Spring

I know this old, but i finally found the issue. The rod that operates the EGR valve was completely broken. It was still actuating like it was supposed to, so it never threw a code. This was not allowing the exhaust to escape properly and was building manifold pressure.

Just looking for some insight on the best transmission fluid. Price doesn't really matter, I want something good. I run my truck in the oil field, lots of dirt roads and low gears. I do not haul anything overweight. Truck is a 2008 with a maxi torque 18 speed. Also curious if adding Lucas or an other stabilizer is worth it. Thanks

Mack Tech you sound pretty sure there, I am a truck driver that tries to fix his own truck when possible. I do not know what a VGT nozzle ring is... Is that a serviceable or replaceable part? Also where might I find it? Mazidyne I appreciate you input also. Fortunately my egr cooler is relatively new.

Rob Everything is electrical but the problem is not a bad gauge. I know this because I can feel the back pressure on the engine when it shows high pressure when not on the throttle. You mention problems that come with a clogged exhaust and I have none of those. If that were the case the regen system would d-rate the truck and it probably won't even move. Mr Grumby The test you ask about was not performed but it sounds like a simple test. If the turbo veins were sticking wouldn't that cause problem during all engine operation? If works fine while pulling and jaking

In gear Quickfarms

So I will try to explain this the best that I can and hope that it makes sense. I have talked to the local mack dealer, and pretty much everyone that I know and I haven't found an answer yet. First off my 2008 MP8 will build and hold 42 psi of boost on a good long pull. It sits at idle with around 3 psi. Sometimes in between gears or if i gave to stop really fast (like throw it in neutral and slam the brakes) my truck will be at idle with 12- 13 psi of boost. the real weird one is this, lets say I'm driving the truck down the interstate at 65 mph. the road is either flat or has a very slight downhill grade with the engine brake turned off, cruise control turned off, not on the gas brake or clutch, just free coasting down the road, the truck build 12 psi boost and start to slow the engine down. The effect is not as strong as the engine brake on the low setting but it makes a similar although quieter sound and does very slightly try to hold back the motor. The actual speed doesn't matter, the grade doesn't matter, and the gear doesn't matter. I did replace to boost pressure sensor. This problem has existed for a while but now and then more recently during a driving regen the turbo will spool up so hard the the boost gauge goes to max and something rather load pops under the hood. any thoughts or idea would be great. I really don't want to start out by replacing the turbo, but I will if it comes to that. -Thanks Spring