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Greg
Greg, Technician
Category: Car
Satisfied Customers: 7065
Experience:  Automotive diagnostic tech
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My 2006 wrx hesitates,splutters,bogs down under

Resolved Question:

my 2006 wrx hesitates,splutters,bogs down under acceleration. when i release the throttle slightly, it picks up again. obd reports 172 code rich mixture. exhaust is black. local subaru agent has replaced front and rear air-fuel-ratio sensors and the pcv valve, to no effect. also the spark plugs. no improvement. any ideas?
Submitted: 1 year ago.
Category: Car
Expert:  Greg replied 1 year ago.

After the work was done and codes cleared what code are you now getting .

Any other codes .

Do you have a code reader or scan tool .

Greg

Customer: replied 1 year ago.
hello greg. thanks for contact. my bluetooth scan tool reports renewed fault code p0172 powertrain system too rich (bank1),pending fault. i am using torque pro software on my cellphone.
the dealer reports identical code on his equipment and had cleared the code. there are no other codes shown.
Expert:  Greg replied 1 year ago.

Okay then you are running rich ,do you have live data on the scan tool you are using as i woyuld like to see what the St trim and MAF sensor reading are at idle then at 2500rpm.

Greg

Customer: replied 1 year ago.
hello greg. here are the data that you requested,by way of attachments.
Customer: replied 1 year ago.
it is not clear to me whether my message of 16th july 22:53 irish time with the attachments was actually sent by the webserver. your website was down, error code 503. i am retransmitting herewith.
Expert:  Greg replied 1 year ago.

Hi .

Sorry for the internet issues .

Looking at the first reading at idle the Fuel trim is -25 a high negative reading which means you are running very rich

this could be a bad fuel regulator .

Are you using a Oiled air filter and cold air intake .

Greg

Customer: replied 1 year ago.
hello greg. i am not using an oiled air filter,just standard clean paper. my air intake is standard also. i attach subaru's fault tracing procedure. the problem may indeed be a fuel supply issue, although it feels to me that i am not getting enough rather than too much.
from idle there is a reluctance to react to accelerator inputs,for about 1/2 second. then performance appears normal up to about half-throttle with plenty of turbo boost. beyond half throttle, the engine labours,bogs down, bucks like a bronco,until i release the throttle slightly, when it picks up again. there are no misfire readings on the obd, but i think i can hear explosions in the catalytic converter.
Expert:  Greg replied 1 year ago.

It will start to feel like not enough fuel as the system is compensation the mix .

Did you do the fuel pressure test .

Also do a leak down test lets see if you have bad Injectors (leaking)

You said A/F sensors where replaced where they OEM..

The Explosions are unburnt fuel reaching the Cat .this will damage the cat if this happens too much .

Disconnect the MAF sensor then try and start the engine when you get it going let it idle then recheck the fuel trim by checking the exhaust for black smoke and on hyour OBD .

Greg

Customer: replied 1 year ago.
hello greg. i disconnected the maf sensor and the throttle response is now much better. i took the car for a drive and it went fine,although i feel that i am not getting full power. attached are the disconnected obd readings. i am leaving the car in to an independent workshop this evening,who have been recommended as being competent.
Expert:  Greg replied 1 year ago.

Okay wonderful .replace the MAF ,

You could first try and clean it with MAF spray cleaner first and retest .

Otherwise replace the MAF.

Rgds Greg

Customer: replied 1 year ago.
hello greg. i have already sprayed cleaner into the maf intake, without effect so far. please explain the procedure. in one of the forums i have come across reference to potting compound exudations interfering with proper functioning. the car is at present with the independent family-owned multi-generational enterprise trading as james travers garage in kilkenny, and judging by their vitrine of race and rally cars, they might just find the solution...
thank you for your suggestions so far.
i omitted to answer one of your questions: there was no noticeable smoke coming out of my exhaust visible in the rear-view mirror, while the maf was disconnected. coincidentally, one of my neighbours was driving behind me at the time, and i shall ask him whether he saw any.
Expert:  Greg replied 1 year ago.

Hi .

I nwould try another MAF just to check .

A/F sensors MAP/MAF sensors,coolant temp sensor ,are the major sensors for fuel getting too rich or lean.

Greg

Customer: replied 1 year ago.
hello greg. the car is now with the mechanics for the last three days and they have just put another fresh man on the job. it's beginning to feel like a wild goose chase all over again. you did query whether the replacement lambda sensors were oem. the front one was new and very expensive,the rear one i obtained second-hand and that may yet turn out to be the problem. sorry that i couldn't rate your answers yet, as the issue is not resolved.
Expert:  Greg replied 1 year ago.

Hi .

Get them to confirm the following .

Fuel pressure ,return fuel lines .

Bad injectors these are reported in a TSB for causing the P0172 codes .

Greg

Expert:  Greg replied 1 year ago.

Okay just been informed by Subaru tech that this car is not the regula fuel injection system it has a Subaru Pulse width

modulated fuel pump .

So tell them to take a close look at this system as when it does start to fail the first thing you get is a rich fuel mix .

Rgds Greg

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Customer: replied 1 year ago.
hello greg. thanks for all that. i got the car back today from travers garage and they really spent a huge amount of effort and time on it. they dismantled the front and rear oxygen sensors to check them. ok. they then replaced the maf sensor and hey presto,problem solved. they then took out the spark plugs to check for even combustion. ok. they then checked the cat. ok. new air filter and a dose of fuel additive. i'm testing the car for the weekend and then we propose to do some more fine-tuning. i've been considering a reflash of the ecu for better response,perhaps raising the tickover rpm a little to bridge the gap. i would appreciate your advice.
in the meantime, i will now attend to rating your service as good. thank you once more. mike.