my 1997 4x4 vortec 4.3 idles very rough, no engine light on, but puts out black smoke when punched in park. Poor gas mileage--new at this game and not too bright either. Can this be egr or mass air flow censor? Thanks

 

Sounds like it could be a plugged cat.

 

thanks for reply---Just bought truck had it certified and shop said cat was OK?

 

so..............are we gonna welcome this one to the fun round here, or what?

 

fun round?

That sounds like the same thing i was going through a few weeks back. mine was a plugged. cat. the same thing happened to me. swartlkk pointed that out to me, shop said it was cool, replaced other crap, brought i back to the shop, demanded a second opinion, what do you know? plugged cat...

could also be: bad plug wire
fouled plug not burning off it's portion of the gas
lazy/old/weak O2 sensor allowing more gas to get to said plugs...
hell even a loose/cracked dist cap can cause that.

all of which will cause more fuel to get to your pre-cat which in turn will help it to melt down and be plugged up.

try a second opinion at a muffler shop. they will throw it on a lift and give it a look-see for free if they are a decent shop...

or give it the old cat check love tap

if you think it is a bad egr or maf, those are easy to check. pop off the egr and scrub it clean, soak it, scrub again until shiney and new. put a new screened gasket on. even if it's not it, it will help later on.
as for the maf sensor, get some q-tips, alchohol, and be UBER gentle. it there are broken or missing connection, there you go! other wise, clean out the screen and shine up the sensors.

 

friggin' key bvoard! hell i need a whole new computer!

after changing the injector & poppets on Monday-which did improve the way the truck ran (power was up again), it's doing the same cap again today.

even checked the temp of the cat on Friday night when it started to get sluggish. was cooler @ the front, which is good, but maybe the damn thing is melted a little-have a bad O2 (can't remember if it's the one infront of or behind the cat that came up).

well, i guess i'm gonna pull the cat tomorrow, change that O2 as well. maybe just "test pipe" it, to test if that's the problem with the thing (have a deep dark feeling the engine is toasted, but i hope i'm wrong). we'll see.

 

so wait... are you spoilher?

the cat delete with straight pipe would be a good way to test the cat. also, just pull the bad o2 and it should run a little better (if the plugs are still good), you have already read and suggested the wire check (mist in dark method) before, so you should be ready to rock and roll with those 3 methods to check WTF is up then

 

I am currently replacing the spider on my 95 and tuning it up. It always run like a** but does not always throw a code or 3. You should look for a black build up on/in the tail pipe and also smell the whats comming out the tail pipe. Mine smells so strong of raw fuel that I could probably run my wifes Envoy XL fully loaded with the fumes.