1987 chevy s10 misses at speed

I have a 1987 chevy s10 blazer with the 2.8L that i use as a winter rat but this year due to problems I have been forced to drive her. Last week she would not start so I replaced the plugs wires cap & rotor & she started right up. A few days ago as I was driving her on the highway she started bucking then she would run fine then about 10 min. latter the same thing. A few months back I had the check engine light come on & got a code for the O2 sensor which I replaced but the check engine light still comes on & reads O2. The person I bought her off of put headers on her so I'm not sure if this is what is causing the light to come on. He also said he changed the fuel pump in her & I changed the fuel filter. This is not the first time this has happened as it did it over the winter I put fuel cleaner in her and it seemed to go away. Has anyone had this trouble & if so what caused it or does anyone know what it might be. To me it seems like the fuel pump! Also the person I bought her from put a holley T.B.I on it and it seems as though it's getting to much fuel this is why I'm stumped. I don't know if the 2.8 came with a holley from the factory but this one has red thottle plates in her. Any help would be great!. Thank you for your time.

 

How is the exhaust set up? I'm assuming with headers you have dual exhaust with the sensor mounted in one of the pipes after the header? That must be a central point injection also.

If all that is correct, I could see where your header setup (mostly the dual exhaust with the sensor reading only one bank) could cause a problem where the 02 sensor is concerned. I would say the fuel feed is probably the issue and anything controlling it would be suspect.

Did you check the fuel pump pressure/regulator pressure? If the regulator is acting up intermittently you could get that type of engine response. Or if the Holley setup is mismatched for the engine, the O2 system may get a little jerky trying to regulate it. The headers would move the fuel/exhaust through the system a little more freely so the combustion chamber time would be cut. This would be just theorizing on my part.

I think I would verify the pump pressure first. Then remove the gauge and run the engine for a short time and shut it off. With the engine shut off, depress the valve where the gauge was attached with an ink pen. You should have a little pressure in the rail. If not, the pressure regulator isn't holding the pressure. Something like that usually means you have to crank the engine for a while to get it started.

As far as the 02 code, did you clear the code from the computer (disconnect battery cable for about 2 minutes)?


Hope this helps,

Bob

 

Check the color and condition of the plugs, including careful inspection for barely visible insulator crack.

What does the engine do when you just idle in Park, compared to idle with foot on brake in Drive, compared to accelerate under load (simulating or going up a hill), compared to high speed cruising, compared to cruising and then compared to at moment of non-load cruising you let off the gas?

 

This is a lot to answer so forgive me if I don't get it all. First of all the O2 sensor is right in the header!. When she is ideling she is fine when I first start off she wants to bog down like she is getting to much gas going up hills she has no power I have to push the pedal to the floor same thing with getting on the highway then she takes off fine. What it feels like to me is when she shifts into third gear she looses power & she has no passing gear. The guy I bought her off of said he put a cam in her but I have no idea wether this is true or not. The gas milage stinks I have had her since nov. of last year. It looks to me like the t.b.i is to big for her but then again give me the old carburated cars with out all this computer stuff. I hope this helps as it is driving me crazy one other thing the other day as I was slowing down to make a turn she stalled I threw her in nutral and she started right back up she has never done this before. I checked the codes and the only one I got was the O2.