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This is one that may just smack someone into diagnostic memory mode.

EJ20G quad cam sti I went for a ride in today has a miss that is suspected to be electrical not fuel. Has been described as a "rich miss" as opposed to a lean miss, after dyno and exhaust analyser testing. Cam sensor has been replaced, crank sensor has not. Coil packs have been replaced with used, injectors tested, cleaned and tested, spark plugs replaced, wiring of the Microtech MTX8 has been checked

Keeping check on the MT display operating temp betwen 82' C and 86'C is where this occurs. It will not happen above or below the op temps. Wondering if this is the key to problem.BIG question is why at operating temp and not above or below??

Has anyone found same sort of temp related problem with plug pack style coils or Microtech experience?

It occurs flat stick in say 3rd gear and about 16psi boost.

Was running fine until someone tried to incorporate an idle air control circuit to aid idle speed for cold start, change settings on MTX8 etc. And to be fair to those helping here, it is a 1987 STi Brumby which explains the non factory ECU,

sounds like the settings have been changed
microtech has a table someware in the menu to set trim vs water temp if the 80-90deg setting has been changed it will change the whole map

ie if it was set a 10% and was changed to 20% 10% more fuel is injected accross the map
but only in the temp range that the setting controls

check what the setting is set to
i think its called coolant temp trim not a microtech person myself but can check with a mate tommorow
it should be close to zero if the tune was done corectly

and if you have a wideband oxy sensor in the car lower this setting % at a time driving the car afterwards to make sure it dosent run too lean
dont try to do this using the standard oxy sensor if installed too lean at that boost would probley blow that engine to peices

Yeah, thanks. The fuel trim has been reset to its original and you are correct - it is set to increase as water temps rise like +4% @ 87', and increases up incrementally.

One good thing about this install is that it was set up without an O2 sensor - so that is ruled out good and fast. Dunno if it had an O2 sensor input - its for race only. An exhaust temp was also not used.

TPS is a four wire and it is not using the fourth wire, the one closest to the firewall, never has, and at flat stick TPS reads 100% on MT screen

Conversion was done four years ago and ran fine for two (325kW at the wheels) and this problem surfaced nearly two years ago and has remained consistent.

Been thinking of wrapping the coil to plug in insulation tape to see if any change, reduce gaps of plugs perhaps.

yeah microtech have an o2 sensor input on some modles but it only displays on the controler no changes are made using it

and the tps will only be using the pot the switch is left out
its the same with my adaptronic

your safe to increase the trim above 4% to see what happens
the engine will just get rich if you go too far

dose the miss happen all through the rev range that can achive 16 psi or is it at a set rpm value

make sure its not the classic coil pack problem (need to replace std with bosch items)

Have you tried replacing the thermo sensor?

It could be dicky and giving false readings, making the ECU compensate for false readings.

Just a thought.

mattl200, from memory it is combo of load and revs and boost at op temp between 82 and 86 degrees displayed on screen, not when hotter or colder at same loads revs speed. Went on a few awsome runs before it presented itself so this beast must keep cool for a long time.AWIC keeps its water at just 2 above ambient !!

Subafury - is the classic coil problem like this just at op temp??

Gannon, thought of it myself it has not been replaced as far as I can recall. Could not even find it from top view, where is it on EJ?

I have had a few problems like that with my ej20g in my brumby (Mine runs a link ecu.).

It Slowly got worse until i put a new set of plugs in it they were only about 15000 k at best. Plugs also are never the same if they have been flooded before either.

Mine sometimes goes the other way it will miss when cold then clean up when it warms up. Or give it it little rev say to a bout 2000rpm.
Guessing One of the plugs are starting to go again.
Plugs have only done about 10000k.

Yes i know they are iridium and should last 100 000 but they sure as hell don't with higher boost applications and if you have flooding/over fueling problems it dramatically lowers the life of them.

Plus a set of plugs are about the cost of 1 coil pack. Good place to start.

Mine is my Daily Driver

thanks Morcs, I'll be passing the info on, yet to hear if he has tried new Bosch coils.

i may be wrong here but i thought iridium plugs wernt recomended for turbo engines
someware i read they gum up

Just no chemical boost for the platinums .

eg N2O

The coil problems can be sometimes be both ways also.
They start missing like a dead plug sometimes intermittently .
Start not to produce the voltage in the plug best way to check is with a oscilloscope.

I added a small capacitor on +12ve for a will seemed to help a little but ended up taking it off ( caps are a form of electronic filter)

I had also been looking at using a set of three wire ls1 v8 coil packs 3rd wire is just a ground.

Also Have aread of this http://www.lextreme.com/sparkplug.html

saw the ute on the weekend - on the back of a tow truck. Repo man?

this may sound a little simple but what is the compression on each cylinder

(compression done with engine cold all plugs removed and throttle open completely)

a large variance in compression can cause a miss under load

TOONGA