[SOLVED] HPFP - Low rail pressure

I have 2007 CX7, but this forum is more active. I have low rail pressure and I think the HPFP may be the problem. If I rebuild/clean it just with an o ring kit and not new internals, should this be OK for a road car that has no engine mods?

 

What symptoms are you getting & what fuel pressure?

More likely failed open PRV, sticky spill valve could cause some issues that can be removed with the pump still installed to give it a clean.

Here is the test procedure for the PRV if you do need to replace it only use an OEM one.

 

What is the pressure you’re seeing?

 

OK thanks for the replies. I only have Forscan with an ELM327 USB interface. It reports zero psi in the HP fuel rail...but the car starts and runs ok at idle, but barely drives as I assume it is starved of fuel. If you disconnect the low pressure pipe to the HPFP gas is being pumped OK, at least on the low pressure side. I have just replaced the fuel pressure sensor (as I had already ordered one) and have stripped the HPFP and have obtained the correct Viton o rings (but no X ring). The internals did not look too bad, so I will clean and rebuild it this weekend. The pressure relief valve "seems" ok...at least you can't blow through it, but I realise that is not 1850 psi.
I plan on putting it all back together and seeing how it goes. Otherwise, would any leaks at injector seals cause no/low fuel pressure?

 

Also when I pulled the pump apart, the shaft with the collett attached came out. Can I reassemble it the way it came out or does the collett need to be removed from the shaft as shown in Johnny Tight Lips post?

 

Also forgot to mention that Forscan gives a P0172 code and the CEL is on (which was not the case before the VVT failure). The car has been sitting in the garage for two years...too many projects. It had VVT failure and bent valves. Finally got all that fixed and recon the head. I pumped out as much of the bad gas as possible and put fresh gas and octane booster in. Timing seems fine and ignition good...just no pressure in the fuel rail. I would have removed the in tank pump to check it...but someone had burred out at least three screws on the pump fitting so that is not coming out in a hurry. However, clearly there is fuel at the engine...just not at the right pressure.

 

If your getting flow to the hpfp that should be adequate I wouldn't worry about the intank pump. The hpfp does most of the work

 

For reassembly you can cross reference the corksport hpfp rebuild instructions I also had the auto Tech hpfp installation instructions up that should help you with everything.

Ground issues can cause some really odd symptoms in these cars, make sure that harness plug on the hpfp in connected, also that the ground on the bracket by it is tight. There's also a ground on the passenger motor mount. To start.

Then work shop manual for the speeds is posted in the metal member section with full diagnostic as well as the wiring schematics

 

Hi, thanks again for the input. I had a look at the Autotech instructions (I was following the Corksport info). The Autotech instructions shows the piston parts as they came out of my pump. So, it seems that you have to remove the spring retainer keepers and put that end of the piston through the threaded end of the piston retainer (through the X ring), to reinstall. It is not obvious to me how to remove the spring retainer keepers...can someone please describe how to remove and reinstall them?
Thanks for the tips re grounds etc. I will recheck when it goes back together. I will reinstall the pressure release valve on the rail as there is no way to test it further than I have. Thanks again!

 

You can use a wrench and a clamp to the bench to get pressure, I was able to just push down in the spring and release the retainers, there's some pics of the wrench trick in this thread
https://mazdaspeeds.org/index.php?threads/hpfp-o-ring-rebuild-michael-rey-facebook-kit.8069/

 

Hi, All good! I cleaned/rebuilt the HPFP with new Viton o-rings and it is working fine. BTW I found in a Corksport pdf for the rebuild that you don't need to release retainers for a stock rebuild. The piston will go back in the same way it came out. I just used a bit of clean engine oil on the piston on reassembly and it went back together nicely. Don't be like me and reuse those shitty T25 torx bolts...replace them with something better.

 

Glad to hear it's working for you. Good hunch on the cleaning