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Mike, Technician
Category: Car
Satisfied Customers: 39198
Experience:  Tech Expert
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Cummings QSC 8.3 running lumpy on tick over, and up to 1500rpm

Customer Question

cummings QSC 8.3 running lumpy on tick over, and up to 1500rpm then starts to smooth out and runs fine from 2000 rpm
Submitted: 2 years ago.
Category: Car
Expert:  Mike replied 2 years ago.
Hello and Welcome...
My name is ***** ***** Im happy to help.
When you say you have "checked " the fuel lines / filter etc- if you haven't renewed the filter, that would be a good move - to be sure. A restricted filter will cause this - and clear as the revs are raised as it purges bear that in mind.
As there is nothing showing on the computer test, then these symptoms do take you back to fuel supply issues.... So in which case - again you say you checked the lines but do bear in mind that a diesel system can suck air - but not always have a diesel -hard to find. But if its sucking even slight air, you will get these symptoms.. so what you need to do is connect the likes of a Mityvac or similar - vacuum pump to the lines to pressurise , to check for any such leaks - the smallest of leaks will cause this.
Other than that - then the fault would be either, the fuel filter body - where the filter screws on ...( these go inside on the vacuum side - you need to then replace the unit )..or, a faulty pump - which for that, you would need a diesel specialist to test -as they have the needed equipment for that.
So working through as above should see this cured for you. Im sorry its not a " it will be this / that " answer - it just isn't in this case Im afraid.
There is a small possibility its an injector problem -but working through as above will find it for sure...whichever it turns out to be.
Let me know how you go..and / or let me know if you need anything further on this..
~~~~ Meantime - Please do click on the "Exc / Ok rating" for me at this time.. "Thank you" in advance for that .
.. Note that you can get back to me anytime at all after doing the rating - it doesn't close you out.
-- Best Rgds, MIKE.