Engine/Transmission (1994 - 1998) Idle problems

[tURBOdIEZEl]

here in the last week or so, my truck's really dogging! i thought i might have gotten bad fuel, but after running 2 tanks of diesel fuel with lots of PS and marvel mystery oil ive rulled that out.

the truck has lost no power, it just seems like the idle is wayyy down there (around 300rpm. ) im still getting decent fuel pressure. this problem only occures after the truck has been running on the interstate. if i come to a stop after driving at normal highway speeds, the truck feels like it wants to fall flat on its face. after an initial startup, idle is around 450-500rpm (still kinda low for my taste. ) ive been looking for fuel leaks and cant seem to find one. it just seems like the truck is also consuming more fuel then usual. i also thought i might have a fuel line cracked, and that it might me sucking air, but im not getting any extra white smoke other then the haze i get at idle. is there a way to manually adjust the idle? does it sound like a possible gsk issue? has anyone here on TDR land expirenced similar problems before?

TIA

 

[Joe G.]

You can adjust the idle with one 10 mm box end wrench. The idle screw is on the back of the pump (toward the firewall). It's vertical with the head resting against the pump lever. You can't see it and work on it at the same time. Find it with your hands. Loosen the lock nut with the wrench. Use your left hand to pull the throttle linkage to relieve pressure on the adjustment screw. Turn the screw with the fingers on your right hand until it's like you want. Tighten the lock nut. It's not hard to do once you have done it. Finding the screw can be a challenge. Take a look at the some of the diagrams to see where the screw is.

 

[tURBOdIEZEl]

thanks! im going out right now to adjust my idle before i go to work. . does this happen often? (idle going out of adjustment)

 

[Joe G.]

The head of the screw wears a little so the idle slows down. No big deal once you have adjusted it once.

 

[bmoeller]

I've seen the jamb nut work loose, and it allowed the bolt to turn when going down the road. A 1/4 turn makes a big difference. Or as Joe said, the head wears down.

 

[tURBOdIEZEl]

Update

thanks joe g! your information helped me locate the idle screw..... took about 4 minutes, bumped my idle to around 1000rmps(seems a bit high, but the truck is running 110% percent better) i also found my throttle linkage to be extremely loose. however, i found another problem. im leaking a little bit of fuel out the bottom of my fuel/water seperator. i just replaced the petcock that screws in under the fuel filter. . i guess that means i gotta take it back to the dealer and ask for a replacement... . maybe a new filter would cure the problem? anyone run into this one????

once again, thanks JOE G and bmoeller.

 

[Joe G.]

There are a couple of little screws that fasten the throttle linkage lever to the fuel pump lever. They can be loose and cause sloppy linkage. You need an 8mm box end wrench to tighten them. If that is not the problem then the end of the throttle rod may be worn. If the throttle linkage is the original (little wire clips to fasten the rod at each end) then there is a safety recall to replace the throttle linkage. It's free.



The leak at the bottom of the fuel filter is a common problem. It may just be the O-ring for the valve. The valve could be bad. It also may be coming from higher up. Watch what is happening with the engine running. Look at the double banjo fitting at the input to the fuel filter. That thing can leak and the drip will be from the bottom of the fuel filter.

 

[sfelts]

I have to say thanks for this post. I just went out and adjusted my throttle. set it to about 850RPM. whin I turn on the AC it drops to 800-750 rpm. Happy i came on line today Oo.

 

[tURBOdIEZEl]

you gotta love the TDR... . my subscription has paid for its self since i have been a member..... the amount of information thats on here is great!

 

[Willys]

You might want to check out this thread for the fuel problem:



https://www.turbodieselregister.com/forums/showthread.php?t=134007

 

[RChesney]

Idle problems and engine dying

Reading this and the thread about the engine dying after towing or running hard, I checked the link suggested. I just hauled 6 tons of hay yesterday in pretty warm temperatures and have a 3 mile uphill pull on a gravel road. Both times when I got to my driveway and put the truck in reverse to back the trailer down to the barn, the engine died. It would start up, but run rough at idle or die again if I didn't give it some throttle. Couple of times it would idle so low that a "check guages" light came on.



The fuel filter issue caught my eye since it ran great until I recently changed the filter. I use filters from NAPA and have not had a problem until now. I also checked my pressure valve spring length and it was a tad short,so carefully stretched it to the length recommended. One thing I've noticed is a ticking sound from the driver's side when the engine is running. Sounds like a loose valve but applying slight throttle makes it quiet down. Not sure what that is but I'm going down today to get another fuel filter and try that route for the low idle and engine dying.

 

[tURBOdIEZEl]

One thing I've noticed is a ticking sound from the driver's side when the engine is running. Sounds like a loose valve but applying slight throttle makes it quiet down.

mine does that... . its not a real loud ticking sound, but it just ticks enough were i can hear it over the stacks... . ive gotta go down this week and pickup a fleetguard fuel filter... .

 

[Willys]

Ticking can be the lift pump from what I've heard. I replaced my pump and don't notice the ticking anymore, but I also replaced the OF valve and a few other things around the same time.

 

[bmoeller]

New lift pumps tick a little. I can hear mine. Put it on last year. No where as loud as the worn out original.

 

[CMckee]

You may want to check your timing as low idle is a sign of the timing having slipped. My idle dropped last year and i adjustedthe set screw s you did. I took it in to get the idle bumped up to 15* instead of stock and the mechanic said mine had slipped to 7*. He said that it probably happened when my idle fell off.

just my 02.

chris

 

[Willys]

You may want to check your timing as low idle is a sign of the timing having slipped. My idle dropped last year and i adjustedthe set screw s you did. I took it in to get the idle bumped up to 15* instead of stock and the mechanic said mine had slipped to 7*. He said that it probably happened when my idle fell off.

just my 02.

chris

WOW!!!! :--) 7*? How did it run? I'm suspecting mine is low, its noticeable quieter than most other 12v engines I've heard- in that the knocking isn't as sharp. Also much less powerful...

 

[tURBOdIEZEl]

that was also sugested to me, that my timing had retarted! if my timing has indeed slipped, its getting timed to 21*... before these problems it was @ 19. 5*. i hear 21* is the sweetspot... . anyone know someone local to the austin/san antonio that could check/reset my timing?

 

[CMckee]

It ran fine, a little smokey on acceleration, compare to the way it is now. FRom what i've been told 15*- 16. * is the best spot for good all around performance. Mine pulls nice and even through the whole rpm range now. It is noticebly louder now, it sounds more like a 24v with the "pop" being sharper.

 

[Berrigan]

My first gen and second gen trucks both did the same thing after a hard pull. The idle would drop about 200 to 300 rpms.



This is what I believe-- The remaining fuel in the tank gets hot due to the overflow valve continually retuning hot fuel to the tank. Hot fuel is what is causing the rpm to drop. To test this I would transfer 20 gallons of cool fuel from the axillary tank just before finishing a hard pull. The rpm drop was much improved. Also on my 2nd gen truck the ticking was loudest (using a mechanics stethascope) on the metal part of the fuel return line. I think the ticking is coming from the overflow valve. Also the ticking is louder with hot fuel and almost quiet with cool fuel. I could be way off base but this is what I have found. It would be interesting to question a Cummins Engineer to see if hot fuel combusts different at idle than cool fuel. Bill

 

[CEdwards]

Same Problems Here Too. Been Putting Up With It For A Year. Anytime Pulling A Load And It Will Die And Run Rough And I Have To Give It A Little Pedal To Keep It Idling. I Also Have A Ticking Sound When It Does This. Tried Everything I Can From The Tdr And Finally Gave Up. Its Especially Hard To Keep It Going In The Hot Summer Months. Sure Wish Someone Would Figure This Thing Out. ALSO THE MILEAGE HAS GONE WAY DOWN TO SOMETIMES 12 MPG AND I HAVE BUMPED MY IDLE UP TWICE HERE LATELY. IT JUST SEEMS TO KEEP GOING DOWN.