C15 ACERT MXS Cat boost pressure, no load.

I would start with an accurate gauge. I have the same engine (serial #, too) and my gauge it has different behaviors. I think that gauge has multiple personality.

 

First everybody needs to know what year and make truck this is in. If it is a newer Pete or KW with the electronic gauges then the boost reading is coming from the ECM. Then you will need a laptop with CAT ET to see if the ECM is showing the same thing as the boost gauge. If the ECM and dash boost gauge are accurate with each other then you have to figure out why the boost is fluctuating in the engine.

 

thank you so much, Mr. Haney. Actually, I'm looking to improve my truck, a 2007 Columbia with C15 MXS. I bought the truck in September 2012 and it was 18 speed, 3:42 rear end, some Bandag 11R22.5 tires and the fuel mileage was scary, 4.5-4.8 loaded at 75000 gross. In the meaning time truck went to a Freightliner dealer in Calgary, they fixed some turbo leaks and some other things, the engine was sodomized with 2 "head cylinder adjustment". One at a Cat dealer and the other one at the Freightliner dealer. Until now, I just cannot decide witch one was the worst. I can hear the valves running in complete chaos. Also, the truck was on a dyno and after that rated at 550 hp, 1850 torque, linear. I've seen a slight improvement on fuel mileage but nothing to make me happy. so, I decided, despite the CAT discourse to change the rear end to 3:75 and also, the truck got new tires all around Michellin Multi energy but low pro. Now I'm running 65 mph, about 1500 rpm and my fuel mileage looks better. I'm not racing the truck and I'm not lugging the engine. I split down about 1350-1400 rpm.
I've told you all these to give a correct image about my truck. The problem is : if I let the engine to feed itself (just touching the pedal) it is OK, the sound it's ok and the boost gauge is acting normal somehow. But if I'm trying to accelerate a little bit faster, that boost gauge it's impossible to read, the needle it's ... actually shacking very bad.
Please, when you got time for me, can you guide me a little bit? I grew up with European engines, but I love so much the CAT engines and I want to learn. I'm that kind of driver who prefers to spend night over the books/internet to learn then to hang out. So, please spend some minutes of your time for me cause talking with different CAT owners and mechanics (controversial advises) made me to wonder if there is somebody who really knows this engine. It seems you do. I know I can make this truck a 8 mpg truck. I had a Volvo engine before and 8.5 mpg average wasn't a surprise with that truck. Now, I think you know where I'm coming from and how bad I'm feeling when I see this poor fuel mileage I got now.
Thanks in advance

 

try torrents or Cat dealer

 

If the guys that adjusted the valves didn't get it right this could cause problems.

The rear gear ratio change was in the wrong direction. I would have went to 3.36 with 22.5 low pro tires to cruise at 1400 engine RPM at 65 mph. This isn't lugging an Acert engine and is actually in the sweet spot for fuel mileage in a standard Over the Road application up to 80,000lb gross weights.

When the boost gauge is shaking bad, are the turbos making any funny noises?

 

It could be as simple (but expensive) as a leaking exhaust manifold. It will cause the boost gauge to flutter and it can make a tapping sound under load and jaking. It will also kill your mileage.