Quote:
Originally Posted by andrewwynn
@ bc. I thought the mechanic replaced MAF but now I recall the dish soap on the o-ring situation I just thought that was from checking for vacuum leaks.
From my research which was extensive, the follow up on almost every example of somebody replacing a fuel filter on an x5 was a shortly after fuel pump replacement. (Because any relief of gaining pressure from new filter was temporary since the fundamental problem was actually low pressure from the fuel pump).
On my wife's x5, there was a huge gas leak on the siphon pump multiplying the effect of low pressure and it may have been a Mfg defect on a batch of cars as I've read a handful of examples where the siphon pump failing. It's practically impossible for a siphon jet to fail but an o-ring failing do to a "rollover" problem during assembly? Much higher chance.
The fuel filter on x5 is huge. On the order of 100 or 200x the surface area of an old school fuel filter I've replaced on cars back in the carbureted days. The regulator is combined and that part is far more likely to fail and annoyingly can cause very similar symptoms it has a much higher MTBF than a fuel pump so when "low pressure problems" exisit I would first check fuel pressure. I'm considering adding an analog gauge on the return line to the left line of the gas tank. That would basically be a "hours remaining gauge" on the fuel pump. Right at end of life, the fuel pump loses power but since it makes more pressure than needed the engine doesn't "see" that pressure it gets the regulated pressure. The left lobe gets the "leftovers". The math doesn't work exactly like this but say the pump produces 60psi and the regulator sends 50 to the engine and 10 psi back to the tank. When the pump wears out and makes 55 psi. The engine gets 50psi the tank gets 5psi. There is a minimum requirement for the return line in pressure and volume. When it drops low enough it won't pull gas from left to right lobe of tank. This will happen before hesitation is obvious at the engine so the drive to zero DTE test is a great way to easily confirm your fuel pump is making enough pressure.
I recommend at least once or twice a year run your X5 down to single digits DTE to test your fuel pump.
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I would not be surprised at all if the problem is fuel delivery. I have never even implied it isn't. And I acknowledge the replacement MAF got rid of the dash warning. But since the mechanic had diagnosed the problem as the MAF and the symptoms did not change and since, as I understand it, OP purchased a used MAF, I think it prudent to confirm the MAF is working properly before moving on to troubleshooting for a fuel delivery problem, close out the possibility of one potential cause before moving to another. If I had said, it sounds like, it appears, it seems to me or I think which are often used in place of assume, I wouldn't have left myself open for criticism. Just as I assumed the mechanic knows what he is doing, it is an assumption that the mechanic did not. When there is more than one problem that can cause the same symptoms we all make assumptions from the input provided to come to our conclusion. Too often there is a race to be right or folks get defensive when there conclusion appears to be challenged or does not become the focus of troubleshooting. I have no problem if the MAF is assumed to be fixed and the focus becomes a fuel delivery issue.
It is not conclusive the fuel pump is bad if your engine quits running at a quarter tank or so. It could be a problem with the fuel level sensor instead of the pump.