A while back I played around with how the 4x4 system works. Bottom line a FDI and FDII function exactly the same way, except the gear ratios, and when the FDII is in the FDII specific low range, [L] 4x4 Locked.
Gear ratios aside, the aggressive BLDS are what makes the FDII able to go offroad in places a FDI can't, since there is limited articulation wheels come up in the air lots, and that's where the BLD;s come in. The older videos are of my FDII 08 Patriot, I now have a FDII 2012 Compass
Video showings FDI mode (all FDII's work like FDI when in [D] 4x4 locked.)
What I decided to do was jack up the front of the vehicle so the front tires were just barely off the ground. I would then try the 3 different modes of the Patriots 4x4 system and see how it behaved. Now of course this isn't totally realistic but it gives a better understanding how everything works.
First video is with
ESP Full Off Gear selector in
[D] with
4x4 Unlocked
I put the Pat in drive and then slowly let of the brake waited a few seconds and slowly eased onto the accelerator
0:18-0:24 seconds is just idling
0:24s+ start applying throttle
As you can see the drivers front wheel does not spin (it is off the ground) and the passenger front wheel starts spinning fast and then slows down, which I belive is due to the ecc sending torque to the rear wheels, you'll notice once the front wheel stops spinning the Patriot lurches forward (indicating torque going to the rear wheels although it is hard to see in the video, I could feel it while in the Pat). The front wheel continues to spin at timed intervals (When my foot was off the gas). Indiciating the ECC was locking and unlocking. As I increase pressure on the gas pedal the front wheel slows and it seems the ecc is progressing to what seems almost full lockup before I let off the gas. My guess as to why the passenger wheel isn't spinning is because there isn't enough difference in the wheel speeds to make the BLD kick in. Had i given it more gas the Patriot would have driven forward off the jack.
Second video is with
ESP Full Off Gear selector in
[D] with
4x4 Locked.
I put the Pat in drive and then slowly let of the brake waited a few seconds and slowly eased onto the accelerator
0:16-0:21 idling
0:21+ start applying throttle
Whats interesting right off the bat is the behavior while in the locked mode when idling, it behaves exactly the same way as when the 4x4 was unlocked, lurching forward at intervals, once I touch the gas pedal everything locks up and unlike the AWD mode there is no progression with the ECC it's locked up until i release the gas pedal. In this mode if I would have used more gas I would have been able to drive off the jack.
Third video is with
ESP Full Off Gear selector in
[L] with
4x4 Locked. This is the FDII mode
I put the Pat in drive and then slowly let of the brake waited a few seconds and slowly eased onto the accelerator
0:16-0:21 idling, foot off the gas
0:21+ start applying throttle
In the FDII mode everything is the same as the 2nd video, rpms are higher and the Patriot seemed to be more eager to jump off the jacks (increased torque i'm guessing) The sound you hear at the end the the Pat shifting on the blocks (nothing broke
)
I think that in all cases when the patriot operates in the AWD mode when there is no throttle is probably to prevent binding in the drivetrain at low speeds, i'm really intrigued how it works because the second there is any throttle input everything locks up (depending on the mode you are in)
In all cases above the patriot was able to transmit enough torque to move the vehicle forward, now whether or not it would be enough to drive over a small bump i'm not sure. Another thing to recognize is that the front wheels had ZERO traction, if your front wheels are on ice there is going to be at least some resistance so this isn't a 100% realistic test.
As the video states 1st part shows the AWD mode (FDI)
2nd part is the 4x4 lock in D also FDI
3rd Part is the FDII 4x4 locked in Low range.
You can also see the Patriot struggling to spin the wheels at times, not enough torque from the little 4 banger (and my heavy tires don't help either)
Here is a quote from part of the explanation of the 4WD system from jeep:
The AWD mode acts exactly as Jeep States and it appears the ECC is able to vary the amount of tourque going to the rear wheels. When the patriot is idling it appears to be in the "closed loop mode". Once you start giving it some gas then the open loop system also comes in and starts working. It also in my opinion shows that the isn't a whole lot of difference between the 4x4 locked (in D) and unlocked (in D) as the ECC nearly locks up in the AWD mode if you give it enough throttle.
I hope to make more videos in different situations in the near future, I was by myself today so I had to really be careful what I was doing.
If anyone has requests as to what sort of things i should try I would be more than happy to test them out.
Last video has a stupid watermark because my neighbor came over and asked what the hell i was doing so I cut that out
Feel free to look over my other videos I've offroaded my compass extensively and tested out the 4x4 system in almost everyway imaginable.