Make it make sense...Negative STFTs, FRP normal, Lowside FP normal, but only 1/2 des fuel mass?

[FDeStruct]

After four days of failure, I am here to see if anyone can point me in the right direction after my car is giving some really strange (and often contradictory) readings and symptoms. (hear me out)

Backstory:
I took my car in to a shop to get my clutch replaced - when I got it back, the shop had a charger attached to the car (which seemed weird because I had never had battery issues before) and I noticed some stuttering and fuel cuts (esp when advancing throttle, even partial). When I got home - the car stalled at idle. The battery was displaying signs of being diminished (had to jump the car to attempt to start it again), and it continued to stall at idle (and sometimes it was obvious it was operating on less than 4 cylinders)

Now - not my first rodeo - I figured they maybe forgot to plug something back in, or the low battery condition was causing some lack of voltage to something important, no MIL so..... okay, AP time.

I plug it in, and get zero fuel related codes, BUT, I did get 2301, 2304, 2307, 2310 ( again... no MIL). Yeesh. One coil going bad is one thing.. but all four? I know the coils should be replaced, but I want to know WHY all four would foul at once with no prior issue (and was curious if it was actually a problem with the coils or some kind of false reading?). I want to treat the issue, not the symptoms.

I have previously had a lot of issues with burning out LPFPs, and since my fuel system has the most of my modifications, seemed like a good place to start. Perhaps a bad connection with the map tap, maybe an issue with pressure in the LPFP, some kind of power surge, a vacuum leak??? Something. Probably something that I broke, truthfully

Anyway - my fuel system / adjacent components:

• XDI HPFP
• Alpha bravo LPFP (340 LPH)
• Bosch 30% injectors
• 3.5 bar MAP

I replaced the battery (which was not holding a charge), reset the BCM, tested all of the relays (not just for the click, but also for resistance / continuity), checked all the fuses (in both boxes), and checked the vacuum lines for leaks. Nothing. I start the car, it presents the same issues. Starts, runs for a while, then stalls but NO CODES.

Okay - maybe its a sensor then? I checked the voltage range / resistence for the sensors on the AP and with a multimeter (both on the connector and sensor sides)

• Lowside FP Input voltage (bc I had had previous issues with fuel pumps)
• Lowside FP sensor V
• Map sensor V
• EGO voltage Actual
• EGO voltage desired
• AIT V
• TIP sensor V

I noticed some anomalies (here is the log) one of which is the discrepancy between Lowside FRP Des and Actual (which starts off as the car reading too much lowside pressure, then too little - but STFT as low as -20%. I also notice my LPFP is reading only 4-6V, but has a brief surge of 25?! (mind you, STILL no MIL despite me starting the car at least 10 times between ).

I tested everything for ground, tested the fuel pump connector (its showing 12v at the pump... which doesnt match what the fuel pump is reading) no blown fuses, all relays are working. No codes for sensors out of range, no codes for anything.

I thought maybe since the clutch was replaced - they could have bumped my camshaft sensor, so I replaced that - no change. I replaced the crankshaft sensor, no change. Replaced VVT sensor (because of some visible wear and tear), replaced the lowside fuel pressure sensor, replaced all of the vacuum lines, checked the boost solenoid connections, tested everything I could think of.

So day 4 of this nightmare - I FINALLY get a cel (well four of them) which are the same as above.

I grabbed another log to display the fuel mass discrepancy at its worst... and you can see the car is asking for a certain fuel volume, and the car is providing roughly half of that.... but continuing to pull fuel


So the AP is reading all four fault codes for the coil pack circuit being too high - just for S&G, I pulled the coils and tested all three pins for resistance to make sure they work... they do

I have no idea what to do next. Im thinking that its one of 2 things:

• the O2 sensor is stuck on rich - so the PCM is pulling fueling until the car dies trying to correct it
• My FPDM isn't working properly

I am at my wits end with this. I have never wished for DTC's more in my LIFE.

I am going to replace the coils tomorrow, even though I tested them and it appears they are working, but beyond that I could use some ideas and help to try and sort out why the car starts fine then slowly dies with hugely negative fuel trims .

Any and all help appreciated!

 

[rfultz]

Did you ever get this figured out? My car is pulling -25 stft as well and stumbling idle and down on power