CM870 Boost

[tsolson]

Hi Guys,

I'm the guy having trouble with the boost on my 2005 Kenworth, Chamberpains made reference too the other day. I thought I'd post what trouble I'm having and the things I've tried to remedy it. This might be a long post!!!

So i bought this truck used, from Prince George, BC. It was in pretty nice shape, eng had been inframed approx 200,000km and never really used, diffs had been done, brakes, batteries, trans. The owner also informed me that the egr had been deleted, but he had never used the truck much after that.

I drove it home 2000km and everything seemed to work fine. Boost pressure would run around 22-24 psi, and egt around 400F. It has factory boost guage, and pyro, and i haven't verified that they are totally accurate with separate guages.

I had gravel hauling job in September (last fall) and i started to see i was loosing boost and egt we're getting high, (900F) took it into the shop and found the turbo housing had started to crack almost all the way around on the aluminum. Purchased brand new turbo and installed and everything worked good again.

I was hauling a smaller dozer from saskatchewan in October when the problem i'm having now started. I was driving along with the cruise on, 95 kph, and i noticed a change in engine pitch. I checked the guages and notices my boost pressure had dropped off from around 25psi to about 15psi. The egt climbed to 800F and seemed to stay there. I drove along for about 1-2 mins and then the boost kicked back in and temps came back down. This problem continued for the rest of the trip. Boost just dropping off, then coming back.

if i shut off the truck while driving, and restarted it, then the boost would be normal. It would run fine for a few mins then drop off again.

I got Cummins Insite so i could attempt to see what was wrong. the first time i hooked up there was 195 counts of VGT actuator driver Circuit code. I check the troubleshooting, said to clean the ground post on the side of the eng. I did that and that seemed to take care to the code for the most part, but i was still having boost issues. I changed the Exhaust Manifold pressure sensor, and the intake manifold pressure sensor. That seemed to help, but problem always comes back. Last week i changed the turbo air control module,($1100) thinking that it must be going bad. I left on a trip north and it ran perfectly. Boost would max out at about 38psi, egt normal. 2 hours into the trip, i had the cruise on and same thing. engine pitch changed and the boost was low and egt climbing. the rest of the trip it would just come and go. If i pressed the accel to climb a hill, the boost would kick in, and away we'd go, as soon as i let off, it would be gone.

I check the codes again after getting home, and there was nothing. i ran turbo test yesterday on insite, said everything passed. today i see the VGT actuator driver circuit code is back again, one count. I've done turbo actuator test, passed. tried moving actuator with a wrench, it moves freely. It seems like an electronic issue to me.

i've kinda run out of ideas here. i don't like to run the truck when its not working properly, and i have no idea if this problem is related to the delete or not. After reading up on the horror stories here, I feel like parking the thing till its resolved. I have three other trucks with N14's but this is a different animal for me!!!!! Chamberpains has given me lots of pointers, but we're both scratching our heads now. If anyone has a clue let me know, and again i apologize for the life story!!!!!!