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

If you want to know for sure go ahead and swap it with another cylinder then check temps. If it follows the swap you know for certain. If not it could be anything from a cracked piston ring to your VP.

Like Mike said, I would probably be having them injectors pop and flow tested if possible. At the very least its pretty cheap and it will rule out the injectors for sure.

True, but like stated when I first dropped these injectors in the miss was the EXACT same as it was with the old injectors. A new crossover tube helped lessen the miss, then I put these drilled out ones in and the miss did not change. This leads me to believe it is a fuel delivery issue, but I could be way off. 

 

If you want to know for sure go ahead and swap it with another cylinder then check temps. If it follows the swap you know for certain. If not it could be anything from a cracked piston ring to your VP.

I think I might give that a go tomorrow just to see if it helps. I didn't think the VP could stop pushing fuel to only one cylinder, at least that's what Mike said. As for cracked rings I guess it's possible but I don't have any blowby out of the valve cover

Hmmm, a couple days ago, you had a 'cold' #6, today, it's #1..

Thatt's why I still suggest pop testing. Then you can rule out the injectors completely. Right now you randomly tossing money at parts without any proof of a fuel issues and where?

 

Hmmm, a couple days ago, you had a 'cold' #6, today, it's #1..

 

But still if it was me I would pull all the injectors out and pop test. While the injectors are being pop tested I would do a compression test just to verify and the injectors are out so it makes getting two birds with one stone.

This is my DD though... I can't have it down at any time. I think I am going to swap #1 and #3 injectors and see if the problem moves to the #3 cylinder. That would rule out the injectors. 

 

Hmmm, a couple days ago, you had a 'cold' #6, today, it's #1..

Could have been changing the crossover tubes.. If 6 wasn't seated and now it is, and 1 could not be seated I guess

Hmmm... Me I would call around and fine a shop that does free injector pop testing. Then see about renting a diesel compression test. Have a friend run the injectors out and have then tested. Then you can do the compression test. By time you finish you buddy should be finish and coming back. Shouldn't take much more than 1-2 hours tops if everything is planned out.

I called around ad couldn't find anyone to test the injectors for free, and everyone wants to take them apart. So I went ahead and switched #1 injector with #4 injector and it made no difference. #1 is still 177F while all others were 212-215F

So what was the difference that made #6 start firing instead of #1? Wasnt #6 the dead one originally?

Latest news on this: I just got back up to college. I went as planned and used an infrared temp gun. I found number 1 was 40-50 deg cooler than the rest. Number 6  was 10-20 degrees cooler than the rest as well. I decided to replace both of those crossover tubes to see if that would fix my issue. It definitely helped some, as the miss only sounds half as harsh as it did before and the exhaust has a less harsh miss feel to it. I didn't not have time to pull the valve cover and loosen the injectors before installing the new tubes.... So I'm hoping that is my issue. I forgot my temp gun at home so I won't be able to use that when diagnosing for the next couple days. Any thoughts guys?

If you look back in the posts I said that #6 was 10-20 deg cooler than the rest.... which it may have been just because the engine was cold and 6 is on the back side of the engine. #1 has always been significantly cooler than the rest and continues to be. 

I think I will go ahead with the compression test to tell me if the internals are okay. If they are I am going to have to look at the VP, ECM or PCM. Any ideas Mopar Man?

 

Does anyone on here have a compression tester they would let me borrow? I would pay shipping and some on top for letting me use it. I just don't want to go buy one of these to use once. 

you dont need to remove exhaust rockers to pull injectors/fyi. use the valve cover bolt and pull them out by hand

could there possibly be something clogging the hard fuel line to #6?

I don't have any 8mm wrenches... So there was no way for me to loosen the right side injector hold down... And to re-torque them properly I had to have it off. And yes I used the valve cover bolt but thank you for the tip! 

There is nothing clogging any of the lines. I had them all off and cleaned the tips and blew them out. 

 

Talked to my performance guy... He is leaning toward a cracked exhaust valve, as is a friend of my dad's who owned his own trucking company for 20 years. 

Oh. I totally forgot those earlier posts!! You may be able to rent a compression test kit from a parts store for fairly cheap. That would definitely be the next place to look for problems. It would appear that you have covered the fuel system diagnostics pretty well. Injectors, lines, tubes, etc. I dont believe the VP could be at fault with only one hole not firing like that.

Just an FYI 8mm is the same size as 5/16".

Cheapest place I found to buy the slug is Cummins   Who would have thought! 56 bucks. Does anyone know were to get a good quality compression gauge for  diesel engines? Not trying to break the bank either

Get a hold of http://forum.mopar1973man.com/index.php?/user/565-pepsi71ocean/I know he's got a compression gauge.

Get a hold of http://forum.mopar1973man.com/index.php?/user/565-pepsi71ocean/I know he's got a compression gauge.

I contacted him when this problem first started and he seemed pretty reluctant on me buying or borrowing it....

Funny... He was the same way about buying a gauge in the first place and was telling me he might want to sell the gauge afterwards to re-coop the loss.

I guess I'll give him another call tomorrow... I need this thing in by thanksgiving though whichever route I go. I plan to test compression and do a leak down test next Tuesday. If all comes back well internally what else could it be?? Is it possible the VP is screwed up? Just looking for thoughts to try if the pistons, rings, valves, and gasket are good. And how likely is a head gasket? I've hit 52-53 psi a couple times but I don't see any leaks around the sealing surface

Edited November 19, 201410 yr by TFaoro

you might try this??

 

http://www.harborfreight.com/12-piece-diesel-engine-compression-tester-93644.html

 

I know it will at least work for a little while or mine has worked through 4 engines for me.

Hmmm I wonder how accurate it is given the price?? Thank you for the link! I may just end up getting it. What PSI should these engines be at?