Alright guys I am experiencing a miss at all RPMs. It is pretty noticeable near the engine with a knock, but is extremely noticeable at the exhaust. It is easy to feel that the exhaust is "puffing" per say. Now I just replaced the injectors with a new set of 125hp sacs, but the miss was prevalent before the injector swap. The swap did not make a difference. Everything sounds the exact same as before the swap. I have fuel squirting out of each connection at the cross over tubes while running.

MoparMan and I spoke on the phone earlier and have decided to take a systematic approach to resolving this issue.

Ruled out: 1. Injection pump: Always supplied good pressure, less that 10K miles and miss seems to only be in one cylinder. 2. Injectors: Swap made no difference.

Possibilities (Almost endless): Burnt/ broken valve, broken piston or piston rings, clogged cross over tube, valves way out of adjustment

 

I should receive the truck Friday from being painted and I can start diagnostics. 

The plan: 1: Pull valve cover and quickly check valve lash - just make sure somewhat close to spec. 2. Use an infrared heat gun on the exhaust manifold right were it come out of the head to try and narrow down which cylinder is missing. If that does work I will pull the cross over tube and replace it (I already have 1 new one that will ship out Monday). If that does not fix the issue I will do a compression test on that cylinder to determine if it is the bottom end or the head.

If the heat gun does not find a "cold" cylinder I will pull all injection lines and cross over tubes, then clean each tube and try to determine if there is debris in one of them. If I can not find debris in any of them I will replace them with the new one, one at a time. If that proves inconclusive I will perform a compression test on all 6 cylinders. 

If any of the cylinders are low on compression I will pull the head and determine what is wrong internally.

 

Any suggestions on the procedure or something else I can do to diagnose what is wrong with this thing??

Edited October 26, 201410 yr by TFaoro

does this happen from cold or after it gets to temp?

All temperatures. From the moment it starts up to 190

 

Well the UPS couldn't find my address today  So I had to head back up to school before getting the pump on and testing for air getting sucked in before the pump. I'll have my father put the pump on and take it to my painter to get waxed tomorrow. I should get home Saturday to test for air in the lines.

The pump was put back on today, and when my dad attempted to tighten the banjo that goes into the bottom of the fuel filter he said it snapped off with less than finger tight pressure. I don't think this could have caused the issue as there wasn't any fuel leaking out and I did not have hard start issues but maybe???

suction side of filter?? <pray>

*getting ready to spike the ball in the endzone* EDIT: Lucy may steal the football here:

Ok, now I remember he has a fass or airdog.. but still, impulses can go back quite a ways, and a crack anywhere could pull minute air in..

Edited January 7, 201510 yr by rancherman

It is doubtful that anything on the pressure side of the fuel system would allow an air leakage.

 

Ed

Sorry guys I'll be heading home asap to hook up a clear line. My dad said it sounded good but I don't know if he hears that well!

Doubtful.. sure, but at this point, apparently nothing is impossible. The man has tested for just about everything except diabetes..

The ONE other thing I can come up with other than a little air in the fuel, is a slow valve due to a sticky guide/weak spring.

MNtom has the other possible valve related scenario.

Well? Inquiring minds want to know. Did it take the old man to install it right? LOL

 

Ed

Long frustrating weekend, but I got the truck back up here at school. I also grabbed a couple feet of clear line to see if there is any air in the lines.

 

Sorry ED I guess he just didn't have the touch!!

Damn !!!!

 

Ed

I wish you would figure this problem out....... We really want to know what is going on. Did you ever watch the valve train when you were spinning the engine over? I mean watch the amount of movement in the valves?

Even talking to Ed he's starting to think there is something wrong valve train wise but not sure either. But is odd how the compression and other test show its in good shape.

I have not had a chance. 20 degree weather and a cold engine aren't fun to work on. It should be around 40 tomorrow, so I'll test for air in the lines then and turn the engine over while watching the valve train. Thanks for the ideas guys!

I am really thinking there is a cam lobe that is going flat. That is why I suggest checking movement of the rockers. I know of an older Cummins (14L) that exibited similar symptoms and it was the cam.

If that is the case... WHY would that happen? I guess I could send in an oil sample to see if there is any extra metal in the oil.

I'm kind of starting to wonder about maybe a weak spring? Or like MNTom said a flat spot in the cam.

I'll send out my dial indicator if you need. That way, you can check at the pushrod end for any differences.

 

Ed

I'll send out my dial indicator if you need. That way, you can check at the pushrod end for any differences.

 

Ed

That will tell you exactly what the lobes are like.

Too cold to test today... 25deg with snow coming down.... Maybe tomorrow!

Too cold to test today... 25deg with snow coming down.... Maybe tomorrow!

I wish it was only 25* today. It was -18* when I got out of bed this morning.

Tested for air in the lines today. I put about 2 ft of clear line between the IP and the fuel filter. Zero air while running. I even took it around the block and came back. There aren't any bubbles.

Interesting though... this miss seemed to have decreased a bit lately, but I was pulling a trailer up a hill in 5th at 50 mph and let the exhaust temps sit right at 1200 for 20 seconds or so, and now it seems to have gone back to a little bit worse. I really think I need to listen to another good running 24V to make sure I'm not just paranoid....