oh no not again .... help needed please (sorted... i Think)

car hesitates around 3.5 - 4.5k rpm
when it hesitates/goes again the exhaust pops
thought it might be loose/broken vacuum hose, sprayed everywhere with carb cleaner and nothing
checked the fault codes, the MAF and Knock sensor are coming up

changed the maf for a new (2nd hand) one last week and the car was fine (flat spot was there) so don't think it could be that (hopefully not)
would a dodgy MAF caust the knock sensor to go on a mad one or could it be the knock sensor that is gone and more than likely whats causing the flat spot?

Cheers
John

Re: oh no not again .... help needed please

Sounds to me like she is boost spiking as she comes on boost, and the fuel cut kickes in hence the hessitation, then it comes back to life as the boost returns to normal, hence the bang!
Do you have a boost Gauge? What she reading?
Dan

Re: oh no not again .... help needed please

Cheers for the reply Dan

it seems to be boosting normal for the most part, although I think I did notice once when this happened the boost seemed to have jumped slightly from 0.8 to 0.9/1.0 on the gauge.
What would cause a boost spike do you know? When it happened again on a take off the car ran crap/spluttery for a few minutes and went back to normal then.

Re: oh no not again .... help needed please

i reset the ecu this morning
the hesitation/backfire seems to be intermittent, it's happening more times than its not
i noticed sometimes between 2 & 3k rpm it was feeling a bit rough to drive
also noticed the "check engine" light came on permanently (car felt dead to drive) when i was nearly at work. i just switched the ignition off and back on it stayed on for a few seconds and went out and back to normal

checked the fault codes when arrived at work now, it's showing 22 & 23 again (knock sensor & MAF)

the only thing i have done before all of this happened was changed the spark plugs (pfr 6b) . it's hardly a dodgy plug??

Cheers
John

Re: oh no not again .... help needed please

Are you sure the second hand MAF you got is the correct one?

I'd replace both MAF and knock sensor with genuine Subaru and see what happens.

Re: oh no not again .... help needed please

Sounds like your engine is going into 'safe mode'. Having similar problems myself. Mechanic (subaru nut) checked codes and got Knock Link also. Told me that it can get dirty with oil and it can cause it to become faulty. Usually a good cleaning of the knock sensor and reset the ECU should do the trick. Not sure about the MAF issue..

Re: oh no not again .... help needed please

cheers Alan will try that when i get home tonight


i wonder would a faulty knock sensor cause the MAF to show up on the trouble codes

was fiddling around last night and remembered there was a Pivot Air Flow Conditioner behind the dash

i switched it off and the car hasn't hesitated/backfired since
i'v only driven it to work this morning (50km) and it seems fine

hopefully it was only that gone faulty, i havent checked the fault codes since i reset the ecu again last night

thanks for the advice guys

[quote author=AlanMcB4 link=topic=22813.msg273541#msg273541 date=1271157356]
Sounds like your engine is going into 'safe mode'. Having similar problems myself. Mechanic (subaru nut) checked codes and got Knock Link also. Told me that it can get dirty with oil and it can cause it to become faulty. Usually a good cleaning of the knock sensor and reset the ECU should do the trick. Not sure about the MAF issue..
[/quote]

I would clean my boost solenoid pipes with crab cleaner

thanks Dagnut, i will do that later, hopefully she will go grand now