Turbo Surge at High Altitude

[Musicman]

I've got a C15, currently set at 475HP with a relatively new turbo. I recently started running water to water and have noticed that when I get much higher than 5,000 feet or so, my turbo starts surging. You can hear it as well as see the boost needle bounce around from between the 20 and 30 lb mark. This doesn?t seem normal to me, but I?m no expert. The truck is currently getting an in-frame so now would be a good time to fix any other problems. I thought maybe a charge air cooler leak might cause this, but I just had the dealer check that and they say it?s okay. Any ideas? Thanks

[BigDaddyD]

Your turbo is activated by exhaust passing by it. The engine is surging and not giving consistent exhaust pressure to the turbo fins that is why you see it in the boost needle.

Another option would be that your waste gate could be failing.

HTH

[allan5oh]

Boost surge is *VERY* dangerous. You can and will blow the turbo. What you are doing is operating the turbo outside it's "operating range".

Definitely sounds like a wastegate, essentially overboosting. What is the "normal" boost for this engine?

What year is the engine?

[BigDaddyD]

Boost surge is *VERY* dangerous. You can and will blow the turbo. What you are doing is operating the turbo outside it's "operating range".

Definitely sounds like a wastegate, essentially overboosting. What is the "normal" boost for this engine?

What year is the engine?

I didn't even think about the wastegate not opening and causing an overboost. Like you said that is VERY bad. With not knowing the normal boost its hard to say if it is overboosting.

[allan5oh]

But the problem is, what is "normal" boost at 5000 feet? If you have 30 lbs of boost at 0 feet and 30 lbs of boost at 5000, you could be running into problems.

[Musicman]

... but I think I'll ask the dealer. KW has had the truck for two weeks now and will finally have it done today, supposedly. I definately don't want to have to worry about taking it back to the shop again after I hit the road Tueasday. God knows I can't afford any more major repairs for a while.

allan5oh, it's a 2003.

Also, I really have no idea about what normal anything is for this truck. I've had it for 1 1/4 years and I don't think it's ever been right. The fuel economy has never been what I think it should have been. When I bought the truck ('03 Pete 387, 475 CAT, Eaton 10, 355 gears, 22.5 lo pros), mpg was horrible. Truck had 456k miles on it and running 70 mph my mpg was arround 5.3. Had the overhead run (hadn't been done since the first one at 60k) and mpg went up to about 5.8, even though the CAT shop said everything was pretty close on target except jakes were off a bit and injectors needed adjusting due to a service update. Slowed down to 62 to 65 mph and mpg went up to 6.4, but then slowly dropped off back down to 5.5 to 6. Truck started runing rough when you'd start it after it set for a couple of hours. It felt like maybe a head gasket deteriorating to me, but Peterbilt said they thought all was well. Oil analysis always looked great (until 50k miles ago) when a sample showed a very minute trace of glycol. Next analysis looked great. Next analysis was high sodium and potassium (indicative of possible coolant contamination) but no glycol or water. Next day, head gasket went in a big way and I limped to the nearest auth. CAT service center (Kenworth in Jackson, MS) who informed me that head gasket was completely gone between cylinder 2 and 3 and head was cracked.

So, here I sit at home, a little lighter in the wallet than I was a couple of weeks ago (about 15k lighter) with little to do but worry about what else might be wrong with the truck.

I admit that my understanding of turbo operation is basic at best. I do most of the simple repair work on my truck (swap parts and services, etc.) but I draw the line at major trouble shooting and extensive repairs, like in-frames, obviously. I hadn't really thought about how waste gate malfunction would affect the turbo, especially since the problem seemed to only occur at higher altitudes. I wil definately be on the phone with KW first thing this morning though.