Ok so I've been reading and researching for weeks.

My 550 has bout 158,000 miles on it and in the last couple months has decided to present the problem which is very similar to this one:

I'm some what new to diesel's but the engine will miss/stumble when it crosses mid 2000 rpms and 20 psi (give or take) on the turbo, when it misses it does puff white smoke. The miss sounds like a knock, like you would hear when you shoot ether into an intake, just much shorter usually just 2 or 3 knocks then it clears up. I can also make it happen but getting off the throttle going down the highway, letting the rpms fall then getting back on it. Doesn't do it every time but often and more so when under load.

My issues is different than the TSB in that it happens regardless of weather. I pulled the hose from the bottom of the CAC and stuck my hand in there looking for a pool of water and found nothing but a little oil.

We just had the valve covers off and replaced the rocker arms, they were wearing pretty good.

2 times since this started the truck had difficulty starting after I shut it down. Engine was still warm the hard start almost sounded like a vapor lock, it really didnt want to turn over. After I let it set for a few seconds it fired right back up. I dont know if this issue is related but it never happened before and has only happend since I noticed the missing/stumble.

 

Is the DPF deleted? Which tuner?

What Oil are you running? How long ago was the Oil filter changed?

When were the two fuel filters last changed with OEM filters?

When was the air filter last changed with OEM filter?

 

Do you have a scan tool that can monitor live data?

Exhaust back pressure sensor
DpF back pressure sensor
Also there is a PID for Regenration

 

Rotella

Oil and filter changed when we put in new rocker arms. That said I change the oil every 3000 miles.

I put 2 new filters in when I first noticed the problem. So 3 or 4 moths ago.

Air Filter.. good question I cant remember when it was last replaced.

 

I dont but my buddy does.

 

Check for codes.

Have your buddy do a ride along with his scan tool so you can safely operate the truck while he monitors and hopefully logs what the real time data has to say - this will get us one TWO steps closer.

 

no codes when it misses/stumbles fyi

 

Right, so potentially a sensor mis-behaving or rust on the VGT which is speculation on my part as I have not been inside of a 6.4L turbo before.... Maybe someone can chime in.

A mis-behaving sensor or rust on the VGT might not though a code.

The ride along with data logging of the sensors is what you need.

 

Sounds to me like you might have an injector hanging open. My truck had an injector stick on and it would start to run rough and have grey-white looking smoke then I would just shut it off wait a few min and start it up and it would run fine for a while. It was intermittent and a pain to diagnose. Never would throw codes and could not get it to fail when hooked up to scanner.