Hello, I just bought my first diesel powered vehicle about a month ago. It's a 1999 Dodge Ram 2500 CUmmins, 5spd, 4x4 Quad cab.. 216,XXX miles I consider myself an above average mechanic on a gas motor but am just learning about diesels.

Is it normal for these trucks to have a "miss" at idle?? Mine does but only after it's been running and is good and completely warmed up. Does not do it when the motor is cold. As far as I can tell the truck has no performance mods,, still has the factory exhaust.. I have changed the fuel filter/water seperator and installed a new lift(transfer) pump and run a couple bottles of injector cleaner through it.

Notice the miss most at this time;
driving down the highway 60 mph or so, come to a stoplight,, slow down and put it neutral and coast up to a stop,, once under 10 mph can feel the idle change, some kind of cycling it does normally,, not sure why just a little bit slower idle i guess when you go that slow. During this time while you sit, can feel a random miss. sometimes it does it, sometimes it does not,, and sometimes it does it more than others or harder than others, but definetly feels like what I would call a miss in a gas motor.

Just wondering if I am worrying about nothing. This has seemed to have gotten a little better over time since I've owned the truck, but still does it about 1/2 the time.

 

I have the same thing. Had it since I bought it 30000 miles ago (now at 85K). Lift pump @12-13 at idle. Does it with or without the Van AAken. Only does it when good and warm. If you bump the idle just the least (maybe 875rpm) it goes away. Also doesn't do it with the A/C on. It acts like every once and a while it just doesn't get the signal to put a shot in the injector. It seems to be a little worse with Rotella DFA. I can't swear, but t seems like some tanks don't do it, others do it a lot.

 

Matt, Jack,

Have you received any check engine lights? How about calling it a stumble as you are coming to a stop?

It could be the crank position sensor. It is a magnetic sensor that sticks in the side of the block that senses the teeth on the tone ring and communicates to the ECM. The ECM then communicates to the VP44. If the CKP is going bad the problem you described will occur at or near idle speeds.

 

Mine used to do the exact same thing. I changed injectors, miss is gone. I bielieve it is due to a weak(low pop when warm) injector. Mine would also do the drop in idle speed once below about 10 mph. After changeing injectors, that went away as well, it actually idles lower now.

 

Smokindog,,, No, I am not getting any kind of a check engine light or any other warning light. I suppose you could call it a stumble,, but it's not quite that bad. The motor never feels like it's going to die,, just a little miss every now and then.

JackRAK,, Maybe I am worring about nothing since you truck does it and has low miles

gamiller,, did you go to high-performance injectors or replaced with stock ones? If I did change mine I wouldn't mind putting some in that would give me more power,, but I'm not sure how big I can go with everything else stock? Also, does it kill your m.p.g. if you do that?

Thanks

 

Does it smoke while it is idling rough?

 

No check engine light here either. I think of it as a slight 'cough' The idle drops maybe 50rpm when slowing to a stop, I figured that was an ECM function (925 dropping to 875???). It idles slower with AC on, and there is never a miss with A/C on. It is just no load idling when warm, sometimes. No smoke at idle, though I can make a decent cloud with the VA if I feather the throttle just right. My mileage is fine, and power is good. I have thought it could possibly be dissolved air in the fuel. That could explain a lot, but not everything. I would love to swap injectors (mach4s anybody? ) , but I don't want to replace the clutch until it dies from a natural old age. I agree with the low pop off idea, if it was consistent, but sometimes it does not do it at all, sometimes it will do it a little, sometimes a lot. Anyone care to refer this to Marco for an ECM/PCM opinion? Right now I am feeling better that I am not alone with this and you guys are chiming in with some good questions and ideas.

 

I replaced my injectors w/RV275's. My fuel milage actually went up 2 mpg w/the new injectors. The miss was not there always when warm, but it was always there if I had been cruising over 1800 rpm, or working it hard. I am 99% sure it was a warm/hot pop off pressure issue w/the injectors. At first it was only a slight hiccup that my wife didn't even notice, but it progressed into a very fast cough that she commented on, said it sounded like ****. Again, this only happened at idle.

 

Mine only smokes when the engine is cold. And you have described what my truck is doing perfectly. If I'm just driving around town, stop/go, not much over 40-50mph,, even once warm it usually will not have the miss,, only after a shot down the highway at 60 mph or higher for awhile will make it have the miss(most of the time) once I come to a stop. It got to the point where my 'ol lady noticed it so I figured it had to be bad... Once it started doing it, I ran a couple bottles of injector cleaner through it, changed the fuel filter, that seemed to calm it down a little or maybe I was getting used to it,, but it was still there. Then I changed out my lift pump and that seemed to make no difference,,

gamiller, did changing your injectors get rid of the "cough"?? I hate to sound stupid,, but I just dont know.. I am very new to diesels, never had one before,, but what are RV275's?? Are they a "bigger" injector than stock? A performance one or just an oem replacement?

Also,, does anybody think that adjusting the valves would have an effect on this problem?

Thanks for all the replies and ideas! feeling a lot better about my truck now that I know this happens a lot! I just hope it's not the injector pump going out

 

Yes, the injector change fixed the cough,hiccup,rough idle. RV275's are bosch injectors used in RV engines. 275 means they are rated for 275HP. They are much better than the ones I took out, more power, smoother, and better fuel milage(2mpg).

 

My truck acts the same way as all of you have explained driving me nuts. And my truck has new VP, IP, Crank sensor, Cam Sensor, MAp sensor, IAT sensor, -8an fuel lines with areoquip fittings( no leaks) and Fp is 15#s idle and 11wot. No codes. Im going to try injectors always wanted them maybe get a edge comp to. All thats left is the APP, or the pick up in the tank is sucking air.

 

well finally I think that other people are experiencing what I have been since NEW. I am pretty sure that it is a corrupted signal to the 44. I think that it is out of the ECM maybe because of the power supply to the lift pump. But it is being told this because of ????? have wasted huge amounts of money and 6 years of hell. Will e-mail anyone who is interested in the osocilloscope readings. the PEP module of the DRB might show it as well.???????

 

I had a rough idle too. I put some nozzles on my factory injector bodies. They had a "miss" when the truck was warm. I had them pop tested before they went in the truck and they popped from 295 to 315 bar. 305 is perfect. So I knew I had some that were popping too high. And this is with my factory injector bodies with 55K on them.

I put some stockers in and the idle is smooth again.

I have the other injectors at the shop to be re-shimmed right now down to or below 305 bar. They should be done tomorrow.

I'll throw them back in this weekend and see if they run better this time.

The IPs wear over time and can't pop the injectors that are set too high.

Bosch specs are something like 9% tolerance, which is a lot at 305 bar!

Jason

 

My truck did that and did it more after pulling hard in the winter time. The RV275 injecors cured it. When I put this engine in it had been sitting for a few years, all sealed up. It had a definate miss at idle. A few thousand miles and changing the injecors around removed the miss but I still have a little injector hammer in it at idel. One day I will put the other set of 275's in it and get these checked out.

 

today we had a ISB come in with a F.C. 368 , the equivilant of the dreaded timing code for Dodge , had the tech put in a VP44 pump , run it on the dyno and no more F.C. , but it had a rough idle, cylinder cut-outs produce nothing, hook up to insite showed fuel demand rising everytime it got rough, told the tech to run the air conditioner and it started running better, got the VP44 hot box which is used to check the pump, and with it on the engine just purred, so to run the hot box you have to supply your own battery voltage directly from the battery, so had them check out the battery connection to the unswitched power wires , which your ECM has and all the ground wires , the problem was with ground wires, so always check your power wires and return ground wires also , also make sure you have a good block to frame ground also , now this wont fix all rough ildes , but it is one thing to check,