2.5L AMC 150 Gas Mileage

[1987Comanche]

I started tracking mpg on my '87 2WD 2.5L 5 speed MJ and it's only showing about 18.5mpg with mostly highway driving. With a vehicle this size and drivetrain configuration I was expecting something closer to 23-25mpg. Does this sound right for this drivetrain? What are other folks getting MPG wise?

It's the SWB Sportruck with no A/C.

[beaterjeep]

I started tracking mpg on my '87 2WD 2.5L 5 speed MJ and it's only showing about 18.5mpg with mostly highway driving. With a vehicle this size and drivetrain configuration I was expecting something closer to 23-25mpg. Does this sound right for this drivetrain? What are other folks getting MPG wise?

It's the SWB Sportruck with no A/C.

I'd almost kill to get that kinda mileage in my '88 2wd 2.5 5 speed. I'm averaging about 13 right now.

[JeepcoMJ]

I get between 15 and 19mpg with my 4wd 4 cylinder 5 speed.

 

that's with 4.10 gears. if I had 3.73's, I'd suffer a bit more in town but my highway would be about 21mpg or so. it's the 3000 RPM's driving at highway speeds that kills it.

[MJ'87]

it would also depend on how much power your 2.5 has.

2.5 5-speed 31"tires 4.11 gears

mine gets between 15 and 18 with 162k.

the new motor should get a lot more ;)

[jaekl]

I've consistently gotten 23.5mpg for 22 years with 86 2.5 5 speed Cherokee. The 88 2.5 4 speed MJ does as well. The Cherokee seems to get better in 4wd. The only maintenance has been fuel filter and plugs at 30,000. The only time I got less (significantly less) was when I borrowed the injector and torn the Oring. Put a new one in and the mileage was back to 23.5. Check the Oring around the injector body.

[Pete M]

I started tracking mpg on my '87 2WD 2.5L 5 speed MJ and it's only showing about 18.5mpg with mostly highway driving. With a vehicle this size and drivetrain configuration I was expecting something closer to 23-25mpg. Does this sound right for this drivetrain? What are other folks getting MPG wise?

It's the SWB Sportruck with no A/C.

 

What size tires? Original CAT? Done a tuneup recently? How fresh is you O2 sensor?

[mjeff87]

My '87 (5 speed) currently has 33X12.5's and 4.56's.

 

Don't ask what my mileage is......it ain't pretty :cry:

 

Way back when I got it, it was 2WD on 205/75/15's and had about 100,000 less miles on it. It used to get low 20's then.

 

Jeff

 

edit: I am putting a new cat and muffler on it soon, hopefully it'll make a tiny bit of difference :D

[1987Comanche]

I believe it has the 4.10 rear but if I drop her into 5th below 50mph she's a dog. If I climb a small grade on the highway at less than 60mph I have to downshift to 4th. The P.O. put 235/75 R15s on it on it and the recommended size on the placard is 225/75 R15. Aftermarket CAT (no idea how old), most tuneup parts have less than 8K (including O2 sensor) on them but I'd like to replace the plugs & wires with Bosch Platinums when I have a chance.

It's entirely possible the injector and/or injector O rings have issues. I don't see excessive fuel spray or dripping but the idle is a bit erratic when she's fully warmed up (hunts up and down about 150rpm).

When I change the plugs I was going to do a compression test as well. What's normal for these engines? 130-150 psi?

Any ideas why the range for these vehicles is 13mpg-23mpg?

[Pete M]

Taller than normal tires will hurt mpg and power (not to mention throw off your speedometer and all of your mpg calculations).

Lots of MJ guys (me included) find the best plugs are the regular ol' copper ones.

I would double check your rear axle ratio. There's always a small chance that the original broke and the replacement isn't 4.10.

[Oizarod115]

Taller than normal tires will hurt mpg and power (not to mention throw off your speedometer and all of your mpg calculations).

Lots of MJ guys (me included) find the best plugs are the regular ol' copper ones.

I would double check your rear axle ratio. There's always a small chance that the original broke and the replacement isn't 4.10.

 

copper cheapie champions are FSM recommended :cheers: for some reason our trucks hate platinum plugs

[gixxerman600]

if your gas has a lot of methonal in it it will disolve platinum just fyi

[JeeperjohnfromPA]

I've got a 2.5, with a 5speed in my YJ.

I was getting about 13mpg, then I installed a throttle body spacer, that pushed me up to 14mpg.

I found that running smaller tires 225/70 r15, (usually run on 235/75 r15), gives me about another 2mpg on top of that.

 

so best case I can get about 17mpg on my YJ, and thats with 271,000 miles on original motor.

 

So I figure you should be able to get somewhere around that.