Engine/Transmission (1998.5 - 2002) Bad Idling

[BWagner]

Has any one had there RPMs jump around alot at idle. My truck seems to have a horrible Idle problem. It has no power loss and does not stumble or jump around on the highway. Could this be bad injectors or a injection pump going bad, I had the lift pump replaced recently and checked recently too so I know that is not the problem. It midly shakes the truck when it does this like it is a missing gas motor. Or just feels like a V8 running on 7.



Help would be greatly appreciated.



Thanks Bwagner:{

 

[ToolManTimTaylor]

Check ground on the comp? Hows that fuel filter? what do you have for fuel pressures? Could be a bad injector (This is when you can crack lines to see what one does NOT change nor ADD to the problem however beware of the seriously high line pressures when doing so wear gloves and cover lines with a heavy duty rag)



Anyone else?

 

[2-ND TIME]

bad Idle

Check the injectors. You might be unplesently surprised that they might not be spraying properly. With mine the EGT was suposidly even they pop tested between 2500 and 3900 PSI well below spec's . This is on a 99 with over 200 KKm's but don't dought that they have been bad for along time. Or this bad connection on the plug in to the injector pump is a good place to start.

 

[jmtandem]

idle?

BWagner,



My '01 sometimes idles a little unsteady. The tach moves about one half needle width up and down at idle. I don't think it is an injector issue and I know several others whose trucks do the same thing. I wonder whether it is the tach moving a little or if the engine is truly increasing/decreasing a few rpm's. It is very difficult to discern with the ear. It doesn't do it all the time and not after a long downhill grade with the throttle closed or at very minimum fuel delivery levels. It is not the lift pump as I have 14+psi at idle. It also has not gotten any worse and the truck has been to the dealer for the lift pump and they made no mention of the idle. The tach moves the same amount at steady driving (2000 rpm's or so) so I am almost inclined to think it is tach needle. But it also has a very slight barely perceptable vibration in the gear shift lever at idle warmed up. It is not the A/C compressor, the fan, nor the heater grids loading/unloading the engine so it beats me what it is.

 

[Ncostello]

A slightly unsteady tach needle is normal to a slight degree because the ECM checks the engine rpm every so many tenths of a second and updates the PCM... which in turn updates the tach needle. Or something like that. There is a little lag in time in there so the tach is not completely showing real time events to some degree... which shows up in a slight needle bounce. Could be 50rpm or so.



BWagner is talking about the kinda miss where his truck actually shakes for a split second as if the key was switched off then back on as fast as one could. Like one cyl didn't fire on that revolution or something. If you go listen to the tail pipe at idle, you can actually hear the miss real well. Might only do it during idle and when up to operating temps... or some circumstance like that.



A Cummins shop can do a computer run of the engine separate of the Dodge computer... using a laptop... that bypasses the PCM. The computer will shut off groups of two cyls then four. They then run it on all possible groups of two and compare the fuel delivery of those two. They do groups of two to see if all deliver fuel all the time and in relatively equal amounts. It can be very tough to determine what causes it. And it could well prove to be the VP44 injection pump has a slight problem. The lift pump wont have a direct affect on the idle quality... it however could have been a cause which lead to the problem. Just my opinion.

 

[jmtandem]

unstable idle

Ncostello,



Thanks for your reply. Your points are well taken. I had a '91. 5 CTD and when the injection pump was going out at 128,000 miles the idle was irregular and from the tailpipe you could easily hear uneven firing. A rebuilt injection pump (fairly expensive at about $1600) fixed it. Otherwise that engine idled perfectly smooth.

 

[tgbol]

My has developed a slight miss at idle. It will drop a cylinder every so often. If I tap the pedal a little it will settle down until I stop at the next light. If it is the injectors what an excuse for some 275s.

 

[Snow man]

Are any of you guys having problems running a fuel additivie regularly? If not now would be a good time to start. I have used Power service,occasionally when i ran out of my favorite (Shaeffers diesel treat 2000). The Shaeffers,is supposed to be a lubricant,cetane booster up to 5 cetane,and keep the pump injectors cleaner,reduce smoke,and soot build up. For the $$ , I think the additive,is the best money spent on the VP44 trucks. I know Howes,and Standyne are also good additives,Id use any of them in my truck. I had a rough idle a while back. I thought it an injectors. I found out it was my flexplate cracked,once replaced,smooth as glass again. i was ready to send my injectors back to DD to get checked,when I found the flexplate cracked.

 

[tgbol]

Yesterday on the way to work the engine really started to idle bad. Instead of dropping a cylinder occasionally it had a dead hole. I had good fuel pressure. I changed the fuel filter, added some Marvel Mystery Oil, and Some Diesel additive to it. Smoothed right out. I have got about 100 miles on it since and not a miss. I told the wife it was time for a tune up. About $300 for the injectors.

 

[MD500E]

Snow man, whats a flex plate? I am guessing its something between the engine and the transmission? My truck idled rough just slightly when it was stock, then I threw in some DDII's and it got worse. Scott at massdiesel even made a comment that it didn't sound right. Now that i have added supermentals and the bad idle got even worse(rattles things in the cab), I am going to have to think it is something else, maybe the injector pump or this flex plate.



thanks, Kevin

 

[Ncostello]

Flex Plate is what connects your engine crank to the torque converter. Its kinda like the flywheel of a manual transmission but its not a friction surface... rather a bolting surface.

 

[jmtandem]

idle

Tgbol,



The fuel filter is very important to keep on top of. Also, if it idles a little uneven you might open the fuel filter's water drain valve and drain any water.

 

[tgbol]

I only had 2000 miles on that filter. I changed it March 18th.

There was no water in the filter when I drained it. I think I got a tank of poor fuel. But I didnt see any thing in the filter when I cut it open.

 

[2-ND TIME]

Bad Idle!!!

Well put in a new lift pump the other day . The pre filter pressure is back to 14. 5 and post is 14 PSI This is what it was last Jan 02 I pumped all that fuel through the engine and all I did was wear out the pump the filter didn't need to be replaced last Dec 02 for it didn't give me any more pressure when they did they wasted more of my money !!!!!!!!! This tells me that if you buy good fuel you don't need to replace the filter nearly as often as they say this saves money in the long run! Now with a new lift pump in the engine temp is up from the 11 position to the 90*C . This has done more to increase the engine temp then new inj pump and bigger Injectors!!! I monitored the cylinder temp with a infared gun and each cylinder changed about 3* f and 3 and 4 cylinders changed about 7*f . Leaning on the top cross member the bounce from the engine was very obvious to the point of moving the red dot. Will be using an osciloscope after the Easter weekend don't have time to spend on it now!!!!! Has anyone else got a infared to test theirs???