Engine/Transmission (1998.5 - 2002) Fluctuating Idle RPM

[LCampbell]

Since new the tack on my 2002 ram 2500 has fluctuated at idle (Idle rpm is slightly over 800)with no noticable engine rpm fluctuations. Now (81000 miles) at idle in neutral or in park the engine rpm will occasionally fluctuate about 50 rpm or so & can be heard & felt. Is this anything to be concerned about? The truck has an automatic transmission

 

[mrtwister]

Is the truck fluctuating when you first start it up or after its already warmed up. During cooler temps the grid heater will kick on and off until the engine is warmed up. Also if your air control knob is on the defrost position or A/C, the compressor will kick on and off. My truck does the same when the A/C / defrost or grid heater is working.

 

[LCampbell]

Today it did it after about a 30 mile ride. Its quite hot here today (100Deg. ) & I had already shut off the AC when I noticed the fluctuation (Thanks for the reply)

 

[trqmnstr]

It might be time for a valve adjustment.

 

[joaker]

81k... . might already be the VP-44 giving attitude, what is you fuel pressure looking like?

 

[LCampbell]

I don't have a fuel pressure gauge in the truck. Also what is the VP-44? This is my first diesel so I am kind of nieve when it comes to some of the terminology. & So far it's been pretty reliable except for a TPS that had to be replaced while it was still under warranty

 

[nps]

I don't have a fuel pressure gauge in the truck. Also what is the VP-44? This is my first diesel so I am kind of nieve when it comes to some of the terminology. & So far it's been pretty reliable except for a TPS that had to be replaced while it was still under warranty

There is a TSB here that describes a procedure to test the lift pump flow rate. In the absence of a gauge, I recommend you perform this test immediately. Use a medium sized plastic bucket (like a cleaning bucket or an old oxyclean pail) and mark the minimum volume on the side of the bucket first using water to show the volume level. Then repeat every week or two until you get a gauge.



The VP44 is the injection pump - about $1000 worth of parts that will be toast if you don't have pressure being supplied by the lift pump. It is at the front of the engine, drivers side, and has the 6 fuel lines exiting from it that run to each cylinder on the head.

 

[LCampbell]

Thanks for the info. I'll check it out.

 

[LCampbell]

NPS thanks for the help. I just finished the the fuel transfer pump check per the TSB. The pump ran for about 25 seconds & pumped 59 fluid oz. with no air bubbles in the line. So that part seems to be ok. I will add a fuel pressure gauge in the near future. I changed the fuel filter before I did the test & the one I removed seemed to be very dirty compared to ones I have changed in the past. Could the filter possibly have been the problem?