Beating a dead horse (4.0 42RLE)

[schmidtke_c]

Whats going on ya'll.

Lets get right to it, so when I bought to jeep 6 years ago it was a solid turd, coming from multiple xj's I had really high expectations because of how capable all of my past jeeps have been. Fast forward though all the bugs builds and thousands of dollars build and rebuilding the jeep working out kinks and so on. When I purchased this jeep it come with a set of 33's on it but had 3.73 gears and was an absolute dog. I was lucky if I hit 60 mph with a tail wind, I could floor it and it just didn't have any balls. Spent some time and countless hours researching decided i was going to gear it and ultimately with with 4.56 gearing which helped dramatically. when i had the 4.56's it would reach 75 on a good day. However, it still needed something. Last spring I ripped the rear axle off and slapped a Dana 44 on it then put gears in and went with lockers and 4.88s and scored a really good deal on a brand new set of 35's.

I don't remember it being such a dog when I parked it for the winter but come this spring when I pulled it out, it feels like it did when i had originally bought it and had the 33's with 3.73 just no balls seems like it tops off at 65 mph, it just seems unusual. It doesn't Throw any codes regularly and every once in a blue moon ill get a Evap code that I've been chasing for the last 2 years or so. I've replaced all 3 cats, the 4 02 sensors, fluid is a nice red color and smells fresh and plugs are fairly new. i keep up on regular maintenance and run all high quality fluids. it gets terrible gas mileage (yeah i know its like running with plywood) I'm not expecting speed but i do need to be able to reach comfortable highways speeds.

Did I miss something or is this 42rle really just that big of a dog? It shifts well, its quiet and I haven't has any issues with it, I don't know if the previous owner ever did anything to it or the sensors but i would think at 101K that it would still cruise along without any major flaws. Also still has the original ecm and again doesn't throw any codes that would lead me to believe it has anything to do with that. I just want to pick some brains that have a some insight, maybe I'm over thinking this and it really just is a turd.

 

[AdventurePig]

Short answer is that neither 33’s/4.56’s nor 35’s/4.88’s are optimal for that transmission.

Optimum gearing for 33’s with the 42RLE is generally held to be 5.13’s.

https://wranglertjforum.com/threads...angler-tj-lj-and-other-re-gearing-faqs.17063/

With 35’s, and 5.13’s, the overdrive gear on ours is pretty useless, and it does take a fairly long time to get up to 65mph, compared to our other vehicles, though I’ve gotten used to it.

If you have a Rubicon, you can go to 5.38’s with 35’s, which I’ve actually considered, but for your rig, i’d recommend a gear swap up to 5.13’s to get the rig back into it’s happy place.

 

[Ashim]

Turn the OD off and take it for a test ride. Then report back with your observations.

 

[schmidtke_c]

Short answer is that neither 33’s/4.56’s nor 35’s/4.88’s are optimal for that transmission.

Optimum gearing for 33’s with the 42RLE is generally held to be 5.13’s.

https://wranglertjforum.com/threads...angler-tj-lj-and-other-re-gearing-faqs.17063/

With 35’s, and 5.13’s, the overdrive gear on ours is pretty useless, and it does take a fairly long time to get up to 65mph, compared to our other vehicles, though I’ve gotten used to it.

If you have a Rubicon, you can go to 5.38’s with 35’s, which I’ve actually considered, but for your rig, i’d recommend a gear swap up to 5.13’s to get the rig back into it’s happy place.

You know, I thought that as well but was terrified that at some point if i ever decided to add a cam or something to add power that i would be over doing the RPM's and eventually send a rod to the moon. trust me I've probably seen well over 1000 forums stating that 5,13 is better but i didnt think 4.88 would literally limit me down to virtually only city driving.

Turn the OD off and take it for a test ride. Then report back with your observations.

I did this yesterday actually on the way home (a few times here and there prior to that). It does seem to help a little for obvious reasons (o.d being .69 : 1 surely don't help) but it still don't want to reach over that 6 5 mph range, I feel like if it was going into limp mode or something it would at least throw a code.. wouldnt it?

 

[Chris]

5.13 is the way to go, and on the Rubicon models being able to go to 5.38 is even more advantageous. You can't go deep enough with that transmission, that's for sure.

 

[Irun]

Whats going on ya'll.

Lets get right to it, so when I bought to jeep 6 years ago it was a solid turd, coming from multiple xj's I had really high expectations because of how capable all of my past jeeps have been. Fast forward though all the bugs builds and thousands of dollars build and rebuilding the jeep working out kinks and so on. When I purchased this jeep it come with a set of 33's on it but had 3.73 gears and was an absolute dog. I was lucky if I hit 60 mph with a tail wind, I could floor it and it just didn't have any balls. Spent some time and countless hours researching decided i was going to gear it and ultimately with with 4.56 gearing which helped dramatically. when i had the 4.56's it would reach 75 on a good day. However, it still needed something. Last spring I ripped the rear axle off and slapped a Dana 44 on it then put gears in and went with lockers and 4.88s and scored a really good deal on a brand new set of 35's.

I don't remember it being such a dog when I parked it for the winter but come this spring when I pulled it out, it feels like it did when i had originally bought it and had the 33's with 3.73 just no balls seems like it tops off at 65 mph, it just seems unusual. It doesn't Throw any codes regularly and every once in a blue moon ill get a Evap code that I've been chasing for the last 2 years or so. I've replaced all 3 cats, the 4 02 sensors, fluid is a nice red color and smells fresh and plugs are fairly new. i keep up on regular maintenance and run all high quality fluids. it gets terrible gas mileage (yeah i know its like running with plywood) I'm not expecting speed but i do need to be able to reach comfortable highways speeds.

Did I miss something or is this 42rle really just that big of a dog? It shifts well, its quiet and I haven't has any issues with it, I don't know if the previous owner ever did anything to it or the sensors but i would think at 101K that it would still cruise along without any major flaws. Also still has the original ecm and again doesn't throw any codes that would lead me to believe it has anything to do with that. I just want to pick some brains that have a some insight, maybe I'm over thinking this and it really just is a turd.

With the 42rle, you need a 5.13 gear, with a Dana 30 front, or a 5.38, if you've got a 44 front and rear. Sorry to say, the 4.56 won't cut it!

 

[Artsifrtsi]

Ask @AndyG about his upgraded computer that he said turned his turd into a rocket...

 

[AdventurePig]

You know, I thought that as well but was terrified that at some point if i ever decided to add a cam or something to add power that i would be over doing the RPM's and eventually send a rod to the moon. trust me I've probably seen well over 1000 forums stating that 5,13 is better but i didnt think 4.88 would literally limit me down to virtually only city driving.


I did this yesterday actually on the way home (a few times here and there prior to that). It does seem to help a little for obvious reasons (o.d being .69 : 1 surely don't help) but it still don't want to reach over that 6 5 mph range, I feel like if it was going into limp mode or something it would at least throw a code.. wouldnt it?

Just fyi - I think you’re doing all the right things - asking for input, road tests, etc.

As to your question about a limp mode, i’m not sure, but yes, i think if there were something WAY wrong with it then you’d probably see some codes/warning lights.

I see in your post you mention that it’s been parked for a while. Here’s some thoughts related to that:

• Is it possible that you’re dragging a brake drum or disc? That would sure slow it down.
• Dumb question but Is it possible for certain fuel blends to have “soured” in that amount of time, octane-wise where a drain/fill of some fresh fuel might be worthwhile?

 

[jjvw]

The 42rle really needs 5.38 to push 33s. But the best you can do is 5.13 because if the Dana 30 front.

Mine has 5.38 pushing 35s and it is still not enough axle gear, even with a supercharger.

 

[Ashim]

I did this yesterday actually on the way home (a few times here and there prior to that). It does seem to help a little for obvious reasons (o.d being .69 : 1 surely don't help) but it still don't want to reach over that 6 5 mph range, I feel like if it was going into limp mode or something it would at least throw a code.. wouldnt it?

You should easily go over 65mph with the OD turned off. Verify fuel pressure while driving at speed.

 

[schmidtke_c]

Just fyi - I think you’re doing all the right things - asking for input, road tests, etc.

As to your question about a limp mode, i’m not sure, but yes, i think if there were something WAY wrong with it then you’d probably see some codes/warning lights.

I see in your post you mention that it’s been parked for a while. Here’s some thoughts related to that:

• Is it possible that you’re dragging a brake drum or disc? That would sure slow it down.
• Dumb question but Is it possible for certain fuel blends to have “soured” in that amount of time, octane-wise where a drain/fill of some fresh fuel might be worthwhile?

Its been about 1000 miles since I've pulled it out, but usually when I like to do is the first tank after its been pulled out I run mid grade though with a can of seafoam just incase that gas gets stale for some reason but I'd don't believe thats the case honestly. Especially because its had a few tanks through it now and seems no better or worse really.

For the hell of it tomorrow I'll put the rear up on stands and see how free it rolls and if there's any resistance. The rotors on the front feel smooth and are not showing signs of hanging up.

 

[schmidtke_c]

@Ashim

That's what makes me so damn curious, I thought for sure that even if it was slow to get there it would have no trouble doing so but that's just not the case. I do know occasionally when I fuel up it will spit back at me once the tank is full but only when it's full never before hand. Topped with that evap code you might be on to something it seems?

 

[schmidtke_c]

Ultimately I'm not opposed to swapping back to 33's if its just a gearing issue, they would be optimal for my suspension off road anyways but there has to be more to this issue other than just gears because its been like this since I bought the jeep and only improved little bits. Plus right now its.throwing the gaslight on at like 175 to a tank thats a 19 gallon tank...

 

[AdventurePig]

Ultimately I'm not opposed to swapping back to 33's if its just a gearing issue, they would be optimal for my suspension off road anyways but there has to be more to this issue other than just gears because its been like this since I bought the jeep and only improved little bits. Plus right now its.throwing the gaslight on at like 175 to a tank thats a 19 gallon tank...

Wow, that’s like 10 mpg’s, right? Pretty crap mileage.

Ours on 35’s and 5.13’s with a good amount of armor will normally get 12-13 if i’m giving it the beans for the whole tank. We can get upwards of 14-15, if i stay out of the skinny pedal.

 

[AdventurePig]

Some idea’s in this thread:

https://wranglertjforum.com/threads/poor-gas-mileage-loss-of-power-uphill.72896/

 

[AndyG]

Ask @AndyG about his upgraded computer that he said turned his turd into a rocket...

It turned my turd into a peppier turd

 

[schmidtke_c]

Some idea’s in this thread:

https://wranglertjforum.com/threads/poor-gas-mileage-loss-of-power-uphill.72896/

When I replaced my cats I bought a flowmaster 2049170 and since I had it down I figured I might as well replace the rest of it so I got the flowmaster flowfx outlaw. My original thought when I started having issues was that it was a clogged cat, that was June of 2020. Its been probably 25k since then and virtually no change compared to prior. Unless there's a hair line Crack in the header that I overlooked or couldn't see i struggle to believe they are already bad again. This is by far the most frustrating issue I've took up.

 

[schmidtke_c]

It turned my turd into a peppier turd

Do tell?

 

[AdventurePig]

When I replaced my cats I bought a flowmaster 2049170 and since I had it down I figured I might as well replace the rest of it so I got the flowmaster flowfx outlaw. My original thought when I started having issues was that it was a clogged cat, that was June of 2020. Its been probably 25k since then and virtually no change compared to prior. Unless there's a hair line Crack in the header that I overlooked or couldn't see i struggle to believe they are already bad again. This is by far the most frustrating issue I've took up.

I agree, in that case probably not the issue.

 

[AndyG]

Do tell?

It worked- there is a thread somewhere but results are a little bit varied

It’s not a dynamic difference but enough I have enjoyed it-

Anything that helps you live with the ol’ 42 transmission is a good thing.