Update...and needing a lot of help!..
OK, so I replaced the lower intake gaskets, and that apparently went well.
The distributor dropped right back into place, and I replaced the cap, rotor, wires, and plugs...all AC-Delco.
Installed the new MPFI upgrade fuel spider (Delphi), struggled just a bit with the lines, but that appeared to go together well also.
While waiting for the parts to be delivered I gutted the catalytic convertor, it had melted down. I do intend to replace it when the truck is up and running, and the bank account recovers.
The muffler does rattle a bit, but I don't think it's plugged..at least my initial back pressure test showed 0 back pressure.
But the truck is running very poorly; sometimes it will idle OK, other times it won't idle at all.
It won't accelerate smoothly, but it will run smoothly at higher RPM, around 1500~2000...sometimes.
I have a good scan tool (Matco Determinator), but I really have absolutely no idea what it's trying to tell me; it's like we speak different languages...

The truck smokes at times also, and it never did that before...but it's white smoke, so I don't know if it's fuel (should be black?), coolant (it don't do it all the time, and sometimes it smokes at startup, sometimes after warmup, so I don't think so..).
There was gasoline in the engine oil, not a lot but enough that I could smell it on the dipstick, but I did change the oil and filter before startup, and the engine don't make any noise at all, and the oil pressure gauge looks good.
I simply don't have a clue as to where to begin looking for the reason it won't run correctly.

Help me folks, cause I'm totally lost on this one.

 

Hey Red, you might want to start a new thread on this. Me thinks there might be a problem with the way the LIM went back together.

 

The injectors on the driver side are in order 2, 4, 6. But on the driver side they are not in order, just like plug wires in the distributor cap. Are you sure you have the injectors and plug wires routed correctly?

 

Yeah, I actually did have the plug wires swapped initially, but I just happened to notice it and corrected it.
I'm pretty certain that all the injectors are installed correctly.
The instruction sheet was pretty specific and detailed...not to say that I couldn't have screwed it up anyway.
But sometimes it runs great...albeit for a very short time.
It starts right up, and sometimes it'll rev up nicely and will hold at 2000~2500 and be very smooth....but most of the time not.

I really think I have a problem with the PCM....I have been struggling with the TPS code, and have followed the flowchart for P0122 and can't find the problem.
After the recent work, as I was test driving it I was able to watch the TPS voltage on the scan tool, and the stumbling definitely coincides with the TPS return volts dropping to near, and even sometimes complete 0 volts.
The strange thing is that every time I test the TPS with the key on, engine off, the TPS looks perfect.
But as soon as I start the engine, the volts drop to unacceptable levels, and the code gets triggered.
I have also had the ABS and Brake warning lights come on several times when it stumbles and runs bad....and I can't figure how that would be connected, unless the PCM is wigging out.

I really need to learn how to use this scan tool, and how to interpret the data I'm looking at.
It's like I said in another thread...I know it's trying to tell me something, but we seem to speak different languages.

 

P0122 is indicating a low input voltage. Most likely on the grey wire, but could also be on the dark blue wire. Connect a DVOM to the grey wire, with the key on, engine off it should show ~5 volts. Wiggle the TPS & the harness and tug on connectors, voltage must remain constant at the TPS. The dark blue wire should show ~.47 volts. Tug & wiggle it also, must remain constant. The black wire must show less than 5 ohms resistance to ground at all times, tug & wiggle that one too. When the scan tool is connected, key on engine off, watch TPS voltage while very slowly opening throttle to WOT, (wide open throttle) and back to idle. It must increase and decrease evenly, no drop outs. PCM's on these things are just about bulletproff and rarely fail.

 

Thank you for the tips.
I have tested the TPS with the key on, engine off many times (using the scan tool) like you suggested, and it has always been very smooth and both the volt and percentage readings on the scan tool have looked very good.
I even charted the voltage reading at 10% increments, going both up and down, and it looked really good.
And it was repeatable.
It's when I start the engine that the voltage, as seen by the scan tool, drops to a very low level.
The strange thing is that while the scan tool reads low volts, and the PCM triggers the DTC, a digital volt meter hooked up simultaneously shows good volts.
I had a Fluke 787 connected with the black lead connected to ground at the TPS connector, and the red lead connected to the TPS return connection at the PCM.
For quite a while, it would only set the code, but drive-ability was good.
But slowly it got worse, and now the truck isn't drivable.
But like I said, I watched the TPS voltage completely disappear as the truck stumbled and died.
I will do the test you have described and see what I come up with.
I'm going to do the P0122 flowchart procedure again and compare it with my previous results.
Thanks again for everyone's patience and assistance.

====================Edited to add====================
Any ideas what could cause the ABS and Brake warning lights to come on during these episodes?

 

Just for grins, did you physically inspect the grounds at the rear of both cylinder heads, and the one near the thermostat housing, for poor crimps, loose bolts etc? I've seen, more than a time or two, where the factory crimp captured insulation and didn't get a secure connection to the copper wire itself.

You've already determined the PCM is not seeing TPS continuously, you need to find out if the TPS, or it's wiring, is the cause.
With your Fluke: attach the red probe to the grey wire as close as possible to the TPS, and the black probe to a good body, or battery ground. Monitor the voltage when the engine acts up. Make sure voltage remains constant ~5VDC. Then do the same test on the dark blue wire at the TPS. This voltage will vary depending on throttle position, but should transition smoothly. Did you check resistance and do the "wiggle test" on the black wire? If so, what were the results?

 

my pcm went out but it was because it had a 12v wire shorting it out...

 

I looked at the grounds at the rear of the heads while I had the lower intake off, and tightened them up.
I couldn't get a real good look at them, but they appeared to be OK, but the left side was a bit loose, right side was pretty tight.
I have done the wiggle test and I'm fairly well satisfied that the wiring between the TPS and VCM is good.
And I did do a continuity test of the VCM ground wire from the TPS back to the VCM, and it tested OK.

I have actually had both volt meters hooked up simultaneously as follows:
Meter #1 - Black lead connected to the VCM ground wire at the TPS connector: (this was in an attempt to verify the VCM ground to the TPS was good) - Red lead connected to the 5v reference wire at the TPS connector: (this should have proven the 5v reference wire combined with the VCM ground wire, both coming from the VCM, were OK).
Meter #2 - Black lead connected to the battery ground, Red lead connected to the TPS signal wire at the VCM connector: (this should have proven the TPS signal wire returning to the VCM is OK).

During this test, both volt meters showed good voltage readings during both the key on-engine off and the key on-engine running tests.

But the scan tool consistantly will show good TPS response with the key on-engine off, but the TPS response goes downhill rapidly during the key on-engine running tests, and especially whenever I try to test drive the truck.

So it seems to me that the TPS is getting good reference voltage, and sending good return voltage back to the VCM...but once the engine is started the VCM gets confused and misreads the return signal from the TPS.
Does any of that make sense, or am I way off base?
And there is the issue of the ABS and Brake warning lights that show up when this occurs, leading me to believe the VCM is going wacko.

Back to the earlier questions regarding the possibility of crossed plug wires or injectors, this morning I had it reved to around 2000-2500 RPM again, and it was very smooth, and I didn't detect any missing or rough running at all.
No smoke either that I could detect.
But when I attempted to drive it, she fell on her face. Quite sad, actually.

 

Your test methods & results were spot on, excellent job.

For the P0122 to set, TPS voltage has to be less than .25VDC for more than 1 second.
Key on, engine off, what is TPS voltage?
Key on, engine running, what is TPS voltage?