for the record my 3 blazers are not all the same year. I just gave a generic 60PSI as once there was a poster here that said 40 PSI was where it should be

 

BTW, Graveyard, how did we determine that this misfire issue is fuel related, and not ignition related?

Did you run any diagnostic tests with your scan tool? Generically, scan tool = single purpose scan tool or (app on (pc or tablet or phone) connected to OBD-II port by (cable or bluetooth device or WiFi device)).

 

Well, I really have just been asking but it seems that these vehicles have fuel issues.
But, last night I was just driving down the road at 45 mph and the truck just stopped running. It didn't jerk around or stall or misfire, I wasn't even sure it had stopped at first.
I was still rolling down the road, I slipped it into neutral as I was rolling and tried to start the engine...no dice. As I called my wife and it rolled to a stop it all of a sudden started back up. I drove it home and got my main ride.
That seemed electrical or like it lost fire.
I also have tested the obdII and haven't seen anything but an egr code. I forgot the code number off hand.
Later

 

He went down the fuel pump testing road because of my suggestion to his observations. But I think he got hung up on meeting a pressure spec at idle. I still want to see dead ended fuel pressure or at least a volume measurement before moving on to other things. To me it seems the logical way to diagnose things. I think that hitting him with too much at once will only discourage and confuse. Please, lets get past the fuel pump before considering all the rest. It's a common problem.

 

Agree if you ask for help, follow us. We've owned these truck for a long time. Please don't ask for help and the do your own thing.

 

Did you see my "keyboard duster" diagnostic recommendation above? When it fails, squirt the iggy module first, see if that fixes it. Then the crank position sensor, try again, and finally the coil. Cooling one of those might resolve the issue. You actually hope you find it while it's still "intermittent" before it completely dies.

You were also looking at OBD-II live datastream items, like misfire counters.

You can use that feature of the scan tool to watch other data as well. A useful diagnostic screen when you have misfires, and are trying to determine whether it's fuel related or ignition/timing related is to look at the upstream O2 (A/F) sensors, and the long term (coarse) and short term (fine) fuel trims. For the O2 sensors (bank 1 sensor 1, bank 2 sensor 1) a graph is the most useful. For the fuel trims, raw numbers or maybe "gauges" work best.

Start the engine and let it warm up while you set up the scan tool for that data. The O2 sensor graphs should settle into a normal rhythm of waves. The quicker they oscillate, the better. A couple times a second is good. 2 seconds between peaks is getting bad.

Take your display where you can see it and work under the hood. Don't put it where it can fall into the fan, though. Don't ask me how I know that. Introduce an "unmetered air leak" by pulling the PCV hose off the intake air piece over the throttle body. The vacuum hose to the brake booster can also be used as a "test leak." That should disrupt the rhythm of the O2 sensor waves, and it should go in the "lean" direction for a second or so, then the fuel trims should go more positive to correct for the unmetered air and the O2 sensors should fall back into a "normal rhythm."

Now, introduce some unmetered fuel. Spray some "intake/throttle body cleaner" into the hole in the air pipe where the PCV hose was connected (or into the manifold fitting if you removed the brake booster hose). Watch the O2 sensors. Give it about a one second long squirt of the cleaner. The O2 sensor voltage should start with a big move in the other direction (rich), and then maybe cycle once or twice, go lean for a bit and fall back into the normal rhythm. As that happens, the fuel trims should first go down (ECM pulling fuel out to keep mixture correct in spite of the "added unmetered fuel") and then return to what they were before you squirted the cleaner in.

Put things back together, get your scan tool, close the hood and get someone to drive for a test drive while you observe the scan tool. When driving, the O2 sensor graphs won't be as fixed rhythm. They'll be doing a "wacky dance" and so will the short term fuel trims. The long term fuel trims should move a little, but stay in a fairly narrow range.

When the misfiring condition presents itself, look at the O2 sensor graphs and the fuel trims. If the misfire is caused by a mixture issue (lean or rich misfires), the O2 sensor graphs will be "stuck" in one direction (lean is more likely, but rich is possible). and the long term fuel trims will probably be high (lean condition) or low (rich condition), not moving around.

If the O2 sensor graphs continue their "wacky dance" when it's misfiring, then the misfire is much more likely to be ignition or timing related, not fuel related.

 

Well, not meaning to sound like an ars hole but I have followed the advice of this forum extensively so far and I appreciate the help. But, there is still issues that are difficult to chase down over the internet. I paid fair price for this truck and have probably thrown in another grand so far. I'm just looking for an end to this problem. As nice as these are in the winter time, I would just sell it. But I'm the type of person that's now going to unload my crap on someone else.
Anyway, like I said earlier, I'm not mad at anyone, I'm just tired of throwing cash at this little ride...lol
Later

 

Racer X and Les, I'm going to start driving with my tablet and obdII adapter running and the software running as I tool around the countryside. Maybe it will catch something interesting. Would there be any type of gauges that I would need to create other than the 6 misfires and my cmp retard offset? I suppose I'm done with the retard gauge for now.
Thanks everyone!
please don't think I was trying to **** anybody off with my rant.

 

If CMP Ret is correct and stable, you don't need it.

Look at the post above. I'd set up 2 graphs and 4 gauges or numeric displays. The graphs are for O2 Sensor (or A/F Sensor) Voltage (bank 1, sensor 1 and bank 2, sensor 1), and the 4 gauges are for Long Term Fuel Trim (bank 1 and bank 2) and Short Term Fuel Trim (bank 1 and bank 2).

I outlined a couple of tests under the hood, inducing a known lean condition and a known rich condition. Don't skip those. Those tests do two things for you. You are applying stimulus to the sensors and verifying that the sensors respond, and that the ECM interprets the data properly and makes the appropriate responses (increased fuel trim for lean condition, reduced fuel trim for rich condition). It also lets you figure out which way is "lean" and which way is "rich" on the graph. I'm nearly certain that a 1996 model has O2 sensors and that higher voltage = leaner mixture. I'm only a coin toss on whether your app tries to "help you" by displaying things inverted, so it looks more like an A/F sensor.

When you have it running with those gauges, it would be helpful to know how quickly the O2 sensors are oscillating. Look at the time scale on the graph and count the number of peaks. Report back "__ peaks in __ seconds" for the "normal rate" at idle. You can also run it up to 2500 RPM's unloaded and let it set there until a "normal rhythm" sets in and see if it's the same at higher RPM's.

Since you're using an app on a tablet, the "voltage" shown for the O2 sensors will most likely be on a 0-1 scale and won't be actual volts you'd see with a volt meter. That (mostly) doesn't matter. When you're trying to find a mixture issue (lean or rich running conditions), it matters which way the graph goes for rich conditions and which way it goes for lean, and how quickly it oscillates, and that it's 50/50 rich time/lean time under constant operating conditions, and how it oscillates and what percentage of the time it's on either side under dynamic conditions.

The long and short term fuel trims are almost like the hour and minute hands on a clock. Long term is the coarse number (like the hour) and short term is the fine number (like the minute).

It wasn't really intended to be that way by the designers of the OBD-II specs, but most implementations use those data points in that way. Unfortunately, most scan tool developers scale things and sometimes display things as though the intent of the design is the way things really work (it's not). That makes figuring out "total fuel trim" a bit of a black art, even if you have both display numbers from some scan tool.

Hopefully Les can help you setting things up. It might also help to "record" or "log" this data.

And don't forget to carry some keyboard duster/electronics duster/aerosol refrigerant.

OK, I'm also not trying to be disrespectful. However, Graveyard doesn't have a pressure gauge set (he borrowed/rented one at O'Reilly's and returned it), and didn't measure the pump output pressure direct to the gauge. We don't know that number.

Your hypothesis is this: He's got misfires -> Misfires can be caused by lean mixture -> Lean mixture can be caused by weak fuel pump. Therefor, best diagnostic test is test the fuel pump.

I get that. He doesn't have the tools to measure the fuel pump output pressure right now. He does have the tools (scan tool app, bluetooth OBD-II adapter) to measure/test for lean mixture conditions. I was pointing out a way to test that, since he can do that with what he currently has. If the data from the scan tool say it's not running lean (based on fuel trims and O2 sensor data) when the misfires are occuring, it's not the fuel pump.

Also, his issues are changing and new symptoms and failures are developing. The new symptoms are sounding less like a fuel pump issue.

 

Wow, that's intense! Ya know I can blueprint a block but figuring out all the settings for ignition and timing and fuel input is a totally different animal. It would be much easier to machine a block to tolerances than it is to troubleshoot an engine...lol