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Gary, Chevy Technician
Category: Chevy
Satisfied Customers: 17152
Experience:  15 years GM master tech
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I have a 2003 Silverado with a 5.3L engine, The engine had

Customer Question

I have a 2003 Silverado with a 5.3L engine, The engine had been idling rough for a couple of weeks, but just recently the engine light has started flashing when I accelerate, but if I am driving at a constant speed or idling it just stays on. It also accelerates really slowly and I have heard some knocking noises which eventually go away. I have also noticed a dramatic loss of power
Submitted: 1 year ago.
Category: Chevy
Expert:  Gary replied 1 year ago.

I am sorry your having this problem

is this 5.3 engine a cylinder deactivation engine or also called active fuel management engine where it can shut off cylinders when driving to save fuel ?

where or what area do you hear this knocking noise ?

Customer: replied 1 year ago.
No it is a 5.3L vortec engine with no cylinder shutoff
Customer: replied 1 year ago.
I also hear like a knocking or clanking sound when i accelerate but it will go away after a while, it just started with the decrease in power
Expert:  Gary replied 1 year ago.

thank you for that information

where do you hear this noise from ? is it a ticking type noise like a lifter noise ?

any idea what the code numbers are set ?

any local Pep Boys or Auto Zone will scan the codes for free for you

we need to know if this is just 1 or 2 cylinders misfiring or most of the cylinders so we know which direction to take next with this problem

this issue can range from a fuel pressure issue to most common a possible cam shaft or lifter failure which will cause the light to be on and blink and the noise

when the check engine light is blinking there are cylinders misfiring

Customer: replied 1 year ago.
AFM didnt come out on the silverados until 2005 and i know it is misfiring, im taking it to get the codes read, but up to right now i wanted to narrow the problem down, but it seems like this website isnt gonna help out much.
Expert:  Gary replied 1 year ago.

the 2 things you have going bad for you right now is this noise and a misfire which on these usually ends up being a lifter or cam failure

if you get the codes read and there is a specific 300 code like a 301-308 those are all 8 cylinders

if say you have a code 304 which is cylinder 4 we would need to be sure the park plug is ok if it is remove the valve cover and see if the rockers are opening up correctly if not the lifter and cam shaft is usually the issue

if the rockers are good then swap 4 cylinder injector with 6 and see if the skip moves or stays at 4 cylinder

Customer: replied 1 year ago.
Took it to get the codes read, said it was the mass flow sensor, oxygeb sensor, knock sensor and miss firing, so something is causing it to trigger all those sensors
Expert:  Gary replied 1 year ago.

the MAF can cause most of those codes to be set if it is not sending the correct air flow reading to the computer

the knock sensor is touch and go if the MAF is causing that code as we have had knock sensors going bad and the wiring harness to them from under the intake manifold

if the fuel pressure tests good and hold pressure i would replace the MAF and the connector at the MAF and shrink wrap in the new wires one at a time so you do not mix them up then clear all the codes and see how it runs and which if any codes come back

Customer: replied 1 year ago.
Been checking some forums online and saw that some people were experiencing the same problems, didnt think much of it and one guy posted that his "service airbags and low coolant" messages were coming out, i had been experiencing the same thing the days leading up to the reduced power and blinking engine light, some of the forums say it can be a ground wire, what do u think?
Expert:  Gary replied 1 year ago.

yes it could be

you need to be sure the grounds are all clean and tight on the engine and the ground # ***** in this picture must be clean and tight and the grounds on the drivers side lower of the engine where the negative battery cable connects to the engine there should be the negative cable and another small ground together