would a performance chip help? 525i 1991

The gas mileage is pretty bad (18mpg). Would a performance chip help? I see some of them claim to increase efficiency. (there's some on ebay for ~40) I don't know my ECU # though. Anyone know how I can check, and if it will even help, and if I can do it myself?

The ecu would be where the wires for the engine harness lead to which is under the plastic cover on the passenger side right behind the shock tower when you pop the hood the other is for the transmission if you have a auto. You will need to know that number before you buy a chip so read the number on the ecu. The chip will require you to use premium gas so if you are already you’re missing out on the extra potential your engine has to offer.

You will get a
Higher rev limit
Top speed limiter removed
More Hp/Tq over the stock powerband resulting in better acceleration and better feel of power delivery from the engine like a wake up.
Mpg would be the same maybe better, many things could be a factor to 18mpg

Tire pressure, air filter, fuel filter, O2’s, alignment is bad, sparkplugs, oil, carbon build up, Auto or manual trans, how you drive, these engines need rev to move these cars fairly due to their lack of low end Tq and short diff ratios.

The engine you have is a non vanos, it makes 3 less tq than the 93 up M50’s and has a weaker low end for tq. Vanos engines make a little more power with a chip. The nonvanos M50’s also sound louder as the engines are not fine tuned from the factory for 91-92 525s and 92 325i’s.

http://www.turnermotorsport.com/html/subcategory_detail.asp?modelcode=E34&subcat_id=74
Peak gain 20hp@6000rpm
Peak gain 13tq@4500rpm
7000rpm rev limiter

http://www.dinancars.com/store/product.php?productid=1517&cat=416&page=1
Peak gain 15hp@6000rpm
Peak gain 13tq@4500rpm

Ebay you can try it I don’t know if the specs are true, but if you do let us know how it works and who sold it to you.

I found my ECU to end in 405, and eBay came up with two chips-

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=220381413168&crlp=1_263602_263622&ff4=263602_263622&viewitem=&guid=2d1a39ef1270a0b583207bd0fff4efe0&rvr_id=&ua=%3F*F%3F&itemid=220381413168

http://cgi.ebay.com/ebaymotors/91-92-BMW-E36-325i-is-E34-525-Ecu-405-Performance-Chip_W0QQitemZ360238388197QQcmdZViewItemQQptZMotor s_Car_Truck_Parts_Accessories?hash=item53dfe193e5

They seem to have similar specs to the chips you mentioned, so it seems like a possibility that they are a copy of the software found on the brand name chips. Is it worth $40 to find out? (I can always just put the stock chip back in if it doesn't help)

Search the feedback on this item from the lister and see if there is good reviews on the same chip look for atleast 3 reviews but check them all use your F3 key