1st a question in return:

- How has the damaged valve been taken care of? (How has it been fixed? - Valve, Seat, reshape seat, etc.?)
- Pulling the plug on #6 what does it look like now?

2nd a word of caution:
-Having no combustion in a cylinder but fuel injected will wash down the oil film on the cylinder which will lead to damage to the rings and cylinder in very short time.

3rd what I would probably do:
- No codes is at least something
- Make sure you correctly understand the sensor output. I'm NOT into the OBDII Blazers and do not have reference material on the 99. Try to get a hold on a knowledgeable source, the diagnostic and electrical manual (rockauto.com has them - and yes they seem to cost a fortune at some 150$ but are worth every penny)
- Make sure you get a grip on the readings of the O2. Some O2 sensors do actually a waveform pattern in the output voltage.

- Compression testing on #6? What is the outcome now?
- Spark on #6 yes/no/maybe?
- Combustion on #6 yes/no/maybe?
- Does the spark plug foul with fuel?
- Is it running rough? Maybe two ignition wires swapped?

That's my 5 cent at the moment.

 

A -11 fuel trim would indicate a rich condition so the computer is allowing less fuel. 11% is within the realm of computer correction. General rule is that if the combined trims are under 10% not to worry. The question is whether the computer was getting good information when it did the correction by leaning out the air to fuel mixture or whether a bad O2 sensor was causing it to do something that it should not have. O2 sensors are supposed to swing wide so it sounds like one one of yours is not performing properly. Do you mean one of your sensor jumps between .1 and .8 volts? That would be normal for a pre cat sensor. The sensor that is between .4 and .6 is the one I'd change. You could also swap them and see what changes you get.

I guess the $64 question is whether the bad sensor is on bank 2 and whether the computer withholding fuel because a bad o2 sensor caused the burnt valve. You can burn a valve by running too lean. My thought is that a legitimate fuel correction of -11% shouldn't have burnt the valve, but if the O2 sensor was bad and the computer was making a lean engine run even leaner, then, yes this could have been the cause of the burnt valve. Before you put ton of miles on the new head, I'd replace the O2 sensors until you see the swing between .1 and .8 or .9 on both up stream sensors.

 

Thanks for the input guys. I will be setting the crankshaft retard this weekend and going for a test drive and rereading the fuel trim and o2 sensors. I will also pull # 6 plug and read it. Then I will pull a plug on bank 1 and compare the it against a bank 2 plug. It is running smooth, but I want to double check everything so this does not happen again.

 

Ok guys, After working on it today, this is what I come up with. Set the crankshaft retard to -.002 ( close enough ). Ran compression check on # 6 and it came up 165 psi. Installed 2 new upstream ac delco o2 sensors and went for a test drive, came back and pulled the # 6 plug and it is a nice light tan. Pulled the # 5 plug on the other bank and it is the same. Hooked up the scanner and ran the fuel trims and o2 sensors and all came back with very little correction. Both o2 sensors were bouncing between 1 and 9. I am going to call this fixed unless someone disagrees with me. P.S.: add Launch CRP123 to the list of scanners that will read crankchaft retard.

 

Great - looks like you got that one fixed.

 

Thanks, Now on to the blower motor replacement.