4.3l v6 No Power after 40 mph

2000 chevy silverado 1500 with the 4.3l v6. Sat up for 10 years at my dads. Flushed all fluids, changed fuel pump and filter, got it running. Then i took the road test, 1st, 2nd, and 3rd gear rev up fine, a little sluggish, figured age, but 4th i had no power and 5th wanted to stall. Putted around town in it, and 3rd started to lose power. Now it doesnt even get above 40 mph after changing plugs and wires due to codes i pulled. Cleaned the egr and throttle body, low end torque is where it used to be, comparable to new, but still no power at 35+ mph. Not a clogged muffler, but maybe a clogged cat? Also if i remove air intake it runs ROUGH and if i apply gas, it stalls. Im thinking injectors or cat. Any thoughts would be greatly appreciated, thanks.

Seems like a clogged cat. Is the CEL on? Has it thrown a p0420 code? If the cat’s clogged it probably isn’t working very well so I’d expect a code. If no CEL…

Check to makes sure some rat family didn’t make a nice home in the exhaust over the 10 years it sat You may have crammed a bunch of nesting material, and a corpse or 2 from the cat to the tailpipe bed when you fired up the engine. Unhook the exhaust after the cat and drive it to check if that fees it up. At least you can get a peak into the cat then, too.

Injectors are a possibility but they would tend to get a little better as fresh gas runs through.

CEL was on and blinking. I dont know the exact code, oreily guy said misfire on cylinder #5. Went away after i changed plugs and wires, but came back on after test drive. A buddy said might be Mass Airflow Sensor, disconnected it and reset computer. Drove around the block and no CEL has popped back up.

I did pull the muffler and there was no change.

When a Check Engine light flashes, it indicates a major misfire is occurring.

And a major misfire can destroy a cat.


My vote is for a clogged converter.

You stated you pulled the muffler. That is not the converter.

This could be easily checked with a vacuum gauge.