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After the car is warmed up starts missing then stalls

Tiny
DJKLEIN
  • MEMBER
  • 2008 SUBARU LEGACY
  • 2.5L
  • 4 CYL
  • 4WD
  • AUTOMATIC
  • 115,000 MILES
The car starts fine then when it is warm it starts to miss a little then a lot until it stalls. New throttle body, spark plugs MAF, MAP, fuel pump and filter, EGR, purge solenoid, PCV and hose, new coil and wires etc. I'm ready to get a new brake booster and injectors. Three shops have tried and failed.
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Saturday, April 30th, 2022 AT 6:32 PM

27 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Hi,

Has anyone checked the crankshaft position sensor? When they begin to fail, oftentimes, they will fail when they get hot. Once they cool, they work again for a bit of time, and then the same thing happens.

Take a look through this link and let me know if you feel it mirrors what you experience:

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

If it does, you can check if the RPM signal is lost during cranking when it won't start. Or you can check to see if the spark plugs lose spark. Here is a link that explains how that is done:

https://www.2carpros.com/articles/how-to-check-for-ignition-spark

If you find that there is no spark or no RPM signal, here is a link that explains in general how to replace the sensor:

https://www.2carpros.com/articles/crankshaft-angle-sensor-replacement

I attached the directions below specific to your vehicle.

Let me know if this helps or if you have other questions.

Take care,

Joe

See pics below.
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Saturday, April 30th, 2022 AT 10:46 PM
Tiny
DJKLEIN
  • MEMBER
  • 16 POSTS
No, but this makes perfect sense. The crank sensor, I thought about this, I'll check.
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Sunday, May 1st, 2022 AT 6:10 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Hi,

If you can, let me know what you find. I have a feeling this is where the problem is coming from and am interested in knowing.

Take care,

Joe
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Sunday, May 1st, 2022 AT 6:40 PM
Tiny
DJKLEIN
  • MEMBER
  • 16 POSTS
I got the sensor and after 1/2 hour it starts stumbling until it stalls. David
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Thursday, May 19th, 2022 AT 3:11 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Hi,

By chance, do you have a live data scan tool? Also, is the check engine light staying on while it runs?

Let me know and let me know if you checked for codes.

Take care,

Joe
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Thursday, May 19th, 2022 AT 7:50 PM
Tiny
DJKLEIN
  • MEMBER
  • 16 POSTS
Good Morning,

I do have a hand live data tool. The first code I got in the past was P0171. We did that round and replaced bank 1 and 3 injectors and most of the parts listed above this email then P0420 came up. Found a hole in the cat and replaced the pipe along with both 02's. Then P0457 came up and replaced the evap canister in the back panel. Then I found you online and I hope you can help me with this never-ending problem. Thank you, David
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Friday, May 20th, 2022 AT 1:34 AM
Tiny
DJKLEIN
  • MEMBER
  • 16 POSTS
The check engine light in all cases did stay on until I got rid of them. They did not come back.
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Friday, May 20th, 2022 AT 1:37 AM
Tiny
DJKLEIN
  • MEMBER
  • 16 POSTS
We replaced the crank sensor. I think this thing has Cam sensors too. Just to throw this on the table?
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Friday, May 20th, 2022 AT 1:53 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Hi,

You are correct, it does have a cam sensor. See pics 1 and 2 below. So, if I understand, each time you got a code, it was repaired by replacing the component. Are there any codes at this point?

Do me a favor. Using the scanner, check the short-term fuel trims and when the engine is cold, check what the ECT is signaling. If the vehicle is cold, it should be close to ambient temperature.

When you check the fuel trims, the engine will need to be at operating temperature.

Let me know.

Joe
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Friday, May 20th, 2022 AT 9:21 PM
Tiny
DJKLEIN
  • MEMBER
  • 16 POSTS
Bear with me, I'm helping my 85 year. Old mom. My friend has a better scanner to look at this. Thank you, David
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Saturday, May 21st, 2022 AT 6:53 AM
Tiny
DJKLEIN
  • MEMBER
  • 16 POSTS
Hi, a friend brought over his computer with a data cable and we data-logged from a cold start to when the car started stumbling and stalled.

We have the data-log file if you want it, just tell us how to send it to you.

In the meantime, here are the data points you requested:

Cold start
AFR Learn #1 = 0.00 (on 2nd new O2 sensor)
AFR Corr #1 = 0.00
AFR Learn #3 = -53.00 (on 2nd new O2 sensor - suspect short in wiring harness? )
AFR Corr #3 = 0.00
Engine Coolant Temp = 53 degrees
Intake Air Temp = 83 degrees
Ambient Air Temp = 73 degrees
Engine RPM = 1324

Operating temperature
AFR Sensor #1 = 14.70
AFR Learn #1 = 14.02
AFR Corr #1 = 2.54
AFR Learn #3 = -51.00
AFR Corr #3 = 0.00 (the ECU is not adding correction to the learned value)
Engine Coolant Temp = 192 degrees
Intake Air Temp = 104 degrees
Engine RPM = 710 to 730

The engine started stumbling after 20 minutes of running time, we had to add throttle up to 1,500 RPMs before the stumble stopped completely. The ECU was adjusting the Throttle Angle to compensate and try to stabilize the idle.

Thank you for your help.

Dave Klein
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Saturday, May 21st, 2022 AT 9:45 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Hi,

The air/fuel ratios look good. You want it to be around 14.7:1. By any chance, do you also have the short-term fuel trims? That will help me identify if the computer is compensating.

Also, if you could record it and upload it for me to hear, it may help.

Let me know.

Joe
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Sunday, May 22nd, 2022 AT 7:35 PM
Tiny
DJKLEIN
  • MEMBER
  • 16 POSTS
AFR Sensor #1 = 14.70
AFR Learn #1 = 14.02
AFR Corr #1 = 2.54
AFR Learn #3 = -51.00 (that is negative 51.00)
AFR is short term fuel trim I believe.
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Wednesday, May 25th, 2022 AT 12:37 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Here is my confusion. AFR stands for air/fuel ratio. That is what the O2 sensors are indicating. Fuel trims are what the computer is doing to reach a target ratio.

ARF Learn #3 is interesting. If that was the fuel trim, it would indicate the engine is running extremely rich and the Corr (if that is a correction) wouldn't be 0.

Something isn't adding up. Are you noticing any smoke from the exhaust, specifically dark gray or black?

Let me know.

Joe
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Wednesday, May 25th, 2022 AT 6:43 PM
Tiny
DJKLEIN
  • MEMBER
  • 16 POSTS
Good morning, I Googled is ARF the same as short-term fuel trims? I found it to be true. My friend and I disconnected the downstream O2 and connected the old O2 and left it on top of the air cleaner in the air not connected to the engine. The ARF stayed at Negative 51. When we gassed it, it moved to negative 63 then kind of stayed there. Shortly after the car stumbled then stalled again. The downstream was not connected.
I did not notice any smoke from the exhaust, specifically dark gray or black.
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Tuesday, May 31st, 2022 AT 7:42 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Hi,

Is it AFR or ARF?

If you have a negative 51, the computer is trying to lean the fuel mixture. At this point, we need to check fuel pressure and how quickly the fuel pressure is dropping off.

Fuel pressure drop (in this case) could indicate leaking fuel injectors causing the engine to run rich. Here is a link that explains how it's done:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Most parts stores will lend you a fuel pressure gauge if you need one.

Also, I listed the directions specific to your vehicle which include fuel pressure specifications below.

Let me know what you find or if you have already done this.

Joe

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Tuesday, May 31st, 2022 AT 8:11 PM
Tiny
DJKLEIN
  • MEMBER
  • 16 POSTS
Hi Joe,

I checked the fuel pressure. At start I have 50.7 to 51.4. Good. When warmed up and beginning to stall it is 50.8 to 51.3. I have a window in the fuel tester and was looking for bubbles. No bubbles. Thank you, David
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Tuesday, June 14th, 2022 AT 10:45 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Hi David,

The fuel pressure is nearly perfect. Have any of the codes returned? Also, by chance do you have a voltmeter gauge in the vehicle or is it a light?

I think it's time to look at other possible issues. For example, low voltage. Let me know if you have a gauge or light in the vehicle.

Next, I have to ask, has the P0420 returned? Is there any ticking or anything you can think of? Also, have there been any codes related to the cam sensors?

Let me know.

Joe
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Tuesday, June 14th, 2022 AT 8:33 PM
Tiny
DJKLEIN
  • MEMBER
  • 16 POSTS
Top of the day to you, I have a voltmeter gauge. P0420 has not come back yet. Ticking from the injectors but, that's normal. No cam sensor codes. I did not replace the cam sensor.
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Wednesday, June 15th, 2022 AT 1:16 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,300 POSTS
Hi,

When the vehicle is warmed up and starts having issues, I need you to check the voltage at the battery. Basically, we are testing to confirm the alternator is doing its job.

Here is a link that explains how to test an alternator:

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Let me know what you find. Also, let me know if you have a live data scan tool. If you do, when you start to notice the misfire, check the short-term fuel trims, and let me know what they are.

Take care,

Joe
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Wednesday, June 15th, 2022 AT 10:00 PM

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