Comanche power/towing

[Jeep Driver]

I'll add one more thought-

 

I posted a vid of my new engine at idle in my build thread, mainly to show that after mods the engine ran well. 

Previously I had found an ignition module NOS, OEM,  Siemens, dated 1994, it sat in a box for 24 years, complete with coil. 

I was saving it for future replacement after the original failed. I decided to go ahead and swap it. Idle is much more even or flat or constant, throttle response is more crisp.....it runs even better. 

I've not posted on this because, some will say electronics are electronics, they work or they don't. I'll disagree, after thirty years of use, heating, cooling...........age.

 

All things wear out, they tire. Aftermarket parts are not the same quality as OEM. 

 

Yet, after 30 years we expect them to perform as new. 

 

 

[SatiricalHen]

The truck has a 1990 ecu in it, so a little more pep and power than an 87 ecu. I’ve done most of cruisers tips. Most if not all sensors on it are factory, but the ones I’ve checked are in spec aside from the IAC which I’m getting one from a friend next week. I don’t expect to be able to stick it in 5th and cruise down the highway just fine, but I barely get to 5th ever. I understand you need to downshift at times, but it shouldn’t be riding in 4th 90% of the time. This thing feels worse than my 2000 Jetta I had and that was a 5 speed 4 cylinder that had serious oil burning problems with who knows how many miles on the engine. That car weighed the same or more than the Comanche. Obviously the aerodynamics are different, but they also had at least 80 hp difference factory, and 100 less ft/lb of torque. I could stick that sucker in 5th and cruise. Maybe it’s just time to park the Comanche till I have the funds to do the engine build I want.


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[DirtyComanche]

4 hours ago, Jeep Driver said:

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.

 

Nope, 4.56 with 35s is effectively lower by a fair margin.  Using 1:1 drive (4th gear in the manual trans, 3rd in the auto) and 65mph you will tach 2400RPM with the 28s and 2850RPM with the 35s.  Now that said the auto would normally come with lower axle gears, as the first gear ratio is fairly high, but it's honestly a mistake on the design end that they did this from a street driving perspective as the converter slip allowance means the AW4 first gear is "lower" than the Peugeot or Asin manual tranny.  There is also a slight difference in OD ratio between auto and manual, .75 for the later AW4 vs .79 for the Peugeot, but it doesn't matter as much as the auto shifts automagically so people don't notice the lack of power in OD.  Basically what I"m getting at is that the 3.07 gears were a terrible idea from the perspective of the driving experience, but they did make sense as far as meeting fuel economy requirements because they gave you a true miser gear for coasting.

 

Factoring in OD ratios will produce about 1900RPM for the 5spd, and 2140rpm for the auto.  200 and change RPM will still make a significant difference to how it drives when you're that low in the RPM range.

[SatiricalHen]

 
Nope, 4.56 with 35s is effectively lower by a fair margin.  Using 1:1 drive (4th gear in the manual trans, 3rd in the auto) and 65mph you will tach 2400RPM with the 28s and 2850RPM with the 35s.  Now that said the auto would normally come with lower axle gears, as the first gear ratio is fairly high, but it's honestly a mistake on the design end that they did this from a street driving perspective as the converter slip allowance means the AW4 first gear is "lower" than the Peugeot or Asin manual tranny.  There is also a slight difference in OD ratio between auto and manual, .75 for the later AW4 vs .79 for the Peugeot, but it doesn't matter as much as the auto shifts automagically so people don't notice the lack of power in OD.  Basically what I"m getting at is that the 3.07 gears were a terrible idea from the perspective of the driving experience, but they did make sense as far as meeting fuel economy requirements because they gave you a true miser gear for coasting.
 
Factoring in OD ratios will produce about 1900RPM for the 5spd, and 2140rpm for the auto.  200 and change RPM will still make a significant difference to how it drives when you're that low in the RPM range.

Although the gearing is slightly lower, the Cherokee also weighs over 1000lbs more according to the scrap yard scales. There is also much more rolling resistance, and there is much more drag with it being lifted 5.5”. All of these comparisons are really apples to oranges. Just really feel there is something up with it.


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[Eagle]

18 minutes ago, SatiricalHen said:

Although the gearing is slightly lower, the Cherokee also weighs over 1000lbs more according to the scrap yard scales. There is also much more rolling resistance, and there is much more drag with it being lifted 5.5”. All of these comparisons are really apples to oranges. Just really feel there is something up with it.
 

 

The Cherokee weighs 1000 pounds more than what?

 

Curb weight for the 89 MJ ranged from a low of 2897 pounds for a 2WD shortbed to a high of 3130 for a 4WD longbed. (Source 1989 MJ Owners manual)

 

Curb weight for an XJ was 3357 pounds (source Wikipedia -- weight not given in '94 FSM). I've seen other sources that said the Comanche curb weight was higher than the Cherokee.

[SatiricalHen]

 
The Cherokee weighs 1000 pounds more than what?
 
Curb weight for the 89 MJ ranged from a low of 2897 pounds for a 2WD shortbed to a high of 3130 for a 4WD longbed. (Source 1989 MJ Owners manual)
 
Curb weight for an XJ was 3357 pounds (source Wikipedia -- weight not given in '94 FSM). I've seen other sources that said the Comanche curb weight was higher than the Cherokee.

The Cherokee weighs 1000 lbs more than the Comanche according to the scale at the local scrap yard. You have to remember the Cherokee has 35” tires which weigh more, 4wd, long arms made of 1/4” wall dom tube, 2x6 3/16 wall rock sliders, plate bumpers and the Comanche is a bone stock stripped down 2wd 5 speed swb truck. Nothing really stock on the xj anymore.


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[Eagle]

3 hours ago, SatiricalHen said:

The Cherokee weighs 1000 lbs more than the Comanche according to the scale at the local scrap yard. You have to remember the Cherokee has 35” tires which weigh more, 4wd, long arms made of 1/4” wall dom tube, 2x6 3/16 wall rock sliders, plate bumpers and the Comanche is a bone stock stripped down 2wd 5 speed swb truck. Nothing really stock on the xj anymore.


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So you're talking about your modified Charokee, not "the" Cherokee.

[SatiricalHen]

 
So you're talking about your modified Charokee, not "the" Cherokee.

Yes, I’m comparing my 4.0 Comanche to my 4.0 cherokee since it’s the only other 4.0 I have easily available. I had stated this previously in this thread also.


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[johnj92131]

Hen,

 

I suspect that your Comanche engine has a problem if the 4.0 is underperforimg a 2.5 XJ in the same or near same towing situation.  Also the issues with running in 5th gear tell me some thing is not right with your engine.  My sister-in-laws 4.0 91 XJ had a 5 speed and 3.07 and it would tow a boat with no big issues.

[carnuck]

HO injectors in a Renix rig can up the power some but it also drops the fuel economy. In the past I found an ‘87 XJ 2wd with 4.0L, BA 10/5 5 speed and 2.72 gears. It worked well with stock tires but the O/D was 0.70:1

 

 

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[SatiricalHen]

Hen,
 
I suspect that your Comanche engine has a problem if the 4.0 is underperforimg a 2.5 XJ in the same or near same towing situation.  Also the issues with running in 5th gear tell me some thing is not right with your engine.  My sister-in-laws 4.0 91 XJ had a 5 speed and 3.07 and it would tow a boat with no big issues.

Not sure where the 2.5 xj came from, but there’s definitely something wrong.


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[SatiricalHen]

HO injectors in a Renix rig up the power but also drop the fuel economy. In the past I found an ‘87 XJ 2wd with 4.0L, BA 10/5 5 speed and 2.72 gears. It worked well with stock tires but the O/D was 0.70:1


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It’s already got upgraded 4 hole injectors, but I’m not trying to up the power. I just want to know what’s wrong, not how to possibly bandaid the problem.


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[rokinn]

I did a 2500 mile R/T this last fall towing 1400 lb popup trailer and a bed full of gear and water.  My rig is pretty similar to yours .  It's a slight gradual elevation gain from CO to WY and then strong head winds on I 80 west about as far as eye can see.  5th gear was pretty much a down hill only event and, 4th and sometimes even 3rd depending on the up grade and headwinds.  When it started to rain as I got near to the end of the trip out it got even worse.  This led me to believe I had a spark plug wire problem which I checked when I got to my destination.  Sure enough my # 6 wire had begun to corrode at the spark plug.  On the return I could cruise at 75/80 on the flat in 5th, uphill incline of any significance still required 4th gear but overall it was better.  I may still have other items of performance to address but I've also concluded that the 3.07 just isn't going to cut the mustard so I intend to re-gear to a 3.54 or 3.73 in the D44 I have.

 

I welcome any thoughts as to which might be preferable if anyone cares to comment (don't want to hijack the thread but perhaps it applies to OP also).  I'm leaning to 3.54 given the type of uses and driving I do.  Also I think it will be easier to find a front axle in 3.54 or 3.55 for later possible 4wd conversion?   

[gogmorgo]

3.55 d30's are for sure easier to find. Almost every auto XJ has one.

[SatiricalHen]

3.55 d30's are for sure easier to find. Almost every auto XJ has one.

If it’s staying basically stock 3.55 is a lot easier to find.


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[saveevryjp1998]

I can say i never crunched a 4wd drive 4dore xj that weighed under 4000 manual pukegoat or aw4 renix or late model and i have crunched well over a dozen. There is not a snowballs chance in hell that Wikipedia is right on the xjs curb weight. Even a 2wd 2.5 xj vs a 4wd 4.0 xj isnt the difference of over a thousand pounds 25% overall weight. If that wad the case the shear power to weight ratio would make a 2wd 2.5 look like a firebreathing dragon. We all know that isnt true. I had a an 88 mj 2wd lwb with a bad rear main seal. I also had a 4wd swb 88 mj at the same time. These were my first mjs. The lwb was a pig compared to the swb even though it had the small stock tires and 2wd. I let it go just kept pouring oil in her. She now has a hole in the block near the engine mount on the driver side about the size of a fist. It kept running I just lost power till the end. I think I drove it about a mile with that hole. I did park it though since on the next mile after that I heard an even louder thud. My oil pan now looks like either a metal eating monster got really hungry or you took a grenade and put it in the oil pan after you bolted it to the block. Id run a compression check. I know the gearing is drastic, but without a trailer empty I'm with you something is up and my father taught me "your machine your in control of should be an extension of your finger tips". You know your fingertips and your feeling something weird.

[saveevryjp1998]

The curb weight of an xj is closer to 4400 lbs. Many guys gut the doors carpet and plastic to ditch close to 500lbs. Which again for power to weight makes a huge difference especially in an offroad rig with xtra weight in bumpers, armor, winch, tools, tires, heavier suspension components(lifts) and potentially loaded with passengers. Those doors help keep the xj s unit body from twisting as much, but a hot day of wheeling with hot engine makes you give up the 4 doors fast to wheel longer and cooler. I always hated it though feeling like I would be crushed like a soda can in a rollover since auto glass and some skinny folded 18 guage sheet metal posts don't make a good cage for the 4000+ lbs on top off it.

[SatiricalHen]

My Cherokee has a lot of the power options, added insulation and sound deadening under the carpet, 2 amps, subwoofer and box, 35” spare, a decent amount of tools, and lots of armor. It’s a heavy pig.


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[schardein]

My 91 4x4 auto 4dr XJ comes in at 3700.

My 1991 short bed 4.0 2wd MJ weighed in at 3500 lbs, and 3560 with a bed mounted toolbox, rubber bed mat, plastic tailgate protector, and a small tool kit on board.

[gogmorgo]

Yeah, I'm not sure how the factory obtained their numbers but they're pretty low. I rolled over a scale in my MJ with me and some tools on board, at 1800kg. 1100 front axle, 700 rear. I'd estimate ~350-400lbs on board, so that's at least 3600lbs for my completely stock '91 lwb/aw4/231 with some of the redneck lightness/air con added. Um, rust.