Thanks for the clarification on the vacuum lines to plug and the routing descriptions-- that was very clear! I did, and hopefully other did the same, plug everything up like recommended in order to isolate the air coming into the throttle body after the MAF. I utilized my scantool and watched the short and long term fuel trims. They performed just like they do when everything is connected. I then took some propane with a hose attached and went around the entire intake manifold and up around the throttle body. The idle never changed and the fuel trim numbers continued their consistent pattern and eventual escalation.
I also looked at my O2 readings and they were in the low-voltage area but fluctuated like they were getting good signals; no flat-lines or extended values. The rate at which they updated was very fast and I don't believe that either bank ever reached the upper-most voltage indicating a rich condition-- correct? If .5 volts is the median then they were consistently below that in the lean range...
I also have the ability to actuate some specific functions like the EGR valve. At idle it read 0% and it never moved. However, when I made it go to 10%, and even 20%, it didn't make a difference with my fuel trim numbers. The EGR was also, at times, slow to respond and sometimes it even dropped back to 0% despite the scantool actuating 10-20% open. The idle quality did fluctuate some but not my fuel-trim readings. Perhaps the Pintle is stuck open a little?
My injector pulse width was consistently around 4.4-4.6ms for both banks...

Fivspeed...
Any new reading on your end? Have you isolated your problem area(s)? Perhaps we can find the solution to our situations with the assistance of this thread and by teaming up by comparing our numbers... I hope that I'm not walking on your toes! Definately not my intention!!

 

I'm happy to have two mechanically inclined people bouncing ideas off of each other about a problem very similiar to mine. I don't mind at all.

I haven't had a chance to do much with it, nor am I really skilled enough to really dig into it at a fast pace. I will say though that when I unplug the EGR, it makes acceleration noticably smoother. I still have a huge bog on the first press of the accelerator of the day and I still notice some stumbling during driving, just not as pronounced as before.

I also took a double look at my air pump and it appears to work correctly; runs for about 20 seconds upon startup, found the air intake for the pump and its pulling a good amount of air (more than I expected). All the hoses are intact and I double checked the hoses going to the exhaust manifolds and not exhaust is leaking back into the hoses.

On a side note, the only I/M monitor check that hasn't completed according to my scan tool is for EVAP. I might not find that odd except that I have never had a pressure release/vacuum when unscrewing my gas cap. Seems like every other car I've owned would have some sort of pressure/vacuum release when I remove the gas cap to put gas in the car.

Thats all I have for now. Keep the ideas coming.

 

Fivspeed, the note on the EGR valve is interesting. Have you thought of fabricating a block-off plate as a temporary means of removing that potential problem area from the diagnosis? Some 18ga sheetmetal, metal sheers, a drill, and a gasket is all that is really necessary. Stack them up as follows: gasket, plate, gasket, & egr valve to effectively seal off the EGR system. See how it runs then. It will trigger a CEL, setting an Insufficient EGR flow code (or something to that effect), but it is a valid diagnostic approach.

The note about the EVAP monitor brings up a good point though. It too gets its vacuum source from the intake manifold and, if there were a problem with that system, it could be allowing more air into the engine than the PCM is seeing. Disconnect the line to the EVAP purge solenoid (near the ignition coil) and plug off the end at the solenoid. See if that has any impact on engine operation.

 

Any new information or results here? I have attempted a couple of things and thought I'd share; and maybe receive some feedback. I did a vacuum test with a gauge connected to the PCV line to read intake vacuum-- it read 18 and stayed dead-solid; no vacuum leaks. I then plugged the pcv valve and plugged the breather and attached a vacuum gauge to the oil dipstick-- no vacuum; actually a little pressure so apparently no lower intake leak. My ltft-- both bank 1 and 2-- are still upwards of 16% and the stft remains most consistent in the positive area. However, after recording my o2 values on a graph with my ltft values in the same graph, my o2 readings are actually more consistent in the 'rich' area above .45 volts. That seems odd and I'm wondering if the VCM is bad due to the fact that, if my o2 are reading correctly, then the stft and ltft should decrease (lean out) with the high o2 values. But they're not. Perhaps the computer isn't in control of the fuel trims based the 02 values for some reason. Fivspeed, do you get the same results with your o2 readings plotted with the ltft values? Swartlkk, have you ever experienced this? Thanks all!
By the way, my Blazer does not have the K18 RPO for the Secondary AIR Injection for some reason; if that makes any possible difference.

 

If the O2 sensor readings contradict the STFT & LTFT values, then there is either something amiss with the O2 sensors or the PCM.

Have either of you tried to induce a lean or rich condition? If you were to purposefully disconnect a vacuum line with the engine running, you should see the O2 sensor average drop below 0.5V while the line is disconnected which would be a lean condition. With that same vacuum line disconnected, spray carb cleaner into the line. This should cause the O2 sensor average to rise above 0.5V in response to a rich condition. If either of these two tests does not result in the suspected outcome, then there likely is a problem with the O2 sensor(s) (which ever sensor does not respond as expected.

Another way to check the O2 sensor response, independent of the PCM, is to back probe the sensor reference & return wires, connecting the test leads to an oscilloscope or to a DVOM & raise the idle speed to 2000RPM. Watching O2 sensor trace at idle can be somewhat misleading since the lean to rich & rich to lean transitions occur over a longer period even with a properly functioning O2 sensor. A scan tool capable of bi-directional controls helps here as you can command the engine to 2000RPM instead of manually holding the throttle & observing engine RPM.

Here are some how-to's from Youtube for ya:
http://www.youtube.com/watch?v=-SuVs4T-c_I
http://www.youtube.com/watch?v=24Rp7BghSLM

Good for some comedic relief as well.

 

Thanks swartlkk for the video links as well as your thoughts. I already replaced both oxygen sensors with Denso o2's. I did so in the thought that they might be contaminated on the outside and therefore wouldn't be reading the ambient oxygen levels correctly. However, based on my Autoenginuity graphs, they are performing much better than the old ones that I removed but they still graph in the 'rich' area on a more consistent basis than the 'lean'. I drove it for about 30 minutes in the record-mode and chose a number of different parameters in whch to graph; b1s1, b2s1, rpm, stft 1 and 2, ltft 1 and 2, tps, maf, iac desired, and iac position. I do have those graphs saved and I can view up to 4 sensors in 1 graph. It really seems as though the PCM is disregarding the o2 sensors and not 'learning' the fuel-trim based on the o2 readings. Is this possible? Also, I have noticed that the ltft's begin at 7.69 and they do not go back to 0 at the new ignition cycle. They also will not reset with the actuation command from the scanner software. Perhaps they aren't supposed to...

 

What you are seeing through the scan tool is what the PCM is seeing. The reason I stated to test the sensors is that perhaps there is a problem with either the sensor reference or return that is causing it to misreport to the PCM. Perhaps not and it is a problem with the PCM itself, but you first need to see if the sensors are doing what they are supposed to do in response to a force lean/rich condition that you initiate. This may require removing the wires from the connector using the appropriate weather pack terminal disconnect tool in order to force the reference to ground and then monitor the return with an oscilloscope or multimeter.

And the LTFT's are stored values so it makes sense that they would persist after an ignition cycle. It does not make sense that they will not reset to zero if doing a full reset.

If it does turn out to be the PCM, go with a PCMforLess, Wait4me, or BlackBearPerformance tune and just trade your PCM in for one that is already reprogrammed for your truck, performing the CASE relearn when you get it.

 

Hello again,
I had some time tonight to try the forced vacuum leak and carb cleaner thru the vacuum line test. Both made the 02 sensors behave correctly; low voltage with vacuum leak and high with carb cleaner. However, I also tried unplugging the fuel pump power connection at the pump to see what my voltage was. My wife turned the key on, obviously with the engine off, and the voltage was in the neighborhood of 11.97 or so. When she turned the key off the voltage went up to the neighborhood of 12.35. I had her do this 3 different times and the results were the same. Perhaps the pump is getting too low of voltage at operation and thus not getting the correct pressure. I'm not sure what the running voltage is because the pump was unplugged. Am I on to something? Fivspeed, what voltage are you getting at the pump? Have you checked? Swartlkk, any input on these developments? Relay issues? Thanks!

Update: I put my voltmeter on the battery as I turned the key on and engine off. I got the same readings as at the fuel pump; 11.97. When I turned the key off I got the same readings as at the fuel pump; 12.35. The headlights apparently took the .38 or so volts without the engine running. When I turned the headlights off the battery voltage jumped back to the 12.25 or so volts. Therefore, I believe that my voltage at the pump is indeed correct. The alternator is putting out 13.98 volts at the battery when the engine is running. Now what? Frustration sets in... haha

 

This one runs a red flag up the pole.... Ignition timing in negative degrees means timing is ATDC, which should never occur. Basically it's telling you that the ignition timing is retarded. On this engine, "ignition timing" is not adjustable however, there is a "work around" if camshaft retard is not within spec. After the intake gaskets were replaced, did you check/adjust camshaft retard? Should be zero degrees plus or minus 2 degrees.

DTC P1345, (crankshaft to camshaft correlation) will not set unless camshaft retard is off around 24 degrees or more, (basically one distributor tooth).

 

Captain Hook,
Thanks for your input on this thread. Fivspeed and I seem to walk parallel paths as I just returned from a brief highway trip with my scan-tool recording my spark-timing along with my rpm's. I too have 2 instances where the timing dropped to -10 and that is precisely when the fuel was shut-off during rapid and prolonged deceleration; both times when exiting the ramp off the highway. My 73mph, 2100 rpm 'cruise control' driving yielded a consistent +41 spark advance. At idle-- about 650rpm's-- I have timing advance of +16 to +20. The lowest, besides the -10 readings, was +12 during high acceleration. Odd?