C20let misfire under hard load

[Chevette madman]

Right not a nova but mk2 Astra gte 16v with c20let just fitted
engine was fully rebuilt and runs spot on when driving steady if I slam the pedal down it will pop and bang at any rpm only when hard throttle is applied sometimes I can nurse the pedal and get rpm up to about 4K before it starts it like your turning ignition on and of and others it just pops misfires boost when it does to around 9 10 psi Amal valve is fitted etc
spec is completely standard engine
Standard ecu
massive front mount and 2.25 pipe work
volvo t3 actuator fitted
everything else is standard

NOW IF I UNPLUG AFM CAR TICKS OF HIGH AND LUMPY BUT BOOST RUNS FINE UNDER FULL THROTTLE ???

i have changed

new fm coolant temp sensor
new cap new rotar
new leads
new bkR7eix plugs tryed 2 sets at 40 quid a go !
new fuel pump relay
new cool and amp
new afm

all parts fitted were brand new not second hand losing faith in this now I've spent so much
eml is wired up and flashes no codes ???
Odd how it boost fine with afm unplugged


any ideas ? I will pay for the right person to sort it
cheers in advance

[Will F]

What plug gap are you running?

[Chevette madman]

0.75 I have tryed 0.6 also also tryed standard let plugs no different like I say unplug afm it flys which makes me think it Carnt be spark related ? I may be wrong it's my first let I am fully qualified mechanic done many crazy conversions Volvo t5 in manta etc but this I Carnt just put my finger on cheers

[Plug]

What are you boosting at? Is it not over boosting

[torquey]

Checked wiring to afm?

[Chevette madman]

It's boosting to 10 psi then settles on 9psi when it does boost !
checked wiring mate all way to ecu plug

[meritlover]

check the vac hose to your FPR.

[Will F]

Plugs should be RS Turbo NGK (cant remember the p/no) gapped at .6mm

I am also assuming you've tried another AFM? (notorious weak spot)

[Southie]

[QUOTE=Will F;2286616]Plugs should be RS Turbo NGK (cant remember the p/no) gapped at .6mm
Plugs are NGK bcr9es.

[Chevette madman]

Still the same tryed ts turbo plugs on Sunday no difference tryed a new non gen afm ran like shit so I guess I need to get a Bosch one to try does any one on here live local to Stoke on Trent Buxton with a good working afm I could borrow for 5 mins to try cheers if u unplug it its spot on boost fine ?