Turbo Problem?

[Parshal]

A very strange thing has begun to happen (or, at least, I just noticed) traveling at 80 mph. If I keep the same speed (better with the cruise control) going down slight downhill grades the truck will begun to shudder (can't think of a better word) almost likes it's not getting enough fuel or there's water in the fuel. If I press the accelerator it will speed up with no hesitation. This was happening intermittently for 150 miles or so. I noticed after a while that when it happens the turbo boost is dropping by 1/2 to one pound of boost on the boost gauge. None of this happens at speeds below 78 mph or so.



I stopped at a truck stop and checked to be sure the air filter wasn't clogged and that the lid was on tight as well as drained the fuel filter in case it was water. If this isn't something simple I can't imagine what it's going to be like to get the dealer to even witness the problem at these speeds.



Thoughts?

 

[Prairie Dog]

I've never suffered it but it kinda sounds like the dreaded "death wobble".

 

[Blakers]

Parshal,

Do you mean the whole truck shudders, or the engine shudders? Does it actually shake or is this something you hear?

 

[Parshal]

The truck slows down or hesitates as if it's losing power and, at the same time, the boost gauge drops 1/2 to one pound of boost. The truck doesn't actually shake but loses power when the boost drops and you can feel it as if you all of a sudden hit 50 mph headwind. It comes back on it's own. That would have been a better explanation instead of shudder. It only happens when the truck is coasting downhill at 80 mph (I haven't tested at faster speeds). I have full power for acceleration. I usually drive with the cruise on but it does it with or without the cruise. No other gauge shows anything abnormal.

 

[rbattelle]

Maybe a wastegate problem? Like the wastegate is opening a little bit when it should remain closed? You must be running a decent amount of boost (>12 psi) at that speed.

 

[Parshal]

Originally posted by rbattelle

You must be running a decent amount of boost (>12 psi) at that speed.

That's about right.

 

[RSWilliams]

Mine started doing it on level ground. Thought that it was a cruise control problem - couldn't decide if it should speed up or slow down. It has now started doing it when cresting a hill. It feels almost like a gas burner missfiring.



This is my first post - read lots but this one has my interest.

 

[Parshal]

Hopefully, someone knows an easy answer to this or a fix that can done by the dealer without arguing with them. I checked for codes and found none so I suspect that I'll be told nothing is wrong.

 

[Mathew Clausen]

Driveline vibration? I only say this because I had a dakota that would do that at higher speeds. It only happened when going somewhat downhill where you had very little load on the driveline, but still high speed. Let clear off or apply power and it went away. Fixed with new bushings in the tailshaft housing. Of course the ram drivetrain is different but does have a slipper tailshaft housing.



Mathew

 

[cpizz]

Does it feel like you are choking the engine? Like on a dirt bike or something when you pull the choke and it kind of bogs down? It comes on and off like there is a switch turning something on and off. The truck seems to run rougher and have less power. Like you said when you hit a strong head wind.

 

[Parshal]

Matthew, no, it doesn't feel like vibration in the truck, it's like I hit a 50 mph wind gust and, at the same time, the boost gauge shows a drop in boost.



cpizz, it's sort of like that except it doesn't run rougher.



I went to the dealer and will take it in on Wednesday. He said they'll put it on their dyno at 80 mph and see what happens.

 

[cpizz]

I had that problem on my '03. The accelerator was not as responsive when it went into that mode. I have not really noticed it on my '04. The other thing that I noticed was that the '03 did not get very good mileage. The '04 seems to be getting better mileage and it only has 2000 miles on it. Both trucks were identical in specs. You are the first person that I ever ran across that noticed it.

 

[Parshal]

That's a bit different than what I have, though. If I give it any bit of accelerator it immediately responds with no hesitation. I've got 45k miles now and just noticed it.



Why did you get the '04?

 

[cpizz]

I was spending more time at the dealer than I was at my office. I had numerous things repaired on it. As well as things I was told were "normal". The funny thing is that the "normal" problems were not present on the '04. With the exception of the notorious "vibration".

 

[Parshal]

I must be lucky. I've not had the vibration problem on this truck. I had it on my Tacoma and they couldn't fixed it so I sold it after 7 months and got a Tundra. Nice truck but not a diesel.

 

[Parshal]

Well, I haven't had a chance to take it to the dealer. I noticed this weekend running at 75 mph with the AC on it did it twice. However, this time, I wasn't going downhill when it happened. The turbo dropped boost a few lbs. and the truck felt like it was starting to stall. Pressing the accelerator, the turbo spooled right up and the truck accelerated. A friend who used to work on older diesels said that it sounded like a fueling problem and that the turbo would do just what I described. I've changed the fuel filter.



Anybody else got any ideas? This doesn't look as though it would be covered under the 7/70 or 7/100 Cummins warranty.

 

[RustyJC]

Lemme throw this out for consideration. I have a friend with an 03 3500 DRW HO/48RE. When idling, his truck would intermittently drop RPM's, start shuddering and act like it was going to stall. Before it did, RPM would jump back up to around 1100, and then it would settle back into a steady idle.



After a lot of diagnosis (and some input from this forum), the dealer finally convinced DC/STAR that the common rail fuel pressure sensor in the HP fuel pump was bad. This would let the fuel pressure drop, then the sensor would finally see it and call for increased fuel pressure. The bad news was - the sensor was not a service part. The HP fuel pump had to be changed out.



Could this sensor cause the same problem at cruise?



Like I said - just trying to stir the thought processes... .



Rusty

 

[CJEliassen]

Are you coasting, or actually slowing down? If you are coasting, I would expect the fuel to shut off. My TDI does this and boost drops to near nothing.

 

[Parshal]

Originally posted by CJEliassen

Are you coasting, or actually slowing down? If you are coasting, I would expect the fuel to shut off. My TDI does this and boost drops to near nothing.

The cruise is still engaged but starting to go downhill it's coasting. It's not the fuel shutting off completely, the boost drops while it slows down but the boost will intermittently drop 1 - 2 lbs. and the truck starts to stutter. Touch the accelerator and it picks right up.



On Sunday, I noticed it at 75 mph with the A/C on but I was not going downhill. I was on a flat.