Hello guys I have a couple of questions. First I own a 2003 1500 Express. 4.3l 85,xxx

Back in November I replaced my fuel pump.I always use 87 gas. Then 2 weeks ago I changed my spark plug wires, rotor and Cap because I was misfiring cylinder 3. Van was running beautiful. After the I changed the wires I decided to put 91 octane. 5 days later I started getting long cranks and 2 codes popping up P0171 & P0174. What can it be? Gas? O2 censor?

 

Never use the wrong gas. I did that to my car when I was younger and it ran like crap till it was gone. run down that tank and go back to 87 unleaded and see.
Those codes are lean conditions. Could be o2 sensor, (precat) or vacuum leak. But start with the right gas....

 

I went back to Regular gas and deleted codes and nothing has come back.Symptomwent away.

 

I never heard of using a higher octane gas causing a problem.

 

 

Sure can. Made the mistake myself once with a 97 geo metro. put 94 in it and it ran like crap till the next fill up. Never was a problem again after going back to 87 regular.
Some vehicles can handle it if the computer system can advance the timing and so on to account for the higher octane. Like my wife's HHR. Other cars...nope.

 

Regular Gas fixed my problems!!