X5 stalled/set codes while being inspected!

[workingonit]

Originally Posted by andrewwynn

Ever fix your siphon jet and was fuel near 2/4-3/8 tank?


–awr–

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I never looked at the siphon jet, because the fuel pump was so obviously dead (used a Power Probe to inject 12v to it, without movement). Why look further?

On my first test drive following the repair, I put in 9.6 gallons, so the fuel level must've been at 5/8 tank.

[80stech]

Check the vent line and fuel pressure before you jump to conclusions. If it really is higher than it should be there is a chance that the return line or maybe a syphon jet line got pinched or restricted somehow when you installed the new pump. You'll have the pump out in 5 or 10 min. the second time and then also have a look at while the fuel gauge isn't working. What is with your syphon jet ??

[80stech]

Actually lower voltage means higher current and is harder on the fuel pump so when the inspector plugged in his scan tool after the car sat idling for a while it might have been the last straw for a pump that was on it's last legs anyway so 'maybe' not so much coincidence.

[andrewwynn]

When i did wife's fuel filter i didn't remove the under body panel i only removed enough screws/rivets to lower one side. (made it much easier to reattach: it was auto aligned and one side was being held up like a hinged door).

If there's a problem with fuel supply, it can be related to the three hoses that come into the right tank from left.

Until the tank is lower than 27L or so that doesn't come into play though since the left tank floods to right at about 27L.

If you didn't add fuel since the cornering hiccup, i would open the tank and make sure the level is not at the flood stage and check the siphon side. If it's never been addressed there's a very good chance it's failed.


–awr–

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[workingonit]

Originally Posted by andrewwynn

...

If there's a problem with fuel supply, it can be related to the three hoses that come into the right tank from left.

Until the tank is lower than 27L or so that doesn't come into play though since the left tank floods to right at about 27L.

If you didn't add fuel since the cornering hiccup, i would open the tank and make sure the level is not at the flood stage and check the siphon side. If it's never been addressed there's a very good chance it's failed.


–awr–

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I never opened the left side of the tank, nor did I see the three hoses you mentioned, inside the right tank. Only ever touched the hose that attaches on the top of the fuel pump I replaced.

I'm not sure if I'm understanding this fuel system (I've got your AWR-fix: e53 Fuel pump / siphon pump details thread, RealOEM, and NewTis up on other Window tabs right now, trying to wrap my head around this weird fuel system). If I added 9.6 gallons (36.34 liters) on the immediate fill-up, does this mean that the left side tank/siphon pump went dry, and is failing now?

What should the "flood stage" level be, now that I've only driven 33 miles on a filled tank?

i'm trying to formulate a plan of action to diagnose and fix my fuel delivery system, before I tear everything apart, and maybe make things worse. Is it possible that resetting adaptations screwed up driveability, somehow?

This could take me awhile...after all, i had been trying for four years to find the reason for lean fuel trims, before the fuel pump failure, and never did. I'd sure like to get back to the old days, with points ignition/mechanical fuel pump/carburetors. I understood all those....

Perhaps I should ask this way... someone once asked for something to be explained to him, like he was a 5 year-old, so I'm just a 5 y.o., too, (plus 70), and in my 5th year of BMW ownership, so I'm slow on the grasping of the split tank operation scheme.

I've got other, newer vehicles that still use the conventional in-tank pump set-up, so I'm hoping that if/when I get my X5 back to operating condition, I won't have to go back to school to replace a failed pump, next time.

[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?

[andrewwynn]

If the tank is over 3/8 full it will not be siphon related. I would get a measure of fuel pressure at the rail and make sure it's rock stable. It should not change other than maybe 1/2 to maybe 1 psi drop when you punch the throttle.

New ≠ fixed you could always have a bad new part but over pressure at the pump will just mean more fuel back to the left tank.

A constant rich situation usually means MAF sending a bad signal or possibly bad O₂ reporting incorrectly but you will usually see mismatch of banks in that case.

When FPR goes bad as [mention]80stech [/mention] mentioned it's very unlikely to over pressure but if the symptoms match you need to confirm/rule out that possibility.

There's a vent hose from the FPR which looks like typical FPR that is used to compensate for vacuum at the intake but I've come to understand it's just a vent in case of diaphragm failure that will suck fuel/vapor to the intake.

That condition should lead to rich running : both from gas getting into the vent but also if it takes more pressure too open the valve because the diaphragm is letting fuel through.

So back to basics: you need to measure the fuel pressure. It should be 50 ±1 but rock stable. When wife's FPR had a failed o-ring the pressure bounced with each injector pulse.

The symptom she had was occasional very hard starts.

The worst case was the last drive to the shop to fix: took about 50 seconds of total cranking.


–awr–

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[workingonit]

Here's what I'm thinking: installing a brand new fuel pump, changing nothing else, might've over-powered the aged (possibly bad) fuel filter and new-ish Bosch FPR (since I didn't buy it, nor install it, it could possibly be bad or even a counterfeit part?), and the increased prssure from the new pump caused the instantaneous change from lean fuel trims to rich fuel trims. If so, and the fuel pressure readings show more than 50+1 psi (or much more, or even way under...though I think that's hardly likely), then I'll assume that I need another filter +FPR (leaning towards Hengst or Mann).

Do I even need to open up the left tank at this point?

The proven-good Siemens MAF hasn't out-of-the-blue gone bad simultaneously, and the O2 sensors, working fine in every test I've made (and working fine in the current series of photos I've taken of my dashboard display, in post #72 of this thread), haven't suddenly gone bad. Coincidence (even my luck with bad incidents coming in threes) doesn't quite occur like that, when only one component was changed.

I learned a lesson while racing & modifying my race car, that I should never change more than one thing at a time (from bad experiences doing the opposite).

[andrewwynn]

You need to know fuel pressure before doing anything else


–awr–

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