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Help With Misfiring On Boost Problem

BSK

By BSK,
in Engines & Forced Induction

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BSK Enthusiast

BSK

Posted
Posted (edited)

After returning from europe and picking my car up from the paint shop it has started to misfire on boost. now while i was away an auto electrician was called in, with out me knowing, to take a look at a problem with the car not starting which he ended up replacing the plugs with NGK platinums? (are they good?) which apparently fixed the starting problem....

anyways driving it home when hitting any boost over 0.4bar it would misfire.

now a theory i have is this misfiring only seems to happen when the injectors are at full duty cycle, the reason being is i have a tomei eprom which runs very rich. to my understanding its programmed to dump max fuel soon as the turbo spools up. when i got home i swapped the eprom for a toshi one i recently got thats tuned alot leaner but rich at hi boost (at my request) and the problem was gone but only when running upto 1.08 bar. when i turn the boost up over 1.1bar the problem reappears...

now its an RB20 with a hks2510 and GTR injectors 040pump so im assuming at 1bar with the leaner toshi tuned eprom the injectors are yet to reach max duty cycle but anything over that the injectors are at max duty which is where the problem occurs.

i have also been told that maybe the gap of the plugs fitted may be the cause of the misfiring but why would the problem behave differently between the 2 eproms, unless these particular plugs cant cope with all the fuel ?!?

im yet to learn generally about spark plug gaps and associated tuning problems.

maybe a semi blocked injector?

both the panel shop and auto sparky have claimed no responsability as the car ran ok whilst in their care. (moving it around the yard at idle).... MOFO's

any help appreciated guys!!

Edited by BSK
r33_racer Grand Master

r33_racer

Posted
Posted

The gap on the plugs might be too big and causing the mis. Aim for around 0.8mm gap. But i dont think you can modify platinum plugs, cause the coating can crack off. Try a set of plain coppers.

BSK Enthusiast

BSK

Posted
  • Author
Posted
The gap on the plugs might be too big and causing the mis. Aim for around 0.8mm gap. But i dont think you can modify platinum plugs, cause the coating can crack off. Try a set of plain coppers.

if the gap is too big then shouldnt it miss more often/randomly? or is the over fueling effecting the lack of spark between the large gap .. kinda like flooding the chamber with too much fuel causing an insulating effect on the plug?

rob82 Mentor

rob82

Posted
Posted
if the gap is too big then shouldnt it miss more often/randomly? or is the over fueling effecting the lack of spark between the large gap .. kinda like flooding the chamber with too much fuel causing an insulating effect on the plug?

Chances are that it was started cold everyday and not driven enough to clean the plugs so they are probably just a little fouled. There could be fuel and timng differences between the two maps the more fuel in the chamber the harder it is to ionise the gap - the same rule applies with less ignition timing.

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