My dads 03 has been acting up lately. The first symptom was no acceleration on full throttle. It would just rev up real high (after a delayed downshift) and accelerate about the speed it would at 1200 rpm. A day later it died, restarted fine, died later, and barely restarted. After a couple changed fuel filters he had the tranny fluid changed. Seemed to work, we took it on vacation this weekend ( and got 18.76 mpg ), but still didnt want to accelerate under full throttle. Occasionally it would get up and go, faster than my ol 7.3, but more often than not it would just rev sky high and speed up like a grandpa. Today he was coming home from the farm and it died on him. I towed him to the shop where I am currently searching for answers. No check engine lights or anything. It acts like my truck did when the valve cover gasket harness went bad and it would only run on 4 cylinders. Its got 125k miles and has never been in the shop or had any previous problems. Any thoughts before we have it towed? I did notice when I drove it on vacation the throttle would act "jumpy". Hard to explain correctly, but if i held my foot steady on the pedal at half throttle or whatever the rpms would go up, but not steadily. It was a very slight jumping ( maybe 100 rpm or less) it would jump up instead of slowly accelerate. I figured it was nothing, and it probably is just the nature of the beast, but I thought id throw it in there. Thanks in advance for the help

 

Well I went out and played with it for a bit and heres the news. Will currently start. Idles rough, rpms jump between 400-1000, shakes, will rev up fine or sluggish and shake. After reachin high rpms and comin down it will smooth out and idle normally for about 10-15 seconds before getting rough again. Im too afraid to take it for a road test. But it does run, just very rough and shaky.

 

Well I went out and played with it for a bit and heres the news. Will currently start. Idles rough, rpms jump between 400-1000, shakes, will rev up fine or sluggish and shake. After reachin high rpms and comin down it will smooth out and idle normally for about 10-15 seconds before getting rough again. Im too afraid to take it for a road test. But it does run, just very rough and shaky.

 

1st, when were the fuel filters last changed and #2 try unplugging the icp sensor and see if there is any diff. Just some suggestions from a backyard mech.

 

We've been running the truck on biodiesel (homemade, but good quality fuel) and thought maybe it stirred something up and clogged the filter. Now the truck will run ok sometimes. My dad took it for a drive earlier. Started a lil funny, so he took the battery cables off and cleaned them and that cleared it up for awhile, but its still "off". Where would I find the icp sensor? Im not familiar with the 6.0's

 

On '03's it's in back of the turbo -

Page 11: Component Locations

 

you still didn't answer when the fuel filters were last changed. I would start there since you are running home brew for fuel.

 

fuel filter was last changed 600 miles ago, and at that time it didnt help. had the tranny oil changed and then drove 500 miles on vacation and ran good until i got home.

 

i have been having these exact same symptoms with my truck. i had the wrong oil in it for about 5000 miles and when i was doing some heavy towing is when it acted up. i took it to a shop and they said i needed a new fuel pump and one injector was bad then they fixed that and still didnt run the same. took it back and they said another injector was bad so i had them change it and still nothing. i ended up hearing about what old oil will respond in a truck and was kinda what i was experiencing so i changed the oil and it ran pretty good but still didnt quite come all the way out of it. then it would act up again and barely run so i would change the oil again and it would be fine. i was told that my injectors are probly gummed up so i got some hot shot secret addative and ran that through and it ran good for awhile then did the same thing. got another bottle just today and have had my truck running for about 3 hours now and still isnt looking good. since i got a full tank of diesel im just gonna let it run for hours and hours maybe even days. the shop is lost at what is going on and so am i. these engines have so many different problems its hard to even narrow it down. in my case i dont see it being injects cuz sometimes it will run good and sometime it wont and me or anyone ive talked to ever heard of an injector going bad then getting better. so any ideas would be very appreciated. have you tried changing your oil? or even try some of that hot shot stuff. im not sold on it yet but i got my fingers crossed lol