Since I purchased my truck a year ago, it has had what feels like a miss at low RPM's and at full throttle (In Neutral or Park).
I took it to the local Cummins shop and they used an infrared tester and determined that the number one exhaust was reading cooler than the other five exhaust ports.
They tested the injector and it was fine. With that, they assumed that the problem was in the injection pump.

I finally got around to taking the truck in for a new pump this week.
They replaced my pump with one that has the 175 kit (Kit includes new injectors and rated at 175 as opposed to the stock 160 pump that came on 1994-95 trucks).
After they put the new pump and new injectors in, the miss is still there.
They did a blow down test on the #1 cylinder and it was fine.
(They have since agreed that the engine fan blowing across the number one exhaust port is causing a miss read from the infrared heat reader)
They have replaced both the supply and return fuel lines.

At this time, the truck is still in the shop and still has the miss.
They are going to replace the new pump with another new under the assumption that the new pump may also be flawed.

I thought that maybe I have a cam lobe going flat. However, I have had the valves adjust twice since owning the truck and they adjust fine. I would think that a flat cam lobe would cause problems when trying to adjust the valves?

Just as additional information, on cold mornings when I first start the truck, the engine runs pretty smooth (The miss is still there, but very, very slight.
After the engine warms up, the miss is more noticeable.
After a long run (3-4+ hours) the miss is really noticeable and shakes the entire truck when at an idle.

There is no smoke outside of the normal brown/black smoke under hard acceleration.
I dont lose any oil between oil changes and Im not losing any anti-freeze.

So, with all that said, what ideas can any of you come up with?

 

Im thinking timing. Have them advance it and see if it goes away. I would start at about 16* and slowly work up from there.
Good luck,
Scott

 

You could begin by cracking each injector line one at a time to determine which cylinder is bad. Also have the shop do a compression test on all cylinders. Next have them check valve LIFT.... just because valve lash is easily adjusted does not mean the lift is ok. Also check for forein objects in the intake and exhaust manifolds.

 

I think my new ('97) has the same problem. We determined that it is being caused by the pump timing actuator. Basically, the turbo has a pressure line going to a daphragm on the back of the pump. As the boost changes, the diaphragm advances or retards the injector timing.

My "vibration" is very slight at an idle, and more noticable just off idle, at about 1200 RPM's. We discovered that my turbo is just starting to give boost at 1200 RPM's when the engine is not under load.

At this point, the turbo is causing the pump timing to advance, which causes the engine to enter a rich condition (I think) which causes the exhaust temp to decrease slightly, which causes slightly less boost. This change in boost causes the timing to change again and leans the engine out, which increases the exhaust temp, which creates more boost, which advances the timing again...and the cycle continues.

On mine, once you put it in gear (automatic) the problem disapears, which would be expected, because it creates a load, which "damps" the oscillations.


...Now, just because I can explain it doesn't mean that this is supposed to be happening. I'd be curious if it turned out to be a leak in either the pressure line, or the diaphragm...

 

Thanks guys,
I have not had a chance to speak with the guys at the shop yet this morning.
I'll run these ideas by them and check both the timing and the both the pressure line and diaphragm.

I'll also ask them if they checked each cylinder with either a pressure check or by cracking one injector at a time.
I believe they did the injector test and could not definitively isolate one cylinder, but I'll double check.

Thanks again guys

Rich.

 

cumminsfan, as far as I know the timing on a 12 valve is set and never changes unless someone changes it or the gears slips.

 

From what the guys at the Cummins shop say, infidel would be correct.
However, Im still going to have them check it.

Thanks
Rich

 

The guy at the Dodge shop that was diagnosing my problem said that I have an "inline" style pump, which has this feature, whereas the older "rotory" style pumps don't. I don't know what year they switched though, or whether or not there is any truth to what he was saying...

 

Being that your truck is a 97, I believe they could be referring to the difference between the p7 style and the VP style pump.
The p700 pumps were used on the 1994- 1998.5 12 valve engines.
In 1998.5+ the 24Valve engines ran the VP44 pumps.

Rich

 

The rotary pump is the VE series used in pre'94 1st gen trucks.
'94-'98 has the inline P pump.
The VP used from '98.5- '02 has electronically controlled variable timing. On the two old style pumps the timing is fixed.

 

Thanks infidel.

Is the VP44 a rotary style pump?

Rich

 

The VP is called a electronic rotary distributor pump. There are only three pistons whereas the P and VE pumps have six, the pistons "share" injectors on the VP.
You can read about it here http://dodgeram.org/tech/dsl/ISB/Vp44.htm

 

Is it possible the '97 has turbo controlled variable timing, or was the mechanic just blowing sunshine somewhere 'cause he couldn't find the problem?...

 

Buddy I think I would find a new mechanic, sounds like this one is going to cost you lots of money the timing is fixed on yor truck it does not change unless you adjust it yourself,the turbo has nothing to do with timing either.Sounds like your mechanic should have his tools taken away! Good luck your going to need it!

 

Sounds like I'm going to have to get a second oppinion... Fortunately, I bought a bumper-to-bumper extended warantee with the rig that has a $100 deductable. $100 sucks, but it's better than what it's probably going to cost to fix it.

Anyone have any ideas as to what may be causing this issue then? The first thing they replaced was the fuel overflow valve on the pump. According to the symptoms in the TSB this should have fixed the problem...but it didn't...

Is there any way that my symptoms could be causing more damage? It's doesn't seem like a very big issue yet...I'd rather hold off paying $100 if I can avoid it.