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+--- Thread: ISX 15 Low Boost (/showthread.php?tid=10617)
ISX 15 Low Boost - Amarchionda - 05-30-2026
Hi everyone
I just bought this truck it’s a cm870 CPl8518
And the trouble I’m having is I only get 22lbs of boost and the Egts will easily get up over 1000f just bobtailing. I also hooked my empty 53’ steep deck trailer to it and it’s the same for boost and Egts. The truck seems like a dog. The other thing is the engine brakes seems to not work correctly. When I have it on the high setting it only bumps the boost up to about 2-5lbs. Where do I start on this? Thank you!!
RE: ISX 15 Low Boost - Rawze - 05-30-2026
== Start by flashing (or re-flashing) the original factory program that belongs in it back in there.
== take it on a test drive, monitor the boost in a hard pull.. then do it again with exhaust disconnected behind turbo. see if it picks up a few psi or not. - it could be a clogged exhaust system/muffler.
== Do a CAC leak test on it and make sure it does not leak more than 10 psi in 60 seconds when pressurizing it to 30 psi and shutting off air supply.
== check to ensure it does not have an after-market branded (garbage) CAC unit on it that is restrictive.
there;s a lot more, like using insite to check engine state, fuel control state, and doing tests on that turbo and its actuator, and about a dozen more possibilities on why an ISX would make lower than normal boost.
RE: ISX 15 Low Boost - Amarchionda - 05-31-2026
Thank you!! Will be working on it today, wish me luck!!
RE: ISX 15 Low Boost - Amarchionda - Today
I hooked it up to insite and did the turbo test and the actuator said it passed but only got to 83%. Should it be at 100%?