Erratic AFR - running rich/lean spikes/bogging

Slowerp5

Member
:
2002 protege5
First time poster, fairly recent lurker.
I have a 2002 protege5 with problems that I can't figure out. The car ran fine for years and all of a sudden I started getting a bogging/hesitation under acceleration. The afr gauge is all over the place; sometimes idling at 16.x and sometimes idling around 14, but not consistently. While cruising my afr is around 13, but jumps back and forth from about 12.x to 17 with sudden drops to 10. Sometimes it will stay at 10 from cruising to stopping and then accelerating. Which makes it almost impossible to take off from a red light. It's causing serious bogging/studdering/hesitation issues to the point where it's almost undriveable.
I've also recently noticed a rapid clicking noise under hard acceleration coming from the passenger floor board where the ecu is mounted.

Notes to add that may be suspect:
The noise of the fuel pump briefly gets less loud when anything electrical is turned on.
Fuel pressure immediately starts to drop once it's primed with the engine off.

Mods are:
440 injectors
255 walboro
Split second ftc1
Forged internals
TSI turbo kit
Aem wideband
Mazdaspeed ecu
Aeromotive fpr
Aftermarket fuel rail

List of things I've done to attempt to fix the issues.
Changed upstream and downstream O2 sensors
Cleaned MAFS
Pressure tested for boost leaks
Changed wastegate
Changed spark plugs, coils and wires.
Changed the fuel pressure regulator.
Checked compression.

Any ideas of what the problem could be?
 
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Inspect or replace your pressure regulator solenoid valve.

You might want to replace your high pressure fuel filter.. They plug up over time.

 
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The pressure regulator control valve has been blocked off for years without any issue. Also, would the bad filter cause it to run so rich? I would think a clogged filter would only make it run lean.
 
The pressure regulator control valve has been blocked off for years without any issue...

I know very little about mods including turbos. I would have thought you'd throw a code by plugging that valve.(dunno)


..Also, would the bad filter cause it to run so rich? I would think a clogged filter would only make it run lean.

Yea,.. That makes sense but replacing your filter is probably a smart idea regardless.

Fuel pressure immediately starts to drop once it's primed with the engine off.

As far as I know there is no fuel check valve (at least in a stock setup) maintaining fuel pressure is a function of the fuel pump itself.
If your fuel filter is plugged, your fuel pump can be stressed pushing fuel through it and wear out the pump until it stops holding pressure.

I'm guessing you need a new fuel pump and high pressure fuel filter (aka fuel pump housing).
 
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