Turbo ?

1. A new turbo won't cause any problems no matter the miles on the motor.
2. Low boost will cause a huge drop in mpg and many times higher egt. I don't know how the ISX motor are programed, but many CATs will derate over a certain boost. But this boost is usually 5psi or more than what you would see with a stock motor.

My best guess is that you got a boost leak somewhere and that the turbo is fine. Unless the wastegate is opening to soon. Check your CAC very carefully...to many guys replace a turbo when the CAC is really the culprit. Also I would have one of the mods move this post to the Garage where you will get more responses (or you could just start one there). When ya find the problem please post it.

 

When you have them do the leak down test on the CAC, make sure you are clear with them that you want the actual number. When they do those tests they normally only give you a "pass or fail" based on the warrantee specs provided by the manufacturer. The Cummins specs for a CAC is the worst of all engine makers. It is 7 psi as opposed to all the others are 5 psi(which is bad enough). I personally would change any CAC that leaks 3 psi or more. That's why you need to know the number.

 

How much time do they give it to leak down? Is it, for example, 10 minutes or 2 minutes before they recheck the pressure?

 

I think dura lite lists leakdown specs at 5 psi in 20 seconds or so at test spec of 30 psi. Dont know how that compares to OEM specs

 

Do truck motors have a blow off valve i ask is because i have a boosted car and one day it was only running 17 pounds instead of 25 and i found out that the blow off valve was the problem. Maybe check that out.

 

No blow off valve on big diesel's,Western Star say 5psi in 20 seconds with 30psi at the start as well.
I dont think thats to bad as I run mine at about 40 psi,full throttle runs at 50psi but wouldnt hold it there for 20 seconds.

 

Cummins spec is pressurize to 30 psi and it cannot fall more than 5 psi in 15 seconds.........this spec is good for any engine.

 

According to the service manager at Cummins in Memphis,Tn, the warrantee spec is 7 psi in 15 seconds. I know that all other manufacturers are 5 psi in 15 seconds and found it wierd that cummins was 7. Maybe that service manager was full of it. It is really a moot point though as I would change any CAC that leaked more than 3 psi in 15 seconds, like I previously stated.