Posted on December 27, 2009 - by Richard

Saving Money When Fixing 2003 GM Emissions

Symptoms:

Fixing 2003 2003 GM emissions became available to me when I helped my buddy worked on his Sierra 1500 truck 2 weeks ago. The engine was misfiring, would barely idle and the check engine light was on all the time. It had a P0300 code on his scanner which denoted engine random misfire. He did a major tune-up by replacing all the spark plugs, plug wires, distributor cap and rotor. A quick compression test on all cylinders showed reading between 140-160 psi (normal). The main question is: how can you fix this without spending too much money?

Vehicle Specs:

2003 GM Sierra with 4.3L 6 cylinder engine with 4 speed electronic tranny, a multi-port fuel injection system and obd2 complaint.

Diagnostics for Fixing 2003 GM emissions:

Fixing 2003 GM emissions for me starts with using my $200 scanner and monitor the live data so I can view what exactly is happening inside the engine.

Scanner monitor live readings:

Engine at Idle:

Engine at 2500 rpm:

Tips in fixing 2003 GM emissions:

When checking for readings in the scanner live data, look for un-even reading between engine banks. Comparison can be made when engine is idling and when the engine is rev up at 2500 rpm.

I noticed the a defined fuel rich mixture concentrated in one bank only. This I observed when bank 1 kept adding fuel and bank2 kept subtracting fuel.

Final solution to Fixing 2003 GM emissions:

When fuel is concentrated in one bank, this usually denotes a blockage in the exhaust system. Using a vacuum gage, I got a high back pressure reading when tested. To do this vacuum test, rev up the rpm to 3000 rpm and take vacuum reading. A reading higher than 6 psi denotes exhaust restrictions. Dropping the catalytic converter (CAT) connections and retesting the fuel trim showed it returned to nomal which is lower than 10 percent. Replacing the CAT fixed the problem.

Thanks!