2010 Legacy 2.5l premium starts and then stalls almost immediately

2010 Subaru Legacy 2.5l Premium starts and then stalls out almost immediately.
Hmmm...not much to go on.
Start by looking carefully at ALL the hoses connected to the intake manifold. If you have a bad air leak from a broken or cracked hose, ( PCV valve for example) this can throw off the air volume that the MAF sensor reads and will shut the engine down.
Speaking of MAF sensors, when was the last time yours was cleaned?
Good Luck
AMLOR
 
2010 Subaru Legacy 2.5l Premium starts and then stalls out almost immediately.
How long is almost immediately? If it acts like it runs out of fuel then start with the fuel filter. Just replace it but see if it appears plugged. You should have a light for oil pressure shutting you down. If you have a bad maf sensor issue it should toss a code.

Sort of hard to diagnose with no information.
 
Most likely it is the Fuel Pump!! NO CODES! I usually get 80-100k miles, but the last NEW replacement pump failed after only 55k miles & 16 mos.!
E10 gas is now pushing E20-E25!! Pumps are failing early, as result, but after the 12 mos. parts warranty!
OEM is double the cost of 18 mos. ago! Subaru wants to sell only the complete Fuel Pump "assembly" for $900, but separate pump is also available for under $300 ...
part Img

Part No.: 42022AL00A PUMP WITH FILTER 120


FYI: Diagnosing a failing fuel pump is nearly impossible, as it works perfectly until it doesn't, but then intermittently.
Telltale signs:
1. Unexpected stalling.
2. Cold start stumbling & near stalling during the first 30 seconds.
3. Vacuum Leak symptoms (intermittent) @ higher RPM.
... it is possible that putting "MMO" Marvel Mystery Oil in the gas tank will extend the life of the pump. MMO is truly amazing. Reviews are incredible.

DIY is tricky the first time. Pump is in tank with access under back seat on right. I have done this 5 times since 2014, but have not made a video. Just changed another yesterday! Find a video online before attempting, if you are not familiar, otherwise prepare for "frustrations"!

1718134439795.png
 
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2010 Subaru Legacy 2.5l Premium starts and then stalls out almost immediately.
Dear R.,

High concentrations of Ethanol in regular gas causes early fuel pump failures!!
One last "hail Mary" resort may restore your failed Fuel Pump... add MMO Marvel Mystery Oil to your gas tank, wait a few minutes, then attempt a few multiple starts... no cranking needed. Let sit overnight & try again. If no joy, you'll need a new pump.
I just installed another brand new pump Sunday... it started instantly & ran like new again! I then topped off the tank with 8gal. fresh regular. However when I started it on Monday it began the same stalling & idling issues, as before!!
My brother, (ASE mechanic (40+ yrs.) can diagnose most auto issues over the phone in about 5 minutes!!) has been extolling the virtues of MMO Marvel Mystery Oil for years. I decided to try it for the New Fuel Pump in the gas tank... IMMEDIATE RESULTS! Also added to the oil. Now overnight on Tuesday, the 2017 Outback (193k miles on 2nd engine) runs quieter than NEW!!
See my latest post here below, as well.
 

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