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Old 01-14-2013, 07:47 PM   #1
04wrxdan
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Default 04 wrx misfire after fuel pump change

i drive a 2004 wrx. a few weeks ago i installed a vf39 pinks large tmic with an xpt tuning vf39 ots map. car has been running fine the last few weeks. last night i put in a walbro 255lph pump in, didnt boost at all on my way home. on my way to work this morning i was passing a car in 4th gear at wot, just after i hit peak boost my car sounded and felt like it was sputtering or missing, i let off the gas and my cel flashed a few times and went away. so i proceeded to hit peak boost again just to see if it was a fluke. same thing, only this time my cel stayed on afterwords. when i got home i put learning view on it and it came back with 2 codes p0301 and p0302 (cylinder 1 misfire and cylinder 2 misfire) car runs fine when not at full boost. and cel hasnt come back yet, but it still stutters at wot in full boost.

would this have anything to do with the pump i just put in? because it ran fine through the gears at wot before.

one thing i did notice when changing the pump is the kit that came with the new one had a smaller fuel screen thing on it, so i used the stock one, but it didnt seem to press on to the pump as tight as it did on the oem pump. but i used the clip to keep it on the pump, idk if that could be leaking at high pressure?

i couldnt see/hear any air leaks under the hood, and my vac at idle is around 20 and pretty steady.

coud there have possibly been a small leak in injector, and just got worse with the new pump?

any thoughts appreciated

thanx all
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Last edited by 04wrxdan; 01-14-2013 at 10:21 PM.
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Old 01-14-2013, 10:31 PM   #2
Mr.motorhead
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what psi do you hit if you charged anything. its more often an ignition thing. also posible that the new fuel pump has you running rich if your running really rich this can also happen.
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Old 01-14-2013, 10:37 PM   #3
04wrxdan
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it will sputter between like 12-17 psi, at wot. i was to understand that the fuel regulator, and the injectors control the flow, but im kinda new at all this. everything was fine on this tune w/out the new pump, as soon as i put the new one in, thats when this started happening. kinda feels like when its running out of gas, and it doesnt seem like its pulling as hard as it was befor when this is happening
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Old 01-14-2013, 10:42 PM   #4
04wrxdan
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could a leak close to the pump cause that? , maybe one of the hoses, or the fuel screen like i described in my 1st post? im kinda stumped on this, cuz all i did that day is change the fuel pump, nothing else

maybe i just got a crap pump, idk

Last edited by 04wrxdan; 01-14-2013 at 11:04 PM.
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Old 01-15-2013, 12:23 AM   #5
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yeah usually the regulator and injectors are all in controle of that but i know that under high boost levels like around or over 14psi that a really rich AFR can make a car have those symtoms, feel like loss in power and miss fire. and you just so happend to install a more powerful higher flowing fuel pump that could do that. it can also take an engine around 90 miles to fix its maps and reset its ecu.

I also would expect that if you leaned out to the point of missing at high boost that you would have engine knock
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Old 01-15-2013, 12:30 AM   #6
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and sense you dont seam to have bad engine knock my guess is the ecu is running the injectors at the same duty cycle. it would be hard to notice. see if you seam to have bad gas mileage, you prob could drive around for a little and see if the ecu resets. it can foul up your plugs and mess up your cat if you have one. but 90 miles isn't long.
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Old 01-15-2013, 12:40 AM   #7
04wrxdan
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the car does seem to be getting a little worse gas mileage from what i can tell over the last few days, i changed the pump last thursday, and have been driving the car since, i just stay outa boost and it drives fine. also wondering if the new fuel pump may take more power than the oem one, maybe i have a weak alternator(have suspected that in the past due to lights dimming sometimes), maybe if the new pump takes more power, its taking from the injectors? idk, a thought i guess.

i have put learning view on my car, and there is no signs of knock. \

i also reflashed my map the other day after the pump install to see if that helped, but still did same thing.

its just wierd that the problem would start immediately after the fuel pump was put in
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Old 01-15-2013, 12:52 AM   #8
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i can monitor afr, but only narrowband. i knw at wot its around 10 11, idle and normal driving is like 14 or so
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Old 01-15-2013, 01:03 PM   #9
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Quote:
Originally Posted by 04wrxdan View Post
i can monitor afr, but only narrowband. i knw at wot its around 10 11, idle and normal driving is like 14 or so
10 is very rich is about the point of rich where you can see the engine start to miss under high boost. do what you can to lean it out. i really wouldn't go past 12
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Old 01-15-2013, 05:46 PM   #10
04wrxdan
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Quote:
Originally Posted by Mr.motorhead View Post
10 is very rich is about the point of rich where you can see the engine start to miss under high boost. do what you can to lean it out. i really wouldn't go past 12
i was wrong, i checked last night again, at wot it sits at like 11.22
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Old 01-15-2013, 05:52 PM   #11
04wrxdan
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was thinkin about this, when i installed the new pump, the sock that came with it was smaller that the stock one, so i re-used the oem sock, but it ddnt press on to the pump as good as it did on the oem one, maybe a leak there causing this??

tonight im gonna put on the sock that came w/the new pump, and check the plugs, and change the fuel filter(its prob about due anyway) and see if that helps
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Old 01-15-2013, 07:22 PM   #12
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Quote:
Originally Posted by Mr.motorhead View Post
yeah usually the regulator and injectors are all in controle of that but i know that under high boost levels like around or over 14psi that a really rich AFR can make a car have those symtoms, feel like loss in power and miss fire. and you just so happend to install a more powerful higher flowing fuel pump that could do that. it can also take an engine around 90 miles to fix its maps and reset its ecu.

I also would expect that if you leaned out to the point of missing at high boost that you would have engine knock
Installing a pump does not force more fuel into the engine. It just preloads the lines more so that fuel is there when you need it.


You have a fuel leak near the pump. Could be the sock, or could be a line you didn't put on all the way. Check over everything and make sure all hoses are on correctly.
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Old 01-15-2013, 09:55 PM   #13
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If there is a leak why is he still hitting 11.2 air to fuel at WOT, if your hitting 11.2 at WOT I'm assuming your getting enough fuel. so leaning out shouldn't be what causes the misfire.

If your injectors run the same duty cycle under high psi from a more powerful pump more fuel will come out of them. I have seen it before on other vehicles, but admit I have not seen it on this car before so cant be sure.

I guess it could be a leak causing the mis and then the unburnt fuel from those cylinders makes the ecu read rich.
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Old 01-16-2013, 01:33 AM   #14
04wrxdan
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well i found the problem......feel kinda dumb, but here it is...

got off work today and immidiately put my car in the garage, took out the pump, put on the correct sock that came with it, made sure clamps were all tight on the fuel lines. took it for a drive, no change.....put it back in the garage, changed the fuel filter, and took out all the plugs, the diodes were worn down a bit (ngk v power plugs), 1 and 2 hardly had the v in them at all(even though i just changed them less than a year ago) the gaps were way off on all of them, cylinders 1 and 2 (the ones that misfired) were gaped at like .40-.45 and 3 and 4 were gapped at like 35. i must not have checked the gaps when i put them in last time......so i put new plugs in anyway, and made sure gaps were correct, took it out for another drive.........same thing, misfiring after 4000 rpm, but then as soon as i hit 4000 rpm its like i hit a brick wall, the car actually slowed down it was bogging so bad.........put it back in the garage, put in the oem fuel pump and sock and took it for a drive again......same thing.......put it back in the garage, opened the hood and stared at it for like 20 mins(not happy at this point lol)....so i was looking at the intercooler pipe from the throttle body to the intercooler, it is the one that came with the car, because when i ordered all the parts, that hose never came(still havent got it btw) i poked it with my finger and it wiggled, so i checked the clamp, and is was loose, the hose was actually off of the intercooler a little bit on the bottom. so i pulled off the intercooler to make sure the bolts and clamps were all tight under it, bolts and clamps were all loose, tightened them all up, went to advance and got a new hose(the one on there was really soft cracked a bit, put the intercooler back on and tightened everything back up and took it for a ride.......SUCCESS..car runs great now, no cel, no misfire..........musta been just coinsidence that this happened rite after i put in the new pump, given it was a week after the injector/turbo/intercooler install, i suppolse everything lossened up with the heat and vibration, idk why i didnt think about that befor....but now i have the oem pump back in, but it will stay there for a few days i think

sory for the book of a post, but thanks for your advice, and tryin to help me figure all this out.

Last edited by 04wrxdan; 01-16-2013 at 01:42 AM.
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Old 01-16-2013, 02:51 AM   #15
burkorobe
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i was to understand that the fuel regulator, and the injectors control the flow,
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