Pull 4x4/PTU Fuse = FWD Cherokee + Possible Fuel Economy Gains

Tyler-98-W68 · Aug 26, 2017

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.

Mark_ · Aug 26, 2017

My interest is... piqued...

Tyler-98-W68 · Aug 26, 2017

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>

This mod is not for everyone but I like to play around

Mark_ · Aug 26, 2017

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.

IRSmart · Aug 26, 2017

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.

Mark_ · Aug 27, 2017

@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...

IRSmart · Aug 27, 2017

Mark_ said:
@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.

Tyler-98-W68 · Aug 27, 2017

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.

IRSmart · Aug 27, 2017

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.

1jeepnub · Aug 27, 2017

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.

Tyler-98-W68 · Aug 27, 2017

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.

Mark_ · Aug 27, 2017

Tyler-98-W68 said:
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:>

:wink:

Renthorin · Aug 27, 2017

I'm not sure exactly how but I just KNOW this contributes to global warming!!!

That said, it is very interesting

SpeedtekTH · Aug 27, 2017

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.

Tyler-98-W68 · Aug 27, 2017

I replaced the fuse and started it right up after I pulled the fuse the initial time.

Tyler-98-W68 · Aug 30, 2017

Did a bit of a road trip today, Pretty good mileage, this exact route last time was 9.6L/100kms

Now will be a good test for towing. I will be towing an 800lb Seadoo

OldNuke · Aug 31, 2017

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.

Tyler-98-W68 · Aug 31, 2017

I use 87 Octane that "may contain up to 10% ethanol"

I reset the trip computer at my door, and then took the picture at the door where I arrived. 50kms was done at 105kms/h and the remaining was 115kms/h

I just did the towing trip. It wasn't a long trip but it was quite hilly compared to my previous trip. The only difference this time. I took my dad along with me and he wasn't a fan of the loud drone from my exhaust. So I set the cruise at 105kms/h and used the ERS to keep the trans in 5th gear. The result was 2900rpm, but no drone! Now one would think that that would absolutely kill mileage but it didn't. I also didn't see transmission temps any warmer than I normally do (77c)

Fuel economy for the trip was 10.4L/100kms Trailer was a 2009 Seadoo GTX 215 with 30L of fuel in it. Dry weight of the seadoo itself I think is 715lbs, so around 800lbs was my guess. Still happy with the results I'm getting.

I"ll add the pictures later as my phone isn't cooperating

Montaska · Aug 31, 2017

Thanks for testing this out.

GaryCham · Aug 31, 2017

So, I compute US to be 22.5mpg towing. Sounds pretty good!

Shoulder · Aug 31, 2017

Intriguing indeed, this is.

So, have a question about this. You say when you take the fuse out, the SVC 4wD" message thing comes up, which says the 4wd system cannot engage. Well, I know quite a few people, I believe even around here, had this same message under normal driving without messing with the fuse. Is it possible then, the issue for some people is a blown fuse? Obviously, doesn't take into account all the control module failures, and PTU as well, but just a thought if for some reason someone got this message while driving.

But anyway, for the best purposes of testing this, find a simple highway route (start at some fuel station, end the route at the same one), go until a particular exit way, turn around, come back, refill, configure your actual mileage, and redo the test.

And yeah, a simple switch would be interesting. I can see the headlines now. "This simple mod will gain you 5mpg in your Cherokee!!!"

Desoto · Sep 1, 2017

I would be interested to see how the traction in wet weather is affected for those that have done this. I had a couple in service like this when the driveshaft's were on backorder and they seemed a bit off as far as traction control. I did not care for it at all.

gravitywell · Sep 1, 2017

It's bad in dry weather. Lol.

Mine is an issue I've been ignoring, not purposely acquired.

Sent from my ONEPLUS A3000 using Tapatalk

Tmugz88 · Sep 6, 2017

Has anyone attempted this with a switch to "engage" and disengage the system? I know a buddy of mine did something similar with his 03 Ford Explorer XLT with the brown wire which is located under the carpet on the passenger side. The idea is exactly the same it seems , which from what I can remember worked well for him but obviously it's going to be different with two different vehicles .

Here is the brown wire mod I brought up .

http://www.explorerforum.com/forums/index.php?threads/bwm-brown-wire-mod-3rd-gen.194875/

Tmugz88

Tyler-98-W68 · Sep 11, 2017

Just did my large commute again a bit of a headwind this time.

8.8L/100kms Still working

Shoulder · Sep 11, 2017

Have you only been using the computer as a basis for your fuel mileage, or have you manually configured it based on your trip distance, and how much fuel you put into the tank during a fill up?

Not rejecting your results or anything, but I never fully trust the computer when it comes to listing mileage. In my experience, it's either been right on, or off as much a 1-2mpg. It's never been consistent in my case.

matterpro · Oct 6, 2017

subscribed.

Any updates?

Tyler-98-W68 · Oct 6, 2017

Still works as planned, i've had the fuse in and out multiple times

ferny102 · Oct 6, 2017

Been following this thread. Can anyone confirm if the terrain select works in sport mode with the fuse removed?

Tyler-98-W68 · Oct 7, 2017

It does, you still only get FWD because they rear doesn't get any power.

Jeepster1 · Oct 7, 2017

Interesting experiment. And I will follow..................
In actuality how much mpg gain are we talking. I know the EPA difference FWD/4x4 is around 2 hwy/1 city with the 2018 V6. That is mostly due to FWD being the default option in the 4x4 system. The engagement of 4x4 from FWD is minor in the mpg story as you are back to FWD as conditions allow.

Now the real issue is on the road mpg of which many different factors go into that number.
Vehicle weight including fuel, driving conditions, speed, use of speed control, and gas type. That is ethanol or 100% gas. If your pumps are not marked there is no way to tell what you are getting. Lower the ethanol count, from 10%, and your mpg goes up.

I know that with my '14 Cherokee Limited V6 AD2 and tow I can easily get 29-33 on a 300 mile trip to the big city. I take the same hwy and same speeds on those hwys.
The mpg difference can be huge especially if I fill up in the urban area which lowers my mpg coming back. When I fuel outside the urban area on return my mpg stays higher.
And yes, my mpg does go down a bit in colder weather. That is normal and not just the temp that triggers 4x4 mode. All 4x4 mode is probably 2/3 mpg assuming it stays on 100% of the time.
In order to get a legitimate comparison you would almost have to use a track in order to try and keep everything equal. there are just to many variables out there.
I also use ACC as much as possible and that alone will help mpg.

One last point is it is all well and good to pull the fuse to keep it in FWD. But that is negating a powerful function on the drive train. That is on demand 4WD when it is needed.
That can be important if you find yourself in a tough situation with little time to try a manual 4WD switch. The exact purpose of on demand 4WD which is seamless and fast.

Mark_ · Oct 7, 2017

Jeepster1 said:
<snip>
One last point is it is all well and good to pull the fuse to keep it in FWD. But that is negating a powerful function on the drive train. That is on demand 4WD when it is needed.
That can be important if you find yourself in a tough situation with little time to try a manual 4WD switch. The exact purpose of on demand 4WD which is seamless and fast.

OP is experimenting with FWD only on an AWD Cherokee, just to see how much mileage is effected. OP is in Canada and very much aware of the AWD benefits ; the point here is to try and find out just how much rear wheel engagement is hurting mpgs in conditions that typically don't require AWD.

When I see temps drop just below 40F here, I see an immediate 10% mpg drop. I drive in 33F to 40F temps many-many days during the year, so this is a big problem. Driving in rainy conditions or on inclines engages the rear wheels. I too think this system is costing us way too much in fuel.

I myself applaud the OP for his efforts. It's an experiment, not an AWD bashing exercise.

Tyler-98-W68 · Oct 7, 2017

Interesting experiment. And I will follow..................
In actuality how much mpg gain are we talking.

Right now in the summer it was 1.5-2L/100kms strictly highway driving. Those are the numbers I focus on right now because that is all I do.

I know the EPA difference FWD/4x4 is around 2 hwy/1 city with the 2018 V6. That is mostly due to FWD being the default option in the 4x4 system. The engagement of 4x4 from FWD is minor in the mpg story as you are back to FWD as conditions allow.

You are right to a point, however another large thing people forget is the weight of the wheels and tires, if you put stock 17” or 18” wheels and tires on a TH you would reduce the rotating mass of the tires and in turn get better fuel economy. The engagement of 4x4 is not minor. I first clued in to this when the bearings on my driveshaft were bad and would make a terrible sound whenever the rear end got power. This happened in the middle of summer flat ground all the conditions it shouldn’t engage, but it does. Even the smoothest acceleration away from a stop EVERY time the rear end would receive power. Since my driveshaft was making noises all last winter even at highway speeds with the cruise on it would still be getting power to the rear. Fact is there is lots of times the rear end gets power regardless of the official literature from Jeep saying what the triggers are and aren’t. The benefits of this mod is due to the design of the AWD/4x4 system, everything is completely disconnected and there is no additional moving parts (aside from the rear differential being back there).

Now the real issue is on the road mpg of which many different factors go into that number.
Vehicle weight including fuel, driving conditions, speed, use of speed control, and gas type. That is ethanol or 100% gas. If your pumps are not marked there is no way to tell what you are getting. Lower the ethanol count, from 10%, and your mpg goes up.

You bring up a good point, I can’t do any controlled testing like the EPA or magazines do. I can tell you though all the gas used in my Cherokee is 10% ethanol as I run 87 octane regular gas, same with my wife’s Cherokee.

I know that with my '14 Cherokee Limited V6 AD2 and tow I can easily get 29-33 on a 300 mile trip to the big city. I take the same hwy and same speeds on those hwys.
The mpg difference can be huge especially if I fill up in the urban area which lowers my mpg coming back. When I fuel outside the urban area on return my mpg stays higher.
And yes, my mpg does go down a bit in colder weather. That is normal and not just the temp that triggers 4x4 mode. All 4x4 mode is probably 2/3 mpg assuming it stays on 100% of the time.
In order to get a legitimate comparison you would almost have to use a track in order to try and keep everything equal. there are just to many variables out there.
I also use ACC as much as possible and that alone will help mpg.

My highway numbers I’ve quoted in this thread have all been the exact same trip of approximately 200kms or so. I’ve reset at my driveway and driven. This really does work. The first time I tried this and did a small 45kms trip I got 8.5L/100kms and that kind of mileage is what I got stock (with factory wheels and tires). These numbers are from my Cherokee running 40lb per tire tires, approx. 5lbs more than the destination At’s. I also run an intake as well so that helps my numbers, but I’ve had the intake on since basically new so this mod improved mileage above and beyond what the intake did.

One last point is it is all well and good to pull the fuse to keep it in FWD. But that is negating a powerful function on the drive train. That is on demand 4WD when it is needed.
That can be important if you find yourself in a tough situation with little time to try a manual 4WD switch. The exact purpose of on demand 4WD which is seamless and fast.

I fully intend on putting the fuse in for the winter if I need it. There is zero issues with running without the fuse, it’s a failsafe if something goes wrong it still allows the vehicle to be driven. If I actually got stuck, I’d turn the vehicle off pop the hood and put the fuse back in and be back in business.

The only other part of the puzzle which warrants further testing on is my wife's 2014. Ever since her PTU got replaced the slip threshold for her 4x4 to engage is much higher meaning it will spin the tires in auto mode noticeably before the rear kicks in, i will have to pull the fuse on her vehicle to see if there is any gains. I don't think there would be any as she gets between 7.2-8.0L/100kms on the same highway trip that I do right now, but I can't be totally sure until I test it out. I have no such delay in the 4x4 kicking in on my cherokee

Mark_ · Oct 7, 2017

I'll do some converting for our US friends :

Tyler-98-W68 said:
Right now in the summer it was 1.5-2L/100kms (this can't be converted directly, but think 15 to 20% improvement) strictly highway driving. Those are the numbers I focus on right now because that is all I do.

You are right to a point, however another large thing people forget is the weight of the wheels and tires, if you put stock 17” or 18” wheels and tires on a TH you would reduce the rotating mass of the tires and in turn get better fuel economy. The engagement of 4x4 is not minor. I first clued in to this when the bearings on my driveshaft were bad and would make a terrible sound whenever the rear end got power. This happened in the middle of summer flat ground all the conditions it shouldn’t engage, but it does. Even the smoothest acceleration away from a stop EVERY time the rear end would receive power. Since my driveshaft was making noises all last winter even at highway speeds with the cruise on it would still be getting power to the rear. Fact is there is lots of times the rear end gets power regardless of the official literature from Jeep saying what the triggers are and aren’t. The benefits of this mod is due to the design of the AWD/4x4 system, everything is completely disconnected and there is no additional moving parts (aside from the rear differential being back there).

You bring up a good point, I can’t do any controlled testing like the EPA or magazines do. I can tell you though all the gas used in my Cherokee is 10% ethanol as I run 87 octane regular gas, same with my wife’s Cherokee.

My highway numbers I’ve quoted in this thread have all been the exact same trip of approximately 200kms (125 miles) or so. I’ve reset at my driveway and driven. This really does work. The first time I tried this and did a small 45kms (25 miles) trip I got 8.5L/100kms (28 mpg) and that kind of mileage is what I got stock (with factory wheels and tires). These numbers are from my Cherokee running 40lb per tire tires, approx. 5lbs more than the destination At’s. I also run an intake as well so that helps my numbers, but I’ve had the intake on since basically new so this mod improved mileage above and beyond what the intake did.

I fully intend on putting the fuse in for the winter if I need it. There is zero issues with running without the fuse, it’s a failsafe if something goes wrong it still allows the vehicle to be driven. If I actually got stuck, I’d turn the vehicle off pop the hood and put the fuse back in and be back in business.

The only other part of the puzzle which warrants further testing on is my wife's 2014. Ever since her PTU got replaced the slip threshold for her 4x4 to engage is much higher meaning it will spin the tires in auto mode noticeably before the rear kicks in, i will have to pull the fuse on her vehicle to see if there is any gains. I don't think there would be any as she gets between 7.2-8.0L/100kms (33 - 29 mpg) on the same highway trip that I do right now, but I can't be totally sure until I test it out. I have no such delay in the 4x4 kicking in on my cherokee

Tmugz88 · Oct 9, 2017

Now that I am not half asleep, and trying to message you on Facebook Tyler , I did the mod , with a fresh tank of gas going to give it a tank and see . I've been getting about 22mpg on avg, but I have been driving like a mad man because I've been running behind more so then normal . Before our trip to IL in November , I will be purchasing the intake tube , and drop in , but I may get the drop in 1st to see what this mod does stock, with just the drop in, and the full setup installed , just a lot to do in just over a months time .

Tmugz

Pull 4x4/PTU Fuse = FWD Cherokee + Possible Fuel Economy Gains

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