Cummins Rough Idle (1 Viewer)

[jfc]

Hi all,

I am having a very rough idle, but runs decent (a little rough) when reved up

Fuel filters been changed and now lift pump changed.

The only thing I couldn't do is prime it, as I can't seem to figure out how to turn the crank 90 degrees, (What the best way?) I tried priming while it was running but it didn't help.

Its on a 92 dodge

Any sugesstions

 

[jfc]

And do you think 20 min of highway driving should prime it.....cause it didn't

 

[boots4]

If you are concerned about air in the injector lines then you could always crack them right before the actual injector while idling to bleed the air out. Even with a little air mine seemed to work it out and idle smoothly after a 30sec to minute. Maybe you are getting air into the line from a shot seal somewhere. Your injectors could be dirty and not spraying a good pattern (they could also be bad/worn out). Timing could be off. Idle could be low. Could be bad fuel.

 

[jfc]

I'm thinking I got a shot seal, I don't think the injectors could quit all of a sudden, and it runs a lot better with some throttle

 

[canucksafari]

I'm thinking I got a shot seal, I don't think the injectors could quit all of a sudden, and it runs a lot better with some throttle

Generally, if you have a bad seal alllowing air in then you will likely also find it hard to start.

So did it start running rough after you changed the fuel filter and put in a new lift pump? If so, I'd check the seals and connections there. If not, and you suspect and air leak, you may have to fit a clear piece of tubbing close to your IP to see if you are getting air bubbles in the line.

BTW, how many kms has it been since you did your injectors? All it takes is one bad one to make the engine run like crap. You can always try a treatment of Lubro Moly Diesel Pro (two cans). This is a good write-up on how to do it properly: Easy Lubro Moly Diesel Purge How-To - with pics!! - TDIClub Forums. Greg at G&S swear by this stuff. At just over $10 a can, its a cheap fix if dirty injectors are your problem. If they tips are worn, then you need to have them redone.

 

[jfc]

It started rough our first cold day here a while back, so I thought I should change the fuel filter, I did, then I got a leak from the water sensor on the bottom, (poor design IMO to put it there), ran fine for weeks, with the small leak, then the other day started idled fine, as i drove to the highway it jerked a few times, ran a little rough on the highway, and really rough at the lights when I hit town. Then I changed the fuel filter again, for one without the spot for the stupid water sensor/ water drain valve that doesn't seat properly, and it still ran rough, changed the lift pump since its been leaking since Ibought it, still rough....

I got a set of new injector a year ago but have been too bust to put them in, I guess I will try that, probably 330 000 km since the have been done

 

[Tapage]

IMOP to get a really rough idle when it's warm ( normal operative temp ) aren't the injectors ( anycase 300K km .. thought they are really to be serviced ) are air in the lines .. at least with Toyota diesel engines ..

 

[jfc]

ya I would think injectors would degrade slowly an not all of a sudden

 

[Radd Cruisers]

Does your Cummins have the VP44 injection pump?

~John

 

[jfc]

Its the rotary IP, I believe all the 89-93 dodges had the same one, the guys on the cummins form call it the VE pump

 

[Radd Cruisers]

Its the rotary IP, I believe all the 89-93 dodges had the same one, the guys on the cummins form call it the VE pump

That design of pump is very sensitive to losing the lift pump supply pressure, and when it does the injection pump will fail in pretty short order. Failure is often seen as a sudden or progressive loss of power, with intermittent stopping of the engine (like at stop light) that requires re-priming of the injection system. Often higher speed or greater output demand are not well met and the engine will seem to misfire or suffer from fuel starvation.


Hth, YMMV


~John

 

[jfc]

ya I think a prober primeing is in order, but i need to fugure out how to turn the crank 90 degrees, as the fuel pump is run off the camshaft, and the primer on the fuel pump does nothing if the shaft is in the wrong position. Every time I turn the engine off it seems stop in the same position.

I guess its also posible that I bought a lemon fuel pump from NAPA

thanks for your help

 

[canucksafari]

ya I think a prober primeing is in order, but i need to fugure out how to turn the crank 90 degrees, as the fuel pump is run off the camshaft, and the primer on the fuel pump does nothing if the shaft is in the wrong position. Every time I turn the engine off it seems stop in the same position.

I guess its also posible that I bought a lemon fuel pump from NAPA

thanks for your help

I have the same style IP which is also gear driven. According to my FSM you only have to bleed it to the inlet at the IP - unless it is bone dry and then you also need to bleed the injectors. As it is running, your IP has fuel in it. If it is just a fuel filter change, then you bleed it at the filter. It should have a bleed screw on the top of the filter housing where there likely is also the primer pump. If you don't have a primer pump, you might consider fitting one of the inline ones before the filter - like the bosche ones the guys are using on a 3B. Or you could toss the cummins filter housing and go for one like a CAVI or Racor. BTW, have you had a close look at the filter housing. They have been know to crack.

 

[jfc]

I bled the low pressure side, there is a nut above the filter, and the primer i on the lift pump/ fuel pump itself, the lift pump is cam driven, so I had to rotate the cam (I used channel loks (only thing narrow enough I had)) about 180 degrees for it to work, after i primed that, bled all the injectors, and it still idles like crap.

 

[jasondavo80]

it seems that you have bled the fuel system up and the engine starts fine maybe you could try undoing / just cracking the injector lines one at a time with the engine running and see if the idle changes or not as you crack each line you might have injector pump issues

 

[prado t]

Before we get started, I had the 3rd RAM W250 since 1989 sold it when it had over 800,000kms replace the Bosch VE pump for the P7100 pump and started tuning them before they became popular.
1 does the s***y lift pump on the side of the block have some sort of diaphram presure when you lift up and down on the s***y little lever if so good.
2 when it is reving and under load is it missing and can you see blueish smoke
3 when the motor is running did you ever lift the lever on the lift pump ( if you did ) the excentric or diaphram could be fubared.
4 the motor should idle even without the lift pump

 

[jfc]

1 does the s***y lift pump on the side of the block have some sort of diaphram presure when you lift up and down on the s***y little lever if so good. (yes, but s***ty)
2 when it is reving and under load is it missing and can you see blueish smoke (smoke is more grey?)
3 when the motor is running did you ever lift the lever on the lift pump ( if you did ) the excentric or diaphram could be fubared. (I didn't, move it when running)
4 the motor should idle even without the lift pump

doh

I think its my injectors..... as I washed the engine so I could see leaks ext better, and I got a fuel leak aroud the botom of three injectors....only had one leaking a year ago...... thas when I bought a set of injectors and never got around to it...

 

[jfc]

doh

I think its my injectors..... as I washed the engine so I could see leaks ext better, and I got a fuel leak aroud the botom of three injectors....only had one leaking a year ago...... thas when I bought a set of injectors and never got around to it...

nope, not the injectors....even farmed this one out to the local dodge mechanic, he dont know either....maybe bad fuel???...new co-op in FSJ pump 17.... Im gonna stuff a 3B in this damn thing

 

[canucksafari]

If you think it is bad fuel, you could always confirm it by running some fresh diesel right out of a Jerry Can. Just attach a hose from your input connection before the fuel filter and another hose to your diesel return line - both hoses go into the Jerry Can of fresh diesel. If that settles the idle down, then you know your problem is fuel or fuel system related (maybe a clogged pick-up screen). BTW, now that you have this done, you might as well run a can of Lubro Moly diesel purge. Also, when you took the old fuel filter off, did you check to see if it was contaminated by a bacterial bloom? That could be another cause of your problem.

 

[jfc]

no algae I think it gets too cold to have that problem here, could be the screen,