Engine/Transmission (1998.5 - 2002) Idle Problem

[vjohn346]

Fellow TDR Members:



After using the search engine I can't seem to find anything that sounds like my problem, maybe one of the guru's can help.



I have an idle problem that only occurs when the motor is up to operating temperature. The truck idles great until about 180, after that the motor feels like it has a miss, only at idle. I have a fuel pressure gage and all is well with the lift pump.



I have replaced the fuel filter, installed a new IAT sensor, and adjusted the valves. I have considered installing a cam and/or crank sensor but hate to just start throwing parts at the problem. Hopefully it's not the VP44!



The truck has good power and gets great mileage, if I could only fix this idle problem.



Thanks in advance,



Vance

 

[Ncostello]

Hello there Vance:



I have the exact same problem and have thrown parts at it in an attempt to make it stop, including injectors and Crankshaft Position Sensor. I have checked the MAP sensor and IAT sensor but have not replaced either. I'm convinced its the VP44 in my case. Does yours sometimes go away after a minute of idleing or so? Mine, on occasion, will act OK but thats rare. I'd search under just the word "idle". If you look towards the last few available pages of this forum, I discussed this with another member. At this point all I can tell you is I have the same problem too. I tried to get it into Cummins this Friday but they are closed for the holidays, just as we are where I work. Seems like the only days I have off... everything else is closed too!!



PS: I'd search "idle" but only under a title search. PSS: You probably wont find the answer either... but maybe you will.

 

[vjohn346]

Ncostello,



Thanks for the reply. I've searched a few times under idle and can't come up with anything that sounds like my problem. The unique thing about my problem is it only does it when the truck is warm.



It looks like these are the possible causes for a lame idle:



1) IAT sensor

2) worn out injectors

3) valves out of adjustment

4) Crank Position Sensor

5) Cam Position Sensor

6) VP44

7) lift pump



Of course I had to replace the lift pump when I bought the truck, who knows how long it was bad before I got the truck. I guess I can buy the Crank and Cam Position Sensors and go from there.



What I don't understand is the only thing that seems to operate temperature specific is the IAT sensor but I already replaced that.



Well, if nothing else gives, let me know what you find at Cummins if you go there.



Vance

 

[Ncostello]

Vance:



I agree, there are not many threads that explain what you have... except some of the first I ever posted. I too bought mine used, and with a bad lift pump. The owner had also installed a box fuel enhancer that attached one wire at the pump wires. So, even though I only have 80K miles, I'm outta luck on a warranty replacement of the VP44 because of the wire tap.



I had to replace the Crankshaft sensor first as I had a code setting telling me it was bad. (PS: I pretty sure you dont have a cam sensor on a 98. 5, you have a CKP like me) I sure hoped that would clear up the idle but it didn't. I also had to replace the lift pump because it was completely dead (wouldn't even pump fuel to the cannister). I also checked all electrical connections and put some di-electric compound on to seal out moisture etc. No dice.



Exactly as you have described, it only does it when it reaches operating temps. Scheid diesel put it on the INSIGHT computer and told me my 2 and 6 cyls had a miss. They thought it was the injectors. I replaced them all with new ones... no dice. INSIGHT was telling me that 2 and 6 were only getting 60% fuel delivery. Of course, if the lift pump was dead for a while with a box installed, it may well have "burned" up the VP44 due to overheating and no lubrication. But amazingly, it runs great otherwise.



Besides valves being out of adjustment or the fuel cross-over tubes not sealing properly, I cant help but to think its the VP. I'm still in process of checking both of those. But I think if it was the VP, the 2 and 5 would miss cause they are both fed by the same part of the VP pump... I think. . due to the firing order. So, I'm gonna have another go at INSIGHT and get the best possible opinion from Cummins professionals as to what could cause it. I wanna see if the computer tells me the same two are missing. I'm about out of options besides the VP. I am just a little hesitant at spending $1200 on a new injection pump and not have it work too!!