[armend195]

Hello

Looked around the net and could not find a definitive answer.
When reading fuel rail pressure live data on idle the values go up and down sporadically between 27000-30000 kPa (270-300 bar).
Is this normal or should the value be at a stable number?

MAF sensor seems to follow the pattern as it also jumps from 10-25 g/sec.

Car feels as if low boost or lower power on low rpms.

Stage 2 with DPF removed.
I assume that it is not remap related as the car has been working fine after remap, but these issues started recently.
MAP, MAF, IAT sensor cleaned no difference.
No boost leaks, smoke test done.

Thanks

[barf]

Should be stable and shouldn't bounce. Probably bad sensor or quantity control valve on fuel pump, more rarely caused by pressure control valve on the rail.

[armend195]

The n47 has a quantity control valve and a pressure sensor on the rail. Do you know how to troubleshoot this and single out the failing part. The quantity control valve is an expensive item.

edit:

Sorry i was misinformed. There indeed is a pressure regulator and pressure sensor on the rail.
The quantity control valve is on the pump.

[armend195]

Originally Posted by barf

Should be stable and shouldn't bounce. Probably bad sensor or quantity control valve on fuel pump, more rarely caused by pressure control valve on the rail.

I unplugged the pressure sensor, car did not start. While cranking, the rpm slowly started to rise from 200 rpm but it did not feel good to keep cranking it so i stopped and pluggef the fuel rail pressure sensor back in. The first minute the car felt completely different like full power from 1000 rpm then it slowly went back to its old behaviour.

What could cause that? Maybe when cranking it with sensor unplugged there was a raise in pressure that made the car feel more powerful the first minute?

Or maybe the car ran good until the fuel rail pressure sensor values started to differentiate?

Thankful for any input.

[armend195]

Is there any sensor i can unplug to see if the pressure normalizes? For example unplugging the pressure regulator and see if the pressure is stable or if there is a difference?

[barf]

You can't run a common rail diesel without a rail fuel pressure sensor and also without regulation.

[armend195]

Originally Posted by barf

You can't run a common rail diesel without a rail fuel pressure sensor and also without regulation.

barf

As i see it its related to the MAF. Changed MAF, IAT no difference. Unplugging MAF no difference. Car still rough, hesitant and jerky.

Took some screenshots of the live data. The rail pressure gets longer and more erratic low spikes as temperature gets higher.

[Eddamoo]

Given your MAF is is a primary device to control fuelling, i would probably rule out the fuel rail itself and look towards what is causing your wonky MAF readings.

I would get a graph of the following sensors, plus a graph of the "MAF Setpoint/Requested". If the setpoint is all over the place, it will likely be one of the second list. If the setpoint is stable, something is directly affecting the MAF reading itself.

Directly affected:
EGR: If the valve is fluttering open/closed it will cause the MAF air-flow to fluctuate
MAF Itself (you've changed)
MAF Wiring
Air leak (i know you've smoke tested, but the PCV could be bad?)

Indirectly Affected (i.e. this would affect the calculation for the MAF setpoint):
Accelerator sensor
O2 Sensor readings
IAT Sensor (you've changed)
MAP Sensor

[armend195]

Originally Posted by Eddamoo

Given your MAF is is a primary device to control fuelling, i would probably rule out the fuel rail itself and look towards what is causing your wonky MAF readings.

I would get a graph of the following sensors, plus a graph of the "MAF Setpoint/Requested". If the setpoint is all over the place, it will likely be one of the second list. If the setpoint is stable, something is directly affecting the MAF reading itself.

Directly affected:
EGR: If the valve is fluttering open/closed it will cause the MAF air-flow to fluctuate
MAF Itself (you've changed)
MAF Wiring
Air leak (i know you've smoke tested, but the PCV could be bad?)

Indirectly Affected (i.e. this would affect the calculation for the MAF setpoint):
Accelerator sensor
O2 Sensor readings
IAT Sensor (you've changed)
MAP Sensor

Hello Eddamoo

Thank you very much for the info.
When unplugging MAF, the pressure does not change. Does that not rule out that MAF is not issue? I mean, when MAF is unplugged, the car runs on like a basic map or values? But the pressure still spikes like in the photos.
Car is stage 2 with removed DPF and i assumed o2 sensors were issue, went to tuner and removed o2 on new flash. Shows 0.0V when reading etc. Made
No change at all, even after unplugging.

MAP sensor changed, no difference.

What could be faulty with PCV? I’ve changed tube that cracks, the breather pipe that goes into the intake next to the turbo. Also changed the springy type thing that sits next to the oil filler cap/injectos, thats also part of PCV. What else could it be?

Seems like the car behaves like this 8/10 times. Sometimes it just runs normal plenty of power, smooth and low fuel consumption.

I read a long time ago about the accelerator sensor, and maybe i’ll give it a shot. Is it a way to diagnose this with live data? Or should i just go on and purschase used one and change?

And just to double check, i’ll attach a photo. Is it this complete one? Thank you very much for the input and help!

[armend195]

https://ibb.co/ys4XBWF

[Eddamoo]

The accelerator position is loggable so I would just look to log it on your next drive.

If you're still seeing the crazy readings on the fuel rail with the MAF unplugged, I would try graphing as many other sensors as possible to see if any correlate.