4agte misfire problem

[4agteHILUX]

hi im new and ive tryed to find answers but to no avail.
Car:
91 hilux with a 4AGZE converted to a 4AGTE.
t3/t4 turbo
Microtech lt8
Front mount
extrernal WasteGate
BOV
T50 sprinter box
4.23 open hilux diff
fuel pressure reg
?commodore fuel pump i think
ANYWAY

My prob is that its developed a misfire that smoothes out after 4500rpm
since its happened its only been on idle to try find the problem.
it happened after some pretty hard driving, then noticed the mis
Things ive checked or replaced:
coil
leads
dizzy CAP.
fuel filter
tried to check injectors but???
changed plugs

microtech is showing a fault but i cant get to the fault screen on the handset
Flashing red light on ecu.

Would changing injectors change the map program.
havent yet done a compression test. but the thing is that there is no telltail smoke out the back

i dont know if this has been covered but any help would be good.
ALSO ive been told that the light is a sensor fault. there is no air sensor(no maf sensor) but i cant see if that is what it is

[Shifty]

What did the plugs look like? You might have hurt the engine.

Can't speak for the red light on the LT8, been a while since I messed with one - but if it's a sensor warning light then it would pay to check your sensors, in particular coolant temp sensor and intake temp sensor. If they are not giving a reading (dead, or come unplugged/unearthed) or are giving a poor reading (faulty) then that will casue you to run rich which will make it misfire.... and as it gets higher in the revs with more air & more engine speed it might be burning a bit easier hence 'cleaning up'

[Shifty]

Also a lot of people lie about stuff - "happened after hard driving" often means they turned the boost up, pinged the shit out of it, then turned the boost back and now it doesn't run well

anything else you can think of that may have contributed?

[4agteHILUX]

just found the problem today. the cometic 1mm head gasket has blown between 2 and 3. compression test found this. boost has always been set at 12psi.
also decided that the t3t4 turbo is a little big so i'm now going to source a t28 or possibly the gt28 i think its the bb type.
anyone have any guidence on head gasket. i think ill try find a std GZE one or just go another 1mm cometic(i think thats the brand).
the plugs were black but dry.
i'm hoping i dont need to machine the block as i dont want to rebuild the bottom end. Thanks for the reply shifty

[Shifty]

ok well there are two things to do

one is repair the motor - another head gasket might do it (definitely skim the head though) but if it's already been replaced and it's still blown then there might be an issue with the block.

second thing to do is find the problem... if it's old damage on the block then that's fine, but if it's an issue with your tune (as you said, it blew up after you caned it) or a sensor,then you need to get it looked at or you'll blow another head gasket in a few days/weeks/months.

[pandaah]

with cometic gaskets you need to make sure the block is 100%.. if its an old block or you cleaned it with anything too harsh forget it, take it out and get it decked.. even a couple of thou difference with give you trouble with a metal head gasket like that..

[fixeruperer]

no such thing as a too big of a turbo on a 4ag i ran genuine head gaskets with good results, i use a trd one now, well, coz, it has to be better ? .

[trdee]

put a composite (TGP preferably) head gasket on it if you dont wanna deck the block

[old_mr2]

Yep,. go tgp headgasket