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marek4792 · 02-06-2026, **(Subject: Pressurized engine )**

(02-06-2026 )Scoot5869 Wrote: Any idea what I need do a plug size wise? Save from me stopping at 20 places lol

Your local stealership/ cummins shop should have it. If the plugs are the same size across the engine platforms Part # 3678845 and oring #3678846 should work, but incase take the original piece with you.

Scoot5869 · 02-06-2026, **(Subject: Pressurized engine )**

Ok i rigged up a plug a pressurized the system again. I am still getting air coming out of the hole in the crankcase filter.
Is this a sign the head is going bad? It doesn’t use any coolant engine was rebuilt 200k ago all Cummins part nothing aftermarket.
The egr system has been removed and correctly blocked off and I installed a hose in place of the cooler

marek4792 · 02-06-2026, **(Subject: Pressurized engine )**

Not necessarily. The crankcase isn't 100% air tight. To rule out the head you'd have to remove the rocker shafts so all the valves are closed and test. But even then 20 psi boost you'd should hear it pissing air/exhaust somewhere.. Kinda starting to think you may have a sensor in range failure causing low boost and not necessarily a mechanical issue...

Scoot5869 · 02-06-2026, **(Subject: Pressurized engine )**

Ok. What sensor should I be looking at I think I’ve replaced them all in the last two years.
Idk how to view/monitor things on Ct if any of that would help in see what’s going on

marek4792 · 02-06-2026, **(Subject: Pressurized engine )**

Only insite. Look in live data and the engine state monitor. If it's derating it should tell you why. 2 years is kinda awhile for your EGR tuneup sensors and should be replaced yearly and passage cleaned out. Fuel pressure sensor too if it hasn't yet..

Scoot5869 · 02-06-2026, **(Subject: Pressurized engine )**

I didn’t see anything the other day when I ran a load and had it hooked up. Fuel
Sensor were replaced 2 years ago when i did ifsm just checked the exhaust pressure tube when I had manifold off an cleaned that sensor imap was done two years ago I don’t run a lot of miles in a year local work maybe 20-30k. Cam and crank sensors were just replaced. lol I said all the egr stuff is gone and the truck has no exhaust.
The turbo actuator came with the reman turbo from hd turbo so it’s just over a year old