subaru tribeca very lean condition

hi guys,
i have a very disturbing issue and i almost gave up on it. please bare with me as i will describe everything about the history of the car from the moment i bought it.

current status- i have absolutely no normal mechanic or car shops around me. i am not a mechanic, in fact up to 6 month ago i didn’t know how to change oil.

the car: subaru b9 tribeca 2007 100k base
symptoms: 1. serious hesitation when pressing the pedal from ideal
or during driving.
2 . 100% engine load on 2000 rpm with no power

i bought the car with cooling fan bypass, no thermostat ,blown head gasket, bad alternator and a/c system.
the symptoms of the hesitation was there as well.

i did :
head gasket
water pump
new radiator
new alternator
new a/c system
new fuel pump complete original subaru
cleaned the injectors
2 new a/f sensors
4 oil solenoid
cleaned camshaft and crankshaft sensors
new maf sensor
removed cat convertor form 2 sides
new pcv valve

all the parts are from subaru dealer in the state.
fuel pressure is 56psi ideal and at wot.

am using blue driver app for scanner and i have autel scanner .

the problem is , the car runs very lean . on ideal there is no problem and after 2200 rpm when the gas is steady the car moves fine, but if i press the pedal its chocking and after 3 second its starting to get some power again.
also there wasn’t any reading on the long term fuel trim its always on 0%
short term on ideal are ok but when pressing the pedal can go up to 30% once from bank1 once from bank 2, so i know its not something like faulty injector because its affecting both sides.

i didn’t find any vacuum leak.

important: if i disconnect the maf sensor, the car will run normal.
important: the isn’t any dtc on. nothing

remember the bypass i told you? so i removed the bypass and now the fans are working as should , the car reach 95 c and the goes down ,not overheating.
but, i didn’t install the thermostat back, once its on, the car get overheat, i believe because its running lean.

at this point i don’t know what else to check , if you could ask me questions or direct me what to check, i will do so imidiatly and will update.
i am uploading some pictures taken from the scanner for you to see.

thank you in advance

gilgol2710 wrote: hi guys,

important: if i disconnect the maf sensor, the car will run normal.

What exactly do you mean with the above statement? Car runs fine and no problems with the MAF Sensor disconnected? Or it runs the same as when it is connected?

if i disconnect the maf, i get check engine but its not hesitating at all. if i press the pedal it will react immediately . can't drive without the sensor because the cm will limit the car at 4000 rpm but i can see that if i force the cm to read the sos maps, no hesitation on accelerate .

Did you replace the MAF with OEM or after market?

Also, do you still have your old MAF? If so, put it on and see what happens.

oem sensor by part number. both of them are doing the same. the problem isn't the maf, i just mentioned it incase someone will think about injectors, so its not injectors if with the maf sensor disconnected, i think its something that block the signal from the cm to the injectors on load

I am assuming that you have run the appropriate voltage tests on your MAF circuit and everything checks out?

Without your MAF, are you in Open or Closed Loop when test the throttle response?

i didn't check the voltage . do you mean when the sensor is connected, on the plug itself?
i don't have answer yet if it was open or close loop, tomorrow i am changing the tps and i will disconnect the maf again and i will update if it open or close

You mentioned everything is fine at idle. Your third picture attachment shows your TFT at 28%to 29% for both banks at 979 rpm.

If the car runs fine with the MAF disconnected I don't see how it could be the TPS. I would do more diagnosis on your MAF and its circuit.

I would test the TPS before replacing if you go that route. I don't believe that Blue Driver gives TPS voltage to check if it has drop outs. I have a Subaru Legacy and I can only get %'s for absolute and relative. Your Autel should be able to provide this information.

am changing the tps because its the only sensor yet i didn't touch.
about the short term, when i on the car, no touching on the gas pedal, ideal is good , short term both banks are between -3 to -8. the moment you hit the pedal, not even fully, it will jerk ,chock, hesitate and engine load will show 100% and the stft will be between 22 to 33 ,once on bank1 and once on bank2 never together. if you press the pedal slowly, rpm will rise slowly both smoothly .

here is a test i did yesterday engine off key on

so i changed the tps, no fix.
removed the maf and its close loop.

I would focus on the overheat at this point. I've never, not once, had a car overheat from a lean condition. Pre-ignition, yes. Pinging, yes, overheating, no.
I would retest that system for a head gasket issue, then bypass the heater core (yes I've seen a plugged heater core on a Subaru cause an overheat)

checked, its clear, the heater is good, water pass freely . i am in a very hot weather country , 38c most of the day, no need of thermostat .
problem still exist, strong hesitation at accelerate, 100% engine load on 2000 rpm.
the engine temp is between 90c to 105, its normal for this car. before i fixed the bypass the temp was between 65c-90, its too cold, but even then the short term fuel trim always high numbers never rich( when the engine is cold its suppose to be rich).

remember, the long term fuel trim always on 0%, can the problem be the ecu?

i used multimeter on the maf sensor, and i have 14v , good ground, and 1.2v on idle.
when pressing the gas pedal it goes to 2.3-3v.
so i don't think thats the problem.
again , without the sensor, the ecu goes to the default map i wider the injector band, and the is not hesitating . with the sensor, its hesitating when i press the gas pedal instantly.
how can i check that the computer is really sending command to the injectors on time? or how can i increase the band ?

If unplugging the sensor eliminates the symptom I would concentrate on a feedback problem. I would check the MAF circuit. Voltage drop the reference circuit, voltage drop the ground circuit. Compare signal voltage at sensor to signal voltage on scan tool.

You said the MAF sensor is correct by part number. Is the sensor an actual Subaru MAF sensor, from the dealer?

Modern cars are extremely sensitive to minor voltage changes from sensors. Hundredths of a volt can screw things up. I had a Subaru with an aftermarket MAF sensor which had a scale that was shifted by about 0.1v

The vehicle had the exact same symptom as yours. Scoping the MAF sensor showed the sensor to "appear" to be working perfectly. When in fact that slight shift of 0.1v caused fuel trim DTC's.

Replacing that sensor with a OEM Subaru maf sensor corrected the problem. Voltage values must be exact. Seeing something that kinda looks like it might be doing something isn't good enough.

ok Lets get back to basics,,,,
If the car is lean lets start at the pump You should have Psi and volume. You need both you can have psi and run fine but you need the volume for top end and load.

Flue Psi should be 49-50.5 psi now you can do volume test you need to look it up I don't know what numbers you should have for this motor...
You stated something about over heating I know that number f cylinder is famous for bad head gaskets and bad vales .... just FYI..

Does your scanner read maf sensor flow rate ? If so give me warm engine idle numbers and a highest number on wide open throttle run in 1st or 2nd gear I prefer grams per second but I can convert if your scanner reads other increment

Sent from my SM-N920P using Tapatalk