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rough idle

18K views 7 replies 4 participants last post by  Faulkner99 
#1 ·
Hello,, I just bought my first diesel powered vehicle.. it's a 1999 Ram 2500 with the Cummins 24 valve turbo diesel. I consider myself a descent mechanic on any gas motor, but I am just starting to learn about diesels.
My question is about my truck's idle. After the motor is good and warm, most of the time it will have a "miss" at idle. It's not a lope, like from a big cam in a gas car,, but a random miss,, you can hear it and feel it as it slighty shakes the truck when it does miss. Everything else seems fine, runs good and strong.
The truck has 216,XXX miles on it, 5 spd manual, 4x4. I talked to a friend who does lots of work to diesels, he recommended that i install a new "lift" pump? I looked in my Chilton book and couldn't find anything called a lift pump, there is the injector pump and a transfer pump before that,, Can anyone tell me,, are the lift pump and the transfer pump the same thing? some people might call it one thing when somebody else calls it something else
I also plan to service the water/fuel seperator and install a new fuel filter and have changed the oil and run 2 tankfulls of fuel through it with a bottle of diesel fuel injector cleaner.
Thanks for any help
Matt
 
#2 ·
I agree wih your friend. Replace the transfer, lift pump. both are the same thing. I think that on your truck, it is on the frame rail. If you plan on some modifications, look into some aftermarket pumps. more expensive but worth it. Also don't delay. If you starve the fuel injection pump, you will kill it and then it will cost you a bundle to fix it.
Get yourself some gauges, ie...boost pressure,exhaust gas temp, and a fuel pressure gauge. The fuel gauge would be most important on you particular model truck for the reason of fuel starvation to the injector pump. The other gauges will come in handy when you modify the truck.
Good luck.
 
#3 ·
OK, thanks! I'm not sure how many mods I'm really going to do, I am more concerened with reliability/gas mileage with this rig, so I will probably just go with a stock lift pump. I will probably just go with 4" exhaust, maybe a K/N intake,, and a computer upgrade for any modifications..
I'll look into the guages too, I suppose the fuel pressure guage would go between the lift and injector pumps? since it's the injector pump I do not want to starve?
One last question,, do you know of a good source for repair manuals on the Cummins motor? I have a basic Chilton but it covers all dodges even Dakota's for a few years. I would love to find something more specific to the cummins
Thanks again!
 
#5 ·
The transfer pump mounts on the drivers side of the engine block below the fuel filter. If it only acts up at idle try this, Start it up and let it idle and then open the fuel filter drain while its running. If the engine smooths out you have a cracked diaphragm in the injection pump and the entire injection pump will have to be replaced. BTW I'm a technician at the Cummins plant where the build the engine for the Dodge Ram.

Brian
 
#6 ·
OK, I will talk to my local dodge dealer about the manual, thanks for the link!

mrmopar, you are absolutely right about where the lift pump is, under the fuel filter, above the starter,, in a nice hard to reach place.. haha I'll try your test with the drain. You wouldn't happen to know what the pressure coming out of the lift pump should be, would you? If it read the right pressure, then it should be OK, right? or is that pump more volume related than pressure related?

Today I put in a new fuel filter, old one was pretty bad and now it's running a little stronger. That miss I had talked about seems to be getting less and less over the past couple days, but changing the filter did not make it go away completely.. I sure hope it's not the injector pump,,, the injector pump looks really new,, also, somebody had the head off of that motor I'm fairly sure, because the freeze plugs in the side of it look brand new.

I noticed something new about that miss, let me run it by you guys..
As the motor sits and runs,, you can hear/feel it "cycling",, you know,, kind of changes pitch, like you just turned the a/c on or something,, it's a normal occurance as far as I can tell,, something having to do with the way it runs or heats the fuel,,
anyway,, it idles just a hair slower during this period
Everytime I am going down the road(60 mph spd limit) and come to a red light, as I approach it, I'll put it in neutral and coast/brake to a stop.. Every time I get just below 10 mph, I feel that change in the idle,, the "cycling" I mentioned earlier.. maybe it's a computer controlled event? seems normal, that doesn't worry me.. but I did notice that is the only time I really notice the miss. idleing when cold doesn't do it, or just slow driving through town doesn't do it either.

Get this,, I thought a lift pump was going to be about $150 like everybody told me, called mopar today,, $345!!! They just raised the price.. the guy on the phone said it was because most trucks with that model pump were just coming out of warranty and the company wouldn't have to pay to fix them anymore.. isn't that a load of crap?!?! Would be real nice to know for sure if mine's bad now, before I go cough up that much $$.

By the way, mrmopar, I work at the other end of the production,, I work in a Dodge plant where all we build are Ram trucks.. we currently do not build the diesels, but are getting them back at model change.

Thanks again the the help/info!!!
 
#8 ·
Ok, I know this is a 9 year old thread but hoping I can get my answer. I'm having the same exact symptoms to the T as Matt. I have a fass 95gph fuel pump that has been on my truck for quite some time and was leaking but now is not. I've checked for air in the fuel system and found nothing. My question is, did the lift pump fix your issue ?
 
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