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Positive (10) ltft all rpm

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17 Nov 2019 06:34 #35071 by vladislav
Positive (10) ltft all rpm was created by vladislav
Hi Paul and forum members!

I have a pain of a problem with my 06 subaru forester 2.0 116kw/158hp manual transmition. European model.

Like i said in the title my car shows around 10-13 ltft at idle and all higher steady rpm. Under load/driving it will zero out or will be compensated by the stft.

So far i checked for vacuum and exhaust leaks.(but at higher rpm shouldn't get better?)
I replaced front o2 sensor.
Cleaned maf and replaced briefly with one that died in 2 days. (at higher rpm shouldn't get worse)
Checked and cleaned pcv valve.

When i bought the car it had no compression on cylinder 3. Because of no lash on an exhaust valve. And the previous owner drove the car for a short while in this condition. So maybe the cat is on his way. But i don't have any codes. And shouldn't request for more air? Thus negative fuel trim?

It seems to me that it doesn't look like a big issue that can do damage.
But what annoys me is the stumble when i drive off from still. It has a little lag when it has to decide what fuel trim it wants to use at that point.

Please give me some advice!
What should i check next? Or should i recheck?

Thank you!

Also thank you Paul for your videos! I learned a lot from them and i can say that i think i know more that the mechanics i asked around here.

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17 Nov 2019 10:25 #35077 by scannerjohn
Replied by scannerjohn on topic Positive (10) ltft all rpm
although +10 is not bad... its at the limit that most see as acceptable. The stumble is because your running lean (that's why the +10) pcm is adding fuel. Your getting too much air somewhere. The pcm will not throw a code until you get somewhere around +20. Usually high LTFT that get better with higher RPM indicates a vacuum leak.

Check you IAC. A dirty IAC that is not operating properly will act like a vacuum leak. If its clean, check to make sure its opening and closing smoothly. I'm suspecting that its not closing all the way. That exhaust valve may still be causing problems as well.

You cannot replace parts based on codes and replacing 02's 90+ percent of the time does not fix the problem. There are checks you could have done to the 02's before replacing and save time and money.

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17 Nov 2019 13:25 #35088 by vladislav
Replied by vladislav on topic Positive (10) ltft all rpm
Thank you John for your reply! I didn't hope somebody will reply in weekend.

I took apart the engine and rebuild the heads. Adjusted the valve lash and took a compresion test afterwards.

And i cleaned the throtle body back then. That was a year ago.

These symptoms are present since the engine rebuild.
I don't know if they were prior to that because the engine run on 3 cylinders.

I will clean again the throtle body. It's electronical throtle body so the iacv it's the throtle body itself.

Today i finally found the egr valve :))). On the internet it's shown in other places. On european model it's hidden under the intake manifolt right behind the alternator.
I will clean the egr valve and check if it's closing shut.
Also on the internet i read that jdm didn't have the egr. Only usdm. So i thought mine doesn't have one too.
I really hope it's either a dirty throtle body or egr.

I replaced the o2 sensor because i used an adroid app and bt obd adapter that has a slow refresh rate so i thought the o2 sensor is slow to respond to vacuum leak i produced.

Thank you again.

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17 Nov 2019 17:54 #35094 by scannerjohn
Replied by scannerjohn on topic Positive (10) ltft all rpm
If you have a bi-directional scantool, you can check the IAC to see if its working. If you do not have bi-directional their is just no way to properly check the IAC.

Also check your MAP sensor.

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18 Nov 2019 05:06 - 18 Nov 2019 05:09 #35096 by vladislav
Replied by vladislav on topic Positive (10) ltft all rpm
I thought i can test it like this - with key on engine not running somebody to press the gas pedal and me to inspect the way the throtle plate it's opening. Doesn't work like this?

I have a cool software developed by subaru enthusiasts that can do two way tests. It's called fressm. I'm not sure it has the option for the throtle plate/iacv. But it has for 20+ number of solenoid type agregates.

Also the maf looks ok. It shows 2.6-3.0 on idle and volts around 1.06.

Edit: I saw you said map not maf. What should i check? It shows 32-36 psi at idle.

Thank you!
Last edit: 18 Nov 2019 05:09 by vladislav.

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18 Nov 2019 15:00 #35103 by scannerjohn
Replied by scannerjohn on topic Positive (10) ltft all rpm
You would not be able to see the IAC working by looking into the throttle bore... the pintel for the IAC is attached to its motor, the other end is like a plug that travels in and out of the IAC housing allowing air to enter the throttle body. 06 and above incorporated the IAC inside the throttle body as you said.

you can only clean as you did... bad design by Subaru. Older years had the IAC on the outside where you could change and clean.

If your bi-directional software can activate the IAC at least you know the wiring is OK.

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18 Nov 2019 15:41 - 18 Nov 2019 15:47 #35105 by Weycraze
Replied by Weycraze on topic Positive (10) ltft all rpm

Edit: I saw you said map not maf. What should i check? It shows 32-36 psi at idle.


32-36 psi represents 65 + inHG which is not typical of your MAP Sensor.

Using Scan Data are you able to tell :

1. BARO PID, what is the value?
2. MAP Pid value, at idle, and WOT?

To get a reading in the intake manifold you would see on a gauge we would take BARO-MAP( or Absolute MAP).

So in your case at idle, depending on your elevation from sea level, you want to see your MAP PID read a very low number.

eg, BARO = 29.9; MAP=7.4; Therefore there is 29.9-7.4=22 inHG of vacuum in the Intake Manifold.

***BUT*** at WOT you want to see the MAP value raise substantially up to 1.5 in hg within the BARO reading. Anything greater than 1.5-2 inHG from BARO at WOT represents an airflow restriction in the motor. So you want to see for example 27+ inHG at WOT.

OR. your MAP isn't functioning properly!

This one sensor can cause your positive trims across the board.
Last edit: 18 Nov 2019 15:47 by Weycraze. Reason: sp

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18 Nov 2019 17:19 - 19 Nov 2019 17:46 #35120 by scannerjohn
Replied by scannerjohn on topic Positive (10) ltft all rpm
Nice call Weycraze, I missed the MAP number he gave...

vladislav

with the KOEO what are the following readings

BARO kpa
MAP kpa
MAP voltage

also with the engine running and hot, what is the throttle position angle % at idle
Last edit: 19 Nov 2019 17:46 by scannerjohn.
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20 Nov 2019 03:52 - 20 Nov 2019 09:41 #35151 by vladislav
Replied by vladislav on topic Positive (10) ltft all rpm
Sorry guys that i wasted your time.
I meant 32-34 kpa at idle. So 9.44959 inHg.
I'm have trouble at work and i was busy fixing some bugs on a new website that we launched early because of someone else's ambition.
And i didn't receive a notification for whatever reason for you replys.

I attached a screenshot at idle. Here's a gdrive link in case the photo it's not uploaded photos.app.goo.gl/978ZLHvWNyPDtBtH9

And this photos.app.goo.gl/Y7sQgi99Ykv6a3oB9 is a screen recording while driving. Maybe you can see something that is obvious to you.

I will sneak today and do a reading of map at wot.
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Last edit: 20 Nov 2019 09:41 by vladislav.

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20 Nov 2019 09:39 #35161 by vladislav
Replied by vladislav on topic Positive (10) ltft all rpm
So i snook and i cleaned throtle body and egr valve.
They weren't that dirty.
Throtle position got from 11.4 to10.6 at idle.
And egr doesn't leak vacuum.

Also fixed a heatshield that was rattling and caused ignition time pulling.
I reset the ecu and still fuel trim at idle is 10-14.

Map reading at wot is exact same as atmosferic pressure.

I'm out of ideas.
Here are some screen shots



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20 Nov 2019 11:13 #35162 by scannerjohn
Replied by scannerjohn on topic Positive (10) ltft all rpm
In reviewing your live data... your STFT and LTFT get better with increase in RPM. This indicates a vacuum leak.

I know you checked, but I would recheck for a vacuum leak. I would do a smoke test at this time. The leak might be small and hard to find.

Also check your fuel pressure readings. At idle and WOT. Do a snap throttle test, the pressure should increase approx 10% then drop back to idle pressure. Also check the pressure after you turn off the engine. Does the pressure stay or drop. Watch the pressure for 15min. Does the pressure drop and if so, how much.
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20 Nov 2019 13:12 - 20 Nov 2019 13:22 #35164 by vladislav
Replied by vladislav on topic Positive (10) ltft all rpm
It varies a lot when i'm driving. But at steady rpm it's the same ltft. See the pics. Like i said in the title.

I don't think it's somenthing wrong with fuel pressure. Fuel trim should increase with rpm.

Also vacuum leak should get better with rpm increase. Even to be totaly ignored at 4500 rpm.

Nobody even herd here about smoke machine. I tried with a pump and a cigar in the inlet hole. And i didn't hear any whisling or see smoke.

It's a strange behaviour and i can't figure it out. And anybody i asked.
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Last edit: 20 Nov 2019 13:22 by vladislav. Reason: gramar :))

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20 Nov 2019 14:38 #35165 by vladislav
Replied by vladislav on topic Positive (10) ltft all rpm
Could it be a partialy clugged injector or several? I mean for me it makes sense. The quantity of fuel that doesn't make it to pass trough the injectors per fire it should be the same at any rpm.

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20 Nov 2019 19:21 #35171 by scannerjohn
Replied by scannerjohn on topic Positive (10) ltft all rpm
Checking fuel pressure will tell if fuel delivery is working properly. If you have a weak pump or regulator your engine may not be getting the fuel delivery it needs. Checking the pressure will tell.

At idle you should have around 43psi and at WOT around 50psi. After checking pressure, let the system sit with the gauge attached and check pressure after 10min.

The 02 you replaced, is it a wide band (air fuel sensor) or a narrow band 02 sensor.

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20 Nov 2019 20:21 #35172 by Weycraze
Replied by Weycraze on topic Positive (10) ltft all rpm
Your Intake Pressure is 33 kpa @ 725 rpm

Your Intake Pressure is 25 kpa @ 4488 rpm, this is NOT good, it should be 1-2 kpa close to WOT.

This clearly shows the Intake Manifold pressure is not dropping like it should when the throttle plate is opened. Only 2 things can cause this, Intake Restriction or an Exhaust Restriction.

You need to monitor three PIDS O2, Calc Load, and MAP.

@ WOT

Rich O2>Low Calc. Load>High Map>>>>>Restricted Exhaust
Rich O2>Low Calc. Load>Low Map >>>>>Restricted Intake

Lean O2>Low Calc. Load >>>>> Air Measurement Issue
Lean O2>High Calc. Load>>>>> Fuel Delivery Issue

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20 Nov 2019 23:41 #35175 by scannerjohn
Replied by scannerjohn on topic Positive (10) ltft all rpm
Weycraze,
he originally had an issue with an exhaust valve... maybe that valve timing is still off causing additional intake pressure. Vacuum reading at idle is showing -68. Should be 17-21.

vladislav,
you might want to check compression and leak down in that cylinder with the repaired exhaust valve.
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22 Nov 2019 04:13 #35202 by vladislav
Replied by vladislav on topic Positive (10) ltft all rpm
@scannerjohn i replaced a air fuel oxigen sensor. Pre catalytic one.

I don't have a fuel pressure tester. I will ask my mechanic. It's not a very popular tool here. Mechanics here are replacers of new parts :))

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