Fuel system?

MOSHE2002

MEMBER
2008 CHEVROLET EXPRESS
4.8L
V8
2WD
AUTOMATIC
180,000 MILES

With the o2 sensors disconnected and MAF disconnected the engine starts. What controls the fuel at that point?

Sunday, November 6th, 2022 AT 5:04 AM

3 Replies

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Once you disconnect the MAF, the computer compensates by following a predetermined program from the manufacturer. This prevents the engine from turning off while driving.

What is happening? Have you checked for diagnostic trouble codes?

As far as the MAF, if it runs disconnected and not with it connected, usually that indicates the sensor is faulty. Have you tried cleaning it?

Here is a link explaining how it's done:

https://www.2carpros.com/articles/mass-air-flow-service

Let me know what is happening and if there have been codes retrieved.

Take care,

Joe

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Sunday, November 6th, 2022 AT 9:10 PM

MOSHE2002

MEMBER
2 POSTS

The question was, what control the fuel when the engine is off at cold start, the MAF and o2 sensors are disconnected. The engine starts.
How the PCM know how to control the amount of fuel since the PCM don't know the amount of air?

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Thursday, November 10th, 2022 AT 5:53 AM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

The circuit identifies a fault in the sensors. When it happens, it is designed to go into an open loop preset by the manufacturer to keep it running. I suspect that is what is happening when you disconnect the sensors.

Let me know.

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Thursday, November 10th, 2022 AT 6:53 PM