96 Astro misfire?

[RedLance]

Greetings all!

I've got a 1996 Astro 2wd people hauler. I gave it a tune up with new plugs, wires, cap, and rotor. Now, it idles fine, but driving around town, it stumbles, and lags, unless I floor it, then it takes off like it should. On the highway, at 60, it lurches, and the check engine light has been on for months now. The only code it throws is a misfire on cylinder 3 ( i think, passenger side, middle cylinder). Once it threw a code for the air flow meter, but only once, way back when this all started.

Now, right after I changed plugs, I heard a snapping sound, and discovered that one plug was bad, so it's been replaced, yet the other symptoms persist.

Could this be the EGR? It's got 115,000 miles on it.

These symptoms didn't start for a little while after I changed the plugs...

I almost wonder if its the TPS, but I would think that would throw a code other then misfire.

Also, at about 99,000 miles, we had the fuel pump, strainer, and filter replaced.

Any ideas?

Thanks!
Brian

[tableman]

When doing a tune up on the Astros, you have to make sure all you spark wires are nested properly or you will get misfiring happening between the spark wires and the aluminium heat shield on the inside of the dog house.

Especially the spark wire from the distributor to the coil, there is actually a GM service bulletin that states that wire must run under and around the objects in the path rather then up and over, which is what most of us would do when running a new wire.

To verify if this is you problem, take the dog house completely and look closely at the inside aluminium heat shield, if this is your problem you will see little arc holes in the shield, that resemble and spot welding mark.

This happened to me after doing a tune up on my 1996 Astro. 2 weeks after the tune up it started misfiring, it took me a month to solve the problem. I only saw what was happening after in frustration took the dog house completely off to get more access to the engine, and as I set it down my eyes caught the arc marks.

[scottnhalifax]

another good way of checking for a misfire is to get a spray bottle of water and spray some water around the plugs and wires.
make it nice and dark and look for soarks jumpin around when you find them replace wires/ plugs causing problem. also di-electric grease works wonders on boots to make them easier to take off
scott