CM870 misfire under load

[Blackout26]

Hello all. Been a guest for a bit now. Recently purchased a 2005 Kenworth with a CM870, 565HP & 1850TQ. Previous owner demandated it by unplugging the egr. Said he didnt get it tuned and there is a block plate on it. Truck has always loped at idle, performance wise ran great. Yesterday morning I felt a drop in performance and a dead misfire under load. This happend loaded just before Wolf Creek Pass. I stopped and changed fuel filters no change. I continued on, about half way up when everything got some heat it, it stopped. Pulled full boost 32 psi 900 on the pyro. Come down the 25mph side on the jake and hit the flats and it came back. No black smoke during misfire, no white smoke. Boost wise seems to only lose 2-3 pounds during misfire, however there a significant power loss. So, here is a list of things I've done before posting.
Fuel filters = No change
Pressured up fuel tank and checked for external leaks = No leaks
Electric lift pump, key on runs for 2 minutes then shuts off. = good
Pulled valve cover and checked valve train and lash and injector injector adjustments = good
Drove to the local dealership and they gave me a fault print out for free.
Active faults
PID-94 FMI-1 Flash code 2215 or 482
Fuel pressure low -Data valid but below normal operational range - moderately serene level Or Fuel pump delivery pressure - Data Valid but below normal operating range - Moderately Servere.
Fuel level in tanks makes no difference. I think that rules out pickup tube ?

I don't have the compucheck fittings to do fuel pressure checks or access to Insite without paying for it. I can purchase the tools. If I gotta take it to a shop I will, however I would really like to fix this myself.

I appreciate everyone's time.

[Blackout26]

So, small update. I found a small leak at the fuel shut off solenoid, I disassembled and put new Orings and reinstalled at 49 inch per cummins. Truck ran amazing. Stopped a buddy's house and let her idle for about 15 minutes. Jumped back in and the dead miss is back. Returned home, no leak at the solenoid. Unless I pinched a oring and it is not leaking yet. I checked to see if it had a pre-filter. It does not. I have compucheck fittings on order to dig deeper.

[Blackout26]

So, the orings were not pinched. However I did note that during the electric lift pump run time. It was returning fuel to the tank. Is that normal ?

[Rawze]

could be worn out actuators...
info: https://rawze.com/forums/showthread.php?...619#pid619

could be leaky injector(s)...
info: https://rawze.com/forums/showthread.php?...8#pid67948

- And if you remove the guts from the shut-off solenoid, does it run better?. They are notorious for going bad and causing fuel pressure issues. - Th engine does not need that solenoid to shut off properly ... it only serves as a secondary safety valve if one of the actuators is failing.

FYI: If removing the guts of the fuel shutoff solenoid causes the engine to stumble and stutter or not shut off right away when you shut the key-switch off, this is a direct sign of leaking/problematic actuators.


If you drain a bit of fuel from the bottom of the the davco filter into your hand or a freezer baggie..is there any coolant in it?.

And yes,... it is normal for the return fuel to go back to tanks. Those engines returned all return/excess fuel back to tanks (a superior design feature), unlike the newer common rail engines that do not.

Also, if the egr system is disabled,,.. is there a check engine light and fault(s) active for it?. - if not then it had a de-mandate file in it, and its likely a crap one.

And BTW: the boost on an CM870 should hold at about 37~ish psi under full operating load, not 32. ... so its in a silent boost derate for the EGR being unplugged... and if there are no active codes for this.. then its a bad delete for sure, as this is a common sign of crappy programming where things were not dealt with properly.

last but not least, the engine brake solenoids can cause mis-fire symptoms too if they are leaky and/or sticking, etc.

[Blackout26]

It does have the faults for the egr valve being unplugged. I replaced the fuel shut off solenoid, however I did not change the guts out or remove the guts upon reinstall. I inspected the guts and couldn't find any issue that stood out. I do not have a Davco unit. However I have not had to add any coolant since purchasing the truck. I will eyeball the bottom of the tanks in the morning prior to starting and see if i can see coolant puddles in the botttom. I will remove the guts tomorrow and see if the engine acts as you describe. I also purchased the metal gaskets as I am feeling confident enough to take them apart and reassemble them. I also have the compucheck and plate tool to test the injectors hopefully arriving tomorrow. Another note, if i start the engine it will idle smooth till the electric lift pump shuts off, then the stumbling begins again.

Thank you

[Rawze]

(Yesterday )Blackout26 Wrote:  ... Another note, if i start the engine it will idle smooth till the electric lift pump shuts off, then the stumbling begins again.

Thank you

sounds like the gear pump going bad, worn out?.

[Blackout26]

The gear pump is still cummins red. Gauges never showed up. So, i did what I did not want to do and through a part on with out verification. Purchased a new gear pump. Installed gear pump. Truck fired up and idled smooth, still has a touch of lope when cold. No lope when warmed up. I latched on to my big trailer and headed up the hill out of town. Truck pulled great. Slightly less egt's and consistent boost pressure. I can still feel just what i think is a slight miss, however could be my imagination. I still plan on replacing the metering and timing actuators. When the tools come in I will check the pressure and injectors. Thank you for your help and dedication to helping people like me out.

[Blackout26]

Welp, celebrated early. Took her on a job this morning. Gross was around 110k, nothing crazy. Idle still smooth. However, the miss is back. My fuel pressure gauge showed up but not the injector test plate. Watching Rawzes' video and the bubble showing up indicating a bad injector. Could it be possible I have multiple bad injectors pumping air back into the metering rail and causing enough aeration to cause the miss ?? I've never dealt with this engines, I'm sure that is obvious, lol.