2001 Blazer LT 142,000 Miles 4.3 Liter V6
I bought this vehicle used a few months ago. I could not find an issue with it at the time, so I purchased it. After driving it a month or so the check engine light came on. I plugged in the computer and got code P0302 cylinder 2 misfire. I began to try and find the problem. In that time I have replaced the distributor, distributor cap, button, spark plug wires, spark plugs, the old fuel spider with a new one from Oreillys and serpitine belt. I have checked the compression on each cylinder which has around 175 psi on each one, I have done a fuel pressure check and leak down test. Start the car pressure is right at 60 psi. I turn the car off and it holds that pressure for several minutes. I made sure my new spark plugs are gap properly. I took my inductive timing light and clamped it on each individual spark plug wire. The light flashes in the same rythem as each other. If I am on the highways and I reach 70 mph the Check Engine light begins to flash until I slow below 60 MPH. I am lost as what to do. I have read many articles on the internet and in my Haynes book. The only thing I have not done as of yet is make sure the grounds from the PCM G103 and G105 are in place and secure. I have read articles that say they are located behind each side of the back of the engine. I cannot seem to find them because I am not sure exactly where they are. Can someone please take the time to aid me in my current situation? I also even tried tapping the side of the PCM while the car was running to see if it would effect the car or throw odd codes as the book suggest. The car idles smooth and runs great. The gas was not at all that great before I replaced the old spider. I was only getting 11 to 12 miles to the gallon. I just recently replaced the old spider so I have not been able to see how many gallons to the mile I get yet.

 

You should do a cylinder leakage test. Pressurize the cylinder with compressed air when its at TDC on the compression stroke and then listen for air coming out the exhaust or the throttle body.

Have you checked cam retard?

 

Camshaft retard must be within spec for cylinder misfire detection & identification to be accurate. There is a GM technical service bulletin that addresses misfire, typically under load, (uphill etc). The cause is valve stem clearance is not sufficient, and the valve can stick in the open position intermittently. The TSB instructs to hone the valve guide approximately .002

As Burned mentioned above, a cylinder leakage test might be helpful to diagnose the issue. Keep in mind that when you apply compressed air to the cylinder, the piston is forced, (pushed) down to BDC, (bottom dead center) and both valves are closed.

Edit: it doesn't matter which stroke the engine is on: both valves are closed when the piston is at BDC.

 

Thank you Captain Hook and burned. I will check these things in the next few days. I will keep you posted on my findings. I have read and learned a lot about these Blazers over the past few months. I have not heard about the test you two posted about. Thanks again.

 

If I do infact hear air escaping, what does that mean I must do or have done next? Thanks.

 

With compressed air connected to the cylinder: If the air is escaping from the tail pipe, the exhaust valve is not sealing/closing. If you hear the air at the throttle body, the intake valve is not sealing/closing. Either way, the cylinder head must be removed to repair the problem.

 

Thanks Captain Hook. May I ask, is that any different then doing a compression check? I did a compression check earlier before I ever posted this thread and I got between 170 and 180 PSI on every cylinder. I was told when I purchased the vehicle the owner had the enginer overhauled. Thanks.

 

In very basic terms, a compression test tells you about your engine's ability to generate cylinder pressure, and a leak down test tells you about it's ability to hold pressure

 

^^^^ perfect!