Replaced the O2 sensor again and now the voltages are correct. But it still has a rotten stumble and miss at cruising speed.
I'm suspecting the carb primary circuits now.
I'm suspecting the carb primary circuits now.
Lean miss problem - help!
- Thread starter 87MonteSS
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I would check the TPS sensor to be sure it is reading correctly then too. It is adjustable with a small Allen head screw on the top of the carb if it is just a little off and reads in a linear fashion.It could also be something as simple as a vacuum leak or a bad power brake booster. There are a lot of vacuum lines under the hood of an 80's GM product, so I would check all of them next. Is the CEL on? If so, read the codes and see what the computer is spitting back.
One more thing about the E4ME Quadrajet: If you ever take the airhorn off, be sure to compress the TPS sensor's plunger with a flat screwdriver while you are reassembling it. Failure to do so will break off the plunger causing the computer to read WOT and hydrolock the engine with fuel! I made this mistake with a HO 305 in a 1984 Z-28 once and it completely filled the engine with gas. The only remedy if you do this is to pull the plugs and pump the gas out with the starter or by hand turning it ( smarter than running an electric motor with all that gas!)
One more thing about the E4ME Quadrajet: If you ever take the airhorn off, be sure to compress the TPS sensor's plunger with a flat screwdriver while you are reassembling it. Failure to do so will break off the plunger causing the computer to read WOT and hydrolock the engine with fuel! I made this mistake with a HO 305 in a 1984 Z-28 once and it completely filled the engine with gas. The only remedy if you do this is to pull the plugs and pump the gas out with the starter or by hand turning it ( smarter than running an electric motor with all that gas!)
I would check the AIR injection system and hoses.If you have removed the smog pump, etc, the engine could be sucking air into the engine through the exhaust and cause an off idle stumble, etc. A cracked manifold would also do this, and if you ran it rich enough for the right amount of time, it could have cause a catalyst meltdown which would plug the exhaust and make it run bad. Tap the cat with a hammer and see if the substrate rattles in the housing. If so, it's new cat time. I had this happen on a DSM I was working on that we could not get to boost. Disconnected the cat, and the lack of restriction let it spike to 20psi!
The cat was removed a long time ago. The A.I.R pump has been gone a long time too, but the hoses etc. are still there. The miss and stumbles are there without the air cleaner too, so I'm not sure how it could be drawing exhaust in through the hoses?
There is no CEL and the TPS tests perfect.
There is no CEL and the TPS tests perfect.
Are the check valves still on the manifolds and unplugged? If so it most DEFINITELY will cause the problem you describe. I had the same problem and that is what was causing it. I fixed it by using a set of heater core caps and a couple of hose clamps to seal the holes and the problem was solved.
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