U thank there is a problem?

[btm24]

I keep hearing a lot of people saying there Comanche gets 20-30 mpg when mine get maybe 12 :huh???: have any of yall heard of this? i have a 2wd 89 pioneer 4.0 I6. if there is something that i could do about my low mpg plz let me know thanks

[Unglar]

Sorry, will probably need quite a bit more information to provide an informed suggestion.

 

Last tune-up, what was done? Any mods? Tire size and lift? Got a pic of your truck?

[gl1200aman]

When was the last time you did a tune-up? plugs, wires, rotor, cap? May help. Have you looked at the plugs? The condition of them can tell a lot about how the truck is running. With the reformulated gas, 10% ethanol, it may clog/varnish some parts so you may want to try carb, injector cleaner or seafoam in a few tanks. You need to do some basic checks to see what is going on.

 

My 88 4.0 with 296k 5 spd 4x4 in 2wd gets 20mpg at 65-70 and 21+ at 55-60.

[btm24]

When was the last time you did a tune-up? plugs, wires, rotor, cap? May help. Have you looked at the plugs? The condition of them can tell a lot about how the truck is running. With the reformulated gas, 10% ethanol, it may clog/varnish some parts so you may want to try carb, injector cleaner or seafoam in a few tanks. You need to do some basic checks to see what is going on.

 

My 88 4.0 with 296k 5 spd 4x4 in 2wd gets 20mpg at 65-70 and 21+ at 55-60.

 

I just "tuned" it up by washing out the motor (long story) and only 2 mouths ago i replaced the spark plugs caps wire and what not. it has brand new 31" tires, auto and has no lift. and the pic below is my truck hears a link to the most up to date build http://www.cardomain.com/ride/3859502 i have not started one on hear YET . tell me if you need more info

 

Thanks Brandon

[Unglar]

Stock with 31" tires? Whats your gearing? I bet your speedo is off.

[btm24]

Stock with 31" tires? Whats your gearing? I bet your speedo is off.

 

oh yeah its off i know that but b4 i got the new tires with the supper old bald tires i got 14 on a good day. so i thank now I'm getting about 14mpg. i drove on the old tires for 1.5 months (after tune up) and 14 mpg was the average. my gearing is what ever the truck came with idk

[Unglar]

Alot of the stock trucks for that year came with 3.07 gears which are terrible for larger tires. Somewhere on here is a guide on how to figure out what your gearing is.

[btm24]

Alot of the stock trucks for that year came with 3.07 gears which are terrible for larger tires. Somewhere on here is a guide on how to figure out what your gearing is.

 

well when i got for the 4x4 convert i will get a dana 44 with 4.10 gears. but till then u thank that is what the issue is?

[Unglar]

I doubt it is the only issue, could be a combo of gearing and speedo, but there may be other issues also, like a vacuum leak causing it to run rich will lower mpg's.

[btm24]

I doubt it is the only issue, could be a combo of gearing and speedo, but there may be other issues also, like a vacuum leak causing it to run rich will lower mpg's.

 

how would u check for a vacuum leak?

[freakjeep93]

I doubt it is the only issue, could be a combo of gearing and speedo, but there may be other issues also, like a vacuum leak causing it to run rich will lower mpg's.

 

how would u check for a vacuum leak?

spray something flammable around you vacume lines . if the idle changes you have a leak

 

 

 

i thinkthat auto 4.0 mjs came with 3:55 gears. but remember its just a thought

[btm24]

I doubt it is the only issue, could be a combo of gearing and speedo, but there may be other issues also, like a vacuum leak causing it to run rich will lower mpg's.

 

how would u check for a vacuum leak?

spray something flammable around you vacume lines . if the idle changes you have a leak

 

 

 

i thinkthat auto 4.0 mjs came with 3:55 gears. but remember its just a thought

 

 

ok not a vacuum leak, what else could the bad mpg be from?

[gl1200aman]

When you replaced the plugs, did you check the gap?

[btm24]

When you replaced the plugs, did you check the gap?

 

yeah they are fine. thanks tho

[jpdocdave]

I doubt it is the only issue, could be a combo of gearing and speedo, but there may be other issues also, like a vacuum leak causing it to run rich will lower mpg's.

 

how would u check for a vacuum leak?

spray something flammable around you vacume lines . if the idle changes you have a leak

 

 

 

i thinkthat auto 4.0 mjs came with 3:55 gears. but remember its just a thought

 

many many auto 4.0's are 3.07, including my big ton. Its great for gas mileage in stock form, if you keep your foot out of it. I get 17-18 around town. 31" tires and 3.07 gears is a pretty big factor, that gear ratio is now closer to 2.07:1 than 3.07.

[gl1200aman]

If you have larger tires then your speedometer and odometer are registering less than what you are doing. Depending on what you're difference is you may be getting better mpg. Like the others said, the larger tires are causing your engine to work harder and less mpg.

[dasbulliwagen]

With larger tires, you can no longer go by the odometer to calculate fuel milage. Youll actually be traveling farther than what your odo says, so with that being the case, like a previous poster said, you may be getting better fuel milage anyways and not know it because your odo and speed are off. If you can find the original tire size, get its circumference, and measure the circumference of your existing tires, then divide the two together, this will give you a percentage that your speed and odo is off and then you can add that percentage to your per tank milage for a more accurate reading.

 

Does this sound right guys? I think it does, just let me know if it is wrong.

 

I did this method to my truck except with the rear end gearing to know the percentage difference between the old 3:55 gears, and the new 4:10 gears with no other changes. I think it worked out to be around 15%, and I use that percentage to know how far fast my speedo is now.

[mvusse]

I doubt it is the only issue, could be a combo of gearing and speedo, but there may be other issues also, like a vacuum leak causing it to run rich will lower mpg's.

 

how would u check for a vacuum leak?

spray something flammable around you vacume lines . if the idle changes you have a leak

 

 

 

i thinkthat auto 4.0 mjs came with 3:55 gears. but remember its just a thought

 

many many auto 4.0's are 3.07, including my big ton. Its great for gas mileage in stock form, if you keep your foot out of it. I get 17-18 around town. 31" tires and 3.07 gears is a pretty big factor, that gear ratio is now closer to 2.07:1 than 3.07.

 

The factory used 3.55 gears for 4.0/auto. 3.07 was used for 4.0/5 speed stick.

 

My 87 with 130,000+ neglected miles got 24mpg cruising at 60mph after a full tune up on stock tires. 20mpg going 70. 33x12.50 road tires I got 18mpg cruising ~75-80 (CBs are great to get Smokey reports from trucks....).

 

All these numbers have been corrected for odometer being off and double checked by GPS.

 

Now with my 35x12.50 soft rubber MTs mileage is down the drain. 16mpg at best, but mixed driving closer to 12 (stock tires was 17).

[88pioneer]

Yes auto= 3.55 gears. My question is whats your driving style like? If you put your foot in it everywhere you go, your MPG's won't be pretty

[btm24]

With larger tires, you can no longer go by the odometer to calculate fuel milage. Youll actually be traveling farther than what your odo says, so with that being the case, like a previous poster said, you may be getting better fuel milage anyways and not know it because your odo and speed are off. If you can find the original tire size, get its circumference, and measure the circumference of your existing tires, then divide the two together, this will give you a percentage that your speed and odo is off and then you can add that percentage to your per tank milage for a more accurate reading.

 

Does this sound right guys? I think it does, just let me know if it is wrong.

 

I did this method to my truck except with the rear end gearing to know the percentage difference between the old 3:55 gears, and the new 4:10 gears with no other changes. I think it worked out to be around 15%, and I use that percentage to know how far fast my speedo is now.

 

Thanks but i all ready did somthing about the same. i had a cop friend clock me where my odo said i was going 30 he said he clocked me at 35.6 mph. at 60 (according to my odo) when I'm rly going about 72.2. by this i now did some math and found that my odo was off by 3.56 mph per every 10 mph. now i found a chart on hear to fix the odo by tire size ive just been to lazy to do it. but when my odo did work right it was reading 14 mpg so i figured I'm running at about 12 mpg now. i have know about the odo being off b4 i got the bigger tires. thats not the problem the problem is that even b4 when i had smaller tires i had horrid mpg. i was wondering what would cause this bad mpg? and thing other then a tune up (which i have done) bigger tires(shouldnt have dropped it more then 2mpg) and the bad gear rate. any thing else?

 

Thanks :D

 

ps i don't drive with a lead foot

[Pete M]

I never got better than 14 in my 88 back in 98 when it was a 10 year truck and my daily driver. It's a truck. It's an old truck. Don't expect miracles. :D Single digits are where I would start to get worried.

 

tire size is more than just the ratio in the axles. the further you are from the sweet spot of ratio to peak engine torque to speed at every given moment, it's practically exponential how much more gasoline it takes to get moving.

[btm24]

I never got better than 14 in my 88 back in 98 when it was a 10 year truck and my daily driver. It's a truck. It's an old truck. Don't expect miracles. :D Single digits are where I would start to get worried.

 

tire size is more than just the ratio in the axles. the further you are from the sweet spot of ratio to peak engine torque to speed at every given moment, it's practically exponential how much more gasoline it takes to get moving.

 

ok well thanks pete once again i just got worry cuz of all of the posts with people who say they got 20 or more mpg. If you of all people say 14 should be ok then its ok to me :thumbsup:

[jpdocdave]

14 mpg is not horrible, thats all I can get with my 96 xj around town, my 90 mj (which is auto 4.0 and 3.07 gears from the factory) gets 17-18 around town, and 24 on hiway easily around 63 mph. From my experience my mj is getting on the hi side of mpgs, your 14 is not really all that bad.

[TrailReadyMJ]

 

Now with my 35x12.50 soft rubber MTs mileage is down the drain. 60mpg at best, but mixed driving closer to 12 (stock tires was 17).

 

What gears are you running? I get about 16-18 mixed and 20+ highway with 35" swampers and 4.56 gears. My speedo reads about 2 MPH fast at 30 (checked by radar station), but I have calculated MPGs by GPS.

I am mainly wondering if it may have to do with the 93' HO engine I put in, even though it's still running Renix injection.

I couldn't fairly compare it to what the old motor got because it ran awful, and got 14 at best.

I am also usually pretty light on the skinny pedal, and that always helps.

 

I also want to add, for those with incorrect speedos, you can simply swap out the gear to get it close. I haven't seen a chart on here yet, there may be one, but I know there's one on naxja or found by google. Last I checked on one it was around $30 from the local dealer (cheaper than a speeding ticket if yours reads low!).

[mvusse]

Still running stock 3.55.

 

Plan is to upgrade to FS Ford axle (high pinion 44 front, matching 9" rear), so I'm not going to regear what I have. these 3.55s are going to go into Booger (4.0HO/AX-15, currently has stock 3.07 gears), and I'm building a 4.10 ratio front axle to go under Sparkles (4.0HO/AW4). Will need to get a 4.10 rear axle before I make it into a 4wd, as it is currently still stock at 3.55.