Thanks Captain. I'll go by Advance Auto tomorrow to see if they can retrieve my fuel trim percentages.

 

Operating temp, at idle, in park or neutral, closed loop operation. Check them again at 2000 RPM. Need both banks, STFT and LTFT.

 

It looks like I'll have to take the Blazer into a shop in order to get the fuel trim readings. O' Rielly's, Autozone and Advance Auto only use readers and not scanners.

This is a copy of a post I found while searching the internet for more whys to diagnose a possible fuel delivery issue.

"There are 6 injectors inside the plenum. The connector for the injector pack is accessible without removing the plenum. In the injector connector, the pink wire supplies battery voltage to each injector when the ignition is in the RUN and CRANK positions. The ECM supplies ground to each injector sequentially to fire them. Make sure the pink wire has battery voltage to #6 injector. The ground wire for #6 cylinder is yellow with a black stripe. It should pulse ground while the engine is running. A Noid light will confirm this. OEM/6 pcs. noid light set (27161) | Injector Signal Tester | AutoZone.com

If that checks out OK, the technical difficulty level goes up a step. Disconnect the injector electrical connector and check injector resistance. If resistance is good, remove the plenum and carefully remove the plastic poppet valve to #6 cylinder from the lower intake manifold and direct it into a jar. Connect the fuel lines to the injector pack and cycle the ignition to pressurize the system, don't crank the engine. If you apply battery voltage to one terminal of the #6 injector and momentarily ground the other, the poppet should spray fuel."

I know I no longer have poppet valves (new injectors) but is this something I can do on my Blazer?

 

Sure! Check all of the pink wires for battery voltage. You can pull each injector out (new style are a pita to get out) of the intake and momentarily ground each one and check for spray, and spray pattern. No dribbling allowed, should be "digital" on and off. Seems like I remember reading somewhere NOT to use a noid light on CSFI though, and DEFINITELY not an analog volt meter, digital is OK.

 

So firestone ran a diagnostics test on it and they came up with +7.6 per. and -1.8 per. on the other bank. They are thinking its a distributor problem. This is the one part I don't believe I replaced.

 

Fuel trim percentages rely 100% on accurate oxygen sensors. Fuel trim tells if a bank, (one side of the engine) is running rich or lean. It does not tell which one of the 3 cylinders has a problem though. It's an overall average of the 3 cylinders. Ideal fuel trim is zero percent, and anything under 10% is considered acceptable. When it gets close to the maximum, (25%) a fuel mixture DTC will be set. The numbers indicate the percentage that the PCM is adjusting injector pulse width to bring the fuel mixture back to stochiometry, (14.7:1 perfect fuel mixture). A positive percentage means the cylinders are running lean, negative percentage means the cylinders are running rich.

On the scan tool, this is how they are listed:
STFT bank 1 .... X%
STFT bank 2 .... X%
LTFT bank 1 .... X%
LTFT bank 2 .... X%

From the numbers they gave you, there isn't enough data to determine which bank has the problem. Did they give you a print out? If so, please post it

The +7.6% indicates that one of them is running a bit lean. The -1.8 is running rich, but darn near perfect. If we had all of the numbers, we could determine which bank has the problem. If it's bank #2, chances are #6 is the problem. Replacing the distributor would be stretch, more likely a vacuum leak or a restricted injector nozzle is causing the problem.

Just an FYI: AC Delco, Delphi and Denso oxygen sensors have the fastest switching speeds and are the most accurate. Bosch sensors tend to switch slower but their accuracy is acceptable.

 

I just called Firestone. They do not have a print out, they just typed into the computer +7.8 for Bank 1 and -1.8 for Bank 2.

I did notice when I replaced the lifters how clean the intake runner was for #6 as compared to the other 5 ports. All them where pretty black but not #6, it was almost too clean.

 

That still doesn't tell us if those numbers are short term or long term. According to that, cylinders 1, 3, & 5, (bank 1) are running lean. #6 is on bank 2 which is near perfect. We need an accurate and complete listing of fuel trims.

As for the clean runner: I've noticed, on every 4.3 that I can remember, that #5 & #6 are cleaner than the others.... not sure why though. The only thing I can think of is #6 air inlet is on the driver side, which makes it the farthest runner away from the EGR discharge tube inside the plenum. Theoretically they should all be the same, but they're not.

Edit: Knowing the crosscounts of the oxygen sensors would tell us if the sensors are switching fast enough.

 

Well, I went ahead and replaced the distributor - it definitely smoothed out the idle more. I also noticed how the older one had a bit of play in it whenever I twisted the rotor and the new unit actually lined up a few degrees in advance to the mark I placed on the firewall. However, I still had the check engine light so I decided to replace the o2 sensor on bank 2. Shortly after driving the truck for a few miles, the CEL went off and I noticed the idle at the traffic lights where almost completely smooth!

I'm going to drive it the next few days to see what happens. I'm crossing my fingers! After all I've replaced, the dizzy, cap, wires, plugs, injectors, lifters, MAP sensor, IAT sensor, IAC valve, TPS, two o2 sensors, catalytic converter, all vacuum lines, and on and on the list goes.

 

Well sounds like you made some incredible progress on getting things in order and it paid off.I`ll keep my fingers crossed with you