misfiring

[86charcoalsierra]

I got a 86 gmc sierra with the stock 305 it recently started to miss fire when i step on the gas it has only been about 2 months since i changed the spark plugs i changed the spark plug wires and the distributer cap but it still misfires what else should i check.

[zieg85]

Misfire, do you mean a popping sound?  Could mean a lobe down on the cam.  One of the spark plugs could be bad as well unless when you changed them the problem didn't go away... My $.02

[Irish_Alley]

make sure a plug wire doesn't have a bad connection, could of had a good one but just popped off

[VileZambonie]

Go through and double check everything in the ignition system. Plugs, gap, wires, cap, rotor, firing order, timing. Is it backfiring or misfiring?

[Irish_Alley]

if it is a backfire wheres it coming from carb or tail pipe?

[86charcoalsierra]

It sounds like it is backfiring from the tail pipe.

[1980c10]

check the wires (inside of your distributor) leading up to your vacuum advance.

[Irish_Alley]

Check all you wires. Is it only when you get on it?

[86charcoalsierra]

It does it when i get past about 20 mph if im just cruising slow it runs good but when i push the gas it starts to misfire.

[Irish_Alley]

Did you change the rotor

[1980c10]

sounds like it is misfiring when the vacuum is pulling on the vacuum advance causing the wires inside of your distributor connecting to your vac.-adv. to seperate. this is a very common wear point. take off your dist cap and rotor and you will see what to check.