Gas Mileage, 3.9 Dakota
From : ron s
Q: just wanted to pass this along maybe it will help someone else. i like a lot of people were complaining about poor mileage in my 96 dakota with 3.9 engine. i was getting 16-17 no matter what i did. the engine had a rattle up front that sounded like marbles bouncing around. turns out it was the timing chain slapping the cover. 149k on it!! to make a long story short i replaced the chain and gears in an afternoon under the shade tree and as soon as i started it up it sounded a lot quieter in the exhaust note. it turns out that the old chain had about an inch of slop in it which had the valve timing retarded along with the ignition timing also i suppose. i am not sure if the computer has any feedback system to compensate for timing errors but i doubt it as the rotor is driven from the camshaft. after my first full tank of gas run through it i have gained 2 mpg just from replacing the chain plus it has a lot more power to boot. the bottom line is if you have a high mileage motor that has a rattle in it up front and gets poor mileage....replace the chain! total parts were only $64 federal mogul and a good afternoon of work. you will get better mileage and peace of mind knowing the chain is not going to let loose on you. ron .
Replies:
From : ron s
i have the 3.501 in it so it is pretty tall. at 55mph the tach is only turning about 1300 rpm give or take a few after the od kicks in. ron i would be glad to get 16-17 mpg with my 3.9 dakota. the timing chain and gears have already been replaced. what gear ratio does your truck have ken .
From : napalm heart
just wanted to pass this along maybe it will help someone else. i like a lot of people were complaining about poor mileage in my 96 dakota with 3.9 engine. i was getting 16-17 no matter what i did. the engine had a rattle up front that sounded like marbles bouncing around. turns out it was the timing chain slapping the cover. 149k on it!! to make a long story short i replaced the chain and gears in an afternoon under the shade tree and as soon as i started it up it sounded a lot quieter in the exhaust note. it turns out that the old chain had about an inch of slop in it which had the valve timing retarded along with the ignition timing also i suppose. i am not sure if the computer has any feedback system to compensate for timing errors but i doubt it as the rotor is driven from the camshaft. after my first full tank of gas run through it i have gained 2 mpg just from replacing the chain plus it has a lot more power to boot. the bottom line is if you have a high mileage motor that has a rattle in it up front and gets poor mileage....replace the chain! total parts were only $64 federal mogul and a good afternoon of work. you will get better mileage and peace of mind knowing the chain is not going to let loose on you. ron i would be glad to get 16-17 mpg with my 3.9 dakota. the timing chain and gears have already been replaced. what gear ratio does your truck have ken .
From : rick blaine
i have the 3.501 in it so it is pretty tall. at 55mph the tach is only turning about 1300 rpm give or take a few after the od kicks in. who drives 55! .
From : fmb
i have the 3.501 in it so it is pretty tall. at 55mph the tach is only turning about 1300 rpm give or take a few after the od kicks in. who drives 55! well i for one drive 55 mph at least 4 times a day sometimes more sometimes less but on most days at least 4 times. -- fmb only one b in fmb .
From : mac davis
on wed 23 jun 2004 031626 gmt rick blaine fernjames-nospam@shaw.ca wrote i have the 3.501 in it so it is pretty tall. at 55mph the tach is only turning about 1300 rpm give or take a few after the od kicks in. who drives 55! hmm... people with 3.9 engines actually i do.. when im building up speed to merge onto the freeway... mac .
From : nikoli yetti
i recently took a 250 mile trip and had time to spare. i drove 60 on the highway and i kid you not; i almost doubled my gas mileage. also i only put my ac on going down hill. i usually drive 70 +. i have the 3.501 in it so it is pretty tall. at 55mph the tach is only turning about 1300 rpm give or take a few after the od kicks in. who drives 55! .
From : n cass
mac davis wrote hmm... people with 3.9 engines actually i do.. when im building up speed to merge onto the freeway... mac is it just me or does this motor run out of horsepower after 45 mph i have owned an 89 with tbi and i drive an 87 carbureted daily for work. both trucks were pretty sorry for passing or even accelerating to merge with interstate traffic. the 87 is even worse since it has the 3 spd automatic. just curious. -- nick remove number one if replying by electronic mail .
From : napalm heart
mac davis wrote hmm... people with 3.9 engines actually i do.. when im building up speed to merge onto the freeway... mac is it just me or does this motor run out of horsepower after 45 mph i have owned an 89 with tbi and i drive an 87 carbureted daily for work. both trucks were pretty sorry for passing or even accelerating to merge with interstate traffic. the 87 is even worse since it has the 3 spd automatic. just curious. -- nick remove number one if replying by electronic mail my 97 seems to have enough power for what we use it for. itll hit 80 without any problem. ken .
From : Annonymous
on wed 23 jun 2004 225408 gmt n.cass mrdakotasport1@netscape.net wrote is it just me or does this motor run out of horsepower after 45 mph i have owned an 89 with tbi and i drive an 87 carbureted daily for work. both trucks were pretty sorry for passing or even accelerating to merge with interstate traffic. the 87 is even worse since it has the 3 spd automatic. just curious. mine runs fine. i drive about 60mph on backroads everyday till i hit a short highway stretch before work and run that at 70. long highway trips at around 75 are no problem. the longer the trip the better my mileage gets and ive run the truck with tailgate up and down with no difference in mpg; the same goes for a/c. john .
From : n cass
napalm heart wrote my 97 seems to have enough power for what we use it for. itll hit 80 without any problem. ken i guess there must be a big improvment when they went to the magunum style engine multi-port injection. the 87 i drive will hit 80 mph also just need to be going downhill with the wind behind you to help acheive that speed -- nick remove number one if replying by electronic mail .
From : n cass
scirocco@prexar.com wrote mine runs fine. i drive about 60mph on backroads everyday till i hit a short highway stretch before work and run that at 70. long highway trips at around 75 are no problem. the longer the trip the better my mileage gets and ive run the truck with tailgate up and down with no difference in mpg; the same goes for a/c. john what year is your truck my 87 le runs good most of the time the rest of the time it is carburetor issues. maintains a constant 16 mpg whether in town or on the hwy. if i turn the a/c on i might as well get out and push. i usually average 1000 miles a week on this truck. now the 91 we have runs great. throttle body injection 319000 miles and it is still running. -- nick remove number one if replying by electronic mail .
From : Annonymous
on thu 24 jun 2004 224337 gmt n.cass mrdakotasport1@netscape.net wrote scirocco@prexar.com wrote mine runs fine. i drive about 60mph on backroads everyday till i hit a short highway stretch before work and run that at 70. long highway trips at around 75 are no problem. the longer the trip the better my mileage gets and ive run the truck with tailgate up and down with no difference in mpg; the same goes for a/c. john what year is your truck my 87 le runs good most of the time the rest of the time it is carburetor issues. maintains a constant 16 mpg whether in town or on the hwy. if i turn the a/c on i might as well get out and push. i usually average 1000 miles a week on this truck. now the 91 we have runs great. throttle body injection 319000 miles and it is still running. oops forgot that part. its a 98 4x4 .
From : napalm heart
i guess there must be a big improvment when they went to the magunum style engine multi-port injection. the 87 i drive will hit 80 mph also just need to be going downhill with the wind behind you to help acheive that speed -- nick remove number one if replying by electronic mail my neighbors got a late 80s dakota and thats what weve concluded. mine seems to have a lot more power than his does. it will go faster than that 80 but i dont like to take it there. its got about 177000 miles on it. the timing chain and gear set have been replaced but the rest of the internals are original. ken .
From : ol duffer
on wed 23 jun 2004 225408 gmt n.cass mrdakotasport1@netscape.net wrote is it just me or does this motor run out of horsepower after 45 mph i have owned an 89 with tbi and i drive an 87 carbureted daily for work. both trucks were pretty sorry for passing or even accelerating to merge with interstate traffic. the 87 is even worse since it has the 3 spd automatic. air resistance starts to become a significant factor at about that speed and its probably shifting into overdrive somewhere around there and you probably didnt spend the few extra bucks for the 3.92 axle ratio that should have been standard with that motor so yeah that sounds about right. .
From : chris
jez and to think i can do over 80 in the 1/4 mile. had it up to 105 with plenty left to go. oh well. must be the high flo cat and exhaust the modified ecm modified throttle body rear gears through are 4.101 but still get 17 mpg around town. just have to stay off of the nitros. that cost a lot. on 25 jun 2004 112433 gmt ol duffer dontsend@mespam.com wrote on wed 23 jun 2004 225408 gmt n.cass mrdakotasport1@netscape.net wrote is it just me or does this motor run out of horsepower after 45 mph i have owned an 89 with tbi and i drive an 87 carbureted daily for work. both trucks were pretty sorry for passing or even accelerating to merge with interstate traffic. the 87 is even worse since it has the 3 spd automatic. air resistance starts to become a significant factor at about that speed and its probably shifting into overdrive somewhere around there and you probably didnt spend the few extra bucks for the 3.92 axle ratio that should have been standard with that motor so yeah that sounds about right. .