Gas Sending Unit faults -Help!

[taosx5]

Originally Posted by upallnight

Most likely your transfer pump is history, and the gas on the left side of the tank is not being transfer to the right side. The gauge is on the left side, but the fuel pump is on the right side. If the transfer pump doesn't transfer the fuel, the right side of the tank will be pump dry by the fuel pump.

Hey Upallnight, I have done lots more reading which led me to more reading trying to figure this out. There is a diagram in this thread from Qsilver http://www.xoutpost.com/bmw-sav-foru...nk-filled.html. He talks about a Test 6. Is this Test 6 something I can do with my OBC or does it require some sort of special scan tool?

I respect your opinion that you think it is the transfer pump. I am thinking it could be but not the sole problem. The fuel light does not come on now which would indicate the transfer pump. But even with that light not coming on and after it was determined it ran out of gas, it took 23.3 gallons to fill. The fact that when filled up it registers 3/4 tank might mean the fuel level sensor 1 might be the culprit or part of the problem. Also after driving about 200 miles, the gauge went from 3/4 to 2/3 tank and we parked and left if for about six hours. When we came back the temp rose about 20 degrees but the gauge registered 1/4. Weird!

I was concerned about these gremlins so I filled the tank and it took 11.2 gallons to complete full and gauge registered 3/4 again.

After work I took the rear seat off and took a look at things. I checked wires, used a hammer and banged it several times to see if the gauge moved or anything. Since this car has over 150K miles I would probably opt to replacing the fuel pump and maybe both sending units. Do you know of any threads that have good directions on changing a ll of these? Thanks in advance.

[upallnight]

Originally Posted by taosx5

Hey Upallnight, I have done lots more reading which led me to more reading trying to figure this out. There is a diagram in this thread from Qsilver http://www.xoutpost.com/bmw-sav-foru...nk-filled.html. He talks about a Test 6. Is this Test 6 something I can do with my OBC or does it require some sort of special scan tool?

I respect your opinion that you think it is the transfer pump. I am thinking it could be but not the sole problem. The fuel light does not come on now which would indicate the transfer pump. But even with that light not coming on and after it was determined it ran out of gas, it took 23.3 gallons to fill. The fact that when filled up it registers 3/4 tank might mean the fuel level sensor 1 might be the culprit or part of the problem. Also after driving about 200 miles, the gauge went from 3/4 to 2/3 tank and we parked and left if for about six hours. When we came back the temp rose about 20 degrees but the gauge registered 1/4. Weird!

I was concerned about these gremlins so I filled the tank and it took 11.2 gallons to complete full and gauge registered 3/4 again.

After work I took the rear seat off and took a look at things. I checked wires, used a hammer and banged it several times to see if the gauge moved or anything. Since this car has over 150K miles I would probably opt to replacing the fuel pump and maybe both sending units. Do you know of any threads that have good directions on changing a ll of these? Thanks in advance.

Yes you can perform this test with OBC.

If you do replace the fuel pump and the sending units, use Genuine BMW parts.

I would drive the X until you have less then a half tank of gas in it, since most of these parts are submerge in gasoline and you don't want a lot of gasoline dripping all over the interior as you remove the parts.

[taosx5]

Originally Posted by upallnight

Yes you can perform this test with OBC.

If you do replace the fuel pump and the sending units, use Genuine BMW parts.

I would drive the X until you have less then a half tank of gas in it, since most of these parts are submerge in gasoline and you don't want a lot of gasoline dripping all over the interior as you remove the parts.

Thanks for this info. How does one do this Test 6. I will try to look it up on the forum but I can probably figure it out. And thanks for the heads up on doing any replacement with a lot less fuel. Makes a lot of sense to me.

[upallnight]

Here's how to unlcok the OBC.

https://www.youtube.com/watch?v=cXrWrkEqClU

[cn90]

- BMW fuel pump is made by Pierburg. So if you can google "E53 fuel pump Pierburg" and see what you get. Be careful about counterfeit, if any.

- The fuel pump itself is cheaper, about $150.

- The fuel pump assembly is more, about $270 at dealer:
PN 16116755043:
BMW Parts - Chevrolet GMC Cadillac BMW Mercedes Benz Parts and Accessories

- Fuel Sending Unit (Driver's Side) is PN 16116762044, about $85.

I understand you have the itch to replace fuel pump b/c of the mileage of 150K, but the car runs fine, so I'd leave the system alone for now. The sticky sender unit is a well known problem and Techron usually fixes it.

Anyway, best is try Techron and see what happens. Most fuel pump failure happens people allow fuel to run dry (less than 1-2 gallons). If you never let the fuel runs below 2 gallons where the pump is located (this means "above 1/4" in BMW with "failed siphon pump"), the pump easily lasts beyond 200K.

[taosx5]

Originally Posted by upallnight

Here's how to unlcok the OBC.

https://www.youtube.com/watch?v=cXrWrkEqClU

Thanks this is awesome. I suspect this is where you can program oil changes, and Inspections and other cool stuff. I do things like oil/filters/tire rotations, change out miscellaneous odds and ends, but I will play with this and see what else I can do. I am not gonna rush into this fuel system problem. I will do more research and try this test and see what I come up with. Thanks again.

[taosx5]

Originally Posted by upallnight

Here's how to unlcok the OBC.

https://www.youtube.com/watch?v=cXrWrkEqClU

Before going to work this am I went in and unlocked the OBC. I did Test 06. This is the result. 0.0/12.6/12.6L

While performing the test the gas gauge currently shows about 2/3 full.So with this info I guess this tells me a couple of things. That the sending unit on the left side is not registering, and the other that with 12.6 liters (approximately 4+ gallons) on the right side that the sending unit on the right side is not registering properly. Here is why.

There is about 200 miles on a full tank so that means there is realistically a little over 200 miles or a little over 1/2 tank. The range left on OBC is at 301. We just did a road trip hence the 200 miles so this range of 501 at about 21 mpg seems realistic but something sure is screwy.

Anyone??

[cn90]

Well known issues in many BMW models, including E39 (the 5-series).

The OBC fancy computer only works if BOTH sender units function properly.
Otherwise, you get all these ghost readings, and you only waste your time playing with these OBC thingies.
Best is to ignore these for now and use the trip odometer as a general guidelines as to when to fill up.

Do the Techron thing, use only good fuel (avoid El Cheapo gas stations).
After a 6-pack of Techron, report back.

[jsoto]

Techron or any FSC works best when you let it soak---aka, short tripping. While still better than nothing, I would avoid it if it's just pure freeway driving.

[upallnight]

You can read this poster problem and solution:

Bimmerfest - BMW Forums - View Single Post - Fuel Gauge/Tank problems

The entire post starts here:

Fuel Gauge/Tank problems - Bimmerfest - BMW Forums