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Discussion Starter · #1 ·
I was reading about people pulling the fuses on their awd cars in order to get them to run in fwd mode. is that possible on the current generation s40's? I've been searching and can't seem to find any info on whether or not that is a bad idea. I will be purchasing a s40 t5 awd with a manual transmission in the next month and the ONLY reason that I want AWD is for frequent ski trips in the rockies, the rest of the time I'd rather get the better mileage that I would get with fwd, even if there is some understeer. However, I read that running a manual transmission awd car in fwd by removing the fuse can damage the differential in some way. I am in no way a car expert, but I did not want to intentionally do something that could damage my car. Is this a bad idea?
 

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Re: pulling awd fuse on 6spd t5 awd?? (chanke4252)

I do not know whihc fuse it is or if it is possible but its not like the car is a full time 50/50 awd car. Keeping your foot off the floor is probably your best bet.
 

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Re: pulling awd fuse on 6spd t5 awd?? (awd)

right, youre right, but given the sometimes huge mpg differences that people may report between the awd and fwd variants, I felt it was worthwhile to ask. Plus, I was hoping there was some way to make the drive feel a little less assisted, and maybe somehow (once again, not a car guru) lessen the wear and tear on the awd system. Supposedly, the s40 awd normally splits power 95/5, I just figure that if its going to be that biased towards the front, might as well be 100/0 when I know I'm not going to need the awd.
 

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While the AWD is about 150 pounds heavier than the FWD, I believe the largest difference in mpg is attributable to gearing...disabling the AWD won't affect this.
 

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Re: (Seven)

Reasons for AWD fuel economy difference (in approximate order of importance)<p>1) Final drive ratio: AWD 4.00:1, FWD 3.77:1<br>2) Extra rotating mass of angle gear, driveshaft, Haldex.<br>3) Torque transfer to rear 95/5->50/50.<p>Pulling the fuse only affects #3. Which fuse depends on which model and which year, but for daily use it's a bad idea.<p>The easiest way to disable AWD is to raise the handbrake one notch, btw. In my V50 it apparently must be done while moving. If you raise it at a stop, the brake warning chimes and it appears to stay in AWD.<p>Tom.
 

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can u disable awd in order to do a dyno test? for there is no awd dyno here <br>are there any negative effects ?
 

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Re: (pasat)

Yes, you can and should disable for a 2wd dyno test, maybe even for any dyno test because the Haldex is never fully on, the variability will throw off many 4-wheel dynos.<p>I would pull the fuse for that purpose, and I did when dynoing mine. The car shows an "Anti-skid failure" message and then throws a brake control code when it sees the fronts going 100mph and the rears standing still. But, the car resets when you restore the fuse and all's well. I posted about this a while back, you can find which fuse I did but I really suggest looking at your manual because cars can vary. Look for the "DEM" or "Differential Electronics Module" fuse.<p>When lifting the handbrake, no message is produced, and the only evidence I have is that the car spins only its fronts on snow. I am not <IMG NAME="icon" SRC="http://www.vwvortex.com/zeroforum_graphics/screwy.gif" BORDER="0"> enough to try it on the dyno, I pulled the fuse there.<p>Tom.
 

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Re: (tmtalpey)

OBTW it occurs to me that the DEM fuse is shared with the transmission (TCM) fuse. This makes pulling it impossible on cars with an automatic. In that case I'd really recommend doing a 4-wheel dyno.<p>e.g. <A HREF="http://apps.volvocars.us/ownersdocs/2005/2005_S40/05s40_10b.htm#pg164" TARGET="_blank">http://apps.volvocars.us/owner...pg164</A><p>Tom.
 

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What are the probable differences between the Dyno HP vs actual if you were to remove the AWD fuse?<p>I mean if the stock AWD is 218hp at the crank then assuming the standard 25% drivetrain loss for AWD (Hearsay....is this true even if you are not fulll time AWD?) what changes to the calculations would be logical.<p>Obviously from my posts regarding my ECU issue, i want usable data...and i dont have stock data.<p>Thanks
 

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Re: (PornSStar)

The dyno would become more accurate in FWD, because only the front wheels would be applying power instead of the car distributing torque between front and rear dynamically. However, pulling the fuse won't change drivetrain losses much, since all it cuts out is the rear differential and rear wheels/tires, plus the gear loads. And on the other hand, maybe you want to measure the AWD behavior.<p>If you're looking for a perfect crank HP measurement, you need to go waaay up market in the dyno business. It needs to be a hub-mounted eddy brake unit (not wheel-friction inertial like Dynojet), and it needs to measure spindown and steady state to accurately factor out the various components. I personally don't see any reason to go there - relative measurements are plenty for my purposes (what was the gain for doing X). Chasing absolute dyno numbers is a different game.<p>I believe 15-20% is a reasonable figure for drivetrain losses on our AWDs. But if you go back to the same dyno, tie down the same way, and keep your tires constant, you'll have a reasonable baseline regardless of what the loss actually is. <p>Tom.
 
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