Some time back, you reported: "I get no misses or skips at idle or free reving to any rpm and holding it there.I also ran a tank of fuel out yesterday and filled up at a different locations just to take that out of the equation.Since our area started with the 10% to 15% ethanol blended fuels,I can't run anything under premium 92 or 93 octane without having serious spark knock."
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Adding ethanol to the mix will raise the octane to my knowledge as the ethanol puts out less BTU/volume, and would work better with a higher compression ratio. Again, what I've read.
You should not have spark knock with 87 octane with <=10% ethanol.
It runs smooth at idle and will rev up smoothly, per above. Only when you put a load on the engine does it start to mis-behave. When you put a load, it will demand more fuel, which it was previously getting in buckets. Once you replaced the FPR and the O2 sensors you said it ran better, but not quite right.
Does it still pour out black smoke? Not as bad.Occasionally under heavy load it will barely put out black smoke.I had to follow the truck to see it. Get 9 mpg(or ?) vs the normal 300+ per tank?I am up to 250 miles to a full tank.
Have you checked the TPS for good resistance as it could be misleading the computer, so it would not know the proper amount of fuel to flow? I don't have the specs and my Chiltons service manual don't have anything on it. In most cases, 'falling on its face' is a fuel delivery problem or a MAF that is lying to the computer or has 'stuff' on the wire(s) that biases the reading.
A good smooth idle cannot be produced with bad valves / rings, etc. So the basic engine should be good. You replaced the belt, but I never heard that you had checked for the triangle on the cam sprocket to be 'at' the pointer behind the belt cover at TDC. Is it there? The cam,crankshaft,and oil pump are all timed properly.Triple checked. If not, you'll have an engine that runs poorly, or will be gutless until it reaches higher rpm. If you have checked it, ignore, but if you haven't, it is definitely worth while. When I have done these, I found I had to rotate the crank a couple turns after install to make sure all the 'slack' got on the tensioner(water pump) side of the belt, otherwise things didn't work right. I also tried to set the timing (dist) and must have missed the 'static' window advertised where the SPOUT jumper could be left in. Re-time, and the difference was amazing.
Don't give up. It has served you well for a while, and doesn't deserve to be squished. If not you, then someone would get good use, and maybe be very happy.
tom