barf Posted June 1, 2011 Share Posted June 1, 2011 hey i'm after some opinions and thoughts on my lancer which misfires (ie; non/weak ignition) under full load only using stock ignition components and pretty sure it's all up to snuff, have tried replacing transistor unit, plugs, leads and coils. no boost/vacuum leaks that i can find. higher power coils are the next thing i'm trying, plugs blacken quickly when the misfire occurs but otherwise stay clean. its a pretty fresh (~1000km) engine and compression is 181-182 psi all round, its a 7-bolt flywheel '96 narrowblock 4G93 the factory wastegate is 1.0 bar. what other gremlins haunt a turbo car? Quote Link to comment Share on other sites More sharing options...
Jase Posted June 1, 2011 Share Posted June 1, 2011 i'm thinking crossed up vacuum lines tbh... just a guess but could be that simple no play in the dizzy shaft? FUEL will know no doubt... Quote Link to comment Share on other sites More sharing options...
kpr Posted June 1, 2011 Share Posted June 1, 2011 other than what you've said already. overly rich can do it. if its air flow meter (don't know mitsis well) a boost leak will make it run rich. even some vac hoses mixed up as above could cause it. but would be looking for something that would only leak under pressure, or it would run like a bag of ass all the time. how much boost is it running? not hitting some kind of boost cut? other than that, check the plugs and ground on everything. as alot of the time wiring issues wont show up untill under some load. have even had dodgy injector plug cause a miss fire under load Quote Link to comment Share on other sites More sharing options...
smokin' joe Posted June 1, 2011 Share Posted June 1, 2011 go round every vacuum hose and nip 1/4" off each one and replace. Quote Link to comment Share on other sites More sharing options...
Ogre Posted June 1, 2011 Share Posted June 1, 2011 ^^this, works a treat Quote Link to comment Share on other sites More sharing options...
mikey Posted June 1, 2011 Share Posted June 1, 2011 ^^ +1 Quote Link to comment Share on other sites More sharing options...
mjrstar Posted June 1, 2011 Share Posted June 1, 2011 What plugs are you running (what gap) and are there any fault codes? Any signs of turbo smoke at high boost? it could be the afm load cell (commonly called fuel cut or boost cut) but normally you'd have to run around 17 psi to hit that (or less with a bigger turbo) Quote Link to comment Share on other sites More sharing options...
EvoBilly Posted June 1, 2011 Share Posted June 1, 2011 we had that issue on a spec'd up engine turned out the plugs were to weak and the boost was in a way blowing them out closing the gap a bit made it better but we ended up getting better coils and some costly better plugs is sayin that have you looked at your fuel system is it keep pressure up and keeping up with demand? Quote Link to comment Share on other sites More sharing options...
barf Posted June 2, 2011 Author Share Posted June 2, 2011 thanks for the replies everyone, very helpful ! i've got the service manual to refer to for vacuum diagrams and the hoses are all correct, wastegate actuator can be seen moving and it operates at 1.0 bar (Boost). there is no distributor it is wasted spark. plugs are new, NGK iridium IX's. no fault codes on OBD-II diagnostic equipment. also have replaced the fuel pump and while i don't have a fuel pressure gauge, it empties a tank in minutes so pretty confident i've eliminated fuel issues, short of building a flow-test bench for my injectors. it's a new turbo too, and the manifold pressure gauge i have does sort of float up to almost 17psi before it settles down at 14-15, with a quick stab on the throttle. if i chase the throttle the problem is much harder to reproduce. it's something small and obvious i bet :-\ first thing i looked for was boost leaks, and i did find and fix some so i may revisit that issue. Quote Link to comment Share on other sites More sharing options...
mjrstar Posted June 2, 2011 Share Posted June 2, 2011 I'd say 17psi would be getting close to max airflow cut-out, (espeially on a cool morning)but when you hit this is not really anything like a miss-fire, it is more like a hard cut-out (well at least it was in my evo) If it was my car I would be mildly tempted to introduce a small boost leak and take it for a run to see if it actually makes your symptoms worse. (does it then miss-fire at a lower boost level) Also does the car rev out cleanly off boost? ie: make revs climb gently at 1/4 throttle in second or 3rd gear whilst still showing vacuum on the boost gauge. Quote Link to comment Share on other sites More sharing options...
barf Posted June 2, 2011 Author Share Posted June 2, 2011 Also does the car rev out cleanly off boost? ie: make revs climb gently at 1/4 throttle in second or 3rd gear whilst still showing vacuum on the boost gauge. yes it's smooth running at all times except for when i do a throttle stab, ie; 3rd gear cruise at 2500rpm to full load, no hesitations except for at a high level of power. this is a factory mitsi 1.0 bar system i havn't modified anything. i don't think it's the cut-out because i'd see an OBD trouble code presumably for that, and plugs go black when it happens but the overboost is a fuel cut on this AFAIK. Quote Link to comment Share on other sites More sharing options...
fuel Posted June 2, 2011 Share Posted June 2, 2011 I wouldn't bother with iridium plugs, NGK copper plugs are probably better for your application, but make sure they have a 0.6-0.7mm electrode gap. Quote Link to comment Share on other sites More sharing options...
mjrstar Posted June 2, 2011 Share Posted June 2, 2011 i don't think it's the cut-out because i'd see an OBD trouble code presumably for that, I never had it throw any codes in my car when hitting the cut. Not too sure that you could accuratly check plug colour after a missfire unless you turn it iff as soon as it miss-fired? at high reves, which might be pretty uncool for the turbo bearings.... Otherwise the colour would just reflect the last driving or idle condition?? I could be wrong though?? Das the car had anything done to improve airflow, dump pipe, exhaust, camshaft, compression ratio,intake? Quote Link to comment Share on other sites More sharing options...
barf Posted June 3, 2011 Author Share Posted June 3, 2011 I never had it throw any codes in my car when hitting the cut. it's from 1996 - it has an OBD-I trouble code for "engine overboost condition" Not too sure that you could accuratly check plug colour after a missfire unless you turn it iff as soon as it miss-fired? at high reves, which might be pretty uncool for the turbo bearings.... seriously?? i check my plugs after every session at the track, matched with datalogs it's a good engine 'barometer' Das the car had anything done to improve airflow, dump pipe, exhaust, camshaft, compression ratio,intake? [*:1rjtzids]180psi compression[*:1rjtzids]3 inch exhaust (2" to 3" conical flange attached to turbo)[*:1rjtzids]K&N air filter[*:1rjtzids]standard turbo, tune and manifolds fuel; i tried NGK copper plugs and the problem was even more apparent. Quote Link to comment Share on other sites More sharing options...
kpr Posted June 3, 2011 Share Posted June 3, 2011 did you gap them down as fuel said? standard plugs will come with a .8mm gap. something with 11 on the end is 1.1mm gap. gap them down to .6mm and see what happens. Quote Link to comment Share on other sites More sharing options...
QCADTA Posted June 3, 2011 Share Posted June 3, 2011 Checked battery/engine grounding back to the (-) terminal? has it got a bov leak under boost? Quote Link to comment Share on other sites More sharing options...
barf Posted June 18, 2011 Author Share Posted June 18, 2011 thanks again for the replies everyone! what is obvious to some totally slipped past me! gapping down to 0.6mm did hide the misfire, but it's still missing power and i suspect still burning rich at high loads. i know the rule of thumb is to reduce spark gap as cylinder pressures go up but, that idea has one very important flaw: if the energy in your spark remains constant but cylinder pressures are increased, reducing the gap only serves to create a smaller area of ignition with the same amount of heat. this provides for slightly less ignition of the fuel/air mixture, compared with same gap and more voltage, or am I mistaken? Quote Link to comment Share on other sites More sharing options...
kpr Posted June 18, 2011 Share Posted June 18, 2011 correct me if wrong, but i would think it would be more to do with electrical resistance. more cylinder pressure = more resistance for the spark to jump. so too much resistance and there wont be any spark at the plug. it will find some place easyer to complete the circuit. bad leads etc. or just not happen at all. misti coils usually have plenty of spark. have run 25psi on misti wasted spark coils with no issues Quote Link to comment Share on other sites More sharing options...
barf Posted June 19, 2011 Author Share Posted June 19, 2011 just read a few journal articles online about spark gaps and discharge, the UC library is awesome the breakdown voltage of the gap increases with pressure, and gap size. the gap has near-infinite resistance until this voltage is reached, and reached with sufficient current (minimum dwell time). you get a spark when you discharge an induction coil which has more potential energy than that breakdown voltage in atmosphere (1 bar) at 20C that voltage is approx 10,000 Volts / millimeter from what i can gather, there are three methods to yield the best flame kernel expansion in cylinder, assuming an optimum air fuel mixture and ignition event timing. * increasing voltage beyond breakdown voltage * decreasing electrode sizes * increasing spark gap Quote Link to comment Share on other sites More sharing options...
mjrstar Posted June 19, 2011 Share Posted June 19, 2011 would option 4 be to provide more volts??? or possibly make the volts closer to the plugs ie: COP instead of running long leads? I ditched factory coils in favour of a COP set-up (still wired up in waste spark configuration) Maybe the car is sensing knock and switching over to the low octane map/table (richer a/f with less timing) ? This can be a Bastard of a trap when tuning a factory evo ecu as you have to adjust both tables take and take it for a run then add in you saftey margin on the low octane map again before you finish off the re-flash. Quote Link to comment Share on other sites More sharing options...
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