GAVINPERKINS11

Hi all, gotta 99 wrx, which seems to be holding back in 3rd 4th 5th gears, from about 4000 - 6000 rpm the power seems to hold back then pull well then hold back again and then as i shut off the throttle it backfires. The fault is intermitent, and has only came since i put a full decat system on the car. I checked the ECU fault codes and it came up with lambda sensor, so i change that, reset the ECU, but faults still there. i have changed plugs, cleaned the boost pressure valve and changed the maf sensor but still no joy. Really dont know what to try next

Jolly Green Monster

iTrader: (4)

overboost? hitting fuel cut due to increased exhaust flow and boost.

perhaps..

do you have a boost gauge?

Simon

Jolly Green Monster

iTrader: (4)

Also being a 99.. when was the last time you replaced the maf?

GAVINPERKINS11

Changed MAF today, aint had no change. I dont have a boost gauge, this is my first scooby only had it a few weeks so everything is new to me, how would i know if its over boosting? the fault doesnt always happen, just now and again as if there is something breaking down. i notice it on a motorway run mostly when im in 5th and put my foot down its like a flat spot which comes and goes as the revvs pick up. I got told that it would be doing this because i havent had it remapped, could this be true? i am going to get a re map but wanted to get this fault sorted first.

Jolly Green Monster

iTrader: (4)

if it was boost cut it would put you through the screen rather than flatspot..

possible the map but difficult to be sure from a description.. could be coilpack or plugs if it is like a missfire.

Simon

GAVINPERKINS11

its strange it seems to splutter like its over fueling and pops then it will pull through it, mostly happens in 5th when on the motorway. I though if it was a coil pack id have a continuous missfire. The plugs have been changed but i will fit new ones tomorow just incase there is a fault one fitted. I was just reading a similar one which suffered with the knock sensor? the way is going ill be replacing all the sensors . would this fault be picked up if i took it to be mapped? or would it be best to sort it before?

Jolly Green Monster

iTrader: (4)

wouldn't necessarily misfire all the time with coilpack.. they can cause a misfire under load.. as can plugs.. check the plug gaps are 0.7mm before fitting.

It is possible it is a map issue if you have some mods on it..

the fact it is worse in 5th would indicate load and boost related..

I certainly health check a car before and whilst mapping etc...

Simon

GAVINPERKINS11

Ill change the plugs tomorow and check the gap, any plugs you recomend? also is there anyway of checking a coil pack if its faulty?

Jolly Green Monster

iTrader: (4)

NGK PFR6B or if over 300bhp or going to be then NGK PFR7B

Simon

GAVINPERKINS11

thanks for the help, ill change the plugs tomorow and my mate got a spare coil pack which he said i can try so ill let you know how i get on and also contact you for the re-map in the next few weeks, thanks again

Jolly Green Monster

iTrader: (4)

no problme hope the plugs sort it

GAVINPERKINS11

FAULT FOUND AND SORTED finally sorted the fault after changing many sensors. It was all down to the forged dump valve, the spring was too weak causing it to leak while the boost pressure was building up, which caused the holding back or flat spots, which in turn was telling the maf sensor to give more fuel causing the pops. Fitted the standard valve back on the car and she runs like a dream pulling through the the revv range without missing a beat. Hope this helps a few people out, as this problem drove me nuts.

Jolly Green Monster

iTrader: (4)

well found!

jonny_693

iTrader: (5)

Bloody dump valves again!

shaunwrx

i had the same problem yesterday changed the dump valve back to standard and no problems now.

GAVINPERKINS11

im running standard valve now and its still perfect, but i miss the hiss and ithas given me a bit of turbo lag, i did have a forge dump valve fitted which gave me the fault, just wondering does anyone know of a good make valve a to buy or are forge good and i just had a faulty one?