Misfire

[Treefeller90]

Okay I need to bounce some ideas off you guys. So I have a 97’ with the 5.7 in it. When I drive up a hill or accelerating the engine misfires/chugs. If I step on the gas it goes away.
I replaced the fuel pump, the guy I bought it from said it has new plugs and wires. I looked at the computer and when it does misfire it all does it at once. It’s not just one. I’m just running out of ideas, so if a more mechanical minded person is out there. I’m open to suggestions.


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[Erik the Awful]

If it goes away when you step on it, I'd suspect a vacuum leak or an ignition problem. If it were a fuel problem it would get worse when you step on it.

Check the distributor cap and rotor first. Then check for vacuum leaks.

 

[Treefeller90]

If it goes away when you step on it, I'd suspect a vacuum leak or an ignition problem. If it were a fuel problem it would get worse when you step on it.

Check the distributor cap and rotor first. Then check for vacuum leaks.

Before I replaced the fuel pump it wouldn’t accelerate at all. I thought that might of fixed but I guess not. It did improve afterwards but still having backfiring issues.


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[Fast_Z71]

It sounds like it’s some short of ignition problem or a vacuum leak. How long has it been since you changed your plugs, wires, cap and rotor button? Also did you change the fuel filter mounted on the frame when you did the fuel pump?

 

[Treefeller90]

It sounds like it’s some short of ignition problem or a vacuum leak. How long has it been since you changed your plugs, wires, cap and rotor button? Also did you change the fuel filter mounted on the frame when you did the fuel pump?

I am not sure about the time frame. It was done before I bought it. I looked at the plugs and wires and they look brand new.
Yep I changed the Mount.


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[Schurkey]

Verify fuel pressure.

Connect a scan tool, look at the data stream. Short- and long-term fuel trims, throttle position sensor voltage, MAP voltage, knock sensor data, O2 sensor voltage, cylinder-by-cylinder misfire history, etc.

Verify ignition coil spark output using a spark tester calibrated for HEI ignition systems.