M60 Fuel Level Sensor

[nk530]

Hello All,
I've got a curious problem. M60 won't start. Can't hear the fuel pump running. I've got power to the fuel pump connector, and I took the pump out and ran it off a battery (it runs). Here comes the curious part: I checked for continuity across the connector going into the tank (part of the level sensor) and found both contacts on the bottom (in-tank side) connecting to the same pin on the top of the connector (which I think is +12). What do ya 'spose would cause something like that?

Needless to say, the pump doesn't run with +12 to both sides of it. Is there more going on inside that connector that I don't know about? The wiring diagrams show a straight-up connector, i.e. no switching or anything.

Thoughts?

EDIT: I should mention that the rest of the level sensor appears to work properly. No evidence of any damage.
-Nate

[632 Regal]

Needless to say, the pump doesn't run with +12 to both sides of it.
-Nate

One side needs to be a ground.

[shogun]

these pics might help you
94 530i Won't Start (fuel pump relay suspected) HELP! - Bimmerforums - The Ultimate BMW Forum

[Ferrett 1962]

Just went throuh the same thing, had power to connector and even heard the pump run for a second when I did the relay bypass, after that the car would start then cut out. I removed the pump and it also ran on a battery while not pumping fuel but I think failing under load so today I put a new pump in and the car started and ran well so it seems the pump can still run but not develop preasure. After the noise when I first jumped the relay the pump could not be heard.

[nk530]

I've read a lot about how the pump is only active when the engine cranks, but I can tell you that I get full battery voltage at the connector on the tank with the key in the on position. 'Only on when cranking' may be true for other production dates or geographic locations, but my 03/1994 530i originally sold in Maryland is not this way. It is also shown explicitly 'hot in run and start' in the wiring diagrams. I thought I'd throw that out there. There seems to be a lot of back and forth about it.

Thanks,
Nate

[Ferrett 1962]

My comment was more about the pump, with mine I removed and connected to a battery on it's own and it worked, I also wired it back up while still out of the tank and plugged the connector in and jumped the relay so I had constant power to it and the pump still ran. I was carefull to cover access to the open tank and make sure to vent the boot (trunk) and clear fumes, and not to run the pump while dry for too long as that will kill it. A mechanic I spoke to suggested using a container of fuel and holding the pump in it connect an outlet hose to direct flow and run the pump to see if will work under load. Set up right this could prove if the pump will pump the fuel, I didn't have a safe place to do this and thought the risk of fire was too high if done wrong but like you my pump worked out of the tank it could not build pressure at all under load and would fail. I left the pump and level sensor out in the air till the fuel evaporated before connecting the pump and wire harness, you would not have to jump the relay just turn on the key and if the pump runs like that the connection is ok the fault would have to be with the pump. If not I would do the relay jump just to eliminate this.

[nk530]

Could also be a difference with ASC+T? I've got a different layout in my e-box from the pictures you linked to, Shogun.
Anyway, the relay can't be the issue if I've got voltage at the connector, right?

Ferrett, as much as I don't want to spend the money, it sounds like I might just have to buy a new pump anyway.

Thanks,
nate

[shogun]

yes, the fuel pump starts with ignition on and runs for a few seconds till there is enough pressure. If engine is not started, fuel pump will stop.

[nk530]

Explanation time. I was getting 10.8 volts at the connector (top of the tank) with the ignition on. I mistook that for batt. voltage. I thought it was just low because I had been cranking the engine for a while trying to diagnose this s*%t. Turns out, the fuel pump only runs when it sees 12v. I'm still not sure what's happening inside that connector, but the ~11v is enough to power the level sender, but won't start the pump. Lern sum'n new every day.

[nk530]

So, just for closure of this thread, there is nothing wrong with my fuel system. The car wouldn't start because the drive-away protection system was sending a no-start signal to the DME. Still don't know why. Don't care. I just disabled the drive-away protection by cutting the wire going to the DME. Pin 66 on mine. Green wire. Thanks to 632 Regal and his '850 No Start' thread and everyone who contributed therein.