This truck develops a miss, mild to severe after it is warmed up; driven 25 to 30 miles.Really noticable at 55 to 60 mph.
Spark plugs and fuel filter, and air filter, and pcv valve.
Has the injector pump quit yet?
The 5.9 is a diesel, no plugs in it.
A diesel won’t miss long before it lets you know why. Basically, you need 3 things to run, compression, fuel, and air. The chances are it’s not an air problem if it’s only 1 cylinder, so that leaves compression and fuel.
Fuel could be several things. Your injector pump could be down on one cylinder. You could have a bad injector. You could also have another problem in that cylinder that affects compression. It could be a busted piston, broke valve, cracked head, broken glow plug that’s causing a compression leak. (some Cummins do not have glow plugs, some have manifold heaters.)
That’s hard to diagnose with not much information on it.
5.9 is not a diesel,its a 360.
The Cummins is a 5.9 as well, suppose it could be either.