Yesterday while diving to a friends house from work, I ran the truck like I was towing heavy, kept rpm about 2500 in 5th gear for about 10 minutes. When I got to friends house, engine had developed a miss while I was waiting for egt to get down to 300 degrees. After visit(beer and pool) was done, about 2hrs, truck ran fine, no miss.
My question(s) is, could the VP cause this? Could it be an injector w/a weak spring when it gets to a certain temp? Truck runs fine, and has good power, no check engine light, good fuel preassure. Have only noticed the miss at idle.
Thanks for taking a look, and thinking about this.

 

OK, noone seems to be able to answer, so I am rephrasing.
Since I know little about how the VP, or any rotary vane pump works, is it possible for the VP to not pump to 1 injector consistently for say 5 mins causing a miss.

 

I am wondering if it is a VP problem. I have read that the VP sometimes causes a no start condition that can be helped by cooling the pump. Have you tried scanning it for codes? I really don't know that much about the 24v, so I am just guessing.
Tom

 

no. I belive the vp44 is a varible start constant end pump. flow to all injectors are all derived from the same plungers so it would miss on all if the injection pump was the problem.if the injector had a weak popit valve spring it would not miss as the spring holds the valve shut and the fuel pressure opens it on the 99 i think the opening pressure is 19,000psi. I can't tell you anymore unless i actually hear and see the problem. as a side note the injection pump is actually two pumps the vane pump justs supplys fuel to the the rotary part of the pump. If i get a chance to look at some of robert bosch text books from when i was back in school mabye i can help some i generally don't work on bosch pumps so mabye someone else knows more than i do.

 

I did a little test today on my way home. After being on the road at 70 for about 45 mins, I came to a light, when I stopped, the miss was there, not always constant, but very noticable, so I turned off the engine, and restarted, no more miss. After thinking about the problem, I came to the realization that I started noticing the miss, when the weather cooled off, and I quit using the a/c. So I ran another 5 miles at speed, when I stopped, the miss was there again, this time I turned on the a/c, no more miss. This must be some kind of sensor, maybe the IAT??

 

I also have a stumble miss at idle, and when the engine is under load. Fuel pressure runs 14psi at idle and no less than 10psi when working hard. To date I've replaced:

VP44
ECM
Injectors,
IAT,
Cam Sensor (my rig doesn't have a crank sensor)
Replaced fuel lines from pump to pump with 3/8" lines and fittings

Cleaned IAT
Cleaned MAP
Moved Drag Comp ground wire around.
Went to a TST box
Removed all boxes

I firmly believe it's in the wiring harness from the IAT or Cam Sensor to the ECM, or from the ECM to the VP. I've raised the little tangs inside the female plugs with a pointed exacto knife which has seemed to help quite a bit....but it's still there.

At idle tach jumps around, dyno runs show the stumble, and it can be felt while loaded or accelerating.

Hopefully we'll find this Gremlin!

 

You might just have an injector going south. Turning on the ac would increase the load on the engine. I had one once that missed on occasion at idle especially in the cold weather. When I changed the injectors it went away. Good excuse to go for larger injectors

 

yes the injection pump can drop a cylinder. the 98.5 and newer have the abitity to drop out a cylinder. with a scan tool a dealer can drop any cylinder with a push of a button. the newer injection pumps have a lot of electronics in them. i would not be to quick to blame it as the miss you have. i did see one 99 that when you ran it at a steady speed for a few minutes and came back to idle it would miss. shut it off and restart it the miss was gone. we tried everything. a new injection pump cured it. it was under warranty. if yours only did it once i would not be to concerned.

 

Well, I guess I need to get a scan tool of some kind, maybe the autotap or something like that, that I can install the software on my laptop, and keep it on there and diagnose the problem for awhile. Anybody had any experience/recommendations w/the autotap or similar products?

 

I've used the autotap, it's pretty good if you want find and erase codes or monitor sensors and outputs, but it cannot access the actuator tests that the dealer's scantool can, such as cylinder drop tests. snap-ons' scanner would probably do such tests.

 

tenbrooks,

I have an interest in the autotap but am reluctant because of unknowns.

Does this software access all/most of the Cummins/Mopar nervous system?

I understand it will not get as deep as a dealer scan tool to perform cylinder drops etc, but will it pull the codes, especially the VP related ones??

I just want to be able to read (and weep) the codes from a maintenance/trouble shooting point of view on my 98.5

Anyone's comment/experiance welcome

 

The autotap will pull codes from the mopar system but i'm not sure about the cummins system. the software I've used is about 2 yrs old and I don't know if it has been revised. with the one i used when you plug it in, it gives a list of parameters to choose from and whether you want a guage or a line graph to show the reading. ie intake or boost pressure,intake temp,rpm,vehicle speed,tcc lockup,engine temp,engine load %,tps %, and tranny governor pressure. some vehicles give more info than others.