6.9 Misfire - Need Help

[FrozenMerc]

I need some help from the brain trust on here.

The short story. Over the last week I replaced the head gaskets and studded the heads on my '85 6.9 IDI in preparation of a future turbo kit and to hopefully address a magically disappearing coolant problem. The motor has 122,000 miles on it, and other than a few dents (digested glow plug tip???) in the top of #3 piston, everything looked really good inside. Nice clean bores, etc.

I got it back together and fired it up. After a few seconds of cranking, it hit on all 8 right away, and I shut it off after only running for a few seconds last night. This morning, I put the hood back on, buttoned everything up and went to back it out of the garage. Again it fired instantly, ran on all 8 and idled smoothly at 800 rpms. I backed it up to a pile of branches that came down in a storm last Friday and loaded those. Figuring a quick trip out to the dump site would be a good way to warm it up and break it in. I left it idle while I loaded the rear. After taking off, it started puffing white and I soon lost a cylinder or two, within the first mile. Limped back to the house to start diagnoses.

Now, it will start right away, but idles roughly, down to maybe 600 rpms, which to me indicates a misfiring cylinder. I can rev it up, but it is definitely rough and there is a large amount of white smoke out the tailpipe.

I cracked each fuel line at the injector, thinking maybe there was air trapped in the system. There seemed to be good fuel at each injector. I have checked each exhaust port with an el-cheapo IR gun, #7 is definitely cooler, but it is also the hardest to get to, so I am not 100% confident in the measurement. The rest are fairly equal within 5 or 10 degrees.

My thoughts are for the following problems:

1. Injector is hung up. Could have gotten contaminated during teardown or reassembly. The injectors are about 4 years and 20,000 miles old.

2. Timing is off - I did pull the injector pump, gear and cover as one unit. The motor was at TDC and I dropped it back down with the "Y" straight down, but I can't verify that it isn't 1 tooth off. Again, the way it initially fired rules this out in my mind, but I am running out of ideas.

Any other thoughts or items I should look at? Any help is greatly appreciated.

Thanks

 

[79jasper]

If it is actually shaking like a miss, you are probably drawing air while running.

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[FrozenMerc]

That is a good thought. I will look for an air leak.

 

[david85]

What's the fuel level in the tank?

 

[Sorro71]

I had something similar happen to me, tons of white smoke that you could smell the unburnt diesel in and running rough, it turned out to be a broken rocker and post on the inlet valve on #8 cylinder. Found it after doing a compression check. All the other cylinders were above 350 psi and I think #8 was less than a hundred.

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[FrozenMerc]

Fuel Level: Back Tank is full, front tank is at 1/2.

Took the injectors into a Diesel Tech shop, and it looks like the injector from #5 is not firing. Going to put a new set of injectors in when they come in later this week, and hopefully that solves the problem. Probably got a bit of dirt or debris in it when I had stuff taken apart to replace the head gaskets. Shame, these injectors are only 4 years old.

Also going to replace the lift pump. Output fitting is tweaked, and possibly cracked and letting air in.

Thanks for the help everyone.

 

[Team Dirt]

Fuel Level: Back Tank is full, front tank is at 1/2.

Took the injectors into a Diesel Tech shop, and it looks like the injector from #5 is not firing. Going to put a new set of injectors in when they come in later this week, and hopefully that solves the problem. Probably got a bit of dirt or debris in it when I had stuff taken apart to replace the head gaskets. Shame, these injectors are only 4 years old.

Also going to replace the lift pump. Output fitting is tweaked, and possibly cracked and letting air in.

Thanks for the help everyone.

Have you installed the new injectors? I’m having a very similar issue with idiling and smoking. Rebuilt injection pump in the spring and truck has been great but now has developed a miss at idle with smoking. Was leaning to injectors for sure.

 

[FrozenMerc]

I did. The new injectors did not solve my problem. Turns out that the pushrod on the #5 exhaust valve was not fully seated when I put the rockers back on, and it popped out from under the rocker. That caused the dead cylinder / misfire. I felt like a complete idiot farting around with everything else when it was something so simple, but I couldn't hear the rattle due to the noise of the injector pump. The good thing is there was no damage, the motor now runs great. I hooked the car hauler to it the next day and made a 900 mile pull with my foot on the floor the whole way and it never so much as skipped a beat and all the coolant was still in it when I arrived. I really hope Wes got my Turbo kit shipped out last week....

 

[The_Josh_Bear]

Fuel Level: Back Tank is full, front tank is at 1/2.

Took the injectors into a Diesel Tech shop, and it looks like the injector from #5 is not firing. Going to put a new set of injectors in when they come in later this week, and hopefully that solves the problem. Probably got a bit of dirt or debris in it when I had stuff taken apart to replace the head gaskets. Shame, these injectors are only 4 years old.

Also going to replace the lift pump. Output fitting is tweaked, and possibly cracked and letting air in.

Thanks for the help everyone.

These injectors are pretty easy to tear down and clean if you want to keep that second set on hand. I can't imagine what would keep #5 from firing but it's worth a look.

Glad you got her figured out!