Can't Rev over 6,000 RPM

[blkshp]

Hi everyone

Just wondering if anyone may have an idea what is wrong with my car

I\'ve got a 1993 wrx which has a few mods such as 3" exhaust (no cat), TD05 turbo, chipped ECU, aftermarket fuel pressure regulator, yellow top injectors

When the car is under load i get to approx 6,000 RPM (just below this to be honest) and its like i\'ve hit a wall? The boost guage is still showing full boost, the fuel pressure gauge doesn\'t drop or anything. Once i change gears it bogs for a little bit then back into life untill i reach that rev range again

If its in neutral i can rev it while not moving and it will go over 6K

No fault codes are coming up also

Any idea\'s would be great I\'ve tried another ECU (factory one) and that didn\'t change anything - Also i put the chipped ECU into my friends wrx and it went fine

I\'m currently trying to get hold of another MAF sensor as i have been told these can play up?

[loner]

How much boost are you running?

[Marky]

How much boost? Sounds a lot like airflow / fuel cut, description doesnt sound like spark or a misfire, but thats easy to diagnose by closing plug gaps up (its normally a bit more random though)

If the problem has just started check for any intercooler / pipe leaks

Try lowering the boost, see if problem persists

[syphe]

you could be hitting boost cut. I was getting similar problems but 5000rpm in 3rd gear, cause was a split in the hose from the boost controller to wastegate causing it to never open and overboost.

[blkshp]

Running just over 14psi. I have had a boost controller in there to turn it up and down (which i should have mentioned before) and it was doing the same thing

Will double check all pipe connections tomorrow i think just to be safe

[Guest]

Try bypassing boost control and run a line from comp to actuator see how it behaves.

[lachlan]

is it afm or map ? what afm ? if its a green ? then 14psi on a tdo5 will max it about then

[Guest]

Wouldve thought boost cut would be somewhere around there anyway.

[Johnnynz]

My little brothers 93 Hit boost cut just over 14PSI when we were playing with it a few weeks ago. Was boosting 12PSI when he got it and it looks stock as a rock.

Pretty sure the BC RS Hit boost cut around 15psi. Seems probable its a similar setup.

[blkshp]

green afm

boost cut has been removed with the gizmo chipped ecu - but i have put a standard ecu in for testing and didn\'t change a thing

even running 10psi (borrowing a friends EBC) it was doing the same thing

evowrx - will try that tomorrow

[madmike]

Could be sparkies too..

[blkshp]

 evowrx said:

Try bypassing boost control and run a line from comp to actuator see how it behaves.

bypassed the boost solenoid so it ran wastegate pressure (around 7psi i think?) rev perfect over 6,000 RPM

looks like i didn\'t try to lower it enough when i have the controller on there - time to invest in one i guess!

[Rosssub]

If it\'s holding solid boost (10?) over 6000rpm and not boost spiking when it cuts, then it\'s lack of fuel isn\'t it? Would an AFC help? Adjustable fuel pressure?

[bc5rs]

mightwant to check timing marks i had a similar incident and it was 1 tooth out

[Marky]

The fuel cut comes about (in simple terms) when you get too big a signal from the afm for a given RPM.

Generally that ties in with 100% duty cycle on the injectors

This is in broad terms mind you. There\'s also a boost cut which is purely down to if you hit X psi it will cut. Some cars will give a little wiggle room with a bit of time delay, I have no idea if the legacy does this or if it just cuts. You can get a fuel cut to happen with lower pressure than the "boost cut" if you run a larger than stock turbo for example

Changing the fuel pressure will not change this as the ECU does not know what the pressure is to start with

An SAFC can be a hori workaround, when you lean off the AFM signal just enough at the point it cuts. The risk is that it will also advance the timing, and obviously will also lean off the fuelling.

You can juggle the fuel pressure and the AFC signal sometimes to kinda see-saw one and the other to get a good result, hell sometimes it\'s so rich that it does no harm to lean it off anyway but subarus generally are quite advanced and close to pinging to start with, so not much room to move

Bear in mind if there is a post-turbo air leak, it can cause this exact symptoms too - air blows out, AFM reads too high, fuel cut ensues. Might not show in normal driving or in vacuum either, could be something blowing open with enough pressure.

Just ideas