Car won't start -- help with electrical checks

[blee]

Hey all -- my car last started about 4-6 weeks ago during the snowstorms we had around here. Let it sit and idle for 10 minutes or so while I did other things, then turned it off. Tried to start again today, no dice. Pulled plugs, ran starter with the fuel pump fuse removed, put in new plugs, tried to start, no dice. Been trying to follow the Bentley guidelines to diagnose. Here's what I have so far:

Fuel pump: Checked the fuse, fuse ok. Went to the fuel pump relay, ran a jumper between 30 and 87. No sounds. Does the key have to be in a certain position for this to work?

I thought this might be the problem right there, but I kept going just in case...

Main relay: Good power to 30 and 85. I don't know how to check for ground on the brown wire on the harness. Checking for voltage across 87 and 87 got me nothing with the key set to "on." Not sure what any of that means, as far as diagnosis goes.

Coil: Checked voltage on the frontmost ignition harness, no problem. Pulled the sparkplug after an attempted start. Smelled gas...not a ton, but a little bit.

Adding to all of this, my battery is dead, so I have to do all this with another car pulled up and jumper cables running between the two. LOL

Any hints? If running the jumper wire across 30 and 87 on the fuel pump relay socket causes no noise, and if I don't smell much gas in the cylinder, is it definitely going to be the fuel pump that died?

[Dave M]

Hey all -- my car last started about 4-6 weeks ago during the snowstorms we had around here. Let it sit and idle for 10 minutes or so while I did other things, then turned it off. Tried to start again today, no dice. Pulled plugs, ran starter with the fuel pump fuse removed, put in new plugs, tried to start, no dice. Been trying to follow the Bentley guidelines to diagnose. Here's what I have so far:

Fuel pump: Checked the fuse, fuse ok. Went to the fuel pump relay, ran a jumper between 30 and 87. No sounds. Does the key have to be in a certain position for this to work?
I thought this might be the problem right there, but I kept going just in case...

Main relay: Good power to 30 and 85. I don't know how to check for ground on the brown wire on the harness. Checking for voltage across 87 and 87 got me nothing with the key set to "on." Not sure what any of that means, as far as diagnosis goes.

Coil: Checked voltage on the frontmost ignition harness, no problem. Pulled the sparkplug after an attempted start. Smelled gas...not a ton, but a little bit.

Adding to all of this, my battery is dead, so I have to do all this with another car pulled up and jumper cables running between the two. LOL

Any hints? If running the jumper wire across 30 and 87 on the fuel pump relay socket causes no noise, and if I don't smell much gas in the cylinder, is it definitely going to be the fuel pump that died?

Best guess is yes, your pump puked. With the relay proerly jumped (I added a pic for fun), you will hear the fuel circulating through the rail. Its easy to hear, so if you don't, your pump isn't working. While it may have puked, I'd check the connector under the access port in the trunk. Mine was fairly corroded and caused me some grief a while back (again, see pics).

Location for fuel pump relay jump:


Fuel sender connector in trunk:


Corroded connection:


Dave

[Dave M]

Oh, forgot to add, check for power at the connector to help determine if its the pump. I don't recall which terminal in the third pic is power, but you'll find it. One of em should give you ~12V when grounded.

Dave

[whiskychaser]

Think Dave says it all. But isnt there an in-line fuse between the relay and the pump? Long shot but cheap and easy

[Dave M]

Think Dave says it all. But isnt there an in-line fuse between the relay and the pump? Long shot but cheap and easy

Very good point.

[blee]

Hmm. Where is this fuse located?

[Dave M]

Hmm. Where is this fuse located?

I assume its in the same place as mine. Check for black box between strut tower and fire wall on the drivers side. remove top and check for the fuse 'menu' on the lid.

Dave

[bubba966]

Hey all -- my car last started about 4-6 weeks ago during the snowstorms we had around here. Let it sit and idle for 10 minutes or so while I did other things, then turned it off.

Adding to all of this, my battery is dead, so I have to do all this with another car pulled up and jumper cables running between the two. LOL

If your battery is this dead using another car to jump it isn't usually going to work. The batteries in our cars are huge. It's probably much larger than the battery in the car you're using to try to jump it.

When they're dead they draw a large amount of current from the battery you're using to jump the car. When they're severely dead like yours is they are an even bigger draw on the jumping battery. So much so that you won't have enough current to start the car.

Try pulling the battery out of the jumping car and installing it into your car. Or you could just fully disconnect your battery from the car and run the jumper cables to your battery connections if it's too big of a pain to pull the battery from the jump car.

If you're not getting enough power to even start the car it does no use to try electrical trouble shooting. Try it with a new battery or with your battery fully disconnected from your electrical system.

[blee]

Well, with the jumper cables in place and the donor car running, everything seems to work correctly (except that the car doesn't start of course). With the fuel pump relay bypassed, I get 12V to the fuel pump harness in the trunk. I take this to mean that my fuel pump is done. Is it really possible that my fuel pump would fail to work on jumper cables, even if the starter engages and all of my accessories seem to be working fine?

[Tiger]

Hey, your fuel pump is dead. It is very common in BMW. There is alot of cheap fuel pump you can install... just check ebay or other website that sell only fuel pump.

OEM is expensive... but there is alot of alternatives that is far cheaper.

Stop testing that fuel pump or otherwise, you are gonna blow yourself up. All it take is one spark by gas tank.