misfire on my GMC 1993 4.3 truck?

Check the inside of the distributor cap and the distributor rotor. I'd replace both of them before the knock sensor as they can cause misfires and trigger the knock sensor code.

Hi so it is the ignition timing which is out of adjustment. this might very well be the distributor and wear.

Post the code, they rarely mean the sensor is bad. More often they're simply doing their job and reporting the real problem.

Also, what's the 8th digit of the vin #?

You say you did a "tune up" but no cap and rotor? Gotta love that generic tune up term.

"You'll keep guessing unless you start testing!"

What are the compression readings?

Fuel pressure?

Vacuum test results?

Doubtful the distributor cap is the culprit, but it could be. Once you eliminate the miss, the knock sensor code will most likely go away.

knock sensor is not part of routine tune ups. you're going about this the expensive way.

complete the ignition tune up. rotor and cap. likely the anti knock issue will go away as distributor cap/rotor damage/corrosion does allow for spark jump.

also ensure the advance fly weights return the distributor pick up plate after hand turning it via the rotor. to ensure the springs are doing their job. little shot of WD-40 through the pu plate to the fly weights won't hurt either.

there's a knock sensor tool that can be employed to test those. just a rattle type pen, touched near the sensor to fool the sensor. likely local auto parts store has them in stock.

air leaks, another issue that causes the anti knock sensor to activate.

also check all vacuum hoses/tubes/fittings for air leaks. me thinks (not sure) this is a break year for TBI vrs EFI. on TBI set ups, you have some of the same types of air leak issues as a carb set up. so re-torque all fasteners on the TBI-save set screws and ensure the TBI base mount bolts are properly torqued. ensure the intake bolts are also secure.

further, this is OBD1. though it maybe somewhat limited, reading codes, interpreting them properly, can be key. go to autozone.com, sign up. totally free to sign up and use. enter vehicle info under "my vehicles, go to "repair help, look under emissions, go to reading codes and learn how to make the system produce blinks that can be counted, converted into info. that's how this system can be read w/o a scanner tool. paper clip can act as a terminal jumper.

caution,

make no adjustments to anything till all is done. do not want to adjust things to faulty conditions. I see more of that compounding issues than anything else. test all components in Q b4 replacing them.

good luck.

The 4.3 in that era was notorious for the EGR valve sticking open.

You should replace the mechanic with someone that uses diagnostics to locate the problem rather than a parts replacer.

I think you need an engine tune up.