Series 3 au wagon miss fire giving me the *****!!!!

imbhvn · 08-10-2012, 06:13 PM

Hey guys, i have a series 3 wagon, has a miss fire on idle and when de-accelerating.

also, if i give it a bit it smells of alot of un-burnt fuel. And when slowing down holds revs at about 1000 rpm until completely stopped then drops to about 850-900.

I have just replaced the coil pack, put iridium spark plugs and new leads but hasnt fixed the problem. Since i've had the car i've replaced the fuel pump assembly, fuel filter, oxy sensor, tps, fuel pressure regulator and air filter.

Its really starting to irritate me, any suggestions on what it is/could be?

Thanks in advance,

Tim.

Maka · 08-10-2012, 08:34 PM

Hi imbhvn, petrol smell- inlet maniflod gasket or iat sensor in the intake maniflod? You've replaced nearly everything so i'm going with that, but also maybe a vacuum hose has come adrift some where. When you replaced the plugs, the old ones were all the same colour aye? If not, maybe wiring to the coilpack? Ecu? You can extract fault codes from the ecu if you take it to a mechanic, will make things a bit easier. Hope you sort it out asap mate.

cheers,Maka

imbhvn · 08-10-2012, 10:01 PM

Hey maka thanks for your reply, i had thr ecu scanned for faults and it came back with nothing, all 6 plugs were white in colour. What is the purpose of the iat sensor? Could it be the map sensor aswell?

Maka · 08-10-2012, 10:51 PM

Quote:

Originally Posted by imbhvn

Hey maka thanks for your reply, i had thr ecu scanned for faults and it came back with nothing, all 6 plugs were white in colour. What is the purpose of the iat sensor? Could it be the map sensor aswell?

Hi imbhvn, the iat sensor is the map sensor on a au Falcon, have a look at the inlet manifold gasket first as its the cheapest (if you havent already)- check if the bolts are loose & tighten if so. You can still tighten the bolts and find the gasket may be too damaged so just be aware of that situation also.

That petrol smell is coming from the front & not the back? What about your coolant temperature? In spec? Not running too cold? If so that'll cause it to run rich too. Ect sensor at the back of the cylinder head controls that stuff. Thermostat not jammed open? Worst case scenario get a compression test done to eliminate burnt exhaust valve. Other members got a suggestion?

cheers,Maka

imbhvn · 08-10-2012, 11:24 PM

The un burnt fuel smell is coming from the exhaust, i done a comp test on it a couple of months ago and all came back around 160 psi. My temp guage sits between the n and the o where it says normal, ive been told its okay. Ive tested the thermostat and seemed to be okay also.

I forgot to mention that on take off if i put my foot flat to the floor the car doesnt pull until 3000 rpm (you can actually feel it push you back into your seat) but if i accelerate less than half it seems to pick up speed faster than it does when its flat. If that makes sense?

imbhvn · 10-10-2012, 02:09 PM

I was just fiddling around with things under the bonnet while car was running, sprayed water around inlet manifold didnt change idle so assuming gasket is fine. I disconnected the mechanism on top of the throttle body revs dropped from 1000 on idle down to 500 took it for a drive and has ALOT more power, what is the purpose of this mechanism? Still has a missfire though :( its pretty much every revolution.

Maka · 11-10-2012, 09:26 AM

Hi imbhvn, i would still check the bolts on the inlet manifold for peice of mind, the iac valve is on top of the throttle body & it controls idle in conjunction with other sensors- take it off & clean out with carby cleaner etc then lubricate the plunger shaft, reset idle to specs. Also may pay to clean out throttle body too. If you can pull the plug on the iac valve & the motor dont nearly stall your idle may be out of spec.

cheers,Maka

mik · 11-10-2012, 02:59 PM

vacuum lines, oxygen sensor?

imbhvn · 11-10-2012, 06:05 PM

Hey maka, i am driving around with the iac unplugged, its a bit **** on startup in the morning but after that its fine, seems to be better on fuel too.

imbhvn · 11-10-2012, 06:07 PM

Oh and btw with the iac connected and the idle screw completely unscrewed the car idles at 1000 rpm.

Maka · 14-10-2012, 11:32 AM

Hi imbhvn, iac seized up? May pay to get another iac & see if its any better at idle. Do a ecu reset & go from there.The inlet manifold bolts need to be physically checked- my bolts were loose after checking, i sprayed stuff around the gasket & didnt change engine note- checked bolts & they were loose. Also check your pcv valve, heres some excellent info from au3xr6 about correctly setting idle-

"if your base idle has never been touched leave it alone is is not meant to be changed unless there have been major changes and what ever you do don't just screw it up or down trial and error style there is a precise method for setting the base idle. it involves getting the engine to operating temp (the fans have run then stoped )and with all accessories off and the wheels straight ahead stop the engine and dissconect the wire from the IAC valve insert a 0.75mm feller gague between the throtle stop screw and it corresponding tab connect an accurate tacho and start the enging. with the fans not running adjust the base idle to 700 RPM +or_ 20 RPM stop engine remove feeler gague and reconnect IAC valve start engine and rev to just over 2000 RPM to reset the IAC valve. of course this should only be done with the engine in good order with no other faults"

cheers,Maka