No boost or very low

[6speed]

Was traveling out west from GA with 3 cars. Wt was about 28K. As I was climbing a grade of about 5-6% and in 115 - 118 degrees and at about 7000 FT, i started losing boost At that configuration i would be pulling that type of grade in 4th gear (MT). I have gauges that tell me more than I probably need know but I have them. I ended up in 2nd and the thoughts of bad fuel, collapsed air filter or even a boot blown off went thru my mind. When i got to the top I pulled over to investigate. As I was sitting there looking and thinking what could be the problem i could here the turbo spinning pretty good. Didn't find a thing. I began my trip down the incline and everything seem normal. I have never experienced that situation before. i wonder if the altitude and heat had that effect I figure with those temps and altitude, I must have been about 14000 ft of corrected altitude. I know the turbo can make up for some of the air that high up. On return trip back to GA I had no problems what so ever and made all the boost I needed. Any thoughts? I may not respond right away as I traveling out of the US for few days. Curious as to what some may say. Have a good day

 

[Ozymandias]

9800ft above sea level the Turbo reaches its design limits for full boost, and only under high rpms.
Your rpm range for full boost goes up above 6000ft, steadily climbing up the rpms.
Means you have to downshift to keep the rpms up just for the reason to keep the Turbo happy.
So, what happened to you seems likely normal to me.

 

[6speed]

Well Ozy it still has the stock turbo. I have been looking at a FLeece Cheetah and maybe towing twins. That is all this truck does is tow. I don't feel so bad now that maybe with the right conditions it reached its max

 

[petersonj]

Wt was about 28K. As I was climbing a grade of about 5-6% and in 115 - 118 degrees and at about 7000 FT, i started losing boost At that configuration i would be pulling that type of grade in 4th gear (MT). I have gauges that tell me more than I probably need know but I have them. I ended up in 2nd

Since this post is titled "No boost or very low", and you didn't provide any boost numbers, it his hard to tell whether or not you were having an issue. The "No boost" is particularly interesting.

I would think that you would have easily attained 25 psi or higher boost at 1800 rpms (or higher) under the conditions you listed, even without the tuner.

There will definitely be a loss of power as the truck goes up in elevation, especially with very high ambient air temperature, but the turbo just spins faster and compensates by gathering more air. So, loss of boost pressure wouldn't be significant, but, for example, loss of power would be noticeable because there is less oxygen available per cubic foot of 20 psi boosted ambient 115° F air at 7,000 feet as compared to say 20 psi boosted ambient 115° F air at sea level.

Do you recall what the boost readings were at a specific engine rpm when you were seeing no or low boost conditions?

I haven't experienced towing at 7,000 feet at 115° F, but I have towed over a few 11,000 ft mountain passes in Colorado at around 65° F, and had no trouble pulling 25 to 30 psi boost at 1700 rpm or more.

- John

 

[6speed]

Yeah it was about 6-8 lbs. Rail pressure was 16-17K exh about 1050 and about 1800 rpms

 

[petersonj]

Yeah it was about 6-8 lbs. Rail pressure was 16-17K exh about 1050 and about 1800 rpms

In my opinion, that boost is very low for maximum boost under those conditions. If the engine was pulling hard, the boost should have been more like 25-30 psi and EGT's around 1,400° F.

I think your engine may have gone into a de-rate mode for some reason.

- John

 

[Ozymandias]

He said he started to feel a loss at 7000ft and was at 14000ft finally.
Sure he won't make boost at that altitude and only between 1050-1800rpm, this is way below the power band at that altitude.
Wenn I went over Independence Pass I had to floor mine too and it took forever to build at least some boost.

 

[petersonj]

He said he started to feel a loss at 7000ft and was at 14000ft finally.

I have never experienced that situation before. i wonder if the altitude and heat had that effect I figure with those temps and altitude, I must have been about 14000 ft of corrected altitude.

I believe that he was comparing the 115° F heat at 7,000 feet to 14,000 feet of "corrected" altitude - he did not say he was at 14,000 actual altitude.

He also said that the exhaust temperature was at 1050° and engine rpms were 1800, not engine rpms 1050-1800.

- John

 

[6speed]

Well everybody that commented on my situation pretty much tells me it was an isolated incident. After that I never another problem during the trip. FYI its all stock except for a smarty on like 2 & 3 and injectors were replaced at 300K with S&S's latest version for my setup.

 

[AH64ID]

DA for 115°F at 7000 PA is 12,500’ and that’s up there.

Yeah it was about 6-8 lbs. Rail pressure was 16-17K exh about 1050 and about 1800 rpms

This sounds like a derate or fueling issue, since it was a one off I’d guess a derate but if it happens again I’d be looking for a fuel issue.