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  #131  
Old 09-10-2018, 11:05 PM
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- I test drove a 2005 X5 3.0i with 60K, nice car. Gauge showed 1/4 for a while and did not drop even with driving!

- Car then stalled, code P0442 (EVAP leak) and P0301 (misfire cylinder #1), then code of misfire in many cylinders etc. Long story short...

- Mechanic checked: fuel pressure low, opened the tank, there was only 1 gallon in the fuel pump well!

- So the issue of stuck fuel level sensor (driver side) is interesting. I see that in E39 5-series, E-46 3-series cars and also E53. I don't why the sensor is stuck, maybe people let the tank run dry so often, so fuel evaporates and left behind residue. The solution is to fill it up and add Techron etc.

- Then it occurred to me that BMW engineers copied the E53 design from the E39 5-series (I own a 1998 528i)...When you think about it, if you were an engineer, you would design with the fuel pump on the LEFT side of the tank and use the siphon pump on the RIGHT side. This way the fuel pump always sits on the bigger side...and you can run the tank down to 10% or so, although I always fill it up when it gets below 1/4.

- Anyway, just a thought on the engineering aspect of this!
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  #132  
Old 09-10-2018, 11:09 PM
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It's on purpose and makes more sense this way. They want the pump to be submerged in gas even when the car is at a sharp angle up or down.

By putting the pump in a 5L "dent" on the right side the pump is submerged when the tank has 0.0L on the gauge.

If the pump was in the bigger side it would take about 20L of gas to submerge the pump but more importantly when you are pointing down or up the pump would be dry.


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  #133  
Old 09-10-2018, 11:43 PM
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Quote:
Originally Posted by cn90 View Post
Mechanic checked: fuel pressure low, opened the tank, there was only 1 gallon in the fuel pump well!

There is always only one gallon on the right side once the total fuel quantity is about 1/3 of a tank.

If the fuel pump was submerged in gas the fuel pump itself is the likely fault.

The NORMAL reason for gas starvation when the gauge reads 1/4 for example is that the siphon jet connection is leaking at the o-ring. The left tank usually will have 15-20L of gas and the right side will mere ounces of fuel.

I would love to know what the follow up early with that car because what you are reporting doesn't logically make sense.

I have personally had the right side sensor hang up and that will give you a few liters of error. I hadn't seen a case of the left sensor hanging up but like I said if there's "a gallon of gas" on the pump side that's enough to drive 20 miles you won't stall unless the pump is worn out and can't provide 50psi.
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  #134  
Old 09-11-2018, 09:00 AM
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The factory design is fine AS LONG AS the siphon pump works.
The BMW engineers did not anticipate siphon pump failure somewhere down the road!

What I meant is: build a tiny recess on the L side and put the pump down there. This way when the siphon pump fails, you can still drive until 1-2 gallons remaining.

Again, they did not predict siphon pump issue.

It is all because of the driveshaft tunnel issue...
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  #135  
Old 09-11-2018, 10:52 AM
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The tiny bump you describe would poke out of the bottom of the car.

They didn't anticipate the siphon jet o-ring failure hence my description as a "design defect". Your proposal would not be an improvement. The car would starve of fuel with 40% full tank when you go up or down a steep hill. that's the beauty of the design. By putting the pump in a dent in the raised part of the tank, the pump is submerged down to about 3L of fuel regardless of the pitch angle of the car.

Just like 100 other systems on the car there are required subsystems. Once we know about it though it's easy enough to keep on top of things.
By monitoring the fuel level with hidden menu 6, watch the right tank level and if it drops before the left tank goes to zero the siphon jet is leaking. You can prevent getting caught with fuel starvation with 1/4 of a tank remaining.
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  #136  
Old 09-11-2018, 11:33 AM
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Having 2 fuel pumps or even a separate pump for the syphon jet would solve a lot of issues.
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  #137  
Old 09-11-2018, 11:39 AM
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Oh hell no. Siphon jet has no moving parts in theory it woukd last indefinitely. An oversight in the design of the flexibility of the plastic causes this failure. An electrical/mechanical pump would be far less reliable. Also the beauty of this system is it's no more effort to pull fuel from the front and back of the main tank to account for up and down hill operating.


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  #138  
Old 10-02-2018, 06:16 PM
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Hey guys!

I have a 2006 BMW X5 3.0i, with 128,000 miles, and have some fuel gauge issues. A couple of months ago, the X5 ran out of fuel when the fuel gauge needle was between the 1/4 and 1/2 hash mark. This all started after another shop replaced the fuel pump and they said it was nothing that they did. Last month, I added a full tank of gas and needle moved to 1/2 mark. I removed both fuel sending units and didn't find anything wrong. I reinstalled it and the needle went to full. I figured that maybe something got stuck and now it was fixed. A couple of weeks later, the car died again because it ran out of fuel and the needle was just under the 1/2 mark. I took it to a shop to read faults and they said I had the following:

Stored in the DME:
- (141) 8D PLAUSIBILITY, TANK FILL LEVEL, NOT PRESENT. OCCURRED 2 TIMES.

Stored in the Instrument Cluster:
- (199) C7 TANK SENSOR #1 (FUEL PUMP SIDE), NOT PRESENT. OCCURRED 0 TIMES.
- (215) D7 TANK SENSOR #2 (WITHOUT FUEL PUMP SIDE), NOT PRESENT. OCCURRED 0 TIMES.

I removed both fuel level sensors, checked the resistance when I did the sweep test and didn't find any opens in the resistor. I reinstalled it and the needle dropped to the 1/4 mark. I found out about the instrument cluster test and got the following:
Tank Sensor #1 = 21.8 liters
Tank sensor #2 = 8.1 liters
This is roughly 7.8 gallons which looked liked it did when I last checked it.

I then added 16.18 gallons of fuel and the needle went to the 3/4 mark. I did the cluster test again and got the following:
Tank Sensor #1 = 55 liters
Tank Sensor #2 = 27 liters
This is about 21.66 gallons so this should be a full tank right?

I am also getting" TNKANZ: 58.8L, Phase 1"
58.8L equals 15.53 gallons. Phase 1 means both sensors are OK but I don't know if I believe that or not.

To my knowledge, the drivers side fuel sending unit has never been replaced. I am starting to think that the drivers fuel sending unit or the instrument cluster itself could be faulty.

Any thoughts?
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  #139  
Old 10-02-2018, 07:05 PM
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The gauges only read to full minus ten liters. (The floats hit the top of the tank).

If it says phase one as your surmise, car is getting realistic values from the floats. If you are getting intermittent drops in value sounds like a bad connection somewhere.

Two things most likely cause of fuel starvation at 1/4 tank: leak on the siphon jet or a weak fuel pump. It's tedious so get measurements of the fuel pressure but I just crack the left sender open and turn the key to determine if the siphon jet is leaking


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  #140  
Old 10-15-2018, 05:39 PM
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Hi to all,



I've done my timing guides, it was a pain but its done and runs beautifully so I decided to take a look at that fuel sender.


What I did was take out the fuel pump and having the tank low on fuel, I used my iphone and is flash photography to take a picture of the offending fuel sender in situ :





As you can see its correctly seated but the plastic holder is broken and the sender is hung up (I'm guessing on a broken resistor plate).


The only explanation I can find is that my tank vent valve leaks under the engine's vaccume and this compresses the tank...



Is there anything else that pulls vaccume from the tank or would explain compression?


I'm thinking my only way of testing my theory would be to change the sender and unplug the vent hose before the pump. is there any other way?


Of course I'm very open to ideas, if anyone opens their sender unit, I'd be interested of knowing the distance from the rim to the bottom of the "bump" on a tank that doesn't eat its sender units, maybe even the distance from two points (towards the center of the car and towards the door) of the rim to their respective sides of the bump to see if my tank is deformed for ever or not.


Thanks for the help.
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