[SOLVED] Fueling Issues - fuel pressure

EDIT: The fuel pressure sensor itself was my issue, not the ITFP relief valve. I wrote a thread about replacing it.

After swapping the motor in my 2012 Speed3 at the end of July because the stock one threw a rod I started experiencing some fueling issues. The engine ran great across the rev range at pretty much any speed, and the HPFP pressure held steady...until it didn't and randomly dropped to 0psi. Not 400. Not 200. Zero.
At first the fuel cuts were pretty intermittent and momentary, happening most often at 5000rpm. A couple days later they started happening at 2-3k rpm too. Then at idle. Then instead of being momentary cuts it would be at 0psi for seconds at a time (the engine still ran somehow). After 3 weeks the car was pretty much undriveable.

So I did some searching on the forums and elsewhere and followed the typical advice of checking the HPFP/spill valve, PRV, and in tank fuel pump. The HPFP was in great condition but I took it apart and gave it a cleaning just to be safe. I decided to tackle the ITFP next and got myself a Deatschwerks DW300c (here's the thread I referenced while swapping it: https://mazdaspeeds.org/index.php?threads/how-to-itfp-replacement.1186/). Swapped it in without much trouble and was about to reinstall the whole assembly until I accidentally broke off the nipple on top where the fuel line connects to.


Here's the ITFP assembly out of the car. I had to buy an entirely new one since there was no way to reattach the broken nipple. They retail for $200-$250, but I found a cheap one on eBay for like $60 and just swapped my new fuel pump into it. After I did though, I decided to inspect my old assembly.
Note the skinny black tube on the side. It's connected to a low pressure relief valve that (usually) opens when the fuel pump primes but the fuel lines are already pressurized, dumping fuel back into the bottom of the plastic tub.


Taking off the top part of the assembly reveals a flapper at the end of the low pressure relief line. It was at this point I noticed the valve looked kind of deteriorated, so I took it out for a closer look.


It was totally shot. While this wasn't what was causing my fuel issues, it might be worth replacing since having loose bits of rubber in the fuel tank isn't exactly good. For context my car has 176k miles at the time of writing and I've never run anything but pump gas.

 

Thankyou for your valuable info here...and welcome.
How long have you owned the car and perhaps what fuel(s) were you running? Do you run Eth? Curious if there could be a correlations...for future readers.

 

Thank you! I bought it in November 2020 w/ 155k miles. I never ran ethanol but got the car w/ a tune from Dramatune making around 300hp/315tq (according to the previous owner). Other relevant mods are a V3 Accessport, COBB CAI and boost controller, and Autotech HPFP internals. I'm sure some shitty 93 octane throughout the years contributed to the flap disintegrating but I never ran anything it shouldn't have been rated for.

 

Thanks for the write-up, I'm glad you got it sorted.

moved to knowledge base section as this is good info to have, also added tags so that it shows in searches better

Edit: OP sent me a message saying it was actually the fuel pressure sensor, moved back to troubleshooting section