Just bought a 1997 528i with 91k miles and stick at auction. Misfiring.

[Donut0389]

I guess I should say why I don't trust used Control Modules.

7-8 years ago I had a 1990 Volvo 240. One day the check engine light comes on. Fairly common part to fix. Get the part. Light doesn't go out. Look it up online. General concensus is a bad ECU. So a buy a $90 used one...

What followed was $500 worth of parts to "fix" various components and STILL have a check engine light. I was at wits end. So I say "screw it" and plug the old ECU back in to see what happens...light goes out.

Damn $500 in parts. Caused by a faulty used ECU. The only silver lining in it is that something in that $500 worth of parts fixed what was causing the check engine light in the original ECU.

...then five months later my hood with newly installed hood hinges comes unlatched at 45 mph, does not catch the safety catch, destroys the new hinges, bends the hood real bad, and nearly causes me to poo myself.

I miss that 240. It was named Problem Child.

[Donut0389]

Not a fan of those red coils. I wouldn't be surprised to find they are the cause and CERTAINLY wouldn't use them after this.
If you post in the genl mech help section you may get a reply from a fellow there capable of diagnosing your DME and cloning a used one.
I believe you can check the coil drivers yourself, I remember seeing an ohm value for them once.

I have access to a Bentley manual now. Good coils should have a 0.8 ohm resistance across pin 15 and pin 1. I'll test all 7 of them (there was a 7th coil in package in the trunk) and see what's up.

EDIT: "Took the cover off the DME. Yep. Mosfet for cylinder 2 is melted with slight heat damage to an adjacent component"
I see you've found it.
I've recently been playing with SMD soldering. If this isn't too tiny I'd be happy to have a crack at it provided the component(s). No guarantee of success but at the end of the day worst case is it's still NG and you're out a quarter for the MOSFET.
OR, I also have a spare known good 41.1 DME I'd sell at the going rate as a core

After reading up on the EWS system in these cars, I really like the option of RPMs "unlocked" DME units that bypass the EWS system. Like a dead key fob battery can cause a no-start. I'm just worried about that system screwing me over in the future. I'm currently waiting for RPM to open so I can call them and get some technical questions about thier bypass system answered. But timezones being as they are, they aren't open for another 3 hours.

[mattmar1]

dead key fob battery will not cause a no start issue, the battery is used for remote opening and alarm stuff. the EWS antenna transmits a signal which is received by the chip in the key fob (if you look inside yours, its a chip separate from the main ckt bd in your key, later models its mounted on the main ckt bd). the signal energizes the chip which enables data transmission back to the ring antenna to the EWS module, enabling engine start. if youre uncomfortable how this works, remove the battery (ies) from your fob, 1 or 2 depending on which you have. you can then unlock the door manually with the key, and start the car. no fob battery.
if going with a refurb DME, keep in mind that your VIN wont match the car. in my mind a + for having your existing one repaired. all data in the DME stays as it was.

if you want a good read for how the EWS works, look here

http://www.unofficialbmw.com/images/BMW_EWS.pdf

start at page 19 for EWS 3.3

[Donut0389]

Well you learn something new every day. Either way I'm a firm believer in the KISS method, "Keep It Simple, Stupid". So removing a possible failure point is A+ in my book. I'll keep the old DME on hand in case I ever sell the car and the new owner wants the lockout re-enabled.

On another note the fobs already don't function as intended. I work at an Advance Auto. I used our RF fob tester and at least one fob sends a signal. But that fob still doesn't lock or unlock the doors. Not a big problem for me. I just use the key to lock/unlock everything anyways. I'm old fashioned that way.

[Jason5driver]

Title says it. My beater E28 is on its way out and in searching for a replacement I found a manual 1997 528i that was going up for auction. Listed issues were a cel, misfire, and oil leak. Snagged it for $1300. Only code currently showing up is misfire cylinder 2. Here's what I've done so far...

Oil leak is standard valve cover gasket issues. Doesn't look too serious so that project goes on the backburner.
Removed a crappily installed cold air intake. Previous owner was kind enough to leave the stock plumbing in the trunk.
Temporarily sealed cracks in the rubber baffling just after the MAF. Need to find a new one but it's OKay for now.
Swapped coils around...misfire still on 2.
Swapped plugs around...misfire still on 2.
Plug that was originally on 2 appears as if it just wasn't firing. The rest have your standard wear from use. Plug on 2 is clean as if it's getting fuel but is not getting spark. Def not oil or coolant fowled.

Came here to get opinions from you guys.

My guess is that the injector needs servicing or to be replaced...

[cnn]

This problem (bad mosfet feeding an ignition coil) is so rare!

Below is a good video on a different model but worth watching

Re replacing mosfet...either find the exact PN and get it from place such as:
1. Arrows Electronics
2. Buy used used DME as an "organ donor", unsolder the donor mosfet and transfer it to your DME.

[Donut0389]

Update! Success! Ordered an unlocked DME from RPM Motorsport. Plugged it in after testing coils. Problem solved. Just got him back from inspection/emissions. Needed both inner tie rods and an outer to pass inspection. Otherwise, passed with flying colors!

[amancuso]

Great!

[BimmrMeUpSnotty]

Nice man! I think this is only the second or third time I’ve seen a burned up mosfet in a DME. Glad you figured it out!

[Donut0389]

Just realized I never posted a picture of the DME carnage. Well here it is. Cylinder 2 mosfet catastrophically burned out with scorch damage to the board and slight melting of the cylinder 1 mosfet.

[Jason5driver]

Just realized I never posted a picture of the DME carnage. Well here it is. Cylinder 2 mosfet catastrophically burned out with scorch damage to the board and slight melting of the cylinder 1 mosfet.

How / Why does this even happen ?

[mattmar1]

glad ya got it going. only the 2nd DME mosfet ive ever seen burnt up as well.

- - - Updated - - -

How / Why does this even happen ?

internal fail with the mosfet most likely.