G'day all!

Been trying to do some research on the forum to whittle down possible solutions. The vehicle in question is a 2003 Blazer LS, 4WD, 4.3L, approx. 150,000 miles.

Was driving the other day and the truck felt particularly sluggish. When I got to an open stretch of road, I gave her the berries to "clear it out" a little bit. By the time I came to the next stop sign, it was idling like it had a dropped cylinder, and the SES light was flashing. Ran very roughly all the way back home.

Took it to my dad's house, who used a Bosch OBD1350 to pull the codes. It was showing a large number of Cyl. #1 misfires, but no misfires on any other cylinder. For what it's worth, all six spark plugs (including #3), all wires, and the distributor cap were replaced in 2011, and the ignition coil was replaced in 2014.

Pulled the #1 plug. It was mildly oil fouled, but nothing earth-shattering. Replaced it with a new Iridium plug - still getting misfires on cylinder #1.

Checked the plug wire for resistance and continuity - got a zero reading on the multimeter. Just to be sure that we were testing things correctly, we tested the plug wire for the #5 cylinder, and everything seemed normal. So it appeared that the plug wire was bad, and not the plug itself.

Replaced the plug wire with new - still getting misfires on #1, but now we're also getting occasional misfires on #3. This is a new development, as the error code records didn't show any history of misfiring on any cylinder except #1.

Called it a day at that point, and we'll look at it again tomorrow. The plan is to replace all the wires with new, since I already purchased a full set. In the meanwhile, I wanted to see if anyone her has experienced similar problems that weren't fixed by the seemingly obvious remedies (replacing the plugs and wires). I'm especially confused about why we're now getting misfires on #3 now, when there was no history of it before. With two cylinders now misfiring, the truck is spitting raw fuel out the tailpipe and will barely idle (though it will smooth out a little bit if you rev the engine up to 2500-3000 rpm in Park).

 

You'll see on this forum that the fuel pump is the most common issue. However, in my experience, a flashing SES usaully is a secondary ignition issue. In your shoes, I would personally do a complete tune-up. It is important to use AC Delco parts for this. Somewhere on this forum you will find where one of the most experienced folks (Captain Hook) landed on non AC Delco wires that do just as well. But these trucks are finicky about the remaining secondary ignition parts, so I suggest you stick with AC Delco and stay away from iridium, etc. A complete tune-up in my opinion would start you out with a clean slate and personally I think doing it after 5 years wouldn't be uncalled for.

Then clear your codes so the fuel trims go back to their base and do a GM Drive Cycle test which you can find on the internet to see if any codes pop up. In addition do a fuel leakdown test which you can find in a sticky in this forum also produced by Captain Hook.

 

After much diagnosing, it's determined that I have a burned exhaust valve on #1. 90% leakage.

*Ugh*