This is a little long, and I just wanted to say thanks before hand.

I don't even know how I would search for this. I have a 91 Z28 350\700R4. Not my daily driver. Well, usually I don't drive the car Monday through Thursday, but I will take it to work on Friday. Then I will drive it on the weekend. It drives fine on Friday and then Saturday it might run horrible\it might run for a while. Sunday depends as well. When it runs bad it is very lumpy and barely goes down the road. I will give it half throttle and it will lump down the road, then it will combust and I will do a peel out down the road and then it runs super lumpy again. At first we were thinking fuel pump, but sometimes when this happens I can still drive decent, just really rough. So it is getting gas. Replaced the O2 sensor already. When it runs bad my air to fuel ratio gauge it always going crazy. Either all over the place or not on at all. I will get frustrated and not drive it until Friday, and then it runs like it is brand new. So, I don't think it is the O2 sensor cause that works fine when it is driving ok. I was thinking maybe a clogged cat. When I let it sit for a while the stuff clogging it cools down\does whatever and gives enough room for it to work. Then after I drive it for a while and it heats up it starts to stop the flow. The extra back pressure causes my O2 sensor to read wrong. I do have 2 cats though. I am really lost. Once again, sorry this was so long and thanks for any help.

 

Bad fuel injectors?

 

I was wondering that too. I am not the smartest person with cars, so I am willing to consider anything.

 

Get a fuel pressure gage on it. I have a Bonneville that ran worse & worse the more it was driven; the fuel pump was getting weak. If it was allowed to sit, it would "feel better" until it had been going awhile again.

 

if it is air to fuel problem like that youd assume it has something to do with the fuel....could it possibly be a computer issue? I would think it to be weird if you had a fuel problem that it would be on and off.....so if your air to fuel ratio is all over the place my minds jumps to what controls the fuel delivery and thats the computer.

EDIT: after thinking im wondering if maybe it could be a compression problem? I would run a compression test across all the cylinders and see what you get.

 

Sounds good. Thanks for the ideas.