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04 Subaru Outback Cali Spec that belongs to a friend. Car…

Customer Question
04 Subaru Outback Cali...

04 Subaru Outback Cali Spec that belongs to a friend. Car was brought in because of a PO420. The owner had already replaced the Bank 1 CAT, all Exhaust gaskets on Bank 1, both Bank 1 O2 sensors, Fuel Injectors were rebuilt, and knock sensor. Car was fresh off of a tune-up, plugs were replaced, and all fluids were changed. Now that I have the car I scanned and confirmed the PO420, Cleared the ECU and drive cycled to ensure the code was still active. After about 6 miles the code becomes pending, after 30 miles it turns on the MIL. Brought it back to the shop and cleaned the MAF very well, drive cycle and again MIL. I noticed the car was a bit doggy, so I figured I would check the Fuel Pressure. First time out fuel pressure was ~32psi. Disconnected the FPR and no change in fuel pressure. I then began to restrict the return line. Pressure was increasing and I stopped restricting when I hit 50 psi. Just to double check, I then pulled the vac to the fpr again, now all of the sudden it jumps to 45 psi and holds steady. Not sure what happened??? After a few restarts with the fuel gauge still attached to the engine I suddenly noticed that on one restart the idle fuel pressure was bouncing violently from about 30-40 psi. But if I pull the vac off the FPR momentarily and then stick it back on the idle pressure is solid at 36 psi.

Mechanic's Assistant: Have you located all of the vehicle's oxygen sensors? Are the wires leading to and from each intact and in good shape?

Yes

Mechanic's Assistant: Are you fixing your Outback yourself? What have you tried so far?

All described above

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

No, PO420 still remains. Just curious as to the opinion of why the Fuel Pressure is acting the way it is...and why the FPR seemed to semi come back from the dead when I restricted the return line.

Submitted: 6 months ago.Category: Subaru
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Customer reply replied 6 months ago
Just attempted to upload a video. Got lucky and got the idle fuel pressure fluctuation.
Answered in 3 hours by:
1/6/2018
Subaru Mechanic: Matt, Engineer replied 6 months ago
Matt
Matt, Engineer
Category: Subaru
Satisfied Customers: 23,314
Experience: Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
Verified

Hello and welcome to Just Answer

to get a P420 then either there's a problem with cat or the post cat O2 sensor?

and as these have been replaced there must be an issue with the wiring from the O2 sensor to the ECU?

So I'd suggest to disconnect the O2 sensor (post cat) and the ECM socket and then do a continuity test between the two to confirm that the wiring is undamaged as it should be 2-3 ohms at most

regarding the fluctuating fuel pressure I'd say to replace the pressure regulator with new and also check the condition of each injector to ensure that none are dribbling / leaking

if the injectors aren't leaking then I think you may have a cracked diaphragm in the reg

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Subaru Mechanic: Matt, Engineer replied 6 months ago

Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

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