Hi everyone, Some engine info: Cat 3306PC, Serial#66D200xx, Arrangement#6N3323I. I'm having an issue with this engine misfiring but only at high speed when it has a load on it. I'm unsure of the history on it but I'll try and give as much info as possible. I should add that this engine sat around for several years but was started occasionally. First, it starts within 2 or 3 seconds when cold (without preheat) and smooths out and hits on all six within a few more seconds. Very light blue smoke for a minute or so after cold start. Idles perfect hot or cold and sounds very smooth at all rpms when there is next to no load on it. When it's pulling a load at over 1500 rpm or so it develops a misfire. You can also hear it if you smack the throttle open from idle to full speed in neutral. The intensity of the misfire seems to vary, but it sure sounds like a consistent miss on one cylinder and not a random breakup. It smokes lightly (black) when loaded enough for it to misfire. I would guess it starts to miss at 50 or 60% of full power. I just did a top-end set on it and also had a good look at everything under the cover. No broken valve springs or noticeably weak springs either. Also checked fuel pressure and have about 30 psi at 2000 rpm. Only checked at no load however. Also checked for air bubbles with a clear return line from pump and found none. New fuel filter too. I've never seen low pressure cause just one cylinder to misfire though. My next step is to pull injectors for testing. Does anyone know what the crack pressure is for them in this engine? I'd like to test them myself and save 2 hours driving. Cat tech guy says maybe injector or delivery valve in pump and I am inclined to agree. I'm just wondering if anyone here has run into the same problem? Thanks!
You can't really pop test the PC nozzles. See if you can pin it down to one cylinder by loosening each injection line in turn, then exchange a good cylinder nozzle with a bad cylinder nozzle and see if the missfire follows the nozzle. New nozzles are available aftermarket for very little money.
I'll just toss these out, but you've probably already considered them. Worth a shot. Cam lobe? Lift height? Worn cam lobe? I've also seen lifters wear and faces break off on 3306's. Broken ones are easy to determine. Boost pressure? Leak somewhere? With no load rpm, a boost leak may not appear distinctively. Bad fuel? Seen it do all kinds of nasty things.