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

400-450 PSI is typical good compression.

http://articles.mopar1973man.com/general-cummins/34-engine-system/144-compression-testing

Came back to the apartment today and was letting the turbo cool down when it went to a complete dead miss for 2-3 seconds. Shook the whole truck then went back to it's normal half miss. To me that sounds like fuel delivery not valve train or piston/ ring related

Once again here we go go back and have the injectors pop tested. Still might not be a bad idea to compression test the engine while the injectors are out of the head.

i'd pop test the injectors, and then boar scope the cylinder if you can. i'd bet if you keep driving it this way your gonna hurt it more.

Once again here we go go back and have the injectors pop tested. Still might not be a bad idea to compression test the engine while the injectors are out of the head.

I will be compression testing this coming Tuesday night (1 week from now) If the compression test comes back all good I WILL have the injectors sent out Wednesday morning. 

If I could stop driving it I would... But this is my DD and until next Tuesday there is nothing I can do but drive it and hope nothing gets destroyed. 

I am wondering, why couldn't this be the VP44? Remember these pumps have the capability to shut down three cylinders.

I am wondering, why couldn't this be the VP44? Remember these pumps have the capability to shut down three cylinders.

 

If engine coolant is over 140*F it can't start 6 cylinder or 3 cylinder.

 

If engine coolant is over 170*F all 6 cylinder and 3 cylinder modes are cancelled till coolant temperature falls below 140*F.

 

So it not going to be a injection pump or ECM thing. But... It's very possible for a injector(s) that is pissy or pop pressure is off to create a misfire condition. It very possible for a cracked piston to create this problem too. JL Welding was the one that comes to mind that spent huge amount of money chasing misfire problem that turned out to be a cracked piston. Hence why I'm still suggesting injectors being pop tested and compression test.

If engine coolant is over 140*F it can't start 6 cylinder or 3 cylinder.

 

If engine coolant is over 170*F all 6 cylinder and 3 cylinder modes are cancelled till coolant temperature falls below 140*F.

 

So it not going to be a injection pump or ECM thing. But... It's very possible for a injector(s) that is pissy or pop pressure is off to create a misfire condition. It very possible for a cracked piston to create this problem too. JL Welding was the one that comes to mind that spent huge amount of money chasing misfire problem that turned out to be a cracked piston. Hence why I'm still suggesting injectors being pop tested and compression test.

What I am saying is that there must be an electrical/mechanical way for the pump to shut three cylinders down. Isn't it possible that one of the valves needed to shut down a cylinder may have a problem? If the VP had no way to shut down any cylinders then I would say no way.

3 cylinder mode is done by telling the ECM not to fire. So the electrical pulse is not present. So the solenoid slaps closed and no fire is give for said cylinder. Then next cylinder the solenoid is fed a signal to fuel. Mostly the ECM that does this. As far as I know there is no way for the VP44 PSG unit to do drop cylinders on its own.

 

Still in all pop testing and compression test are much cheaper than a VP44 replacement.

3 cylinder mode is done by telling the ECM not to fire. So the electrical pulse is not present. So the solenoid slaps closed and no fire is give for said cylinder. Then next cylinder the solenoid is fed a signal to fuel. Mostly the ECM that does this. As far as I know there is no way for the VP44 PSG unit to do drop cylinders on its own.

 

Still in all pop testing and compression test are much cheaper than a VP44 replacement.

I certainly do agree that pop testing is the next step and the least expensive route to go, but since you are saying there are solenoids in the VP there is a possibility (however slight) that there is something wrong with one.

I certainly do agree that pop testing is the next step and the least expensive route to go, but since you are saying there are solenoids in the VP there is a possibility (however slight) that there is something wrong with one.

I like your thinking here, but if the solenoid were to be "messing up" I don't think it would only be on one cylinder. I would have more cylinders misfiring. Pop testing is free through DAP because they are under warranty, but I think my luck has run out. This misfire started VERY small and slight almost not able to notice over the summer and has slowly gotten worse. I got the egts really hot once messing around with my brother and I think that's what did it

well,  if this is any help;    it went from   'maybe a miss, not sure which cylinder'   to   a    DANG,    IT'S SHAKIN THE TRUCK APART'    type  symptoms.            

It won't make it any easier on the  wallet to fix,   but   in a weird way,   it makes it  easier for  'me' (psychologically)   to dive  deeper into an engine.    

 

Can anyone hear the "mission impossible'  theme playing in the background?      The man needs  his truck  for  Thanksgiving next week...    

 

 

 

The  VP,     there is  3 modes????     normal 6 cylinder,     4 cylinder,  and  3 cylinder???  I was aware of the  3 cylinder mode.      And  the   solenoid  is needed  to operate each impulse for  'normal' delivery???    Dumb. Very dumb.      If they  needed  ANY REASON  for  shutting down    any amount of  cylinders,,   they should've  used the solenoid   to  BLOCK, OR  REDIRECT INTERNALLY   those  particular  cylinders'  impulse.   "NORMAL"   should've been   'nothing energized'.    I'm sure the path they took was  the cheapest.

Ah,  heck,  no sense on  debating  this now,  on a   pump design  that is  16 years old... 

well,  if this is any help;    it went from   'maybe a miss, not sure which cylinder'   to   a    DANG,    IT'S SHAKIN THE TRUCK APART'    type  symptoms.            

It won't make it any easier on the  wallet to fix,   but   in a weird way,   it makes it  easier for  'me' (psychologically)   to dive  deeper into an engine.    

 

Can anyone hear the "mission impossible'  theme playing in the background?      The man needs  his truck  for  Thanksgiving next week...    

 

Since it is getting worse I'm pretty sure it is a cracked piston or valve or something internal that will cost way too much to fix! That's what happens when you don't look at the egt gauge I guess. If it is internal the truck will be parked until at least Christmas and possibly until spring depending on funds.  College is eating my money like there's no tomorrow   30K + per year....

that compression tester is great for determining if you have a cracked piston or valve. Like i said for $30 it will at least work for your truck. I have had pretty good luck with mine and it seems to be accurate enough to tell you if you have a bottom end problem.

that compression tester is great for determining if you have a cracked piston or valve. Like i said for $30 it will at least work for your truck. I have had pretty good luck with mine and it seems to be accurate enough to tell you if you have a bottom end problem.

This is the second thing to do right after you get the injectors on their way. You will then know for certain if there is internal damage this way.

Well I've got everything ordered and on the way to do the compression test. Once again I'm not going to have the injectors tested if I find something internally wrong. There is no point in getting them tested now if there is a cracked piston or burn valve. As I said before these injectors probably have 500-1000 miles on them

Ordered? Ok so what did you pay for it? From who did you order it?

IF  you find  internal damage,  then you'll really want to test your injectors then.    On the otherhand,  the old injectors  may have  done the damage,  and  the current  injectors are innocent!

This is what's bad... People start doing the swapping of parts and never exactly know what had failed or failing and continue to install parts till its fixed. This is a very expensive method of repair. I'd rather invest money in a few tools and bench test properly and know without a doubt what has failed and deal with it properly than guessin'.

Ordered? Ok so what did you pay for it? From who did you order it?

The "slug" or whatever it's called that goes in the injector hole I ordered from Star Products. They say it will work on the CR too, so at least I can use it on my brother's truck if need be. I went to Cummins today and the guy I talked to had the wrong part number. He looked up some sort of injection psi tool??? Come to find out Cummins doesn't even make it. I couldn't see spending 120 bucks on a snap-on one when this one was 49.70. I looked it up and people on other forums seem to have had good luck with it. As for the gauge I went with the one Mulcher suggested. It should be accurate enough to tell me if there is internal damage on any of the cylinders. 

 

This is what's bad... People start doing the swapping of parts and never exactly know what had failed or failing and continue to install parts till its fixed. This is a very expensive method of repair. I'd rather invest money in a few tools and bench test properly and know without a doubt what has failed and deal with it properly than guessin'.

Admittedly that probably wasn't my smartest move, but I did want to get a bigger set before the warranty was up. It only cost me 100 bucks to go from DAP 90s to DAT sac 125s. And I would have to say these injectors now are WAY better than the 90s.