Tbi 350 has no power on the road

I do own a scanner (modis edge) and can monitor reading from all the pcm imputs, my cousin is dropping off his 91 suburban for me to compare the data inputs from a known good running tbi to this one, I hope if I can find a big difference it might help lead me down a path to looking for say high resistance circuits. Ive already fixed 2 broken wires, one for the transmission input speed sensor, and another one that was behind the distributor, had all the insulation skinned off for about an inch, not sure what it was for, as there are about 30 wires in that bundle. Figured it may be bumping the intake at times. With the scanner im getting what seems to be normal readings but I'm just not 100% sure what the normal readings should be with some of these. Like the (knock) pid, just stays at like 8 if I remember, idk what that's telling me if that's supposed to be some sort of misfire counter or something... I'm hoping I'll find out a better path tomorrow, if not, I'll definitely check each one from your list. I'll be leaving for work again tomorrow night so I won't be with the truck again til Friday.

Oddballcreations said:

If there was a long-standing issue with running, which sounds like it might’ve been by the previous owner dumping so many parts into it. I would definitely check to see if the cats are plugged.

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There is no converter on it, guess previous owner sold it to pay for all the new parts he tried...

H2814D said:

All good advice so far. I know you said they were new, but I would closely examine every one of your spark plug wires. I had a similar problem a long time ago. I actually thought I was having a transmission issue, since it didn't seem to do it when in overdrive. Was a weird thing to diagnose. I replaced the wires and the problem went away. I think one or more of them were sending the spark to ground, instead of the plug.

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I can throw a different set on to make sure, that's a good idea though, I've seen a tiny pin hole ark to the manifold when I was in college, so who knows, the wires look very new, but I'll check it out...

Mitchell93 said:

There is no converter on it, guess previous owner sold it to pay for all the new parts he tried...

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Double check every ground strap and make sure they are actually all there . Anytime there’s some odd weird hard to track down issue it’s always a good thing to check . Had a friend that had this weird odd sporadic misfire did a lot of the same things and just started replacing every part he could think of but it just wouldn’t go away . Turned out someone had pulled the motor at some point and didn’t put Back on the block to firewall and the block to frame ground strap . He replaced both and no more misfire and it ran better than it ever had .

Mitchell93 said:

I do own a scanner (modis edge)

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I'm jealous. That's a wonderfully-powerful diagnostic tool.

Scan tool + graphing multimeter in one box.

Mitchell93 said:

my cousin is dropping off his 91 suburban for me to compare the data inputs from a known good running tbi to this one, I hope if I can find a big difference it might help lead me down a path to looking for say high resistance circuits.

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Not a bad idea to "calibrate" your brain using a known-good vehicle and then check your Problem Child.

Mitchell93 said:

the (knock) pid, just stays at like 8 if I remember, idk what that's telling me if that's supposed to be some sort of misfire counter or something.

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Sounds like a likely source of some if not all of the problem. If the knock sensor is sending false signal, it'll keep the ignition retarded trying to eliminate the knock...which kills power and economy.

But probably not so bad that you can't go more than 30 mph. I suspect additional issues.

A proper cranking compression test might be revealing.

My cousin never dropped his suburban off so that have to wait till next week, but I'm on to something...
With the knock pid, it reads 46 to 254 all the time, just stays at 46 and jumps to 254 so fast I would not see it if it weren't for the graff. It was stay at 46 with the engine off, The knock sensor pigtail was destroyed when I got it, I replaced the pigtail end with no change is its performance, but I just unplugged it just now, and the 46 fell to zero. Test drove it, and it drives the same, but that 254 flair up keeps happening

That's a problem. SOMETHING is screwed-up with the knock sensor circuitry.

Mitchell93 said:

My cousin never dropped his suburban off so that have to wait till next week, but I'm on to something...
With the knock pid, it reads 46 to 254 all the time, just stays at 46 and jumps to 254 so fast I would not see it if it weren't for the graff. It was stay at 46 with the engine off, The knock sensor pigtail was destroyed when I got it, I replaced the pigtail end with no change is its performance, but I just unplugged it just now, and the 46 fell to zero. Test drove it, and it drives the same, but that 254 flair up keeps happening

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Now you have some data that would correlate with the issues you are having. You need to validate that PID. I would go back to your spark plugs and look closely at the porcelain for black specs. It wasn’t clear in the pic you posted earlier. You mentioned the previous owner changed out quite a few components. Did you verify the fuel injectors are correct for your truck? Do you have any major exhaust leaks or loud ticking around the exhaust manifold? Is it a stock exhaust? Any rattling whatsoever on the motor? How did you repair the pigtail end? Splice/crimp, terminals? Test the knock sensor circuit.

JDGMC said:

Now you have some data that would correlate with the issues you are having. You need to validate that PID. I would go back to your spark plugs and look closely at the porcelain for black specs. It wasn’t clear in the pic you posted earlier. You mentioned the previous owner changed out quite a few components. Did you verify the fuel injectors are correct for your truck? Do you have any major exhaust leaks or loud ticking around the exhaust manifold? Is it a stock exhaust? Any rattling whatsoever on the motor? How did you repair the pigtail end? Splice/crimp, terminals? Test the knock sensor circuit.

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So for now I still have a different throttle body I had from a 91 gmc k1500, so it's the same year and same size engine, buy switching the entire throttle body I wanted too rule out fuel pressure regulator, because I had to order an adapter my fuel pressure gage kit didn't have. Also ruled out the injectors, doing that made zero changes in performance. As for the exhaust, the system is for the most part stock, with the catalytic converter removed, and a new muffler with a turn down before the axle. No noticeable leaks or ticking, I will be pursuing this knock sensor issue when I get home Friday. I would like to know though what a good knock data looks like... I replaced the pigtail with one I cut off a truck I got parked in the weeds, used a few extra inches of wire to cut back to good copper, soldered and marine shrink tube, I suspect there could be a intermittent short to ground, but will have to wait till Friday

It's not uncommon to see knock cnts here and there be it communication artifacts or real knocks. What's important is if you are consistently seeing knock cnts and/or they are increasing - i.e. enough to change spark advance. You need to monitor multiple PID's under various conditions to make sense of it. See attached example