Bentley suggests disconnecting the battery (have radio code handy) 1 hour prior to unplugging & removing the DME. You can do this by unscrewing the ground lug behind the plastic cover & panel in front of the right-rear seat foot well below the front edge of the seat bottom, the seat bottom does not need to be removed. You do not need to remove the terminals on the battery posts. The DME is in the "e-box" in the right side of the engine compartment behind the shock tower. Remove the large phillips screws in the 4 corners & lift the black plastic cover off. The DME sits in the back, lift up on the metal hasp & pry the cable connector off. Remove the two 10mm hex-head flange nuts at either side & lift out the DME. Set the DME on an anti-static matt & take proper precautions when handling. In my case I used a cloth place mat on the kitchen table, IC ciruits are fairly robust once assembled & e-proms are not particularly sensitive to static from what I've read. Pry the metal tabs open around the perimeter of the back side of the case & lift off the cover. The e-prom is under a plastic retainer cover, remove the cover with fingers or a small screwdriver. Pry out the original e-prom from the socket with a smooth flat-blade screwdriver, working alternately from each end until loose. Check the alignment of the pins on the new e-prom chip to make sure they're straight & parallel & push it evenly into the socket until firmly seated, making sure the chip notch lines up with the notch on the end of the socket. Re-assemble. I partially folded only a few of the tabs on the cover when putting the cover back on thinking I might have it open again later on. I put a large rubber band around it to keep the cover on, it's not designed to be an RF seal anyway. When putting the nuts back on to install the DME in the e-box, slide them down the shaft of a slender screwdriver so they don't accidently drop down out of reach. Replace the plastic e-box cover, hook up the battery, & prepare for "wood"!
Depending on what model & year, DME details can vary. Here's a URL to a site with instructions for a '95 540i which has the screwed on DME cover & the "butterfly" style dual IC boards inside.
I originally set out to buy the AutoThority chip, it lists for $299 retail. The J.C. Jim Conforti/Turner Motorsports "shark" chip goes for $249. I ran across this Autowerks Chip on Ebay, they usually go for $80 to $90 so at that price I couldn't resist taking a chance on it. I don't know anything about it other than the seller said it's put out by some techies in the S.F. Bay Area. It claims to raise the output by 19 hp & 17 ft-lb torque, & raises the rev limiter by 400 rpm. It is highly recommended to use 92 octane or better with the chip, I started out with 1/2 tank of 89 octane & didn't notice any ill effects. I have since topped it off with 91 octane which should help some with the performance & eliminate any risk of pre-detonation & might even improve the Ave. mpg above & beyond what it used to get with the stock chip, so in my opinion, it's a no-lose modification.
In a word -- WOW!!! It is a definite improvement for a 735i, obvious power (torque) increase starting at about 2000 rpm. I can really feel the power coming on at 3600 all the way up to redline with a definite punch, way more than it used to have. Prior to this, the engine felt "stuffy" like it had a plugged cat but both the feel and sound of that has gone away. Before, it felt like it was waiting for a turbo to spin up but now the power comes on right now. Gone is the former surge at idle, I mean completely gone!, a rock-solid 700 rpm now. A while back I replaced the motor mounts to help cure a bad vibration problem but the new mounts only partially reduced the vibration. The new chip has gone a long ways to further smooth the idle & can barely feel the vibration with it in neutral. There are absolutely no flat spots anywhere on acceleration. After having driven with it for 30 miles now, with mixed aggressiveness, my in-town mpg has averaged 14.7 which is about the same as what I got with the stock chip. I reset Ave2 mpg once I got up to cruise on the interstate & after some spirited driving, it yielded 21.8. I normally averaged 22 to 24 on a trip so I'm not too concerned with what that number does long-term. All-in-all a worthwhile expendature. It makes a good compliment for the Mustang 4.6 liter 19 lb/hr fuel injectors. Next I will consider swapping the automatic transmission e-prom for an aftermarket one, and get a radar detector!
gale, 92 735i
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