Title: 2010 BMW X5 35d (E70, M57): rail pressure error under acceleration, almost everything replaced, mechanic stumped
Car: 2010 BMW X5 xDrive35d, 3.0L twin-turbo diesel (M57), [mileage], [transmission]. About R250k of work has been done at BMW (invoices available).
Problem:
The car has been at my mechanic for about 2 months. He knows what he’s doing, but this one has us baffled.
The day after I got the car, it stuttered and wouldn’t drive, so I had it flatbedded to the mechanic. He diagnosed the low pressure pump and replaced it, but then noticed the tank was actually empty even though the gauge showed about a quarter. He refitted the old pump and had me run the car below the quarter mark to see if it would free up. It started again, so we went back to the new pump, thinking that was the only problem.
After that, whenever I put my foot down the check engine light came on. The car still drove with no limp mode, and switching it off and on cleared the light. I thought it was a one-off glitch, but it kept happening, and I eventually narrowed it down to every time I accelerate hard.
What we’ve done since, in order:
We’re at a crossroads and don’t know what to try next. I know this is a long post, but has anyone come across this?
Already replaced or tested:
Any advice on further tests, or what finally fixed it for you, would be hugely appreciated.
Car: 2010 BMW X5 xDrive35d, 3.0L twin-turbo diesel (M57), [mileage], [transmission]. About R250k of work has been done at BMW (invoices available).
Problem:
The car has been at my mechanic for about 2 months. He knows what he’s doing, but this one has us baffled.
The day after I got the car, it stuttered and wouldn’t drive, so I had it flatbedded to the mechanic. He diagnosed the low pressure pump and replaced it, but then noticed the tank was actually empty even though the gauge showed about a quarter. He refitted the old pump and had me run the car below the quarter mark to see if it would free up. It started again, so we went back to the new pump, thinking that was the only problem.
After that, whenever I put my foot down the check engine light came on. The car still drove with no limp mode, and switching it off and on cleared the light. I thought it was a one-off glitch, but it kept happening, and I eventually narrowed it down to every time I accelerate hard.
What we’ve done since, in order:
- The mechanic found a low pressure warning on the fuel rail and a small leak on the boost pipe. We repaired it and serviced the car, but the error came back as soon as I accelerated.
- We replaced a temperature sensor on the feed line (genuine BMW part). No change.
- A deep ISTA scan suggested the overflow valve on the high pressure pump. Replaced, no change.
- I had the software updated and the diesel filter changed. After that the car started complaining about injector 5. We replaced it, but then the car went into limp mode as well. So the old software was part of the problem, but we still have the rail pressure error, now with limp mode.
- We then replaced the high pressure pump and fitted a new sensor. Still the same.
- The mechanic traced the wiring at the fuel control box and found a lot of bad grounds, an old tracker and poorly crimped ferrules. He fixed and removed those, but the problem persisted. The fuse box also looked like it had been worked on, so he replaced it. No change.
- He replaced the fuel control box. No change.
- He found an error on the ECU and swapped it out. Still nothing.
- We did a full analogue test of the actual fuel pressure in the lines to the rail, which passed. We then replaced the rail and both rail pressure sensors. The fault is still there.
We’re at a crossroads and don’t know what to try next. I know this is a long post, but has anyone come across this?
Already replaced or tested:
- Low pressure pump (new)
- Fuel filter (twice)
- Fuel rail and both rail pressure sensors
- High pressure pump and overflow valve
- Feed line temperature sensor
- Injector 5 (replaced and coded correctly), all other injectors tested and passed
- Fuel control box, fuse box and ECU (all swapped)
- Wiring and grounds repaired at the fuel control box, old tracker removed
- Boost pipe leak repaired
- Software updated
- Low pressure fuel pressure tested, including under load: fine
Any advice on further tests, or what finally fixed it for you, would be hugely appreciated.
