Fuel Pressure Dropping at WOT

[FierceDietyNate]

I have been having an intermittent issue with my 2016 FIST with 51K miles where the car bucks and cuts power when at WOT (most often when going uphill). After a lot of data logging and diagnosis, I think I've narrowed it down to a fueling issue since my fuel pressure drops from around 2000psi to as low as 35psi when the issue occurs. Under the advice of some people on Reddit, I have replaced the HPFP cam follower and the low-side FP sensor but still the issue persists. I am feeling pretty confident at this point that it is the HPFP causing the issue since my data logs show the low-side pressure staying pretty consistent (within 5-10 psi of desired) whereas the high-side pretty consistently shows pressure dropping far below desired every time the issue occurs. Before I blow $180+ on a new HPFP I want to get some advice from people on here to see if I'm on the right track. I will attach a few data logs as well as a video of the issue in case anyone thinks I'm way off and wants to give their two cents.

Below are the links for the data logs
https://docs.google.com/spreadsheets/d/1wyZQfKwypAZ7hUAg44uzeqNfhOsM-y9yKc55UkkvvXE/edit?usp=sharing
https://docs.google.com/spreadsheets/d/1GIM2FKR7OJA6mdPtBTOmrX5PatuimNc1Q-12ED9DNvA/edit?usp=sharing
https://docs.google.com/spreadsheets/d/13HQCp2jc5SjSZv2LwdEfyWaMCZ7yfO20A-NMUBTCdao/edit?usp=sharing
https://docs.google.com/spreadsheets/d/1rSHscHBffMWaiyH_wYFhLshbZjo5BEHYpzg4c9u4CCg/edit?usp=sharing

 

[Jabbit]

I can send you a used HPFP for cheap.

 

[FierceDietyNate]

I can send you a used HPFP for cheap.

how much?

 

[Jabbit]

how much?

Let me make sure I can find it first - $60 shipped.

 

[TyphoonFiST]

LPFS? Low Pressure Fuel Sensor on the supply line near the fire wall. I did a DIY on this also. Where did you get the LPFS from?

 

[felopr]

log LPFS, you should see a steady 600-800 at idle

 

[FierceDietyNate]

LPFS? Low Pressure Fuel Sensor on the supply line near the fire wall. I did a DIY on this also. Where did you get the LPFS from?

Yeah, that's the one I replaced. I bought it from O'Reilly's but it was a motorcraft part.

 

[FierceDietyNate]

Let me make sure I can find it first - $60 shipped.

Let me know if you find it and I'll buy it.

 

[FierceDietyNate]

log LPFS, you should see a steady 600-800 at idle

600-800 psi? Isn't that a little high for the low side fuel pressure?

 

[felopr]

600-800 psi? Isn't that a little high for the low side fuel pressure?

derp that is for the high side, i am an idiot. you are right

 

[FierceDietyNate]

derp that is for the high side, i am an idiot. you are right

No worries just making sure I wasn't crazy lol

 

[Intuit]

Big spike in AFR (lean) at the same time FRP PSI drops so it makes sense to me.
I assume the engine hasn't been altered in ways that would result in it needing more fuel than a healthy stock pump and injector combination were capable of keeping up with.
Will the ECU run the engine with the HPFP pressure sensor unplugged? If so, does AFR still spike lean under the same conditions?

 

[FierceDietyNate]

Big spike in AFR (lean) at the same time FRP PSI drops so it makes sense to me.
I assume the engine hasn't been altered in ways that would result in it needing more fuel than a healthy stock pump and injector combination were capable of keeping up with.
Will the ECU run the engine with the HPFP pressure sensor unplugged? If so, does AFR still spike lean under the same conditions?


View attachment 59296

That's a good idea, I hadn't thought of that. I'll try it tomorrow and let you know.

 

[Jason@dizzytuning]

I'm pretty sure that you will run very rich when the sensor is unplugged. Even at idle.

 

[Raziel510]

Have you checked your O2 sensors?