dnb

I'm after suggestions on what could be causing the misfire/hesitation at high loads my car (MY96 UK turbo with standard ECU map at the moment) suffers from.

I've done the following:
* replaced plugs - gapped at 1mm as book says. (with old plugs gapped to 0.8mm the misfire moves up the rev range and off boost performance suffers somewhat)
* replaced coils (one of mine is cracked but glued together now)
* changed RHS rocker cover gasket and mopped up the spilled oil
* checked and cleaned injector, coil, crank and cam sensor electrical connections.
* checked lambda sensor wiring and voltages - holds 0.8 to 0.9v all the time on boost (Haven't tried with this unplugged yet, but will tonight)
* checked MAF wiring and cleaned sensor.
* checked ECU earth connections

I still have to check the fuel system pressure (change the fuel filter - a service item, not because I suspect it) and sort out another very minor oil leak.

Anything I've forgotten to do? Any more suggestions?

Jolly Green Monster

iTrader: (4)

Dave,

Did you try a different coil rather than the glued one?

Spark plugs should be gapped to 0.7mm and might be your problem.

Simon

Pavlo

unplug breathers temporarily, block pipes at manifold to stop vac leaks, this will ensure it's not caused by oil vapour contamination.

change ALL the coil packs to known good.

gap plugs to 0.7mm

coil packs are not fixed with glue I am afraid. the temperature causes the coil insulation to break down over time. cracks are only part of the problem.

Paul

dnb

Thanks for the oil suggestion. Will try that on the way home.

Yes - I borrowed 4 coils from a friend. I know these all work at 16.5 PSI I had to give them back though! (and they didn't seem to fix the problem) However, this was before the oil leak & associated mess was fixed. This leak fix & clean did seem to cheer the car up.

A new coil is on order to replace the cracked one - the glue is only a temporary measure so I can go to work!!

Why 0.7mm when the user manual says 1mm? I thought it looked a bit big at the time. (Misprint in the book or new thoughts about plug gaps after printing?)


[Edited by dnb - 1/13/2004 2:15:41 PM]

Jolly Green Monster

iTrader: (4)

Not sure why the manual says 1mm.. I suspect it might be an NGK thing as the plugs come at 0.7mm, which is why I am thinking it is enforced by them.

I would say that the 1mm gaps is the problem..

Simon

dnb

I'll try almost anything once!

Jolly Green Monster

iTrader: (4)

No don't say it Simon..

dnb

torment

My 2003 NGK catalogue,Stipulates......SUBARU IMPREZA (TURBO inc WRX)03/94 on.....PFR6B...Gap---0.8mm.

So there is yet another diffrent figure.....?.

Pavlo

No there are as many figures as there are possibly gaps.

What is recommended for a standard engine, and what works best on a modified engine are 2 different things.

Most people that need to run PFR7Bs (ie those over 300) will tend to run them gapped at 0.7mm out of personal preference.

Higher cylinder pressures mean higher spark energy is required to bridge the gap, compensated for by decreased gap. Also older cars tend to have more of a problem with ignition related misfires, and not just down to the age of the coils.

Paul

dnb

I expect my car's getting old then. Since I've got a new chip sat on my desk at work, I may as well go for 0.7mm. It'll save bother in the long run.

Paul - are you hinting that my wiring and the transistors in the ignitor block have started to decay...

dnb

All fixed (for now) Plugs set to 0.8, wiring checked. Car goes like it's supposed to now.

Just noticed crank oil seal is leaking... Damn thing.

dnb

I should add that it works perfectly well with the glued coil too... Thinking about the damage it suffered a bit more, I've concluded the crack came from it being dropped or otherwise hitting something, as there is only damage to the "nose" where it fits over the plug. There was no visible damage to the actual coil bit.

Jolly Green Monster

iTrader: (4)

cool.. the scoob does seem very sensitive to plug type and gaps..

JGM

dnb

It does very sensitive to the type. Even when new, the old plugs didn't make it go like the NGK iridium ones in there now. A whole extra PSI of boost there from looking at Selmon logs

Have to get that chip in now

spence7

Hi

Glad to hear everything is now sorted..I have this problem on my car as well, very sudden/severe engine cut type scenario at 4500 - 5500 rpm....I will check the spark plugs now for sure !!

Anyone know if there's serious damage that can done due to the sudden hesitation ? It feels very severe so thought a sudden stop might cause some damage

Jolly Green Monster

iTrader: (4)

Spence,

That sounds more like boost cut.. if is it putting you through the screen type event.. miss fire on mine is always more like a less harsh stutter.. and often the knocklink would light up.. probably all the unburnt fuel igniting after the miss.

I tried some champion plugs once and regretted it straight away.

Simon