Audi A4 Problematic Sputtering Issue

[acehlis]

I’ve been having a sputtering issue that I first noticed in late May. It would sputter while trying to pass on the highway, or merging onto the highway while accelerating. I took it into the dealer and they ended up replacing my Cam Follower, High Pressure Fuel Pump, and Camshaft.

I took it back, and had a small road trip planned and found the car still sputtered, but especially while going up moderate hills/inclines. So I took it into the dealer and they thought it was the cylinder head.

I lucked out and everything was covered by Audi warranty, when I got my car back everything seemed okay. I took it out on the highway a bit and didn’t feel the sputter, it did hiccup once but thought maybe it was a fluke.

During the process with the dealer I went out and purchased a Ross Tech VCDS cable and hooked it up to see if the hiccup showed up as a fault and found this fault:

000135 - Fuel Rail/System Pressure
P0087 - 002 - Too Low - Intermittent - MIL ON

I thought maybe I should change the fuel filter, so I did that and also put a can of BG 44K to clean out any possible gunk. A day or so later I got some more sputters, again the same fault showing up.

000135 - Fuel Rail/System Pressure
P0087 - 002 - Too Low - Intermittent - MIL ON
Freeze Frame:
Fault Status: 10100010
Fault Priority: 0
Fault Frequency: 3
Mileage: 98211 km
Time Indication: 0

Freeze Frame:
RPM: 2592 /min
Load: 46.3 %
Speed: 121.0 km/h
Temperature: 84.0°C
Temperature: 38.0°C
Absolute Pres.: 980.0 mbar
Voltage: 13.716 V

So for the past week or so, I’ve been trying to get it to sputter when I have the VCDS capturing data. I finally got some useful data.

As I was accelerating up a hill, merging onto the interstate, it started to sputter. All the data leading up to this point was as it should be. Specified Fuel Rail Pressure and Actual Fuel Rail pressure were in harmony. The low pressure fuel pump was at a steady 4.5-5 bar.

As soon as it sputtered (@3200 RPM), the specified fuel rail pressure was stating 109.99 bar but the actual dropped down to 6.1 bar and was an erratic 10-20 bar. As this was going on, the low pressure fuel pump kicked it up to 6.5 bar. There is one time where the low pressure fuel pump is a tad higher than the high pressure fuel pump. It recovered about 4 seconds later. Then the fuel rail actual peaks at about 117 bar. Does anyone have any thoughts as what could be doing this? Could replacing the fuel filter have introduced some air bubbles that just need to get worked out?