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I like to tinker with things, today I pulled the 4x4/PTU fuse. For those that don't know some members have had their PTU's replaced. After doing so the slip threshold before the AWD/4x4 kicks in has been raised, meaning it allows more slip before the back tires kick in. This has positives and negatives, positive is that fuel economy goes up because the rear end is not getting any power (The awd system can completely disengage meaning the driveshaft isn't moving at all). Negative is with the slip threshold higher when driving in slick surfaces unless un snow or sport mode you will see more tire spin than before.
I pulled the 4x4 fuse on my TH, driving characteristics changed alot. Its actually surprising how much power the rear axle gets in warm dry weather. With the fuse pulled I can spin the tires through most of first gear. From a roll anything below 30kms/h a downshift to first causes a lot of tire spin. Now i didn't do this so I could spin tires, I did so to see if there is a fuel economy gain. I can't report on that until next week when I take a long highway trip.


Try this at your own risk.


It the F10 Fuse (20Amp) in the fuse block under the hood.
Make sure the vehicle is completely off when you remove or install the fuse.
If successful, upon start up you will see "SVC 4WD" in the bottom right corner of the Driver Information Center. The message "4WD system unavailable service required" this only happens at startup.
To return everything back to normal, turn the vehicle off install fuse and start vehicle.


 

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Discussion Starter #3
The next step would be, should this be legit and cause a fuel economy gain, would be to add a switch to the fuse, and then have selectable FWD>:D
This mod is not for everyone but I like to play around
 

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The next step would be, should this be legit and cause a fuel economy gain, would be to add a switch to the fuse, and then have selectable FWD>:D
This mod is not for everyone but I like to play around
I would love a feature like this. Nothing I hate more than getting a 10% fuel mileage hit simply because it's 38F outside. Grrrr.
 

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Discussion Starter #5
I would love a feature like this. Nothing I hate more than getting a 10% fuel mileage hit simply because it's 38F outside. Grrrr.
Isn't that the truth.


When the bearings went in my driveshaft, it would make the sound when the rear wheels/driveshaft was engaged. On a hot summer day you'd be surprised how much the rear end is actually receiving power. I would expect to see gains once the temperature drops.
Now this could be placebo but I almost feel like the torque management below 2000rpm seems to be less or non existent now. On both cherokees' I've driven hard launches don't really have much power below 2000rpm. This will require more testing but I think I might be on to something.


Other manufacturers have AWD systems that have a 2WD mode, its interesting Jeep didn't put it in, well probably because its a jeep right?
 

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is this a "simple" fuse circuit, meaning that there are two wires that lead to/from the fuse in question, or is this more complicated where the fuse is just part of the TIPM and is allowing communication between two points when the fuse is in tact? if it is the first scenario, one could expand on this mod and find that wire in the wiring harness and run a simple wire with a switch to it inside the cabin and create 4WD on demand. consequences of flipping the switch while the car is running would be at the risk of the user, however.

EDIT: i totally didn't see post # 3 lol. but the switch wouldn't work if the fuse is just allowing communication between two contacts within the self-contained contained TIPM.
 

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@IRSmart : I also have a gut feeling there is more to this fuse scenario... Doing AWD On/Off like this would be fabulous, but there very well could be strings attached... and problems looming...
 

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@IRSmart : I also have a gut feeling there is more to this fuse scenario... Doing AWD On/Off like this would be fabulous, but there very well could be strings attached... and problems looming...
I couldn't agree more. I am happy to be a spectator in this exploration.
 

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Discussion Starter #9
I think I have an idea................I'm not electrically inclined at all. But would something like this work.



photo sharing


Add something along those lines and wire a switch in, or just go the safe route and pop the hood and put the fuse back in...


Other thing I just thought of. The owners manual states that power should be shut down to the circuits in question when replacing the fuse, so on the fly switching might cause damage.
 

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Very interesting.... 1/4 mile runs and zero to 60 times would be interesting to see with fuse and without.

If the wheels spin as much as mentioned, thats quite a bit more torque being put down.
 

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I think I have an idea................I'm not electrically inclined at all. But would something like this work.



photo sharing


Add something along those lines and wire a switch in, or just go the safe route and pop the hood and put the fuse back in...


Other thing I just thought of. The owners manual states that power should be shut down to the circuits in question when replacing the fuse, so on the fly switching might cause damage.
No, that's a tapafuse meant to grab power from a circuit board without interfering with what it's plugged into. The idea would be to do the exact opposite.
 

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Discussion Starter #12
I just went for a 42km highway drive, round trip a few hills nothing special and no wind, So I got 8.5L/100kms and totally not scientific but I don't recall getting that mileage on the highway with my oversized tires I have on. Something is working here to reduce parasitic losses. As for the tires spinning, its only FWD now so with 271hp/239tq I think its going to spin them no matter what, but it does seem faster. I'm not sure if 1/4mile time would get better since spinning off the line is brutal now, but if it is faster the MPH in the 1/4 should go up.
 

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I just went for a 42km highway drive, round trip a few hills nothing special and no wind, So I got 8.5L/100kms and totally not scientific but I don't recall getting that mileage on the highway with my oversized tires I have on. Something is working here to reduce parasitic losses. As for the tires spinning, its only FWD now so with 271hp/239tq I think its going to spin them no matter what, but it does seem faster. I'm not sure if 1/4mile time would get better since spinning off the line is brutal now, but if it is faster the MPH in the 1/4 should go up.
For our US friends, you got 29.4 MPGs (US) on that short stint.

Of course that small drive is not statistically significant, but...

I'm not putting any pressure on you to continue/push this testing any further. But let us know what you find tomorrow :grin:>:D:wink:
 

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For our US friends, you got 29.4 MPGs (US) on that short stint.

Of course that small drive is not statistically significant, but...

I'm not putting any pressure on you to continue/push this testing any further. But let us know what you find tomorrow :grin:>:D:wink:


29 mpg, goodness! Give me a switch. Where do I sign up? I'm struggling to get 18 after the RDM swap.


Sent from my iPhone using Tapatalk
 
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Discussion Starter #15
29 mpg, goodness! Give me a switch. Where do I sign up? I'm struggling to get 18 after the RDM swap.


Sent from my iPhone using Tapatalk


I'm not making this up





Only change from my Sig right now 245/65/17 AT3W which weigh 39lbs vs the 40lbs of my 245/70/17 AT3W. I'm also running the Torque Tube and K&N Panel filter in the stock airbox.
 

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What happens when you put the fuse back in?
my Only concern would be the PTU might not fire back up properly.....I recall them saying the PTU required some special coding when they replaced it to get it to engage. They did mine twice because they didn't match it up properly the first time.

Might be interesting to have a switch for long highway trips.
 

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Are you able to describe your fuel? Do you have e-10 ethanol to deal with, or do you have clean gasoline? I see your speed for the 2 hour ride averaging 106. My mileage without ethanol at speed 110 is 9 [15 TH 3.2 tech tow]. If I slow to 100 it improves to 8.8. Ethanol (Florida) drops economy by 20% easily.
Everything for me in in miles and US gallons, so I did some converting.
At 79 MPH with e-10 I get a dismal 22 MPG. (10.6 L/100 or so).
This is an interesting thread. I can't wait to see more test results. Since you're towing, I doubt we will see speeds in the 125 range.
 
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