X5 stalled/set codes while being inspected!

[andrewwynn]

You said you added 9.6g but was that all that fit to fill it full? (That was my understanding).

If so you will be way past Flood stage and siphon jet doesn't come into play.

I never measured how much fuel just circulates vs. goes to the engine but at idle I'm confident a lot more fuel goes back to the left tank vs. consumed by the engine.

The tank has two lobes, the left is much larger and has no electric pump, the right is much smaller and it's where the electric pump is located.

The two lobes are connected at the top with a hump in the middle that when enough fuel is consumed they become separated. This happens at ≈ 27L total fuel according to the gauge.

At this point there will be about 5L of fuel in the right lobe, 3.6 which does not register on the gauge and 1.4L that does. (the 1.4 can be different on each car and should be learned by getting fuel lower than 1/4 tank and using test six to read the value).

When the tank has less than 27L, the fuel supply uses the excess gas returning from the fuel pressure regulator to generate a vacuum at two separate siphon jets at the front and back of the left tank lobe.

(2 of the three hoses that go from left to right: the third being to a pressure relief valve in case there's a blockage in the siphon system or any other failure that would put too much pressure on the system)

When working properly the siphons will pull fuel from the left to right continuously but it only matters when less than 27L.

At that point and less, the siphon jets will keep the right lobe overflowing the center hump and the right side will stay filled to 5L until the left side is bone dry.

When the siphon jet fails, it will fall to put enough fuel to the right and the right side will go empty since the pump pushes fuel from right to left but the siphon stops pushing the fuel back to the right.

When people "in the know" realize their car is stumbling but happens to be near 1/4 tank, they will take a hard left turn to slosh some fuel over to the right and make haste to a gas station.

If you happened to be near 1/4 tank, hard turns can easily cause engine performance oddities as fuel gets shot out of the tank by the pump and tossed back in by a hard left turn.

If the fuel level is ≥ 27L the siphon is removed from the equation.

Any questions?


–awr–

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[workingonit]

Thanks Andrew, i might be catching a glimmer of understanding (maybe)- I filled the tank until the pump handle clicked off. The right tank looked to be about 1/2 full when I replaced the fuel pump, so adding 9.6g seems right (I was semi-sure that the tank would be over 1/2 tank, since I NEVER left my vehicles get to 1/4 tank...my wife didn't, but after three times running out of gas, she listened to me...oil pressure gauge inattentiveness cost her a Fiero, though).

"When people "in the know" realize their car is stumbling but happens to be near 1/4 tank, they will take a hard left turn to slosh some fuel over to the right and make haste to a gas station.

If you happened to be near 1/4 tank, hard turns can easily cause engine performance oddities as fuel gets shot out of the tank by the pump and tossed back in by a hard left turn.

If the fuel level is ≥ 27L the siphon is removed from the equation."

The stumbling incidents happened on both (quickly successive) hard left and right curves, so shouldn't the fuel level have already been higher in the right tank following the left turn, but on the next right curve, surely the level wouldn't have fallen too low in just that short distance?

I'm sure that I haven't let the fuel level go down under 1/4 tank in only 33 miles since fill-up (figuring as little as 5 miles per gallon, riduculously low, I couldn't have used more than 6.6g, so the tank should've remained at 73% or more full), so the siphon pump shouldn't be of concern, now?

I ordered another adapter for my fuel pressure gauge kit (the one I was missing has a bad O-ring, which is too small for me to replace), and a new tank seal gasket (in case I damage one) because I guess I'll have to pull both right and left side tank pump & sender assemblies before I find what's happening, but I'm waiting to see what pressure is at the rail, before I order a filter+FPR.

Looking at FCP, RockAuto, and Amazon (probably not the place to get one, from unknown middlemen), i see Bosch, Hengst, Mann, Mahle, and BMW filter assemblies. Listed in price from low to high. Bosch about $50, BMW about $250, but I'm always fiscally-constrained, so BMW is out of the picture. Recommendations?