Boost and HPFP issues

Hi all,

I've been running some datalogs on my 2007 MPS recently and have spotted a couple of things that look strange to me. My only mods are a single piece 3" intake and TIP connected to the stock air box, a high flow panel filter and a second cat delete. It's running the stock tune.

I've attached a 3rd gear wide open throttle throttle log. You will see the boost sits just under 12 psi and the HPFP pressure fluctuates wildly instead of holding a steady pressure. The pressure stays above 1600 psi but only just in places.

Is it possible I have a small boost leak as 12psi seems a little low and what could cause the HPFP pressure to be so erratic under WOT? Note it was a reasonably cold day (around 12 degrees)

Cheers

G'day. I agree the boost _seems_ a bit low. I would have expected it to log 14psi at least. I would suspect a boost leak. The 100psi variation on HPFP seems significant too - I'd be wondering if the HPFP is in good condition. Possibly worn cam follower? How many K's are on the engine?

The car has done 138000km. I did run a Cobb stage 1 map A month ago and saw boost up to 16psi but I guess something could’ve come loose since. I wonder if it’s the 3inch intake messing with the hpfp?

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Originally Posted by LTPC

The car has done 138000km. I did run a Cobb stage 1 map A month ago and saw boost up to 16psi but I guess something could’ve come loose since. I wonder if it’s the 3inch intake messing with the hpfp?

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I can't think of any way for the inlet to mess with the HPFP pressure. I run a similar setup myself - OEM airbox, high flow filter, custom turbo inlet pipe. Your MAF sensor is still in the OEM housing by the sound of it, yes? i.e. MAF sensor and high flow filter are in the OEM housings? That won't introduce any issues in and of itself.

I'm thinking the HPFP pressure relief valve might be in the early stages of failing. I don't recall OEM tuning ever exceeding 1700PSI, but yours is peaking at over 1700 and then dropping back by 100PSI. A stage 1 cobb tune can see 1750PSI on the OEM HPFP but should be steadier than that, and you are on OEM tune. If HPFP relief valve fails it will fail to hold pressure - in early stages I imagine you might well see unexpected variation in HPFP pressure.

The other thing occurring to me is that you aren't reaching wastegate spring pressure of 14psi. The OEM 2 port boost control solenoid bleeds pressure off the wastegate actuator to keep the wastegate closed. With the solenoid bypassed or held in the spring pressure state your boost should reach close to 14 psi. EBC allows the wastegate to be closed longer so boost rises further than 14psi. Fully functional it allows boost to rise to 16 psi or more. If you EBC stuck in the open state I'd imagine overboost conditions more than under.

14psi minus pressure drop across the TMIC with EBC failing to keep the wastegate closed might account for 12psi and no higher.

There are some additional perameters you could log : HPFP commanded pressure to compare against actual pressure - what ECU is aiming for vs what's actually there. I think there may be some similar PID to log for boost or MAP. I usually run my logs using MAP (manifold absolute prressure) rather than boost pressure. MAP will measure 12psi boost as 26PSI = 14PSI atmospheric pressure + 12 PSI boost.

My BL with a stage 1 tune and similar mods (TMIC and inlet) sees 32PSI max = 18PSI boost.

I would be suspecting the HPFP relief valve is early stages failing and EBC solenoid fail - possibly there is a boost leak as well. At 4000-4500 RPM there seems to be enough wastegate duty to expect exceeding 14psi, but it's actually 2psi under spring pressure.

I'd check all hoses, including wastegate actuator hoses, and also confirm your bypass valve has a gasket in it, and the gasket is in good condition.

I'm far from an expert, so there's a bit of edjumacted guessing going on here, but that's what I'd be looking at now, based on the _theory_ I know.

HPFP relief valve suspect
EBC suspect. If EBC dead and stuck in spring pressure state, won't exceed 14psi and won't respond to wastegate duty cycle signal.
bypass valve gasket suspect

Theoretical reason for HPFP variation
Imagine for a moment the EBC is being commanded to reach boost levels of 16PSI
But the EBC isn't working so boost is only reaching 12PSI
When it commands wastegate duty cycle for a 16PSI target it commands HPFP pressure to match.
But it's not reaching target so the additional pressure is not needed or wanted, which might result in HPFP over pressure and unusual fluctuation in HPFP pressure.

I'm thinking EBC solenoid has failed. The rest _might_ be a result of that.

Awesome advice thanks mate! I’ll replace the EBC solenoid and see if that makes a difference. Does the HPFP have replaceable relief valves or will I need to replace to whole unit?

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Originally Posted by LTPC

Awesome advice thanks mate! I’ll replace the EBC solenoid and see if that makes a difference. Does the HPFP have replaceable relief valves or will I need to replace to whole unit?

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There's probably a few checks you can do to confirm it's the EBC but that'd be my bet atm. It could be a loose loom cable/connector.

re: pressure relief valve - OEM units are available through edge autosport....
https://edgeautosport.com/mazda-oem-...cx-7-2007-2012
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