[Jcwoodhit]

Guys this has been an on going issue with my 2SS 1LE M6 car with 50k miles. Every time I press the throttle, my long term fuel trims go negative on both banks. At idle, seems to get better, or steady throttle driving seems to get better. When I'm casually accelerating from a stop the engine will buck around 2k rpm 1st through 3rd gear. Just doesn't feel like it's making the power it should. I have replaced EVERYTHING, all OEM parts replaced by dealer. Injectors, plugs and wires, MAF sensor, new O2 sensors, new PCV, checked for vacuum leaks. All sensor readings look ok. Is this a hpfp issue? Sometimes when I lift off throttle to coast in gear, and am around 1800 rpm 60 mph, I can feel the car start to engine brake but then it will ever so slightly lunge forward, like it's letting off a puff of air, if that makes sense. It's like it has problems, during dfco, I can watch it go in and out of closed to open loop during that moment, and back into closed loop. Please help, ongoing for over a year now!

[ctrlz]

Do you have any modifications installed?
Is the car able to run stoich while cruising in closed loop? And is it trying to hold back fuel to get to stoich in that situation?

Maybe check the intake for clogged filter or rodent's nest.

[Jcwoodhit]

The only modification is Rotofab dry intake. I took the intake off, and put the OEM intake and box back on, refreshed ECU and made no difference. I then put the Rotofab back on took it to get a tune thinking that would solve my problem, to no avail. Sitting at idle, or steady throttle fuel trims seem to get a lot better within an acceptable range -5 or so both banks. But if I even think about applying throttle the long term fuel trims on both banks both go really negative. Around -18 on bank 2 and -15 on bank 1 casually accelerating from a stop, that is also when I experience the drivability issues. Sort of like a fish biting sensation as soon as I reach around 2k rpms usually in lower gears barely applying throttle. During the first dfco event I can feel the car lurch or lunge but it's ever so slight. Would never feel it if you weren't looking for it. It also goes from closed loop topen loop and BACK to closed loop during the first dfco event at temp, and that is usually when I feel the car slightly lurch. I've replaced maf sensor, plugs and wires, pcv, injectors, checked for vacuum leaks, all out of guesses at this point. The only CEL that was ever triggered was a P015B code (primary O2 sensor lean to rich delayed response) and a week or so later a P015D code same thing (primary o2 sensor lean to rich delayed response) on the other bank. So I replaced all o2 sensors thinking that would solve my issue. Nope!! Something else caused it, and I just don't know what it is!!! Symptoms have went on for over a year now, no worse no better, and everyone (dealers) and even the tuner said everything looked good, but it's obviously not.

[ctrlz]

I'll give you my guess, since you are looking for ideas.
I think the problem is electrical... damaged wiring or bad connection, maybe even a bad ecu ground.
You seem to have exhausted the "parts replacement" options which might account for your trouble.
If you have a scan tool which allows you to monitor sensor output in real time, i would start checking the main sensors as you drive to see if anything is going in-and-out. I would guess something like MAF or MAP or throttle position has an intermittent connection, and the problem is worse with vibration while driving.
All guesses, and I welcome other ideas.

[KingLT1]

hpfp

[ctrlz]

Originally Posted by KingLT1

hpfp

So, can this thing blow past his new injectors? Would that foul his oil with gasoline?

[Jcwoodhit]

Originally Posted by KingLT1

hpfp

This is exactly what I was leaning towards. Explains negative long term fuel trims on both banks (slightly more negative on bank 2) Thank you for your input. Would you say the pump is bad? Or just leaking internally if you had to guess? No cel, no rich codes, just negative ltft both banks when applying throttle and bucking and jerking when casually accelerating from stop. Always starts fine, seems to idle ok, but once you give it throttle runs like crack during light load light throttle situations.

[Jcwoodhit]

Originally Posted by KingLT1

hpfp

Originally Posted by ctrlz

So, can this thing blow past his new injectors? Would that foul his oil with gasoline?

The way that I have understood it, the hpfp could be bad or leaking internally. Even if it's a minor leak, it could be drawn up by the pcv system because excess fuel vapor is being leaked into the crankcase, and then when it gets sucked up by the pcv it causes both banks to have negative ltft. That or just a bad pump. Maybe I'll replace the pump and hope for the best. I thought it was either that or bad cats, but secondary o2 sensors read steady.

[ctrlz]

Originally Posted by Jcwoodhit

The way that I have understood it, the hpfp could be bad or leaking internally. Even if it's a minor leak, it could be drawn up by the pcv system because excess fuel vapor is being leaked into the crankcase, and then when it gets sucked up by the pcv it causes both banks to have negative ltft.

Smell of gas when this happens? Gas in the oil?

[Jcwoodhit]

Originally Posted by ctrlz

Smell of gas when this happens? Gas in the oil?

Yes there is a little smell of gas in the oil, it's either hpfp or saturated charcoal canister. When I unplugged my purge valve solenoid trims got a little better, I watched them when I plugged it back up and they went super negative to the tune of almost -30 on both banks, engine bogged down. Every time it performs the evap test upon a cold start, the engine always bogs down. So it's one of the two, I know the purge valve isn't stuck open I already checked that.

[Jcwoodhit]

Originally Posted by KingLT1

hpfp

Hey man, I had the dealer replace my hpfp, symptoms still the same negative long term fuel trims both banks with bank 2 being slightly more negative by a few points than bank 1. Bucking light throttle acceleration only. bogging heavy throttle occasionally. Steady throttle or idle seems fine. Seems to struggle during first dfco event as well (can feel the car lunge ever so slightly when tb closes). Any opinions?