fuel or boost cut
 

righto chaps, 1996 wrx 260ps, with cat back exhaust, simota panel filter, version 7 tmic, avc-r boost controller.

right last week fuel pump went and so i replaced it but the new one was considerablly smaller than the one removed, all seemed fine until i set my controller to high bosst (1.15bar) then when i hit around 5k rpm walllop felt like a fuel cut or summat, revs dropped to 3.5k then back up again all in a split second.............any ideas guys, the only thing i can think of is the fuel pump has not got the flow or pressure for high boost,

Cheers Mark

are you running a fcd? or a chip? if not that's what your problem is, you cant just expect to boost over the fuel cut threshold and not have fuel cut.

i think you have missunderstood me,

before the fuel pump went i was running with no problem, this has only occured since replacinf fuel pump, if i squeeze the pedal slow then it is fine but if i mash it down then i get the cut or maybe it is not a cut it might be the pump cannot supply fuel quick enough............

P600, does this symptom happen when you accelerate in every gear, or does it become more prevalent in the higher gears (i.e. 4th/5th)?

Also, when you say that the "revs dropped to 3.5 k then back up again", are you sure this is what happened? Did you depress the clutch when the revs dropped?

If all you have done is swap one fuel pump for another, it is far more likely, as you say, that the problem is something to do with the new pump's inability to supply sufficient fuel.

When you say that the new pump is "considerably smaller" than the one you took out, what new pump have you actually fitted? Is it a proper Subaru pump, a Walbro (GSS341), some random thing you got from a breakers, or what?

any gear when i accelrate hard, di not depress clutch, and fuel pump if off a subaru garage, when i enquired why it is smaller they said that it is the one used on later subaru's and will be fine, i will be getting a pump the same size as mine this week and go from there, all is pointing to this pump not being able to support the fuel pressure when i need it, should i just go for the walbro 255?

As your car is one of the earlier cars the fuel pump is a bit larger than what was fitted on the later classic/newage cars,and if you take the advice above and buy a walbro 255:thumb: , i am sure you will find it is the same size as the pump you are about to take off,which i presume is a later type which is much smaller. The trouble with fitting an old style (coke can) pump is that most of the ones will be at least 10+ years old now,and like everything is prone to wear ,so no real benefit to be had imho. If you opt to buy a walbro then at least you know that should be your fuel pump sorted for a good few years.

Incidentally i just fitted a walbro 255 to my mates 1995 wrx yesterday,and the only real noticeable difference is when you turn on the ignition you can hear the pump priming for a couple of seconds,which was not as evident on the std unit.

Probably boosting slightly more as it is colder now.

You will need to either reduce the boost target or fit a fuel cut defender (or get it mapped properly)

confused.com, i get the cold air will increase the boost a tad, but it will do this only if i put my foot down say i am in 2nd at 3k rpm, and stick it too the floor rpm will rise to 4/5k and it will cut, boost will only hit .79bar same if i do it in 3rd, 4th, 5th, but if i acelerate and press the pedal as i do then i will boost all the way to 1bar and she will take off like a scalded cat, can't see why it will need an fcd or mapping,

tell you what i will do i will video it and post it so we can see then, but i will get a fuel pump anyhow,

once done will see how it is, also if i get it mapped how much it is a TD05 with Z4 ecu, also i have the avc-r controller...........

Ok so some important new information .. ;) It hits 0.79 bar then cuts.

Coil packs ?
Plugs ?

nope there all good, will pop the pump out later to see what numbers are stamped on it, as splitpin says it should be a gss341 but info i find on that is for nissan, agss342 is for scoobs, a high pressure 255lph pump from race performance