2001 525 IT Random crank without start.

[Robber80]

After going to dinner the other day I walked out to the car and it cranked without start. I took a taxi back to the house, grabbed my meter, and headed back to the car to get some testing done. The fuses were good, so I pulled up the seat and checked the voltage at the fuel pump to find 12v when the wife turned the key forward. I thumped on the fuel pump, the car started immediately with no issues in idle and I drove it home unable to notice any issue.

I figured it had to be a bad fuel pump, so ordered one up and threw it in the next day. The car started fine and I drove it around for 30 minutes good as new. I even cycled the engine many times and it started up well each time with no codes.

Today, (the day after) I went to go to work and of course the car exhibited the same no start issue. After work I got into it, tested the fuel pump and was not getting 12 volts. I located the fuel pump relay under the dash and found it was not getting 12v across 85 and 86, but did have supply on 87. If I jumped 87 to 30 the pump turns on, but the car does not start. I also noticed at this point that the temp gauge is deflecting to hot, my reader says that it is at 80% even though the engine is cold.

Initially I thought the only thing that could cause such an issue would be a cps or computer issue, but now I wonder if the temp reading incorrectly could cause such an issue.

I've done some searching and found similar threads, but nothing seems to be all that clear in regards to this. I also wondered about a faulty ignition switch because I do have an airbag light, but I do not have any other issues and nothing changes when I open/close the vanity mirror. I also noticed the RPM gauge does not indicate anything as I crank it, but I never paid attention to see if it showed anything before it started. Any help would be a big blessing.

[geargrinder]

RobberBaron:

If you're not getting trigger signal across the relay, that obv means for some reason the DME isn't turning it on (or you have a fuse problem). The relay should get 12V on pin 86 via fuse F31 at all times. The relay gets switched on by the DME grounding out pin 85. So you should always have (key on) voltage on pin 86 (also "pin 8" of the relay socket) never see voltage on pin 85 (pin 4), and pin 85 should be open to ground when not cranking/running, but grounded otherwise.

There's EWS stuff that could inhibit the FP from being triggered - if the keys are authenticating, but the EWS & DME can NOT authenticate, then the starter will crank but fuel pump and injectors and ignition will not be fired. Bringing us to your missing RPM signal. RPM gets to the cluster on a late car like this via CAN-bus I believe. If the CAN-bus is having some intermittent problem, then maybe in fact the DME is having trouble talking to the cluster and the EWS. That said, if DME/EWS are not authenticating it will leave behind EWS failure codes so that should be identifiable.

You also have the weird temp signal of course... have you checked the DME pins/connector for contamination by any chance? If it was an M6x I'd go straight there but they have more of a known problem with that than M54, so its a bit more of a long shot.

In addition, the visor-test isn't 100%, it's just a "often this might be a symptom". The car indeed can 'act very oddly' when the switch goes bad, so... you might try cleaning that switch up "just in case".

[Robber80]

Thank you sir, I'll dig a little deeper tonight and report back.

[Robber80]

So, even though the f31 fuse was fine, I was not getting 12 volts (at any key position). I don't have an electrical diagram, but did see some info that a fuse next to the dme supplied power to fuel pump and air pump (I also noticed the air pump is currently not turning on with key turned forward).

I opened up the box under the hood on the passenger side and tested the fuses behind the dme, they were all fine, but I did not get 12v at any of them with the key turned forward. I've tested all the fuses in the back and in the glovebox, along with the fuses in front of the passenger seat on the floor. All the larger wafer type fuses had 12v.

I guess I need to know where the supply for these fuses comes from? Any ideas?

[geargrinder]

Well. You sorta only half-tested what info I gave you. "F31 is fine" OK but is there 12V at F31 when cranking?
Is power showing up at pin 86/8 of the fuel pump relay when the engine is cranking?

Follow through on all the info I gave you. Here's the diag, sorry about font size, but this is the easiest way to send a link.

http://www.bmw-planet.net/diagrams/release/us/svg/sp/SP0000014613.svgz

Re: your other testing, yes there's a "main DME relay", which the DME powers, that then powers up the other 'voltage supply' fuses including the ones you tested, and F31.

I believe the main relay only gets powered when the engine is turning (and the EWS has authenticated). So unless you were testing while someone was cranking the engine, then that test also was incomplete.

The FP fuse F31 isn't shown in the DME relay diagram but it apparently comes off the splice before fuse F1. There seems to be a WDS typo or at least missing info about the splice indicator #, since the relay diagram shows X6961 and the fuse diagram shows X6011, but seems clear nonetheless that's the way it wires up.

http://www.bmw-planet.net/diagrams/release/us/zinfo/HEMFB1214_MS43UBH.htm

http://www.bmw-planet.net/diagrams/release/us/svg/sp/SP0000014604.svgz

The DME relay (like the FP relay) can get sticky/fail, so, if its not the FP relay itself then it could be the DME main relay. That's probably how you found the other info about the DME relay I imagine.

You could either parts-shotgun it and just toss a couple new relays in there, or, continue to test while cranking and see if one or the other isn't clicking over.

Before it gets mentioned - DME failure is EXTREMELY rare and unlikely, its about 100x more likely that its one of these relays - or, that its some EWS error, or, some bus-comms or overall voltage supply error. (still no codes?)

[Robber80]

Thanks a ton GearGrinder, f31 was not getting voltage at crank. I checked that dme relay and found its supply dropping from 12 to 2.5 when it tried to click over, went to those fuses in front of the passenger seat again and had another look around. Fuses tested good and were tight, but after removing some tape I found the PO/mechanic had cut the wires, twisted them back together and left them as is with no solder on em.... After wiggling them at the joints the car started right up, I'm getting out the soldering iron and some shrink tube right now, and she should be good as new in an hour or two. I can't believe I haven't had more gremlins with that shady work! Bought the car around a year ago and she has been pretty good to me besides a keyless issue that I was able to sort out. I think these wagons (especially the silver) are beautiful machines. Mine is actually much like yours except that it has black interior, silver bmw 2 piece wheels, and a lot of road rash on the underside of the front bumper. Thanks again man. EDIT - Our cars similarities are only skin deep - yours is a blown 540! Man that must be a lot of fun! That's funny you also have a Cherokee I had an 01 limited, but parted ways with her before I moved to Cali last year.

[geargrinder]

WHAT THE SH!T!! That's not what I expected (i.e. just worn out relay or something...) Wonder what that cut wire stuff was about!?

Coulda been a removed-mod? Somebody with one of those 'secret theft prevention' switches to keep somebody from stealing the car? Or some ill-conceived aftermarket alarm (if so - frikkin stupid and pointless on these cars they are SO hard to steal without the proper keys... you basically have to swap in a full junkyard DME/EWS/key set...) Some attempt at installing a remote start? (and generally those don't require anything like that either... they intercept the EWS/key interface and provide a key signal via a real key that you screw inside a box...) Finding stuff like that is never encouraging, always leaves you wondering "WTF is next..."

Sounds like our wags are closer than you think, my front bumper is in pretty rough shape these days (damn gravel road to the beach + new england winter sand trucks that often have pebbles in 'em...)