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2016 Forester XT
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Discussion Starter · #1 ·
I'm troubleshooting what I believe is a pinging or detonation issue and I'm suspecting my MAP sensor to be the culprit. No CELs, but when I compare the MAP sensor value to barometric pressure there is a slight variation.

When atmospheric pressure is 101kpa the MAP sensor only shows 96kpa (key on, engine off). Is this normal or should they match exactly?
 

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2012 SH Manual Diesel
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What are you using to measure, or where are you obtaining the 101 kpa from?

Is this a MSL pressure reading?

Are you making any appropriate adjustments to your readings/measurements etc. for your actual height above sea level?
 

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Discussion Starter · #3 ·
Just using a Bluetooth OBD2 dongle with the Car Scanner app.

101kpa is correct for my altitude, which is obtained from the barometric sensor built into the ECU. I would expect the MAP to be the same when the engine isn't running, but would like some confirmation before I spend the $300-$400 on a new one.
 

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Interesting. I've been trying to troubleshoot knock events when the engine is at operating temp. Did not think to consider the MAP sensor. Just checked to see what mine looks like with the engine off: Indicates 13.94 psi or 28.38 inHg (96.1 kpa). According to current weather report: 30.03 inHg (101.7 kpa). So the car's engine-off barometric reading is 1.65 inHG (5.6 kpa) less than official atmospheric pressure.

In short, I'm seeing the same thing you are. Either it's normal or both are equally wrong. Perhaps the straight 12V battery vs 13.8V operating/charging voltage could cause the difference in static reading.

Need more comparative data points from other FA20DIT owners.
 

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Be cognisant of:
  • differences in Barrometric and Absolute pressure readings;
  • how they may be reported (MSL, ASL, Absolute etc;
  • how they may be easily confused, mixed up, interchanged;
  • the accuracy and error in each reading, reporting, apparatus, sensor etc.; and
  • other compensations e.g. temperature, humidity, advancing weather front. And with respect to the car; voltage supply, quality of ground connection, resistance in wiring harness/connectors etc.; and also the age, heat and vibration exposure of the sensor.

Best practice, would be to also test the sensor (pressure and temperarure component), along with the harness and connectors etc. Even if you consider it to be an erronous reading, it may not be the sensor at fault.

Whether the pinging is (in closed loop): a short lived event on initial acceleration; pronounced on initial acceleration, but then noticeably reduces as acceleration continues; or if the pinging remains continual on acceleration; may give you an idea on which components to start investigating first.

Also, Autocraft in Adamstown (Newcastle NSW), are Subaru specialists. They are usually very helpful, and their prices on OEM parts have been cheaper than the Bradstreet Parts/Dealer. They may be able to give you good advice on how to diagnose the overall pinging problem; suggest which components to check first (considering, that they know the cost of parts, difficulty of task, and likelihood of culprit).
 

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Discussion Starter · #7 ·
The pinging is very pronounced on initial acceleration but only lasts a second or two. Sometimes there is a hesitation as well if facing up hill.

I have done the multimeter tests on the MAP sensor as per the service manual and both pressure and temperature are within spec. Will be taking it to the guys in Adamstown when I've run out of ideas. Was just curious about the lower than atmospheric MAP sensor reading.
 

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Assuming that you may still also want help on the issue, other than just the answer to your initial question...?

What are the other Car/Symptom/History details:
  • Auto or manual transmission;
  • Stock engine, or mods;
  • First/Second owner;
  • What fuel standard and brand is used;
  • Any other seemingly unrelated symptoms or problems;
  • Any major work or repairs on car;
  • Is the engine running lean or rich;
  • Is it a recent or ongoing symptom;
  • Does the engine mis, or cut out;
  • Any change in fuel economy;
  • Any change in engine torque, or power;
  • Any change in gear selection;
  • Are all general maintenance, parts, consumables, and scheduled works up to date, and on track;
  • Are services/oil changes done on Subaru recommended mileage;
  • What has the oil looked like, and sign of sludge or varnish buildup;
  • High or low mileage;
  • Any electrical issues with car?

Does this happen on every acceleration event, and across all degrees of acceleration? e.g. standing start, rolling, downhill, fast, slow, heavy load, light load, all gears, some gears, cold engine temp, hot engine temp, all fuels etc.

Are you logging live data?

Have you checked your:
  • MAF;
  • Throttle position sensor;
  • Boost control solenoid, vacuum lines, and actuator;
  • Crank and Cam position sensors;
  • Variable valve solenoids;
  • O2 Sensors;
  • Fuel pressure;
  • Fuel return, purge valve, pressure seal of fuel cap?
  • Have you run any fuel system cleaner, injector cleaner;
  • Have you inspected the spark plugs, what do they look like?
 

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Discussion Starter · #9 ·
Cheers Dogs. Yes I certainly would like help with the pinging issue, I'll try answer your questions as best I can...

  • Stock 2016 FXT with CVT trans
  • Second owner, Purchased less than 12 months ago. Engine failed on the trip home after purchasing (spun rod bearing) and rebuilt by my local Subaru with genuine parts.
  • Usually run BP Ultimate, trying a couple of tanks of 95 at the moment but no change
  • No other issues
  • No other major repairs apart from the rebuild I mentioned
  • I'm guessing it's running lean but I pulled plugs a week or two back and they look normal
  • It's a recent issue, first noticed it roughly 2 months ago
  • There is a miss or hesitation sometimes, depending on the severity of the pinging
  • Fuel economy is good
  • Other than the initial pinging from a standstill, the car runs beautifully
  • Services are up to date
  • Oil looks fine, but it's only been ~2000km since the rebuild
  • 90,000km on the clock
  • No electrical issues
Doesn't happen every single time I accelerate, if I really baby it off the line it's fine. Only occurs from a standstill, not rolling. Both 95 and 98 fuel, cold or warm. Here's where it gets a little weird - it seems to happen more when facing downhill??? I need to test that theory out more though.
It could also be a timing chain rattle, but there's no noise on cold startup when oil pressure would be at it's lowest so I ruled that out.

Haven't checked much else really, except for leaks in the intake piping and multimeter test of the MAF sensor.
 

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Have you got the spark plug codes?

If I was to have a guess, i'd say that gap looks almost the size of the thread pitch of the plug (1.25mm), so could possibly be in that 1.1mm range.

For the turbo engine should have a 0.6mm gap. (1.1 for the N/A engine).

Also if the heat range of the plugs are incorrect, that can cause pre-ignition.

Heat range for turbo is 8 on the NGK scale, which is a cooler plug (7 for the N/A, which is hotter).

Also, below are the MAP sensor readings off my car. Its a 0.2 psi difference, as opposed to the 0.7 psi difference that yours is showing; but it does show that there can be a discrepancy between the readings.
 

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Discussion Starter · #16 ·
Mine uses NGK ILKAR8H6 which are factory set at 0.55mm while the NA has SILZKAR7B11 at 1.1mm. I definitely have the right plugs, I might pull one again to check the gap though.

Interesting that your MAP reading is higher than barometric where as mine is lower, but still, not exactly the same.
 

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Discussion Starter · #17 ·
Could I have a vacuum/boost leak, or a faulty MAF sensor? If you look at the screenshot, air flow rate is not increasing proportional to rpm (when in park/neutral).

Screenshot_20210519-104130.jpg

3g/s @ 800rpm
5g/s @ 1600rpm (should be 6?)
7-8g/s @ 2400rpm (should be 9?)
 

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Discussion Starter · #18 ·
Just a small update...

Took the car into Autocraft today - he is also stumped. At a guess he would say it's timing chain rattle since he picked up on another noise happening at startup, may or may not be related. Suggested I take it to a different Subaru dealer or try a slightly thicker oil for a week or two as a test. The theory is that the thicker oil will help the timing chain tensioners hold pressure.

I've also been logging short and long term fuel trims and every time I hear the sound my STFT has dropped to -12% or more, and LTFT is also in the negative. is that a normal amount? Or could I have a faulty O2 sensor which is causing lean conditions?
 

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Are you logging all engine parameters?

If you can make a graph of all the sensors in realtime, that will help you identify any parameter(s) that is fluctuating at the same time as the symptom.

That sensor may also just be indicating the symptom; but at least from there you might have an easier time tracing back to the cause(s). As you might at least know if its fuel, ignition, mechanical, or electronically related.
 

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Discussion Starter · #20 ·
No not all sensors. I only have a Bluetooth dongle and the CarScanner app which lets me graph up to 4 in realtime.
 
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