I have a couple of days off, so off comes the EGR again and this time a thorough cleaning, and see what happens. Thanks for the info everyone. I guess the up side to this is that I am getting a crash course on these 4.3 motors.

 

Well im glad i read this thread!, my 95 blazer has the same problem. Real rough idle and at low speeds it misses like crazy, but at high speed it smoothes out. Ill have to take my egr valve off too and give er a good cleanin

 

I can only speak for the egr issue with my 95 Blazer. They repeat. Over and over. I lost count. First time I just popped the hard little piece of carbon out of it so it could go all the way shut. Second time I popped it out. Third time I got irritated and spray carb. cleaner and used a brush (old round brush from my Army day - M60 gas tube brush I think) to scrub, along with the carb. cleaner the inside of the passage leading to the egr valve. The fourth time we bought some of that "wonder chemical" from the local Chevy dealer that was called "GM Top engine cleaner", least I think that was the name. Remove the EGR valve and spray this cleaner (expanding foam that is supposed to swell up to contact and dissolve all carbon build up in the egr passage) into it. The fifth time I fixed it differently.

The 96 has never had this issue. Same engine, it just has the Z injection system rather than the W injection system. Same gas (Wawa unleaded) and same driving conditions, back and forth to work, shopping, back and forth to school, etc.

 

Well....EGR taken off and thoroughly cleaned. I got it back on and fired it up. Same thing. When started it idles nicely, then when any gas is given to the motor it lopes and starts to stall out and runs increasingly rougher as the gas pedal goes down with some popping and backfiring. Take the foot off of the gas pedal and it smooths out and idles fairly well. I am pulling hair out over this. I have replaced the plugs, wires, rotor, cap, checked the fuel injection and pressure. I am now thinking either a different sensor or the coil. Of course cash is tight right now too.

 

Does the fuel pressure hold steady or does it bleed down?

If it holds steady, then you may have a plugged up catalytic converter.

 

Fuel pressure holds steady and when running is within specs. Idles a bit rough, and surges a bit...when you give it gas it dies, sounds like it is fuel starved, but revving it up you can hear some backfiring...so it is like there is an electrics issue. I am still baffled, going to try pulling the coil and testing it. According to the shop the sensors were fine, so I guess next thing after the coil is cutting off the cat and temporarily replacing it with some pipe. I pine for the days of points and a carb...

 

Seems like there's a test for a plugged/partially plugged catalytic converter. I don't remember all the details but it seems like you use a vacuum gauge hooked up on the intake, rev the engine up above idle (don't remember the exact rpm) and watch the ga. it should be steady once it reacts to the opening throttle but if the cat. is plugged/restricted the reading will change (again, don't remember if it goes up or down).

The catalytic converter on mine bolts to the cross over pipe but has a clamp behind the converter. If you take it loose/remove it it might be tough to find a substitue pipe that will connect.

 

I'm surprised that no one has mentioned this, but it really sounds like a timing issue with the backfiring and all. Have you done a tune up (cap, rotor, etc)?

 

Yes I have done all of that. I just tested the coil and it is fine so am suspecting the ignition control module. I had a pickup a few years ago do something similar, and am suspecting that this may be the cause.

 

I apologize; I missed that in your original post. But have your adjusted the timing?