Miss and backfire

[scott_williams2]

I have a 97 k1500 5.7 vortec. Recently it started havin a miss and backfire at Idle and low rpm. Soon as I drive it goes away or isn’t as noticeable. Engine light is on for o2 sensor has been on for a while before it started. I’m thinking spark plugs and wires May be the cause any other opinions?

 

[scott_williams2]

I will add it’s an exhaust backfire

 

[Pinger]

I think (given it pulls away OK) I'd look at fuelling first. Weak due to air leak or messy overfuelling from leaking/dribbling injector(s) - the type of things that have a disproportionate effect on idle quality.

 

[Schurkey]

You already know that there's an O2 sensor problem. Fix that first. See what happens.

How long has it been since the vehicle got a proper "Tune-Up"? Distributor cap problems seem to be common, as are distributor gears that have worn-out, and distributor housings that have sloppy bushings. All of this affects timing and spark delivery.

What is the fuel pressure? Still have the crappy "Spider" injectors, or has it gotten the upgrade to electronic injectors?

As always, connect a scan tool and look at the data stream. Can you narrow down the misfire to a specific cylinder? Fuel trims look OK? Coolant temp sensor, MAP sensor, TPS giving good readings? Anything else in the data stream look "odd"?

 

[scott_williams2]

You already know that there's an O2 sensor problem. Fix that first. See what happens.

How long has it been since the vehicle got a proper "Tune-Up"? Distributor cap problems seem to be common, as are distributor gears that have worn-out, and distributor housings that have sloppy bushings. All of this affects timing and spark delivery.

What is the fuel pressure? Still have the crappy "Spider" injectors, or has it gotten the upgrade to electronic injectors?

As always, connect a scan tool and look at the data stream. Can you narrow down the misfire to a specific cylinder? Fuel trims look OK? Coolant temp sensor, MAP sensor, TPS giving good readings? Anything else in the data stream look "odd"?

Check engine light came back on this time with only 1 code. P0300 random/ multiple misfire I’m stumped as to what that could be? I plan to change plugs wires and fuel filter because it probably needs it I’ll start the Monday

 

[Supercharged111]

If you have a bum O2 sensor causing a lean condition, said lean condition can cause a misfire and it's possible to not throw an O2 code for this.

 

[Schurkey]

Check engine light came back on this time with only 1 code. P0300 random/ multiple misfire

Is this REALLY a P0300 code, or is that the generic code reported by a cheap scan tool or crappy "code reader" when the real code is cylinder-specific?

Can you access misfire history? You should be able to pin down which cylinder is actually misfiring. Might be that cheap consumer-grade scan tools don't display that data.

At any rate, LOOK AT THE DATA STREAM and VERIFY THE FUEL PRESSURE.

I’m stumped as to what that could be? I plan to change plugs wires and fuel filter because it probably needs it I’ll start the Monday

I'd be TESTING the plug wires, inspecting the cap 'n' rotor, looking at the plugs...

But you likely need the O2 sensor anyway since you've had O2 sensor codes already. How old is the sensor?

 

[scott_williams2]

Changed distributor and rotor problem solved