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Misfires and missing performance 


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 Post subject: Misfires and missing performance
Posted: Fri Jan 04, 2013 8:41 pm 
Oompa Loompa

Posts: 26

Joined: 8th Sep 2012

Ride: 2006 BF Mk1 XR8

Location: Sydney
NSW, Australia

G'day folks

Wondering if anyone can steer me a little here.
I got a 2006 BF XR8 (Boss 260) manual (In Toxic green :)). Has a CAI, a Xforce Catback with stock headers/cats.
Cars done bout 115,000km's - i've had the car since 90,000km's

Car gets extremely regular oil changes (right on 10,000km's, travels bout 110km's a day so it comes up pretty fast) using Penrite HPR 15. Gearbox and Diff also run Penrite gear oils (awesome oil for the box btw much smoother/quieter than Dex)

I'll make this short. Start of the Xmas holidays, car sat for a few days, when i started her up she had a instant miss (could hear it through the exhaust), any amount of throttle resulted in the car coughing/f@rt till about 2k where it'd rev normally.

Literally 10 seconds after startup, the car is fine, any amounts of restarts during the day have no problems, only when the car sits and gets stone cold. Also noticed the car sometimes cranks long than usual before firing up.

The other issue is the car just feels down on power, Boss drivers will know how much the motor dances around 3k+, mine still does but its just....slower revving (still feel the engine come on power just not as pants hitting as it used to be)

I'm leaning toward a Fuel issue (I'm doing new filter next oil change which is soon).
  • I've tried taping up my PCV rubber elbow (its starting to perish and has collapsed a little bit but definitely doesn't suck air yet, blocking off that hose makes no difference anyway).
  • My Throttlebody is pretty filthy so i'm going to clean that (and maybe take my plenum off and get it all a real good clean).
  • I also used that Android phone torque app to check fuel trims/etc, at 2k rpm longterm fuel trims are pretty well 0, shortterm dances around .5 either side of 0, at idle they bounce around a lot, bank 1 seems a bit lower (negative values) than bank 2 but overally they hang around -3. I'm not sure what idle values should be but i'd assume the 2k rpm values seem fine?

What else should i be checking? OS sensors shouldn't cause this issue straight off would they? the car should be in open loop when stone cold?

I heard of issues like this on BA 260's where the heads had that valve guide issues, but as far as i know that was like the Timing chain guide issue, was fixed on late BA/BF's? (something bout redesigned coolant passages? Does anyone have the Headcasting codes for the good heads so i can compare?)

other than that, i'm not really sure what it could be. Only thing i'm thinking of doing is taking the battery off tonight and reset the PCM, see if its something wrong that way.

Cheers all

ps, Car only ever runs on premium 95, i put a full tanks (bout 61 litres) of 98 in it, has made a bit of a difference but the issues still there
 Post subject: Re: Misfires and missing performance
Posted: Sat Jan 05, 2013 3:42 pm 
EFI Guru

Age: 53

Posts: 4322

Joined: 5th Nov 2004

Gallery: 28 images

Ride: 351 Vogue,XH 5.0,'17 5.0 Stang

Location: Perth
WA, Australia

I'd be lookin at possibly a dribbling injector or a maybe a coil.
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