Help! Cat C12 misfires

[CRHardie]

I hope there is someone in Diesel land that can help We have a 2000 KW with a C12 that miss fires on #1 and #3 under load It idles fine and no load rev up is smooth We replaced 1and 3 injectors after doing a cylinder cut out test with Pro Link Still runs the same The first three shifts are smooth then after 1500 rpm it starts to break up The heavier the load the lower rpm breakup occurs Push inthe clutch and it smooths out We replaced the under valve cover wire harness as advised by local Cat dealer and it still runs the same Also fuel pump and lines to tank and filter heads are new Any ideas would be great Thanks in advance Craig

 

[CPjMech]

#1 Check full load fuel psi after the fuel filter (there is a port on the filter base), should be over 60psi.



#2 Check the injector cam followers. C-12's are pretty common for eui lifter failures. I have seen them act fine on light load and then miss under harder load. Pretty easy to t/s, just remove the inj push tube and w/ a magnet lift up on the lifter and see if the roller pin/roller has a bunch of play. If so, you'll have to pull the head to get to the lifters, then hope the cam is good. Another indicator is to do a quick adj to the inj rockers in question and see if the screws are all close to the same, just like checking for a flat cam on valves.



#3 If you have a new enough C-12 be sure to enter the new trim codes(4 digit # on the inj) into the ECM. Not sure if a Pro-Link can do this, just jot down the # and stop by a dealer. They should do it for free, take 30 sec to change.



Check this 1st and we'll go from there. Good luck.

 

[CRHardie]

Today I threw in the towel Fuel pres was 95 to 105 psi from idle up to wot even under load All injector adjustment screws seem even The guy who runs the shop (he's 75 and a old Cummins mechanic not really up with the electronics)decided we needed to take the ECM to Cat and have them check it They found nothing and did a update to it I installed it on the truck and entered the new injector codes This can be done with Pro Link if you have the Cat cartridge Took the truck for a drive and it was a little better but not fixed If you ease into the throttle it would hit on all six up to 1800 then break up If you mashed it it would start at 1300 This truck has been down for 6 days and normally runs 22hrs a day with 2 drivers Its a 6500gal milk truck We do not have a truck large enough to replace it Needless to say my boss is a little upset So we took it in to our local Cat dealer I`m not proud of it but we did what we had to do I`ll let you know what they find Thanks again Craig H

 

[JFaulkner]

You may not like to pay someone else to fix it however the truck is probably costing you more sitting, and doing R&D yourself is usually expensive. (with non-returnable electronic parts)

 

[CRHardie]

Well I figured it was something stupid There are two places on the filter head to check fuel presure One has a male quick couple on it which is where we tested The other is a plug that after wipeing off grease and grime says PRES on it Thats where the Cat dealer tested At idle they had 40psi and under load it dropped to zero They replaced the hand prime pump and all was good Why it was #1& #3 that skipped they could not tell me CraigH

 

[CPjMech]

I can't say why only 1&3 either. I would guess one of the check valves on the hand pump must have flipped over, used to be fairly common but haven't seen it in a long time. Glad you got her back on the road.

 

[Forrest Nearing]

yeah, there comes a point where you gotta do whatever it takes!



you won't have the same problem again though