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Mike V.
Mike V., Subaru Technician
Category: Subaru
Satisfied Customers: 25199
Experience:  Certified Subaru Technician, factory trained by Subaru.
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I have mystery flat spot on accel missing on 3 cylinder lt

Customer Question

i have mystery flat spot on accel missing on 3 cylinder lt fuel -25 o2 sensor .855 volts av running rich swapped out for none good injectors all plugs black but #3 has 160. comp misses all the way threw rpm intermittentant rough idle when . tell me about the open ,close loop when and when shouldnt they be in it
Submitted: 1 year ago.
Category: Subaru
Expert:  Mike V. replied 1 year ago.

Do you have a misfire code actually happening?

Customer: replied 1 year ago.
no misfire codes dosent appear misfire capabilitys
Expert:  Mike V. replied 1 year ago.

Not sure what you mean by doesn't appear misfire capabilities, lol. It's an obdII system and will give you a misfire code.

Which O2 sensor did you replace? The -25 is the problem here and I have seen this quite a bit with the front O2 sensor. If you replaced the front O2, check it for a sticking EGR, if it has one. Some of these did and some didn't. I would also check for vacuum leaks as well. You might be able to cleared the fuel trims, then start the car and watch the fuel trim, spray some carb cleaner around the intake and see if there is any drastic change in the fuel trim if it sucks it into the system.

Also, I assume you mean you installed a new maf sensor and didn't just clean the one you had in the car, if not, you might actually need to replace the sensor.

Please check these and let me know.

Customer: replied 1 year ago.
had a cam code 341
Customer: replied 1 year ago.
had new or rebuilt maf we are going to try another and another front 02
Expert:  Mike V. replied 1 year ago.

Ok, make sure to get a direct fit, and to clear the fuel trim, just like you would do if there were codes stored. This will get it back to zero, then it can be watched and get an accurate reading.

Customer: replied 1 year ago.
fuel trim back at zero 02 at .920 maf 4.18 running rich tp at.08 load pct 3.9 map 7.0 code po 341 came back checking fuel pressure now
Customer: replied 1 year ago.
fuel pressure 28 w vac 37 with vac
Customer: replied 1 year ago.
no fuel in vac hose to regulator no change when purge hose disconnected we also have swapped computers on this earlier trying to correct this .
Expert:  Mike V. replied 1 year ago.

Fuel pressure isn't acceptable here. I am showing it should run 43 psi at idle. I believe 43 at idle, then with the regulator unplugged it should jump up to 47. I wonder if you have a rich mix due to a bad spray pattern caused by low pressure.

Cam sensor code should't be causing it unless the belt is off a tooth or two, but I have only ever seen that cause a lean mix, not rich.

Customer: replied 1 year ago.
what can cause this thing to stay so rich
Expert:  Mike V. replied 1 year ago.

I think it's running rich because of the low fuel pressure. The injectors aren't spraying mist,, they are spraying drops which would be a rich mixture.

Customer: replied 1 year ago.
The spec I find is 26-30 at idle 34-38 with vac disconnected
Expert:  Mike V. replied 1 year ago.

I show that for the 98 the 99 is the spec I gave you.

Customer: replied 1 year ago.
this is 98 can we put 99 pump on it ?
Expert:  Mike V. replied 1 year ago.

lol, well you listed it as a 99. You can try the 99 pump, but I cannot promise it will resolve it, but running ***** *****ke this, if it's not the sensors then it's got to be getting fuel from somewhere, it's the only place I can think of, especially since you have even replaced the fuel injectors on it.