am saying is you need to be connected to computer or good code reader when it dies to see what sensor was not happy.

PS about low oil pressure - our trucks give warning first

Oil pressure was normal, right around 40 give or take a mark. The only thing not within normal range was the temperature which was about halfway between 210 and the three quarters.

Thanks for the link as well. I thought there might be something similar going on with someone else?s but couldn?t find the thread googling.

best bet for searching.... for me is I just read thread titles as everyone has a different way to describe a problem.