[Imanevo]

Whats up guys. Before I commence, and before anyone throws it in my face without actually helping, I have searched everywhere on the subject only to either have the subject go unsolved or the thread died. So anyways I'm having an issue with my WRX. During acceleration above 15% throttle, sometimes in first and second and definitely in third-fifth, I get sputtering followed by backfiring. With a full tank it only happens after third gear but only when I'm driving normally. When I have less than 1/2 of a tank of gas it starts to happen in first and second and when I'm getting close to my reserve tank it happens consistently through all gears with heavy popping. I have a cobb ap and have monitored some parameters and have noticed that my A/F correction at idle is 0 but as soon as I start to give it gas it'll go all the way to -25%. I have also noticed that my injector pulse width at idle is 0 but as soon as I accelerate it'll jump up to ~2 ms and the farther I open the throttle, the higher the number climbs. It'll climb up until 8-10 ms and then it'll start to stumble, sputter and hesitate. Unless I let off the gas, I've noticed the pulse width has gone all the way up to 22 ms. From what I understand injector pulse width should not be anywhere near the numbers I'm getting, and should definitely be decreasing the faster the engine is spinning. Additionally, when driving normally, I noticed that when I let off the gas to slow down while in gear, my AFR's shoot up to about 22-23 until it tap the gas to bring it back to 14.7. Ive tried to flash the ecu with the cobb stage 2 but that only makes things worse as my sputtering and backfiring occurs at 3k rpm regardless of speed, gear, or gas level and I'm physically limited to 80 mph both on stock map and stage 2. My question is, with the given information, what exactly am I dealing with that is causing these issues? Id like to get some input on this subject before I start aimlessly replacing parts since this is my first Subaru. And even though it can be a pain, I still absolutely love the car. Currently my guesses include leaking fuel injector(s), bad fuel pump, bad fuel pressure regulator causing over pressurized fuel and forcing the injectors to stay open, or a bad ecu (opening the injectors too long and dumping fuel causing sputtering and hesitation). What do you guys think? Thank you in advance for your replies!

----Mod List----
Cobb AP
Cobb Intake
Tomei Turbo Inlet
Decatted Up-Pipe
Custom 3" Downpipe
3" Greddy Catback Exhaust

**Everything else is stock**

 

[SD_GR]

Do you smell raw fuel on cold startup?

 

[Imanevo]

No, I do not. My AFR during a cold start is around a 12.5 and increases to a 14.5 after warming up. I have noticed that after filing up the tank with gas, the car does shake at idle for about a minute before it smooths out.

 

[wrxnh]

When was the last time you cleaned the MAF sensor?

That and I would get either Pro-Tune or Torqued Performance (my choice) for Stage 2.

 

[4EverMetal]

Sounds like you might have water in you gas; how long has this been happening? Wouldn't hurt to try some dry gas.

 

[Imanevo]

Ive cleaned my maf a couple times, most recently was a couple weeks ago. I thought the whole purpose of a cobb ap was so that you could basically tune it yourself automatically? Or is it just a supplemental engine monitoring system and data-logger?

 

[Imanevo]

Its been happening for about a month so I make sure to keep the car out of boost because thats when it seems like its doing it. If I had water in my tank wouldn't I get a misfire when the water eventually dilutes the gas in the engine? Im getting no misfire at all.

 

[4EverMetal]

This might sound dumb, but did you load the correct map for the mods you have? The AP doesn't auto tune you have to load the map to the AP and then flash it to your car.

 

[Imanevo]

I've loaded the map several times and it still has the issues. It's only when I load the "simulated stock" map that it won't sputter until I'm in a higher gear.

 

[rqjoe]

Is this the car that sat in an impound lot for 7 years? If so, I'd say you have a gummed up fuel system.

 

[Imanevo]

Gummed up fuel system would basically mean new lines? Or can I just run a fuel treatment through them? I did that when I first got the car.

 

[rqjoe]

Yeah, when I fix small engines (lawn mowers, chainsaws, etc) I have to take carb apart and gas tank & lines off & soak scrub with carb cleaner to get varnish/gum out. Wherever small holes are is likely the problem area (TB, carb, injectors).

 

[Imanevo]

I thought that my injectors were the problem. If I have a stuck open injector, wouldn't that cause a misfire in that cylinder? Im getting no misfire at all. Ive checked each injector using the "screwdriver to ear" trick to hear it fire and it does indeed fire. Correct me if I'm wrong but isn't the fuel rail constantly pressurized? So a stuck open injector would continuously dump fuel into the exhaust causing a misfire? My exhaust does give off a little bit of white smoke here and there but its nothing too big. After continuous brainstorming I've come to believe the fuel pump is the culprit. It could be that it has poor performance and medium and high engine load making the computer leave the injectors open longer to compensate for the lack of fuel until the fuel pump dumps gas in. I was wondering, do fuel pumps work at 100% all the time? I noticed on my Accessport that its usually at 33% at idle and cruising and will quickly jump up to 100% when I try and give it a bit of throttle leading to the sputtering and lack of power. Not to mention I have terrible throttle response. When idling, I can floor the gas peddle and release it before the rpm's even change. All that happens is that it'll increase from 750-1500 and slowly make its way back down to 750. I suppose I'm just spitballing as I've seen several people have similar issues with no resolution. Tomorrow ill hopefully be replacing the fuel pump with a new walbro 255 to see if that helps at all.

 

[Jordan06WRX]

I thought that my injectors were the problem. If I have a stuck open injector, wouldn't that cause a misfire in that cylinder? Im getting no misfire at all. Ive checked each injector using the "screwdriver to ear" trick to hear it fire and it does indeed fire. Correct me if I'm wrong but isn't the fuel rail constantly pressurized? So a stuck open injector would continuously dump fuel into the exhaust causing a misfire? My exhaust does give off a little bit of white smoke here and there but its nothing too big. After continuous brainstorming I've come to believe the fuel pump is the culprit. It could be that it has poor performance and medium and high engine load making the computer leave the injectors open longer to compensate for the lack of fuel until the fuel pump dumps gas in. I was wondering, do fuel pumps work at 100% all the time? I noticed on my Accessport that its usually at 33% at idle and cruising and will quickly jump up to 100% when I try and give it a bit of throttle leading to the sputtering and lack of power. Not to mention I have terrible throttle response. When idling, I can floor the gas peddle and release it before the rpm's even change. All that happens is that it'll increase from 750-1500 and slowly make its way back down to 750. I suppose I'm just spitballing as I've seen several people have similar issues with no resolution. Tomorrow ill hopefully be replacing the fuel pump with a new walbro 255 to see if that helps at all.

What happened when you replaced your fuel pump, because I think I’m having the same issue you were having.

 

[zoomzoom870]

What happened when you replaced your fuel pump, because I think I’m having the same issue you were having.

Another dead thread with no answer. Great.