[The_E92_Fan]

Ok folks so this is getting weird. A few weeks ago I was enjoying the car and had no problems. I hop in the car to road trip to a car meet 2 hours away. I drove 10 minutes with no problems, filled up on gas, and the car just wasn't having it since then. Anytime I pressed the throttle I was met with severe misfires that would put the car into limp mode citing HPFP pressure fault among other things. Since then I've replaced the spark plugs, HPFP, LPFS, changed tune, got more gas. Still after all that the car immediately misfires and fuel pressure tanks. I monitor engine parameters while this is happening and even cruising at 80 the LPFS shows pressure swinging from 100-5 multiple times a second and AFR go out the window, and HPFP takes a shit. Tomorrow I'll try to take a slow log as I approach the limit of what the car wants to do before losing it. Has anyone else dealt with something like this?

[muncie21]

Definitely odd. Seems you've narrowed down the issue to fueling so sub'ing to see where this leads.

[The_E92_Fan]

Originally Posted by muncie21

Definitely odd. Seems you've narrowed down the issue to fueling so sub'ing to see where this leads.

Removed MOTIV flex fuel, tuned it back to stage 2+, no change. The weirdest thing is the car can cruise and hold fuel pressure at 75 psi and the HPFP holds at 2000+ but as soon as any throttle is applied the LPFS still indicates the fuel pressure is going buck wild and the HPFP literally crashes down to zero. Actually zero. Cold starts are perfect, no long crank. I'm opening the tanks next week. I happen to have a stock LPFP with me. No one seems to have ever had this issue so it's got to be something stupid.

[BSM n54iS]

Hmm well then that calls for stupid suggestions... lol

Have you tried replacing the HPFP sensor also? I noticed you said LPFPs. How many miles, does it seem o2 sensor related to you?

[Dave92N54]

Have you opened the fuel tank and checked the pump? The fact it happened after a fill up definitely seems to point to bad gas. At this point i'd personally pull the lpfp and just take a look at it, it's literally free to do so lol, you never know, you may find a loose line or something wrong with the pump.

Nevermind, I see i'm an idiot and you said you'll be doing so in a week. If stock LPFP doesn't fix it, my next step would be testing the EKP.

[The_E92_Fan]

Originally Posted by BdSM n54iS

Hmm well then that calls for stupid suggestions... lol

Have you tried replacing the HPFP sensor also? I noticed you said LPFPs. How many miles, does it seem o2 sensor related to you?

Haven't tried the HPFP sensor but I doubt it is that as the LPFP pressures swing wildly. It could be O2 but I doubt it. The LPFP is a fuel it walbro 450 bucketed with less than 5k miles on it.

[mapleleaf1773]

Have you looked for vacuum leaks? Any codes? Doubt its the 02 sensors.

[BSM n54iS]

Maybe post a log and see what starts acting up first that leads to all the other issues. I had read AFR and HPFP goes to shit so just threw those things out there

[The_E92_Fan]

Originally Posted by mapleleaf1773

Have you looked for vacuum leaks? Any codes? Doubt its the 02 sensors.

Vacuum leaks don't generally cause issues like mine. Also I've checked them thoroughly. I'm really not willing to flog the car hard enough due to fuel starvation and leaning it out hard. It seems I'd have to damn near let it die to get any codes. I've seen HPFP recover from under 100 psi with no codes.

[The_E92_Fan]

I think this is what my car had after the FRM died so not all these codes are relevant but the issue was present there. It should be noted that this was during a cold start, the HPFP occasionally would plummet and go to its failsafe mode and stick at 50 psi.

[Dave92N54]

https://www.e90post.com/forums/showthread.php?t=1525039

Have you read through this by chance?

[The_E92_Fan]

Originally Posted by Dave92N54

https://www.e90post.com/forums/showthread.php?t=1525039

Have you read through this by chance?

Yes I've read through that. It's not related to my issue.

I've changed the fuel pump to a stock one with no improvement. I dont have many things left to change. I'm going to try changing back to stock coils and I'm about to open the other side of the tank. If that doesn't work, O2 sensors, HPFP sensor....

[The_E92_Fan]

Changed FPR. Issue persists. I'm going to leave it in a shops hands tomorrow.

[The_E92_Fan]

Replaced HPFS. No change. The only things I haven't replaced are the front O2 sensors and the injectors. I don't want to spend $1700 on injectors for a car im trying to sell....anyone got an idea as to what's going on?

Rail pressure plummets until I get a half engine light with 29DC and 29F2. This happens even at idle.

[The_E92_Fan]

Solved. Was the HPFP. Bought a used one and it didn't work out. Had a suspicion it was bad and bought a new one.