The X5 left me stranded. Fuel Pump?

[Auto Parts Guy]

So I'm driving home yesterday after work, about 3 miles from home and she just lost power. I coasted into a neighborhood and would crank barely but then die. Tried a few more times and wouldnt start. Had classic fuel pump symptoms. My scanner shows code 8D (P0461 I think in the generic world), which is fuel level circuit A. Although I have no fuel level symptoms. At first i was thinking the break down and code are related, but now I'm not. Thoughts? No other codes or symptoms.

Of course after a buddy towed me home, she crunk right up and I drove into the shop. I did some tests last night and no glaring issue now. Although the fuel pump sounds pretty weak for what thats worth. I hate to throw parts at it but sure does seem like the pump. Are there any cheaper alternatives besides the Delphi pump assembly for $268 at FCP and $177 at Rock Auto? Unless i can find just the Pierburg or TI pump for much cheaper, not looking to save $5 for just the pump. They seem to be in the $120+ range and not offered at FCP. Car has 187k miles.

[andrewwynn]

187/6=31.167 mph average which is pretty high, fuel pumps don't usually get anywhere near that long. (Average lifespan with E10 fuel is 5-6000 hours).

They also do often have hit and miss operation at end of life. You can often bang on the tank to shake it past a dead spot on the commutator bar to get it running. You can confirm a flat spot on a commutator with an oscope on the power leads FYI.

Caveat: were you close to 1/4 tank? The siphon jet has a design flaw and will with absolute certainly stop pumping fuel from the left side of the tank eventually.

At end of life, a weak fuel pump will be camouflaged by the FPR so it will seem to fail quickly though it's been slowly failing for a year without detection. It's a lot of work to hook up a pressure gauge between the pump and FPR to confirm, most will just replace the pump.

I replaced one of mine with a highly rated Amazon pump, it lasted rev months and was replaced under warranty and the replacement lasted the rest of the time I had the car.

[X5chemist]

For the miles, I would put in a new fuel pump. Mine are @153k miles. Other parts have priority for now. Once maintenance is up to par, new pumps will go in. High resistance on a pump is a good indicator it's going bad. Especially when hot. Until new pumps go in, I keep mine at half tank or more.

[oldskewel]

The fact that your friend towing it home fixed it may be a clue.

@AndewWynn has a great thread on here about the workings of the fuel tank. Basically it has two halves, with the electric fuel pump in the right half, and a siphon pump (passive) in the left half. The siphon pump sends fuel to the right tank, which is only needed once the fuel level drops below 1/3 (?).

If your siphon pump failed (common on these cars, although less predictable than the electric pump failure), it could be that your car died when the right tank ran empty. The description of not starting sounds exactly like a fuel issue.

Then when your friend towed you home (great friend, BTW ), it sloshed enough fuel from the left tank to the right that now you are OK again ... until that fuel runs out.

I know that sometimes with these old cars, the owner really does not know if the part is original. It could be that your electric fuel pump is not original, and should last until 300k miles. If true, replacing it might be worse than leaving it alone.

If you're tempted to keep driving it, and having a repeat of this is not a big problem, you could try filling up with gas and keeping it above half a tank. In that range, the siphon pump is not needed. If you do that for a while and things are rock solid reliable, it points to a siphon pump problem, which could then be confirmed by running the tank down to see if the problem reappears.

If you have the high cluster, you can do some measurements before then - one of the tests in there (#6 maybe) tells you the fuel level in left and right sides. If you don't have the high cluster, you can lift the rear seat cushion up and off (no tools, 15 seconds to do it) and measure the resistance directly on the floats on both left and right sides. Roughly it goes from about 50 to 450 Ohms as empty ==> full. Left tank has only the sensor. Right tank has 2 connections for the sensor and 2 for the pump, with them marked in the plastic cover. I forget what resistance the pump should be, but less than infinity would be good. Probably 10 Ohms or so.

If you do replace the pump, Pierburg (now owned by TI Automotive) is the OE supplier. That's what I got when mine failed at about 170k miles.

16-11-6-755-043 is the PN for just the pump. The plastic full assembly can be reused, which is what I did with no problems.

@AndrewWynn and others have good info here on repairing the siphon pump if you need that. It works on the Venturi effect, and when an o-ring fails and the created suction fails, no fuel is pumped. Very easy to open it up and repair it. I did that one pre-emptively one day when I had some time.

[crystalworks]

Originally Posted by X5chemist

For the miles, I would put in a new fuel pump. Mine are @153k miles. Other parts have priority for now. Once maintenance is up to par, new pumps will go in. High resistance on a pump is a good indicator it's going bad. Especially when hot. Until new pumps go in, I keep mine at half tank or more.

Except about the 1/2 tank thing. I drive mine from dead full to dead empty every time.

BMW fuel pumps are time bombs after 120k miles. They can last much, much longer... but I drive my cars out of town. So I don't like unknowns.

[Happy]

Originally Posted by crystalworks

BMW fuel pumps are time bombs after 120k miles.

Dang! It’s no wonder Andrew says to keep a spare on board.

[Auto Parts Guy]

Good points everyone thank you. I read all of Andrew Wynn's posts last night. Kudos to him, great info and analysis! I actually never go below about 1/2 tank, so she's pretty much full right now.

For the price, I just bought the complete Delphi unit from Rock Auto. Just the pumps were almost the same price as the complete units. FCP was $268 and RA was $177. I agree, at this mileage and hours, it needs one anyway, not worth the risk. I'll take some measurements once the new one gets here.

[Auto Parts Guy]

For what it's worth, i took the back seat out and the passenger cover to the pump off. Hooked up my scanner and activated the Fuel pump, it runs currently, but sounds like it's dying. I was hoping it would fail in the shop so i could confirm but not yet.

[crystalworks]

Originally Posted by Auto Parts Guy

For what it's worth, i took the back seat out and the passenger cover to the pump off. Hooked up my scanner and activated the Fuel pump, it runs currently, but sounds like it's dying. I was hoping it would fail in the shop so i could confirm but not yet.

As Andrew stated, they don't "hard" fail very often, but end up weak. I used to temporarily nurse a failing BMW pump by leaving that cover off and the back seat and giving the pump a few bumps with a weighty screwdriver while someone else cranked the car. Similar to "bumping" a starter with something to get it turn the car over when it's getting weak.

[Happy]

Originally Posted by crystalworks

As Andrew stated, they don't "hard" fail very often, but end up weak. I used to temporarily nurse a failing BMW pump by leaving that cover off and the back seat and giving the pump a few bumps with a weighty screwdriver while someone else cranked the car. Similar to "bumping" a starter with something to get it turn the car over when it's getting weak.

Thanks Crystal for that bit of info. Good to know in a “no fire” scenario, that tapping the pump can possibly get you off the side of the road.

Dang.. I remember the days as a kid, my parents banging on that darn starter! LoL..