Troubleshooting help

[Stephen7891]

I have a 91 c1500 with a 305 that is spuddering when under load. It idles fine and even revs fine in netural but when accelerating it begins to spudder and seams to missfire. Ive replaced the plugs and wires, o2 sensor, air filter and fuel filter i am thinking it is the old cat that is my problem but didnt know if it would make that big of a problem because this problem occured instantly and not slowly. Any advice would be appreciated before i go and cut that cat off to see if its the problem.

Thanks

 

[bowtie-72]

Vacuum leak? Sometimes a vacuum leak will act like this.

 

[shorepatrol]

any codes?

 

[PlayingWithTBI]

Vacuum leak? Sometimes a vacuum leak will act like this.

x2

If you can rev it up fast in neutral, it's not the cat. A plugged cat will slow fast revs. Check your initial timing with the control wire disconnected, s/b 0 BTDC, sometimes you can advance the timing up to 10* BTDC depending on your set up, a quick and dirty way instead of modifying your SA tables in the bin file. Fuel pressure should be 11 - 12 PSI min. If pressure drops during acceleration you may have a bad pump or filter.