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454 7.4 liter vortec 7400 V8 SFI engine with low O2 sensor voltage


welded

Question

Hi All

I am having a heck of a time with my Chevy 454 engine. I am getting low voltage codes(P0131, P0151, and a lean engine condition P0171). I have replaced both oxygen sensors(there are only two on my motorhome) with GM sensors from the dealer. The codes are pending not enough to disable the vehicle but it goes in limp home mode.

I cleaned the Mass Air flow sensor and even bought another set of oxygen sensors to no avail.

Any help would be greatly appreciated. I am using a Actron CP9580 scan tool to monitor all this but I just cant figure it out.

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Low voltage on oxygen sensors generally mean lean mixture. You will want to check for vacuum leaks, as well as check the air intake hose after the MAF and before throttle body for any holes, or leaks.

Basically check your truck like you would check a 72 Pinto. Sensors are the last part to check, not the first. If your scan tool has a monitor screen, you should take a look at all the sensors to read their output as well. But, I would do vacuum leaks, intake hose leaking and you may want to tap the MAF to see if it makes any difference to the idle quality.

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Low voltage on oxygen sensors generally mean lean mixture. You will want to check for vacuum leaks, as well as check the air intake hose after the MAF and before throttle body for any holes, or leaks.

Basically check your truck like you would check a 72 Pinto. Sensors are the last part to check, not the first. If your scan tool has a monitor screen, you should take a look at all the sensors to read their output as well. But, I would do vacuum leaks, intake hose leaking and you may want to tap the MAF to see if it makes any difference to the idle quality.

 

 

Also check your fuel pressure. Low fuel pressure will cause a lean mixture.

 

Ok Guys

Thanks for your help. I took your advice and replaced the vacuum lines and checked the fuel pressure. The fuel pressure with a new fuel filter is a steady 50 psig. when I first turn on the key it goes up to 58psig and once started it holds fast at 50psig. I don't know if this fuel pressure is within range for a 7.4 vortec 7400 V8 SFI that has a throttle-body not fuel injectors. The O2 sensors seem more active now when I graph them than before the fuel filter change. Maybe the attached file is useful?

Thanks again for your help.

454Engine.txt

454Engine.txt

454Engine.txt

454Engine.txt

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