WA2NTK Posted September 6, 2010 Share Posted September 6, 2010 Hi to all, I have a 2001 LL Bean Outback with the 3.0 engine. In the fuse box behind the battery there is an empty slot marked "FWD". If you insert a fuse into this position an icon on the dash ( FWD) lights to indicate that you are in front wheel drive. This tip was passed on to me by a Sabaru mechanic. There is no need for AWD here for 6 months out of the year. I'm wondering if this mod will improve fuel economy and tire wear? Does anyone have any expierence with this mod? Thanks Ralph Quote Link to comment Share on other sites More sharing options...
porcupine73 Posted September 6, 2010 Share Posted September 6, 2010 Hello and welcome to the board! That's a nice Subaru you have. No, putting the FWD fuse in will not improve fuel economy. Why? Because you still have the friction and windage of the rear drive shafts, rear differential, propeller shaft, etc. Even with the FWD fuse in, those items are all still going to generate friction and windage losses and the weight of lugging them around. Also the handling of the vehicle can be different in an emergency manuever when in FWD mode. So if on rain or something there might be benefit of the AWD in a slippary turn but with the FWD fuse in it will be lost. What that FWD fuse is actually for, is if you get a flat and are running the spare tire. Then that fuse should be installed (because if the tires do not all match within 1/4" circumference as measured by a tape it can cause premature AWD wear at the least and damage at the worst). Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted September 6, 2010 Share Posted September 6, 2010 There is plenty of info about the FWD fuse here. The simple answer is don't leave that fuse in. That fuse turns on a solenoid in the transmission which controls line pressure to the AWD clutch packs in the center transfer unit. Leaving the fuse in place delivers a full 12V to the solenoid (which is normally on getting 5 -7V ) which can cause the solenoid to burn out and cause the AWD clutches to permanently engage. The AWD clutches are normally only partially engaged anyway. They engage fully when AWD is needed as detected by the traction control system. Quote Link to comment Share on other sites More sharing options...
OB99W Posted September 6, 2010 Share Posted September 6, 2010 [...] I'm wondering if this mod will improve fuel economy and tire wear? [...] As has already been stated, there's really no advantage and it may possibly lead to failure of the duty solenoid (the duty cycle does indeed go to 100% when the FWD fuse is inserted). The typical split of power is 90/10 front/rear (for the auto trans, which we're discussing) when the AWD system isn't detecting slippage. Hmmm, WA2NTK -- 73 OM, CUL Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted September 6, 2010 Share Posted September 6, 2010 Just occurred to me that's a ham callsign. Quote Link to comment Share on other sites More sharing options...
porcupine73 Posted September 6, 2010 Share Posted September 6, 2010 Really it goes to 100% duty cycle with the FWD fuse in? Interesting, good info I hadn't seen that before. Just that the solenoids were driven around 50Hz 5% to 95% duty cycle typically. Quote Link to comment Share on other sites More sharing options...
1-3-2-4 Posted September 7, 2010 Share Posted September 7, 2010 Just occurred to me that's a ham callsign. Nice! 73, KB1QXO http://aprs.fi/?call=a%2FKB1QXO-9 Quote Link to comment Share on other sites More sharing options...
OB99W Posted September 7, 2010 Share Posted September 7, 2010 (edited) Really it goes to 100% duty cycle with the FWD fuse in? Interesting, good info I hadn't seen that before. Just that the solenoids were driven around 50Hz 5% to 95% duty cycle typically. I believe so, but I'll admit to not having ever verified that with a scope. If anyone knows otherwise, please speak up. I definitely have to modify something I said. While the earlier 4EATs did usually have 90/10 front/rear split, vehicles with VTD/VDC (might be starting in 2001) have more like 45/55. Using the FWD fuse on so-equipped cars would prevent the dynamic control from functioning. Edited September 7, 2010 by OB99W Quote Link to comment Share on other sites More sharing options...
Fairtax4me Posted September 7, 2010 Share Posted September 7, 2010 I assume it's a shortcut and the fuse goes straight to the solenoid. I couldn't find any diagrams showing that circuit right off hand to verify that. I'd be just as interested as you all to find out where exactly that circuit goes. Quote Link to comment Share on other sites More sharing options...
OB99W Posted September 7, 2010 Share Posted September 7, 2010 All the diagrams I've seen show that the fuse just acts as a switch, grounding a pin on the TCU when it's in place. What exactly happens after that is dependent on the TCU electronics. Quote Link to comment Share on other sites More sharing options...
porcupine73 Posted September 7, 2010 Share Posted September 7, 2010 Sounds good, thanks for the information as always. Quote Link to comment Share on other sites More sharing options...
CNY_Dave Posted September 7, 2010 Share Posted September 7, 2010 I believe so, but I'll admit to not having ever verified that with a scope. If anyone knows otherwise, please speak up. I definitely have to modify something I said. While the earlier 4EATs did usually have 90/10 front/rear split, vehicles with VTD/VDC (might be starting in 2001) have more like 45/55. Using the FWD fuse on so-equipped cars would prevent the dynamic control from functioning. The beaners don't have the VTD/VDC. Dave Quote Link to comment Share on other sites More sharing options...
CNY_Dave Posted September 7, 2010 Share Posted September 7, 2010 Hi to all, I have a 2001 LL Bean Outback with the 3.0 engine. In the fuse box behind the battery there is an empty slot marked "FWD". If you insert a fuse into this position an icon on the dash ( FWD) lights to indicate that you are in front wheel drive. This tip was passed on to me by a Sabaru mechanic. There is no need for AWD here for 6 months out of the year. I'm wondering if this mod will improve fuel economy and tire wear? Does anyone have any expierence with this mod? Thanks Ralph Ralph, if that's horseheads NY, you mean it only snows half the year down south where you are? Dave (Cortland NY) Quote Link to comment Share on other sites More sharing options...
OB99W Posted September 7, 2010 Share Posted September 7, 2010 The beaners don't have the VTD/VDC. True -- I didn't mean to suggest otherwise, just wanted folks to know that 90/10 split wasn't all there is, and that using the FWD fuse can have detrimental effects on some models. Quote Link to comment Share on other sites More sharing options...
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