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Fuel issue

Tiny
DAN MARTINDALE
  • MEMBER
  • 2009 GMC ACADIA
  • 3.6L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 160,000 MILES
I show an air/fuel command of 29.3. I'm guessing that shows a very lean mixture. I've replaced fuel pump, fuel pump control module, injectors, and a number of other parts.

When I scan the fuel control module I am showing a pressure of around 79 PSI when the demand is around 43 PSI.

Could I be looking at a fuel line restriction of some type? Actual rail pressure is around 797 which is good for direct injection.

Any ideas?
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Sunday, January 2nd, 2022 AT 6:56 AM

6 Replies

Tiny
SQM
  • MECHANIC
  • 6,383 POSTS
Hello,

Lean air fuel ratio can get triggered for several different reasons.
It could be due to a vacuum leak, intake gasket leak, exhaust leak, faulty mass air flow sensor, malfunctioning oxygen sensor etc.

Many times, dirty mass airflow sensors can trigger incorrect air fuel ratio.

Take a look at this article, it covers the typical lean air fuel ratio issues:

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

Fuel flow could be an issue, but it could be just a sensor issue.
Is the check engine light on? What error code(s) are you getting?
Knowing the code can help with the diagnostics.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

If you know the codes, let me know what they are.

Thank you.
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Sunday, January 2nd, 2022 AT 11:34 AM
Tiny
DAN MARTINDALE
  • MEMBER
  • 4 POSTS
Thanks for your reply. The fact is I have no codes. Scanner shows everything correct. I noticed the air/fuel ratio by doing a live scan. The only other thing I notice is that my Cam counters all work, but the CMP sensor shows 0RPM when I'm cranking. Rail pressure (gauge is over 60PSI. But when I do a live scan of the fuel control module it shows the pressure of around 70 exceeds requested pressure by around 20-25PSI. The live scan shows something else weird. I have a very high cam sensor voltage--it shows all of them over 63 volts. I don't even know if this is possible but that's what it shows. I've had this car for a while. I inherited it from my brother-in-law, and it had issues then. I wondered if the timing chain had jumped a tooth, so I called GM and they said it was unlikely because the vehicle has only been driven about 7,000 miles since it was replaced.

Right now, it will start up, run for about a second and shut off. Thanks so much for your help. I'm decent with cars but this has me stumped. I thought about reprogramming the fuel control module, but it seems I'm just shooting in the dark. Thanks again sir.
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Monday, January 3rd, 2022 AT 2:17 AM
Tiny
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  • MECHANIC
  • 6,383 POSTS
This is puzzling. Have you already check for any vacuum leaks (including intake leak)?
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Thursday, January 6th, 2022 AT 11:57 AM
Tiny
DAN MARTINDALE
  • MEMBER
  • 4 POSTS
Yes, I do have a crank sensor reading and it reads engine RPM. It is the cam sensor that isn't reading RPMs, but it does do counts on all banks.
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Friday, January 7th, 2022 AT 10:09 AM
Tiny
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  • MECHANIC
  • 6,383 POSTS
I wonder if the issue is within the ECM. Have you tried to disconnect the battery for an extended period of time to see if this reset?

Strange thing is when you have this much variation in the air fuel ratio the engine light gets triggered, and you will have few items to look and check off.

Let me see if I can have other experts chime in on this.
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Monday, January 10th, 2022 AT 2:41 PM
Tiny
AL514
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  • 4,812 POSTS
Are you measuring 63 volts at a cam sensor directly with a multimeter? I would check that, I've seen vehicles with high voltage, over 12, over 20v. So, see if that's a scan tool data error or actual voltage. There are things that can cause voltage that high.
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Monday, January 10th, 2022 AT 5:25 PM

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