DaveS

Greatwork!, I don't think I have. That might be worth a try. And moparman, the engine is freshly rebuilt with new pistons and rings. It's just now broken in well and it doesn't use oil or have any blowby. I used total seal rings. So I think I can safely rule out any compression problems

I can hear it at light throttle and low rpm when driving, but I can't tell it under a good load. Has plenty of power Could I hire you to take a look at it if I made the trip over there?

As far as the pump, the problem was there with old pump too. I replaced it thinking it might fix it but it didn't. And yes, I snug the tubes first when I change injectors

They were popped to 310 originally when DAP built them. When I had them sent in again this last time to be checked, they didn't specify pop pressure. I'm assuming they put them back to what I had originally ordered. I've wondered, is it possible that the injectors are behaving differently at test stand temperatures than when they're several hundred degrees hotter? The thing is that the misfire has showed up right away, every time I changed injectors

Hi folks, Well I'm back again with the same problem. In the time since I lasted posted on this topic, I pulled the engine and completely rebuilt it myself. It was in very good shape for the miles but I decided to do everything right. It's bored 20 over with modified Speed of Air pistons. New head with new valves and springs. New everything. 178/208 cam. Fenley 62/67/9 turbo. It was a long expensive project but I decided to do it for 2 reasons. 1, find the misfire and 2, try the new pistons from SOA. When I put everything back together, I cleaned up all the wiring, cleaned grounds, and took my time to make sure everything is put together right. Unfortunately after all that, the misfire is still there. I even sent in the injectors to have them checked. 2 ended up being bad after just 7k miles. DAP replaced those 2 and reset the others. The truck starts instantly but as soon as it starts warming up, it runs terrible just like it did before. Rough running and hunts for idle a couple seconds when I let off the throttle suddenly. It hazes some at all rpms. I'm about at my wits end. Almost everything mechanical has been replaced at least once. The ecm I had swapped with my brother's truck. No change It's hard to believe that the problem is electrical because it only shows up when the truck is warm. In my thinking, hunting for idle comes from peeing injectors, as does the hazing. The random misfire also wud seem to point to injectors. But why would it not show up in testing? And why would multiple sets from different manufacturers do the same thing? The only set that had served me well was made by Weston Shupe. They lasted for 30k before a tip cracked. Sad day for me. Every set since then as been absolute crap and doesn't last long at all. Thanks for any input

The top of the head is dry, no visible leaks. The injector lines are old enough that I do have to make them pretty tight to prevent leaking.

I can try that. Although I did put in new Cummins connector tubes last time I put in injectors. So it doesn't seem to follow either injectors or tubes.

Injectors could definitely be a possibility. It's hard to believe that is tho because it didn't change when I put them in brand new from DAP. Anyway here's the latest update. I changed my timbo apps with a new one and the flat spot and stumbling went away. Since I adjusted the valve lash and changed the apps the truck definitely improved overall. So those 2 things were actually separate problems. But guess what, that persistent misfire still shows up when hot. 😒 So Idk if it's an injector or a cracked piston. I do think the injectors need to be reset because they haze too much. But I don't think they're causing the misfire because it was there when they were new. And through several sets before that too. I'm beginning to think I'm just gonna have to pull the engine to see what's going on.

I'll do that wiring mod once and see what happens. If nothing else it's an upgrade.

Gotcha. So sounds like the most likely culprits are either a cracked piston, bad injectors, or something with the ecm

Great ideas all. I have cleaned all the grounds, checked the cylinder temps with a non contact thermometer, and returned the truck to stock tuning. Battery terminals were replaced with the batteries abt 4 yrs ago. They are clean and in great shape. Truck starts instantly. The only thing I didn't do yet was swap the fuel relay and the IAT sensor. So I can do that. And I could also send off the ecm to have it checked. One thing I did notice lately is that the injectors are starting to haze more, even when hot. Especially since I don't pull anything heavy very often anymore. Mostly just driving around so it's pretty light load. I hope they're not going out again

I hear you, jlwelding, that sounds exactly what I've been doing, throwing money at it and replacing parts. And I wouldn't want to call Mike all the time either lol. It's got 422k on the rotating assembly and it was in great shape when I pulled the head about 2 years ago. Not even a top ring groove and the cross hatching was still all there. But I like upgrading things so I'm seriously thinking of pulling the motor and putting in new pistons, rings, and bearings. I've got some new technology I want to try on that. And reseal everything too. I just hope I find the problem if I go to all that work. For me, I've been trying to track it down for close to a year now. It wasn't bad at first and I just lived with it but it's been gradually getting worse. Which to me does point to a mechanical problem

Yeah I thot of that too. I did a compression test cold and they all checked out 450 psi+. And they were all within 10 psi of each other. But it could be possible that it wouldn't show up so much cold like you said. It has very little blowby at any time.

So it seems like I may have multiple problems going on. The po122, the flat spot and hesitation is most likely the apps sensor. It does run better since I reset the valve lash but it's still not completely smooth. It's just hard to believe it's injectors after replacing them so many times. It misfired immediately after installing them. And it was there with my old pump and also the new one. Hard to believe both pumps would have the same problem

I'll get another timbo and try that