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Old 04-20-2019, 01:00 AM   #1
2002wrexx
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Default Stutter/hesitation in boost/under load

Hey all, before I get flamed for asking WhAtS wRoNG wItH mY cAr, ive tried reading so many pages and threads and different websites, everybodies different solution to their issue and personally nothing seems to work..bare with me through this please, I appreciate any and all help.

2002 WRX, 330whp - 18gxt blouch ,750 dw injectors , 500cc meth injector, tial 38mm ewg with grimmspeed uppipe, Perrin front mount yadda yadda. Original motor and tranny- completely stock in that aspect.

So the problem began after I cleaned my maf sensor with CNC maf sensor cleaner. As ironic as it is my truck had a maf sensor code and I cleaned it, and the code went away. Great. Thought It couldn't hurt if I just cleaned the one on my WRX as I've heard people do it from time to time to help with idle. So I took the two screws out, cleaned my maf sensor , let it dry and reinstalled. Thinking about it after I may have sprayed too much and got it soaked, but just read on for now. Took the car for a ride and no longer was able to drive as the car jerks sputters and hesitates , dumps gas runs super rich. I had the car tuned a month or two before this all happened and I drove the car hard for the month or two, so it shouldn't be tune related as it was all good until I touched the maf sensor.
Keep in mind the car has absolutely NO ENGINE CODES, but I'm not sure if that's because my tuner may have turned off certain ones that could indicate where my problem lies. But I'm not too sure.
So my issue is I cant step on the pedal, in any gear, pretty much any rpm as long as it has load the car HATES it and it's like someone's pulling it backwards with a rope as I try to accelerate. It will begin to sputter and tries to build boost as it jerks violently , backfires and runs super rich. I've replaced just about everything I could think of after hearing solutions and symptoms and what worked for others and I still haven't been able to figure it out.
Replaced all new coilpacks over the last year( 2 at seperate times but all are now new )
Replaced spark plugs 3 times with the same NGK one step colder iridiums that it was tuned on.
Tried a cheap rockauto maf sensor to make sure that wasn't the issue.Also tried a friends known working maf sensor to make sure I didn't get a defective one from rockauto as I heard afterwards that could be an issue.
I noticed 3 of my maf sensor wires were cracked up by the sensor, so bought a new pigtail online and spliced it in, didn't change problem persists.
Had a new o2 put in end of 2017 and hardly drove it then, so it's had a year and a bit on it and I wouldn't expect it to go out that fast.
New Subaru OEM crank position sensor
New Subaru OEM camshaft position sensor
New Subaru OEM fuel pressure regulator
New Subaru OEM fuel filter
I've replaced my throttle body with a used one off eBay that had all the sensors and iacv on it as I stripped the threads on my iacv when I was reinstalling after cleaning. Car ran the same with both throttle bodies so I don't think it has to do with the sensors on that either.
I reflashed my map 3 times onto the car incase the ecu was maybe acting finicky or something and praying I'd get lucky..no dice.
Reset the car a few times obviously .
I had the car checked for vac leaks or boost leaks at a buddies but I was not present, he said there was a few minor ones but he fixed them up for me. Hoping he was correct.
I did a compression test twice when I was replacing spark plugs . Came up 150+ on a cold engine.
I replaced the clutch a week or two before cleaning the maf sensor, had the tranny out ( may be worth noting anyways) but wasn't driving it hard after putting in the new clutch as I wanted to break it in.
Have not done a leakdown test as the local Subaru dealership here doesn't want to work on my car , claiming it is too modified even tho they've worked on it plenty of times. They don't care, but I was hoping they were going to be able to help me out after all I've replaced .... Nothing works .
I also may have replaced more but this is all I can think of on the too of my head, and this problem happened before I put the car away for winter and it is now almost spring haha. Hoping to get it going good again.

May be completely unrelated but worth noting ,I had a problem on my way to my tune (15 hour drive on basemap 4k rpm tune ) I had a cpl of my aem gauge wires burn off my headers that ran into my oil pan, so needless to say the sensors stopped working but I didn't bother to look for the remainder of the trip after I knew they were burnt. It also mustve been grounding out or arcing out somewhere under there. I've since then removed it all and only run the accessport for engine management.

Car ran flawlessly for my 15 hour drive back from the tune, and for the month or two I was driving until I just had to clean the maf sensor. It may be completely unrelated to the actual issue and this just started it, I'm not sure but I'm hoping someone else might have any ideas , I'm all ears... Thanks!

Edit:the only last thing I could think of is a stuck injector possibly but I had them cleaned and flow tested before installed, as they weren't brand new to begin with. Think this could really be causing me all these problems?

Final edit : Ultimately ended up being my timing off a tooth. Didnt damage any internals. Redid the timing belt one night out of sheer boredom and confusion on what it could be. My car is now stock, and will live a happy life. Thanks for the help all!
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Last edited by 2002wrexx; 07-30-2020 at 02:52 AM.
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Old 04-21-2019, 12:13 PM   #2
2002wrexx
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Anybody?? I'm honestly debating parting out the car at this point...
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Old 04-21-2019, 12:24 PM   #3
lowbee
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If it eventually gets to your boost target and only stutter on the way there, than I would look at the BPV not shutting fast enough or it leaks under load. If you can't reach boost target, then it's something else. Hook up an accessport and do a log
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Old 04-21-2019, 02:01 PM   #4
subaru_gc8
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your coils are starting to go
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Old 04-21-2019, 02:36 PM   #5
2002wrexx
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Coils are fine, all new...And I've had a failing Bov and failing Bpv before, I know what they sound like. I'm not saying it's not a possibility, but if the car boosts up fine with the maf unplugged then it's gotta be something else
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Old 04-22-2019, 04:27 PM   #6
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Do you have another MAF you could try? If it's not stuttering with it unplugged it seems like you've found the problem. I'd check and see if you possibly have a short, or if something is corroded/bent/burnt out in either side of the connector. I had stuttering issues in my bugeye, but it was linked to the previous owner putting in copper spark plugs that were gapped almost twice the distance they should have been. I'm not saying it's the same thing, but it definitely sounds like it could be stumbling in the same place. I'd get to about 10 lbs and it would just buck and shake like it was hitting repeated fuel cut.
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Old 04-23-2019, 12:59 AM   #7
2002wrexx
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Quote:
Originally Posted by Sour_K View Post
Do you have another MAF you could try? If it's not stuttering with it unplugged it seems like you've found the problem. I'd check and see if you possibly have a short, or if something is corroded/bent/burnt out in either side of the connector. I had stuttering issues in my bugeye, but it was linked to the previous owner putting in copper spark plugs that were gapped almost twice the distance they should have been. I'm not saying it's the same thing, but it definitely sounds like it could be stumbling in the same place. I'd get to about 10 lbs and it would just buck and shake like it was hitting repeated fuel cut.
I debated putting stock copper plugs in to see if my problem lies with the iridium one step colder, considering I changed them 3 times just to see haha. But I haven't done so yet. As for checking another maf, I bought a rock auto maf and it didn't change a thing. Figured maybe that was some cheap one that didn't work and tried a known working one off a friends Subaru, no luck there
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Old 04-23-2019, 06:18 PM   #8
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Man, the fact that the car was running fine one minute, disconnect and clean the MAF, and the very next time you are driving the car is when the problems start just leaves me to believe the problem is somewhere in there.

If the MAF wasn't completely dry when you started the car, is it possible that something pertaining to the MAF in the ECU got shorted out? All of the pins/terminals for the MAF and plug are fine, as in, no corrosion, all straight and making good contact?

Could be total coincidence, but I would definitely still be looking in the MAF area(plug, wires, ecu, etc.) based off of when the problem arose.

Keep us posted. Good luck!
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Old 04-24-2019, 05:29 PM   #9
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I would check with the tuner. A dirty MAF could have thrown off readings during your tune and now that's it clean it could be reading the values at a different amount. Might even require a retune. I always make sure to clean the MAF before a tune so that when I go to clean it regularly it's not any different from my tune.
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Old 04-25-2019, 07:18 AM   #10
2002wrexx
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Quote:
Originally Posted by Shik View Post
Man, the fact that the car was running fine one minute, disconnect and clean the MAF, and the very next time you are driving the car is when the problems start just leaves me to believe the problem is somewhere in there.

If the MAF wasn't completely dry when you started the car, is it possible that something pertaining to the MAF in the ECU got shorted out? All of the pins/terminals for the MAF and plug are fine, as in, no corrosion, all straight and making good contact?

Could be total coincidence, but I would definitely still be looking in the MAF area(plug, wires, ecu, etc.) based off of when the problem arose.

Keep us posted. Good luck!
I was hoping it wouldn't be some stupid coincidence that something else breaks when I clean the maf, but sure enough here I am. Connection looks good, no corrosion should be fine, but I do agree that , that's where I last touched that happened to mess with it all.
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Old 04-25-2019, 07:19 AM   #11
2002wrexx
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Quote:
Originally Posted by randys13 View Post
I would check with the tuner. A dirty MAF could have thrown off readings during your tune and now that's it clean it could be reading the values at a different amount. Might even require a retune. I always make sure to clean the MAF before a tune so that when I go to clean it regularly it's not any different from my tune.
See I had somebody tell me that as well and my tuner basically told me no part was changed, but I guess the values could've changed when I cleaned the maf. I'll send another email to him
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Old 04-25-2019, 05:46 PM   #12
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As someone said before that a dirty maf while being tuned and cleaned later makes a huge difference.....ESPECIALLY with meth injection. It gets down to ignition timing and fuel curves and literally 1GPH more with mess your tune up.....do a log and sent to the tuner....guarentee your maf readings are atleast 5gph off. Other than that I would look to a new ECU for burned circuit due to wet maf leads shorting. Looks like you had all other bases covered....damn just through a EJ255 in and retune haha
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Old 04-26-2019, 10:18 AM   #13
2002wrexx
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Originally Posted by O2redrex View Post
As someone said before that a dirty maf while being tuned and cleaned later makes a huge difference.....ESPECIALLY with meth injection. It gets down to ignition timing and fuel curves and literally 1GPH more with mess your tune up.....do a log and sent to the tuner....guarentee your maf readings are atleast 5gph off. Other than that I would look to a new ECU for burned circuit due to wet maf leads shorting. Looks like you had all other bases covered....damn just through a EJ255 in and retune haha
Yeah I had a quick chat with my tuner he wanted me to send him a log, so will be doing so. As for a 255, I wanted to throw a 207 or 257 in for a while now just not worth the time , might as well sell and buy an STI. Only thing is, won't make half my money back because WRX ..
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Old 04-28-2019, 06:24 PM   #14
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Did you check your fuel pump?
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Old 04-30-2019, 01:39 AM   #15
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lol you have a boost leak. Seems pretty obvious.

Pressurize the plumbing to boost pressure and find the leak. Fix the leak.

It goes:
maf sensor -> ecu -> injectors.

so if you have a rich condition at the 'injector', its the maf or ecu (tuning related). I guess the ecu could be fried or an injector stuck open/failed O-ring, or similar, but that is very unlikely if the problem popped up out of nowhere.

be sure to disconnect any crankcase vent tube to avoid pressurizing the crankcase. If you are not sure you have done this, take out the dipstick before performing any pressure test and slowly add pressure while listening to the dipstick for airflow. If air is coming out of the dipstick at an alarming rate while you are putting compressed air into the compressor inlet (the proper place to start the boost pressure test) then you have not disconnected the crankcase vent tube properly yet.

I made a video to help understand pressure test
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Old 05-04-2019, 01:19 PM   #16
2002wrexx
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Quote:
Originally Posted by Kingtal0n View Post
lol you have a boost leak. Seems pretty obvious.

Pressurize the plumbing to boost pressure and find the leak. Fix the leak.

It goes:
maf sensor -> ecu -> injectors.

so if you have a rich condition at the 'injector', its the maf or ecu (tuning related). I guess the ecu could be fried or an injector stuck open/failed O-ring, or similar, but that is very unlikely if the problem popped up out of nowhere.

be sure to disconnect any crankcase vent tube to avoid pressurizing the crankcase. If you are not sure you have done this, take out the dipstick before performing any pressure test and slowly add pressure while listening to the dipstick for airflow. If air is coming out of the dipstick at an alarming rate while you are putting compressed air into the compressor inlet (the proper place to start the boost pressure test) then you have not disconnected the crankcase vent tube properly yet.

I made a video to help understand pressure test
Boost Leak Pressure Test methods, basic - YouTube
Hey king, I had a friend whos very familiar with Subarus as he has his fair share of them still, do a boost leak test and as far as I know he said he fixed a few small ones and it was good. I was not present at the time so can't confirm tho... Will be doing it again on Tuesday if everything goes good and I have the time. Will update back.
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Old 07-30-2020, 02:51 AM   #17
2002wrexx
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Just wanted to update all as i spent countless hours and $$ trying to figure this out when in reality it couldve been a FREE fix. All i had to do was the labour and it worked itself out. Bought all new coilpacks, sparkplugs 3 times, fuel filter, fuel pressure reg, crankshaft sensor, camshaft sensor maf sensor 3 times, new iacv etc etc you name it i replaced it, 150 comp all around . ultimately ended up being my timing off a tooth. idk why i didnt bother checking, as it couldve been fixed at minimum a year ago as i parted the car out. anyways, hope this helps! check your timing/realign if youre having similar issues. The problem was ALWAYS the same dead on, never changed. Thanks for the help all!
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Old 09-13-2021, 09:23 PM   #18
Soobiedoobie406
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Default No boost after MAF service

Quote:
Originally Posted by 2002wrexx View Post
Just wanted to update all as i spent countless hours and $$ trying to figure this out when in reality it couldve been a FREE fix. All i had to do was the labour and it worked itself out. Bought all new coilpacks, sparkplugs 3 times, fuel filter, fuel pressure reg, crankshaft sensor, camshaft sensor maf sensor 3 times, new iacv etc etc you name it i replaced it, 150 comp all around . ultimately ended up being my timing off a tooth. idk why i didnt bother checking, as it couldve been fixed at minimum a year ago as i parted the car out. anyways, hope this helps! check your timing/realign if youre having similar issues. The problem was ALWAYS the same dead on, never changed. Thanks for the help all!
Hello all. I'm fairly new here, I've used the forum a lot for several issues and have been able to figure them out with the vast amount of knowledge I've found here, I'm thankful for all the people who contribute for the betterment of the Subaru community, I'm finally joining the revolution.

Lol anyhow, I'm having the same problem on my 04 fxt. Car ran great besides a slight stumble at tip in. Cleaned the maf and boom at 1lb boost it gets super rich (I did however solve the stumble I set out to fix initially.) I've done boost leak and smoke tests several times. I've now replaced the MAF with a brand new OEM along with all the a/f sensors. I've used several cans of starter fluid and also propane, pretty much everything and anything I could think of(besides timing). My E-tuner had me run logs and he couldn't distinguish a problem from those. Besides that "it gets catastrophically rich when it starts to make boost." He said he could tune around it but he informed me that it's way out of the realm of what he normally does in a tune and could potentially be catastrophic. All this literally started after I took the maf out, sprayed it and reinstalled it over an hour later to ensure it was dry, like I said the car drove 10000 miles without a problem until the MAF was cleaned. I'm at a loss at this point and I am also ready to part this thing out, car runs ok if you granny it around and I don't try to spool.

Any ideas on why it caused it after cleaning the MAF, and why it didn't seem to affect it up until the point you cleaned the MAF? I'm checking the timing on it tomorrow, man I absolutely hope that is the problem!

Thanks for any input!

-04 FXT-
13 sti vf48
Sti intercooler
Sti yellow injectors
IAG pickup tube
Go fast bits full recirc valve
Grimmspeed 3 port bcs
Turbo back catless 3" pipe
Innovative wide band afr sensor
Duetchwerks 250 fuel pump
Perrin turbo inlet
Cobb intake
Grimmspeed phenolic intake spacers
WRX front calipers and rotors
New silicone vacuum and ventilation hoses on everything.
Perrin lightened crank pulley
JDM front conversion with skirts
E-tuned

Last edited by Soobiedoobie406; 09-13-2021 at 09:55 PM. Reason: Grammer
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Old 06-13-2024, 10:01 PM   #19
13hatch
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Quote:
Originally Posted by Soobiedoobie406 View Post
Hello all. I'm fairly new here, I've used the forum a lot for several issues and have been able to figure them out with the vast amount of knowledge I've found here, I'm thankful for all the people who contribute for the betterment of the Subaru community, I'm finally joining the revolution.

Lol anyhow, I'm having the same problem on my 04 fxt. Car ran great besides a slight stumble at tip in. Cleaned the maf and boom at 1lb boost it gets super rich (I did however solve the stumble I set out to fix initially.) I've done boost leak and smoke tests several times. I've now replaced the MAF with a brand new OEM along with all the a/f sensors. I've used several cans of starter fluid and also propane, pretty much everything and anything I could think of(besides timing). My E-tuner had me run logs and he couldn't distinguish a problem from those. Besides that "it gets catastrophically rich when it starts to make boost." He said he could tune around it but he informed me that it's way out of the realm of what he normally does in a tune and could potentially be catastrophic. All this literally started after I took the maf out, sprayed it and reinstalled it over an hour later to ensure it was dry, like I said the car drove 10000 miles without a problem until the MAF was cleaned. I'm at a loss at this point and I am also ready to part this thing out, car runs ok if you granny it around and I don't try to spool.

Any ideas on why it caused it after cleaning the MAF, and why it didn't seem to affect it up until the point you cleaned the MAF? I'm checking the timing on it tomorrow, man I absolutely hope that is the problem!

Thanks for any input!

-04 FXT-
13 sti vf48
Sti intercooler
Sti yellow injectors
IAG pickup tube
Go fast bits full recirc valve
Grimmspeed 3 port bcs
Turbo back catless 3" pipe
Innovative wide band afr sensor
Duetchwerks 250 fuel pump
Perrin turbo inlet
Cobb intake
Grimmspeed phenolic intake spacers
WRX front calipers and rotors
New silicone vacuum and ventilation hoses on everything.
Perrin lightened crank pulley
JDM front conversion with skirts
E-tuned
Ever find out what was wrong?
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Old 06-15-2024, 01:11 PM   #20
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He hasn't been here for 3 years and that was his only post.
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