[SOLVED] P0301 error fuel issue?

Locosiete

Locosiete

Paid for the full speedometer & I'm using it all
Greenie N00B Member
Greenie Member
Ok so first off will start by saying I am far from an expert but also not a complete noob so like to tell people I know just enough to know I don't know enough lol

Ok so couple weeks back while driving and the engine light comes on and can feel a pronounced miss. Using Torque app see it is giving a error P0301.
When I get home check #1 plug and looks fine. Only a couple months old so that made me scratch my head. Coils were aftermarket and since they could have 10k or 300k miles on them figured couldn't hurt to start there.
We got the car used from original owner, engine was replaced and from looks engine is all OEM with exception of some basic bolt ons' like CAI and short throw shifter.

Replaced all 4 coils and valve cover gasket and VVT seal while i was there and did oil and filter. Timing chain didn't feel too loose. It ran fine for about 50 miles. Then the miss came back. Car doesn't smoke but still misses while driving. Idle sounds fine. While running Forscan live data idle climbed by itself until I kicked down idle. That happened twice.

This morning replaced spark plug on #1 plug in case that maybe issue, although it looked fine, but still misses while driving.

Using app check PIDs and oddly fuel pressure seemed low without AC on. Took some screen shots at idle and holding idle. The higher fuel pressure was with AC on. Just seems weird to me. Either way hoping someone can shed some light so I don't fire the parts cannon at it or have to sell a kidney to the stealership.
Screenshot_20230802_105219_FordSys Lite.jpg Screenshot_20230802_105202_FordSys Lite.jpg Screenshot_20230802_104627_FordSys Lite.jpg Screenshot_20230802_104615_FordSys Lite.jpg
 
Your images show fuel rail pressure at 49-97psi? Not familiar with the torque setup, but that is confusing. Tank pressure, or post hpfp...?
 
SyntheticAtmosphere said:
Your images show fuel rail pressure at 49-97psi? Not familiar with the torque setup, but that is confusing. Tank pressure, or post hpfp...?
Click to expand...
That is actually from Forscan, I'm assuming it's before HPFP. On torque app it show fuel pressure on HPFP much higher. I'll have to take a screen shot of that since not 100 sure what that was.
 
So last night check fuel pressure with Torque app and was reading much higher which tells me the Forscan app reads before HPFP. But now it is giving error P0300 and P0301. Seen a few other posts that had that nothing that said it was for sure X Y or Z. Not that I think my issue will be the exact same but I'm sure it's probably some small sensor that is causing so much headaches. You can see pressure builds and drops with minor RPM. The spike was at about 2000 rpm

Screenshot_20230802_232248_Torque.jpg
 
The pressure will build and drop based many variables all calculated by the pcm based on injector duty cycle, pressure, cylinder conditions etc. The important part is that the pressure stays high during WOT. However, pressure post HPFP as low as what Forscan was listing was too low.

Fill this out and it will help people better understand where you are at.

Year/Make/Model:
Mileage:
Location:
Concern:
DTC's:
Modifications
ECU/Tuning Software:
Tuner:
Is the concern intermittent?
Can you duplicate the concern?
Recent Repairs:
Correction:
 
Year/Make/Model: 2007 Mazdaspeed3
Mileage: 330,000ish, unknown miles on engine that was swapped
Location: Houston TX
Concern: troubleshooting
DTC's: p0301, P0300
Modifications: CAI
ECU/Tuning Software: stock tuning to my knowledge, have Forscan and versa tuning available, plan on doing minor tweaks once error resolved
Tuner: n/a
Is the concern intermittent? Constant
Can you duplicate the concern? Constant issue
Recent Repairs: plugs, coils, valve cover seals and VVT seal and oil
Correction: temporarily resolved issue once made repairs then returned
 
To start, perhaps you might try a PRV test like <<this>>
...to verify the PRV is maintaining fuel pressure in the fuel rail, plus it cost nothing.
The key is to do it while the engine is good and hot.
 
Didn't see any sensors specifically for HPFP only one that shows on or off and they just switched on and off non stop

Here is what I took. On the dual line that flutter at beginning was holding rpm around 2-3k. The single line was with engine off key on

frp.jpg frp2.jpg
 
You did a relief valve test and your pressure maxed at 883psi? And the engine was hot?
 
SyntheticAtmosphere said:
You did a relief valve test and your pressure maxed at 883psi? And the engine was hot?
Click to expand...

Yes ran for good 5 min and then turned off. Complete drop was with key off for a second. Turning key back on that was my pressure. Not sure I have the right sensor monitored. Gonna play with versa tuner see if I can logg off that. Bought a cable so should work better then cheap ELM327 Bluetooth OBDII I used. Once temp gets below lava outside will redo rest
 
Based on those numbers your PRV could be bad or you didnt get a good test. 800's is really low.
Not sure if 5 min of idle is good enough to get good and hot.
 
Ok redid test. Ran until was up to temp then ran logger with Versa tune with key on engine off. Once pressure started dropping turned off logging.fuel pres.png

1) is holding at 2000 rpm
2) reviving to 3500
3) reviving to 6500
rev pres.jpg

Definitely low pressure from everything I have seen
 
Try an "OEM" PRV. One thing to remember, HPFP pressure is not directly related to engine RPM. You can't diagnose much based on RPM with this design.
Provided you got a proper PRV test, yours could be faulty. Something else to consider as well would be a rebuild for the HPFP if you dont know when it was done last. Corksport, Graveyard and Rey's kits are all available and will upgrade to E85 safe at the same time. Be sure to disassemble and service the full pump including the spill valve. If you dont have HPFP internals (which religiously you should) now is the time to get some...or to verify you actually have them.
Once this has been done, if your issues persist, you will know the pump is good.
To better understand the Speed fuel system, read <<this>>
 
I do understand RPM and pressure is not directly related but just showing it does make pressure just instantly falls off. New PRV should arrive tomorrow so hopefully that resolves issue.
I was planning on replacing with upgraded internals for HPFP if it wasn't already but that was something for down the road. May need to move up that schedule
 
Well replaced PRV and pressure has improved allot but misfire still persists and code P0301. Ran test twice to make sure and results were similar but different. PRV was very black inside. HIGHER pressure was first test. Pressure at idle has also improved too.20230806_162954.jpg prv replaced.png prv replaced2.png
 
That same color will be present in hpfp internally too. If the pump parts are a little too much $$$ at least get the hardware/o rings kit and clean the pump and all internals. Using the instructions, if you can't really find good instructions for help on disassembly and cleaning CorkSport HPFP internals kit has a great link to download the PDF instructions...Your HPFP if even still stock is a timebomb if not clean, it barely works well on completely stock engines. Please upgrade asap.
 
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