the shreksta

iTrader: (20)

so i had a random boost hesitation last week which i was worried about so i took my car over to thwaites to see mark, he plugged his laptop in and went for a spin in the car.

when he came back he said that the ecu was pulling back the ignition by 11.5 degrees between 2200 rpm and 3600 rpm, he checked all of the vac lines/dump valve/sensors etc but couldnt see anything wrong with the car.

he re-set the ecu and told me to run it for a week and to fill up at a different filling station to rule out a bad batch of fuel so ive been out in the car today and filled up from a shell garage miles away and all seems fine,it boosts fine,temps are fine,no smoke and no unwanted noises.

could a bad batch of fuel cause this issue? he said it could also be the knock sensor picking something up. my car does have piston slap due to the type of pistons used and clearances needed so could the knock sensor have picked up on that and mis-heard it? perhaps a spacer under the knock sensor would help.

car is 2007 hawk sti on std ecu mapped by scoobyclinic @350bhp

engine has covered just over 10k
forged 2.5 closed deck block
std rods with arp bolts
mahle 2618 pistons
new crank
acl bearings
rebuilt avcs heads with upgraded valve springs/retainers
11mm head studs
cosworth head gaskets
10mm oil pump

japspeed fmic
forge dump valve
full de-cat 3" downpipe to a 2.5" system with vortex backbox
vf43 rebuilt turbo
750cc injectors
walbro pump
scooby-clinic cone filter induction kit
obp 3 port oil catch can

any ideas on other things that could cause it?

will deffo invest in an aftermarket ecu now

bludgod

iTrader: (3)

i've seen some really sloppy engines but never bad enough for a false knock reading down low like that. Only time i've seen that is when something is loose and rattling about at low RPM or as suggested a bad tank of fuel assuming all is well with the engine.

There's no need to shim the knock sensor, if its purely down to engine noise you can adjust the feedback/fine learning thresholds around the low load area or you can adjust the knock sensor settings at that area to account for the new noise levels in the standard ECU.

As an example I once stupidly left a spanner sitting on the intercooler of my own car years ago, resulted in some tremendous knock readings but once the rattle was removed all was fine. Same goes for heat shields, brackets, bolts and poor fitting down pipes.

the shreksta

iTrader: (20)

Hi and thanks for the reply.

It must be either the pistons or bad fuel, my pistons do sound nasty on tick over (like a skeleton wanking in a biscuit tin) but they quieten down when revs build up. I've had a knocking engine in my 1st Impreza and I know exactly how that sounds.

I'm now 1/4 through the new tank of fuel and all seems fine.

Tidgy

Didnt clinic build the engine?

the shreksta

iTrader: (20)

indeed

Tidgy

Wouldnt have had that issue when it left then so somethings changed.

Did they do all the mods to it?

the shreksta

iTrader: (20)

no mods have been done to it since it was built and mapped by them in august 2016.

i only popped into thwaites as its 20 mins away and thats all i had time for. ideally i need to stop fekking around and get an aftermarket ecu on there but whenever i get some cash it just seems to vanish.

car has ran perfectly in my ownership (almost 1 year) been all over in it and in feb was at the clinic having a health check on the rolling road and all was good.

mark said all the sensors are fine/lines are fine and there is absolutley no det going on.

ive never had to top the oil up or the coolant and apart from a ****e idle (due to drive-by-wire/fmic/open cone induction kit) it has been perfect.

all seems fine with it now so will see how i get on, kev spoke with me about the link ecu so i really ought to start saving hard for it.

Tidgy

Ah i get ya, if it was a problem with the engine it would have been present from day 1 unless somethings failed.