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Old 05-31-2017, 11:49 AM   #26
ImprezaJoe
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Quote:
Originally Posted by whiterabbitrexy View Post
do a smoke boost leak test...... could be a bad fpr leak and not getting enough pressure to pressurize your injectors witch is messing with your afrs? vacum leak will do the same....

also dose you afrs change when on a full tank of fuel compeared to low tank of fuel ?
I check my vac at idle with my stock boost gauge and romraider logger, both read about -9 psi. I haven't checked my FPR (never even looked at the damn thing). I purchased a new front o2 and new MAF and the problem persists.

Silly question: how can I check the FPR for leaks? As I said before, Ive never even looked at it.
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Old 06-01-2017, 11:47 AM   #27
zombiez07
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-9 doesn't sound right. i believe the correct value should be right about -20. you have a leak somewhere.
Put fuel pressure gauge on the car and check base pressure, should be around 35-38psi, then unplug vaccum hose going to the regulator and pressure should rise to 43psi. If its adjustable then someone may have set base pressure higher. If these are correct, but you still think there is problem then put gauge where you can read it going down the road and the regulator should add 1 pound fuel pressure to 1 pound of boost over fuel pressure with the regulator unpluged.

So if you have unpluged pressure of 43psi and you run 20psi of boost, then at peak boost you should have 63 psi of fuel pressure.
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Old 06-01-2017, 12:34 PM   #28
CarmelValleyWRX
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Quote:
Originally Posted by zombiez07 View Post
-9 doesn't sound right. i believe the correct value should be right about -20. you have a leak somewhere.
Put fuel pressure gauge on the car and check base pressure, should be around 35-38psi, then unplug vaccum hose going to the regulator and pressure should rise to 43psi. If its adjustable then someone may have set base pressure higher. If these are correct, but you still think there is problem then put gauge where you can read it going down the road and the regulator should add 1 pound fuel pressure to 1 pound of boost over fuel pressure with the regulator u̶n̶p̶l̶u̶g̶e̶d̶ plugged in.




^^^^^danger danger danger^^^^^


So if you have unpluged pressure of 43psi and you run 20psi of boost, then at peak boost you should have 63 psi of fuel pressure.

when the regulator is unplugged it wont make corrections for boost. thats why it has a hose going from the manifold. it measures boost or vacuum and adds it to the base pressure when its plugged in.

dont run the engine under load without the regulator fully functioning and connected to the manifold.

for more safety upgrade to brand new rubber or silicone vacuum line and add spring clamps on the FPR line.

if the vacuum line is removed or blows off from boost, the motor will run very very lean under boost, (more boost, leaner it gets!)and slightly rich under vacuum situations.

-9psi is ok for idle i think. you cant have -20psi because atmosphere is only 14.7 a complete vacuum would only be -14.7. you should have about -20InHg "inches of mercury" though.

Last edited by CarmelValleyWRX; 06-01-2017 at 12:51 PM.
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Old 06-01-2017, 12:48 PM   #29
CarmelValleyWRX
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Quote:
Originally Posted by ImprezaJoe View Post
I check my vac at idle with my stock boost gauge and romraider logger, both read about -9 psi. I haven't checked my FPR (never even looked at the damn thing). I purchased a new front o2 and new MAF and the problem persists.

Silly question: how can I check the FPR for leaks? As I said before, Ive never even looked at it.
what problem do you have?
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Old 06-02-2017, 01:48 AM   #30
DowdyBro
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I had a similar issue to this in more of a minor sense. Cleaned MAF sensor and changed plugs seemed to do the trick. Bad misfire points to coil packs IMO, which are a common issue on these cars apparently.
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Old 06-08-2017, 12:18 PM   #31
zombiez07
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so weird. swapped pack from cyl 1 to 3 and misfires stopped. at least so far. but still idling rough. i'll update when tune is completed.
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Old 07-20-2018, 04:32 PM   #32
89cmarti
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Originally Posted by zombiez07 View Post
so weird. swapped pack from cyl 1 to 3 and misfires stopped. at least so far. but still idling rough. i'll update when tune is completed.
I know it's a year later but what was the final word on this? Did your rough idling go away? I assume it was plug fouling?
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Old 07-21-2018, 12:37 PM   #33
snow_bound26
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Default Rough Idle, AFR bouncing. maf or 02?

I would like to know as well since I'm having a rough idle once warmed up as well. No CEL being thrown but it's just like described, idles like it has more aggressive cams. Runs smooth otherwise. Makes full boost. -19/-20 vac at idle. Plugs have 2500 miles. MAF is original but everything else has been replaced or cleaned except front O2 sensor. AFR doesn't wander either. Holds consistent between 14.7-14.9 while cruising. Measured with LC-2 upstream from cat.
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Old 07-21-2018, 02:15 PM   #34
Valarius Starchaser
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another good thing to check for an issue like you all are having is the IACV clean/replace I ended up needing to replace mine along with coil packs parts are old problems arise break out that wallet if you expect to keep your 2.0l WRX running like new
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Old 07-21-2018, 06:09 PM   #35
snow_bound26
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Quote:
Originally Posted by Valarius Starchaser View Post
another good thing to check for an issue like you all are having is the IACV clean/replace I ended up needing to replace mine along with coil packs parts are old problems arise break out that wallet if you expect to keep your 2.0l WRX running like new
Cleaned IACV with new gasket when I did the JDM swap. Trust me wallet has been out for a little while. Coil packs came with swap. Not sure itís them as Iím not throwing any codes as mentioned before. It could be the tune which is what Iím leaning toward at this time.
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Old 07-21-2018, 07:41 PM   #36
subaru_gc8
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Quote:
Originally Posted by zombiez07 View Post
late model 04 wrx. recently fixed my motor mount and now i have a rough idle. AFR bounces/surges from 14.2-15.4. coming to stop, sometimes surges to 17.2 before settling back to 15.0. causes pretty bad sputter. also throwing random solid cylinder misfire codes about once per week. they will clear. just come back a few days later. vac holding at -21.
cleaned MAF sensor. cleaned cam and crank sensors. cleaned IACV. compression tested same for all cylinders at 120 psi (forged internals). new block. new headgasket. new timing belt.
thinking 3 possible causes. bad maf, bad front 02, or could just be a need for a new tune? car was tuned with unknown broken mount and slight boost leak (which has been fixed). this car is making me a cranky person.
take your pick and try changing one. my guess would be either the maf or O2
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