I'm pretty confused as to what this could be, and I've read different stuff on these forums (which are great btw, thanks) from a bad catalytic converter to the ignition coils to the distributor and rotor and/or the spider(?). My 95 with 4x4 4.3L CPIwas blowing out black soot from the tailpipe every time I'd start it up (which would usually take several tries), and then it was running pretty rough. Also the area between the front passenger seat lower cushion and the arm rest was getting very warm while the car was running and there was a loud clanking sound from underneath the car. Well that turned out to be the cat converter smacking around internally and when the car was warm it would be glowing bright orange. The computer was coding with fault P0172, from the Haynes manual - system adaptive fuel too rich; autozone OBDII testersaidbank 1 fuel mix too rich. The car was getting about4 or 5mpg (I could watch the indicator move ) too.The compressor is out so it's squeaking alot, but I didn't think it would affect the engine so much with the drag that it'd cause this stuff. So I did some reading and figured I'd try a few things by changing the following:

spark plugs
plug wires
pre-cat O2 sensor
PCVvalve

Immediately the black spew stopped upon ignition, after a week or so the starter started the engine after only 1 or 2 tries and the car generally had more power and after acoupleweeks the catalyticconverster stopped clanking so much and the heat in the seat,whilenice when it was cold out, went away. The milage went up to about 9 or 10 mgp city and ~ 18 highway.

However, after a couple of months I started noticing a very rich fuel smell from the exhaust whenever the car was running that was so powerful I had to turn off the blower whenever I was at a stop or the whole cabin would stink of exhaust and fuel. Now when I hit the gas and the engine gets up to about 3500RPM it feels like there's practically no power, but when it shifts up and the RPMs drop there's a immediate strong boost in acceleration. The check engine light didn't come back on for a while after doing the previous work on it, but it's been back on with the same code as before (P0172) for a good 4 weeks, but it was running ok. It idles rough, and sometimes sputters. Whenthe engine'scold there's occationally a loud hammering typesound underneath the drivers side feet area, like someone tapped ahard malleton the floorboard.

So I changed the post catalytic converter O2 sensor and the strong fuel smell went away almost completely but it stillsmells like exhaust (it's a different smell, like burnt fuel I'd say, and not quite as present as before). Got a catalytic converter and a new muffler thinking that all of the carbon soot might have clogged them up so much that output is getting blocked, and perhaps the catalyst in the converter was damaged, but haven't put them in yet. Also I thought maybethe distributor, rotor, fuel filter and maybe the ignition coils could use a change because the car just passed 100k miles and my mom, who I got the car from recently, didn't take very good care ofthe enginein general.

Also, does anyone know how many O2 sensors this thing has? Autozone only said one, and the Haynes manual says the CMFI and CSEFI have pre and post cat, then it says there are three (?) Someone saidthisis like the redheaded stepchild year of the blazer too so maybe that has something to do with it. [8D]Any ideas on this one?

 

Well I would get that cat installed immediatly, thats what is probably robbing you of your MPG at this point. For the later years there is a post and pre cat O2 sensor, but I cant remember what yer this started. I actually want to say the 95 blazers but I may be wrong. But your banks may be running too rich, so check your spark plugs and see if they look like they have been run rich.

 

I changed the plugs causethey were blackened and oily, and changed the wires.It seems that the ignition coil might be going too, because it's sensitive to plug wear and deterioration, and the distributor and rotor probably need to be changed anyway. The engine just started some backfiring yesterday, and somewhere it said that can be caused by the IC, or is that wrong? This might seem stupid, but what is the definition of a bank, or bank 1 and bank 2 anyway?

 

BANK 1 = Cyl 1, 3, 5
BANK 2 = Cyl 2, 4, 6

You should have a minimum of 2 O2 sensors in either the down pipe or before the connector for the y-pipe. Because if the computer codes are being read by bank then there has to be a sensor for each bank.

What you are explaining could be a fuel leak inside the upper intake manifold. There were three major areas for these leaks:
1. The fuel lines (Nut Kit) coming from the back of the lower intake to the spider/fuel pressure regulator.
2. The fuel pressure regulator
3. The fuel injector distributor (spyder) block.
Depending on where you see a golden washing of the lower manifold will tell you which of these items is doing the leaking. Generally if the fuel washing is on the passenger side then you would look at the fuel pressure regulator to be the source of the fuel washing. If the fuel leak is at the drivers side then you could suspect the fuel lines (Nut Kit) but these would generally leak at the rear to middle of the manifold. If the washing was under the fuel distrubution block (spyder) then you would look at the spyder as the problem to fix..

But you would have to remove the upper manifold to find out...

 

I changed the cat and muffler (which was loadedwith soot, burnt and smelled like sulfur)

Thanks for the info. I was thinking of changing the cap, rotor and plugs first. I was going to do the plugs b/cthere are somecheap bosch's in there now and Kyle or someone said these are picky about ac delco's so I was going to put in some rapidfires. It seems that to get into the manifoldyou have to do the distributor and rotor anyway and drain the cooling system, etc. Would it be worth it just to do it all in one go?

How long do you figure it'd take to check out the things in the intake manifold if there'swashing?