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Comanche power/towing


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So today I towed my dads ranger 900 on a wooden deck trailer. Under 3k for sure. I never touched 5th gear and could barely keep the speed limit. This thing has no guts. Less than my Cherokee on 35s. What’s the deal? It’s got new injectors, cap/rotor, wires, plugs, fresh fluids all around, 2wd 5speed 4.0, and 135,000 miles.

 

 

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Different gear ratios probably .Your Comanche should have 3:07 ,what do you have in the XJ ? 

I’d agree if both were equally built, but my Comanche is stock height with street tires and my Cherokee has 5.5” of lift, and 35” Goodyear mtrs with heavy bumpers and armor. It has 4.56 with an auto and the Comanche is 3.07 4.0 5 speed with over 30,000 miles less.


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aside from the fact that 3.07s do indeed suck and should never have been installed in anything with J-e-e-p on the hood, it could certainly be a fuel flow issue or a clogged cat.  or a sensor that is giving the wrong input.  how well does it drive without the trailer?

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My money's also on the 3.07's. Recently had the experience of pulling a trailer with my stock 4.0/five-speed/3.07 XJ. It's decently quick unloaded, even full of junk, but once hooked up to an empty UHaul 5x8 which they claim only weighs 900 lbs, it was a total dog. Barely even touched 5th on the flat, any sort of hill or a headwind and I was down to 3rd. My MJ, 4.0/aw4, 3.55's (same engine, just automatic and lower gears), doesn't seem to notice trailer weight quite as much. My '01 auto 4.3L Jimmy barely even noticed the UHaul when it pulled it over the continental divide to return it... Same hp with a spit more torque further up the rev range, but also 500lbs heavier than the MJ and 800lbs heavier than the XJ, 30x9.5's vs the 235/75/15's on both Jeeps, but most importantly 3.73 gears.

 

Shouldn't be too tough to find a 3.55-geared MJ d35 if you want something bolt-in, although if you're up to setting up perches on a different axle (or fine with paying someone else to) that would be the way to go to get something with a little more beef... Later XJ 8.25 should be easy to find in a 3.55 and be a pretty good match, or a KJ will be a bit more work to cut brackets off but will likely come with 3.73's and disc brakes, but there are plenty of other common swaps as well... Beauty of a 2wd is you don't need to worry about matching the front ratio, unless you plan on swapping in 4x4.

Just don't waste money and effort regearing a Dana 35.

And like others have said, it really doesn't hurt to make sure your MJ's in decent running condition too. 

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Sure it was under 3klbs? 
 
Either way, with 35s and 4.56s your XJ is effectively geared lower.
 
But I'd look at the cat, as mentioned, along with the other basic maintenance items.

It’s only a 6x12 trailer and my friends 16ft wooden deck car hauler is 1k so I’m sure it’s lighter being single axle and smaller. The ranger weighs about 1500lb. My Comanche weighs somewhere under 3k being stock 2wd swb. My Cherokee weighs 4500 with me in it according to the scrap yard scales. No cat, done a full tune up on it.


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aside from the fact that 3.07s do indeed suck and should never have been installed in anything with J-e-e-p on the hood, it could certainly be a fuel flow issue or a clogged cat.  or a sensor that is giving the wrong input.  how well does it drive without the trailer?

Can’t hold speed on the highway no matter what. Kinda quick around town. Really only like driving it if I’m not going over 45 mph.


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If you're having issues maintaining highway speed in 5th gear on flat ground without either of a trailer or a significant headwind, something's up. I would expect low fuel pressure to cause other symptoms like stalling out or backfiring, or overhearing from running lean, but it's easy to check. 

 

What point do you shift at? In my XJ I won't shift into 5th until I'm up to speed. It's an overdrive gear, so I don't expect to do much accelerating with it, especially not with a trailer, and definitely not with the 3.07's. Without a load behind it it'll still hold speed on steep hills and even accelerate somewhat in 4th.

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what's the fuel pressure and flow look like?  maybe a compression test ?  :dunno:  my 88 is like that on the freeway these days and I know my compression numbers are low and blowby is pretty bad.   

Last I checked the fuel pressure was good, but the pump has gotten really loud. Not much blow by last I checked either.


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If you're having issues maintaining highway speed in 5th gear on flat ground without either of a trailer or a significant headwind, something's up. I would expect low fuel pressure to cause other symptoms like stalling out or backfiring, or overhearing from running lean, but it's easy to check. 
 
What point do you shift at? In my XJ I won't shift into 5th until I'm up to speed. It's an overdrive gear, so I don't expect to do much accelerating with it, especially not with a trailer, and definitely not with the 3.07's. Without a load behind it it'll still hold speed on steep hills and even accelerate somewhat in 4th.

I get up to speed then shift to 5th to try to cruise then downshift for hills then back to 5th down hill. With a trailer it’s never seen 5th.


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you MJ is way older, probably has twice o more miles on it than your 99 XJ, unless has been rebuit recently, it`s not running at its best, also the 3.07 rear ratio doesn`t help...

 

also don`t use 5th or any overdrive when towing, you put a lor of strain the drive train that way, stick to direct gear...

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21 minutes ago, SatiricalHen said:


I get up to speed then shift to 5th to try to cruise then downshift for hills then back to 5th down hill. With a trailer it’s never seen 5th.


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Pretty much my experience. Towing through Saskatchewan the roads are flat enough I could occasionally get 5th but it really didn't take much of an incline at all (to the point I didn't necessarily notice the incline) before it would loose speed, I think the longest I got out of it was 1/4 mile if that. Eventually I gave up. I'm guessing it's the extra drag from the trailer that overcomes the feeble torque you're putting down through 3.07's, not so much the weight of the trailer.

But even unloaded it doesn't really accelerate much in 5th, 3.07's are less than ideal.

 

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you MJ is way older, probably has twice o more miles on it than your 99 XJ, unless has been rebuit recently, it`s not running at its best, also the 3.07 rear ratio doesn`t help...
 
also don`t use 5th or any overdrive when towing, you put a lor of strain the drive train that way, stick to direct gear...

Clearly you didn’t read my post since I stated the Cherokee has over 30,000 more miles. Probably now like 70,000 since the speedometer has been off almost since the day I’ve owned it since I’ve put bigger tires on it, and the gauges would go in and out when I first bought it so who knows how many miles the owners before me drove it without the odometer counting.


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9 minutes ago, SatiricalHen said:


Clearly you didn’t read my post since I stated the Cherokee has over 30,000 more miles. Probably now like 70,000 since the speedometer has been off almost since the day I’ve owned it since I’ve put bigger tires on it, and the gauges would go in and out when I first bought it so who knows how many miles the owners before me drove it without the odometer counting.


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you sure the MJ has not skipped miles? whatever...

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I’m not convinced it’s 3.07 gears. The fact that I can’t cruise highway speeds at all means something is up. I’m sure from the factory with 3.07s a Comanche could cruise the highway in 5th gear or else jeep would’ve made it a 4 speed with no over drive or put different gears in it.


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10 minutes ago, SatiricalHen said:

I’m sure from the factory with 3.07s a Comanche could cruise the highway in 5th gear or else jeep would’ve made it a 4 speed with no over drive or put different gears in it.

 

Exactly. OEM stock tires were all ~27" diameter on the pedestrian models, and 3.07 gears was the "best" compromise for normal everyday driving conditions and best fuel economy. Special towing packages and other options were offered those who did more than pedestrian driving.

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By all means check everything people are mentioning. It is an older vehicle, and things that will affect your power output without obvious mechanical symptoms are frequently caused by components that deteriorate more with age than with use, like plastic vacuum lines, corroding wires, etc. If you haven't done Cruiser's tips that's somewhere good to start too. 

www.cruiser54.com

 

But regarding AMC/Chrysler's choice of 3.07's, times were not the same when the 4.0 came out. The national speed limit was 55. HP levels were barely starting to recover after emissions controls, and fuel economy crises were still within public memory. No one expected a Jeep to be a powerhouse, especially not with a six-cylinder. Despite this fact the 4.0 MJ was a pretty serious contender, mostly because the engine control system was far more advanced than most others at the time. And as Hornbrod pointed out many things that we view as weak were perfectly acceptable to the general populace of typical pedestrian drivers. Dana 35's and Peugeot BA/10's have lived long and happy lives in many MJ's and XJ's, but beefier options were available to people who wanted more out of their Jeep.

And you can't really compare it to more modern vehicles that are expected to cruise at speeds closer to 75mph than 55. Starting in the '90's as the national speed limit was being raised, everything was getting deeper gears, despite increasing power levels. In part this was due to larger tires, but people were wanting more performance out of their trucks, treating them more like regular cars, and it was just what was expected. As an example, the V6 KJ came standard with 3.73's, and tires that weren't really a significant jump from a 235/75r15.   It wasn't until 2005 as fuel prices were climbing and fuel economy became more of a concern again that they put 3.55's back into the manual KJ's. But that's still 3.55's, not 3.07's, and the 3.7L in the KJ is a pretty good hp bump from the first 4.0's. Still then no one would've expected a six-cylinder SUV to be a huge performer, but 3.07's would not have been acceptable to most of the population, despite any modest mpg gains. 3.07 is a very tall axle ratio.

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I think the truck is totally fine, or as good as it will be short of rebuilding the engine, regearing, or adding power through modifications.

 

A 87 Renix is 173HP on the showroom floor.

 

That said, I'm not driving it, and power is subjective.

 

But no, you can't just put it in 5th and cruise around.  It has a gearshifter because you need to change the gears according to engine loading and speed.

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If someone did the math-

 

It would be an interesting comparison between the two, 4.56 on 35 to 3.07 on 28, I suspect the final drive would be a wash, about the same. 

 

Years ago when I was buying XJs and selling, some were peppy, some were dogs, all ran well, no rhyme nor reason.

 

My wife's XJ is very peppy as Jeeps go, compared to my Nisan 4.0, the Jeep is an absolute dog. 

 

 

If you did a compression check, my guess is that two or more cylinders are down around 90lbs.............worn out or at least tired. 

 

I would also suspect aftermarket sensors or a failing sensor. 

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