Bad things happen at 1500 RPM ...

From : slick willy

Q: first the facts and only the facts 99 dakota 3.9l manual trans. 119k on the clock. daily driver with only work done in the last 3 months being 4 new tires. minor tidbits before i get to the crux of my problem. when im slowing for a stop sign or red light my truck will idle right at 1000 rpms until my truck comes to a complete stop. once i completely stop the rpms drop to about 650ish which is where it should be. it has done this consistently for about 1 month but didnt think much of it since it hasnt cause any problems. it was a little annoying but i figured since the mil didnt come on it wasnt anything to stop me from using my truck like normal. no problems with drivability or fuel mileage. my issue... after about 10 miles in the truck this morning the sound of the clutch hub fan i believe thats the name of the fan i hear when i first pull my truck out of the driveway was very loud. the sound was based on rpms as when i pushed in the clutch the sound went away. all internal gauges read normal and no issues with drivability. i pulled over to the side of the road and check underneath the hood. nothing out of the ordinary. serpentine belt was tight and i havent heard any slipping sounds in the am when it is damp out. no visible leaks or noises to draw my attention. i revved the engine a little while listening and could hear the fan spooling up but it didnt decrease as it normally does when i first drive the truck. i continued down the road and again the fan noise increased as my rpms increased. the sweet spot seemed to be 1500 rpms. if i kept the truck below that it ran and sounded like it normally does but if i went over that there were minor changes in performance of the truck. there was a tapping noise kind of like someone hitting a hollow piece of aluminum tube with a ball peen hammer very lightly. it was coming from the passenger side of the engine but i could not pinpoint exactly where it was coming from. the fan continued to increase in noise in relation to the rpms. once i was near my house i increased my rpms to 2000 and the fan noise continued to climb. i didnt want to push it and as it was i could drive 45mph so i got back home and drove my other vehicle into work. any ideas i didnt get a chance to look at anything as i was already late for work but will be looking at it tonight. is there a sensor that controls this fan and if so what is it also any idea what the tapping sound was. any relationship with 1500 rpms thanks and regards slickwilly .

Replies:

From : slickwilly

slick willy wrote first the facts and only the facts 99 dakota 3.9l manual trans. 119k on the clock. daily driver with only work done in the last 3 months being 4 new tires. minor tidbits before i get to the crux of my problem. when im slowing for a stop sign or red light my truck will idle right at 1000 rpms until my truck comes to a complete stop. once i completely stop the rpms drop to about 650ish which is where it should be. it has done this consistently for about 1 month but didnt think much of it since it hasnt cause any problems. it was a little annoying but i figured since the mil didnt come on it wasnt anything to stop me from using my truck like normal. no problems with drivability or fuel mileage. my issue... after about 10 miles in the truck this morning the sound of the clutch hub fan i believe thats the name of the fan i hear when i first pull my truck out of the driveway was very loud. the sound was based on rpms as when i pushed in the clutch the sound went away. all internal gauges read normal and no issues with drivability. i pulled over to the side of the road and check underneath the hood. nothing out of the ordinary. serpentine belt was tight and i havent heard any slipping sounds in the am when it is damp out. no visible leaks or noises to draw my attention. i revved the engine a little while listening and could hear the fan spooling up but it didnt decrease as it normally does when i first drive the truck. i continued down the road and again the fan noise increased as my rpms increased. the sweet spot seemed to be 1500 rpms. if i kept the truck below that it ran and sounded like it normally does but if i went over that there were minor changes in performance of the truck. there was a tapping noise kind of like someone hitting a hollow piece of aluminum tube with a ball peen hammer very lightly. it was coming from the passenger side of the engine but i could not pinpoint exactly where it was coming from. the fan continued to increase in noise in relation to the rpms. once i was near my house i increased my rpms to 2000 and the fan noise continued to climb. i didnt want to push it and as it was i could drive 45mph so i got back home and drove my other vehicle into work. any ideas i didnt get a chance to look at anything as i was already late for work but will be looking at it tonight. is there a sensor that controls this fan and if so what is it also any idea what the tapping sound was. any relationship with 1500 rpms thanks and regards slickwilly even though nobody posted anything in regard to my issue i wanted to follow-up with the resolution to my problem. it ended up being the fan clutch that was bad. my haynes manual has a couple of troubleshooting steps to determine if the fan clutch is bad but mine did not leak as the manual says it will when its bad. anyhow i changed out the part and the problem appears to be solved. drove about 20 miles since replacment and all issues have disappeared. regards slickwilly .