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2002 Express 4.3L V6 Misfiring

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160k miles

P0300 Random Misfire

Sometimes P0303 #3 Cylinder misfire


When I use an OBDII scanner to look at misfire counts, it seems most concentrated on the #3 and #4 cylinders, but all cylinders will have a few misfires.


Testing fuel pressure with an Autozone fuel pressure tester, I was getting 52psi with the motor running (spec is 60-68psi).  After replacing the fuel filter, I am getting around 54-60psi with the motor running, even under acceleration.


Even when actively misfiring and service engine light soon light is flashing, the motor seems to be running smooth.  Not jerky at all.


I've replaced:

* Spark plugs (NGK Platinum, gapped to .060")

* Spark plug wires (NGK)

* Ignition rotor (Delphi)

* Distributor cap (ACDelco OEM)

* Fuel filter (GM Genuine)



Edited by jamesm113
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  • 2 years later...

I had a similar problem on my 2001 Express 5.7. It was due to a bad intake manifold gasket. I replaced the gasket, which was blown out between two cylinders, and the problem was solved. 

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