im usually a ford guy so im new to these impreza's, anyways my impreza timing belt was changed & plugs where done but now its starts but doesnt take throtle, it coffs & splutters it gives a back fire through the k&n when you try to rev it, the timing has been checked 3 times now so thats ruled out, any advice would be great, cheers

its a 420bhp engine, heres the spec if that helps

2.5 usdm short motor with forged internals and sti 5 heads
Full rebuild with every seal replaced (15k since build) 85000 miles total done by KR performance
Uprated oil pump
Full service history
Andy Forest 20g td05
Nismo 740cc injectors
Uneaqual stainless headers
Full 3" turbo back Apexi N spec exhaust
Fully heat wrapped open mouth downpipe
Lightened and balanced flywheel
Re-built gearbox
Short throw shifter
Hks Front mount + hard pipes
K+n intake
SX fuel regulator
Samco intake
HKS SSQV blow off
Walbro fuel pump
Oil catch tank
3 port boost solenoid
Apexi ecu with commander mapped by Andy Forest

 

Anybody??

 

What plugs did you fit, and what did you gap them too??

 

Are you sure that you used the correct timing marks ?

Search on here will confirm.

 

Agree with Dunx here, you have only touched the plugs and cam timing, so it has to be one of the two and if the plugs were gapped incorrectly it would run fine until driving under load and on boost which would only cause a missfire.

It is likely that the wrong timing mark on the crankshaft sprocked has been used.There are 2 of them. One of them is a triangle on the face of the sprocket which denotes TDC and the other is a line on one of the timing teeth at the back of the sprocket.

A subaru is not timed up at TDC it is done at 45deg after, so you should be using the mark on the timing tooth.

Have a look here: JollyGreenMonster.co.uk

 

u still have maf? i thought these were limited to about 350bhp so ive heard

 

The early MY93-96 green label ones are.

But to get 420 - and assuming it's got a MY93-96 top-end - he would have had to fit a Z32, Q45... or OEM v.3/4 orange label MAF.

Unless, of course, he's running the MAFless Mafsim with the PFC.

 

i thought it was only simtec that run mafless. oh right so can a my99-00 runs 350 plus with a maf

 

Apexi PFC IS MAF-based... BUT.. there is a thing called Mafsim which is some hardware/software to use with the PFC which doesn't require the MAF (so MAF can be either dsconnected or removed altogether). However, Mafsim is now obsolete and if it buggers up it will leave you stranded at the side of the road . At least if a MAF 'fails' it does so slowly but you can at least still drive the car - preferably off-boost of course.

Quite apart from the Mafsim add-on, there also used to be 2 versions of the PFC: D-Jetro and L-Jetro (I think they're the correct letters lol). I think the D-Jetro is the version still in use now i.e. MAF-based. The L-Jetro (discontinued) was a MAFless version (presumably using the MAP sensor for air intake reference). Don't know why it was ever pulled - presumably it didn't sell or work very well! Strange.

Not sure what the MY99/00 cassete-style hot-film MAF maxes out at, TBH. Someone will pop up soon to say, I expect...