Help don't know which way to go to fix truck!

[joesherrie12]

I've been out of commission for the past 8 months with two broken legs and a bruised spine. (Motorcycle accident ) and my son in law put his job on hold and took over my truck while I was out. Well now I'm back in the seat again and found a few problems that he didn't tell me about! This is a 871 isx with 860k . to start with I had a real rough cold idle and a knocking sound once the truck warmed up both would go away so I pulled the metering and timing accuators off and checked them front metering was 3 thou. Front timing was 5 thou. Rear metering was 7 thou. And rear timing was 6 thou.so I replaced all of them! It fixed my idle problem but the knocking sound is still there. But I noticed last night when I started the truck as soon as the relief valve on the drier went off the knocking went away! Is this the compressor? I have an air leak that I can't find the sleeper bags would be down when I start the truck could it be leaking back through the compressor? One last thing I was averaging 7.2-7.3 mpg now I get 6.3 - 6.4 seems to run rough after I shut the truck down and unload and get going again. Everything is new on the egr side was done 100k ago except Doser injector. It is time for and overhead set could this be my problem?

[Waterloo]

Well, sounds like your compressor knocking. I had same issue on my 871. Cummins has a head kit, no need to replace entire compressor. Install that and clean the soot out of the lines. The fuel mileage is more than likely winter blend fuel, my mpg is running the same as yours, I normally lose 1 to 1.5 mpg in the winter, this year is no different.

If you have not done the EGR tuneup and still have the mandate, do that ASAP. Also, in regards to knocking, have you replaced your crank shaft damper? Cummins recommends replacing every 500,000 miles. I would do that, when they fail it can get very ugly and expensive. If you replace, paint it, or no warranty.

Also, have you done a recent overhead? I would do that too if it has been awhile. I would also drop the oil pan and inspect the lower end. It is time to do that too. 860,000 miles is getting close to in frame time... I would also check the coolant system for any excess pressure build up. I would recommend going to NAPA and picking up a block test kit. https://www.napaonline.com/p/BK_7001006

Good luck, been there and done that.

[Magard]

That compressor knock grows on you. It's a old school cummins thing. It's how you set your brain in time. In the morning when your warming up and checking your rig for the day. A few more miles and mine will probably start it. I keep listening but not quite there yet. Hey! In time.

[Johnboy]

Replace the dryer filter. If you have the spin on
They normally quite down for me.