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Tool Hut
Tool Hut, ASE Certified Technician
Category: Chevy
Satisfied Customers: 550
Experience:  Owner of a mobile diagnostics company assisting auto technicians with difficult vehicles
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I have a 2009 chevy Tahoe 5.3l flex fuel. Having issues with

Customer Question

I have a 2009 chevy Tahoe 5.3l flex fuel. Having issues with fuel trim readings showing -10 at least both banks (rich condition) all sensor readings look normal only odd thing I see is fuel psi at start up goes to 55psi and then drops down to 45psi. With key off engine off fuel psi will rise per gauge to now is at 80psi never seen this happen before any suggestions on what to check next? Any help is welcome thx.
Submitted: 7 months ago.
Category: Chevy
Expert:  Tool Hut replied 7 months ago.

Hi, My Name is ***** ***** for posting your question to just answer. I am a independent contractor for just answer. ASE Certified Master Auto Technician with 20 years experience. I am confident we can resolve your problem together.Please remember I don't know your skill level. I can't see, smell, hear, or touch the vehicle. It may take a few back and forth replies to get to a satisfactory resolution.There will probably be some equipment needed for a proper diagnosis. If you are not comfortable with this or do not have any test equipment please let me know ASAP. I also give you all of the information you may need in good faith expecting a positive rating. I typically do not recommend phone calls, This is an automated request. DO not accept without me telling you I am requesting it. I am not compensated for my time until you leave a positive rating. Your rating should be based on the service you received.

The fuel pressure is controlled by the Fuel pump control module. DO you have a scan tool that you can monitor fuel pump duty cycle and pressures?

Customer: replied 7 months ago.
snap on verus D10. My skill level I am also a master ase certified tech and have bin for over 18yrs. So discussion at that level will be understood. Fuel psi closed loop 43.5 fuel pump signal command 30-31% fuel psi at rail per gauge 44
Expert:  Tool Hut replied 7 months ago.

If you use scanner and command the pump on what does pressure go to?

Customer: replied 7 months ago.
Koer or koeo? I had engine running to get psi now engin off key on and rail fuel psi has risen to 83psi scanner will not allow fuel pump command. I can adjust fuel psi with engine running by 10psi per step and clarify on fuel gauge.
Expert:  Tool Hut replied 7 months ago.

will it command 100PSI?

Customer: replied 7 months ago.
The highest I could command to was 85psi before test time out.
Customer: replied 7 months ago.
Would this be easier over the phone?
Customer: replied 7 months ago.
Just ran the test again and the highest psi was 60 for fuel psi control. Fuel pump control was able to peek at 85 psi.
Expert:  Tool Hut replied 7 months ago.

Ok. You commanded 60 and it went to 85? Does your scanner have a fuel rail pressure parameter? What does it show?

Customer: replied 7 months ago.
Under fuel pump data desired fuel rail psi is 43.5 actual fuel psi sensor reading shows 43.0 to 43.9 fuel gauge shows 44
Expert:  Tool Hut replied 7 months ago.

So when you commanded 60 it went to 85 on gauge?

Customer: replied 7 months ago.
On my scanner I have 2 different tests that can be run 1 is fuel psi control and the 2nd is called fuel pump control which I assume is pump out put. Test 1 max psi reached was 60. Test 2 max psi reached was 85psi.
Expert:  Tool Hut replied 7 months ago.

What is alcohol % reading? There is a calibration update to address this. see attached.

Customer: replied 7 months ago.
Fuel alcohol content reading 32% I'm currently running 89octain from shell not E85
Expert:  Tool Hut replied 7 months ago.

Can your scanner do an alcohol reset? I suggest updating the PCM with latest calibration