1999 5.7 350 vortec P0304 cylinder 4 misfire

[socal k1500]

Okay if you've done the smoke test and didn't find any leaks then I highly recommend you replace the lower intake gasket

My fuel trims at idle are really erratic

 

[SableSlayer]

My fuel trims at idle are really erratic

That's exactly what mine was doing. It's caused by an internal vacuum leak. I'm not a gambling man but I would put money on it that it's your lower intake gasket. I chased this on mine for 3 years

 

[socal k1500]

It fluctuates like this to the extremes

 

[socal k1500]

That's exactly what mine was doing. It's caused by an internal vacuum leak. I'm not a gambling man but I would put money on it that it's your lower intake gasket. I chased this on mine for 3 years

Is there a way to know for sure?

 

[SableSlayer]

My fuel trims at idle are really erratic

My fuel trims at idle are really erratic

Is there a way to know for sure?

Do your smoke test and if

Is there a way to know for sure?

What app are you using for those readings? It's showing way too many banks.

 

[SableSlayer]

Do your smoke test and if

What app are you using for those readings? It's showing way too many banks.

Have you done a smoke test?

 

[socal k1500]

Have you done a smoke test?

No I haven’t, I was going to test vaccum with a harbor freight vaccum gauge. But I can look into smoke test. The app is dash command. I have a more traditional scanner that shows fuel trim I’ll try that. Thank you for your help and your time

 

[Schurkey]

If it's a Vortec, the main intake gaskets are suspect anyway.

Pull the intake, replace the gaskets.

 

[SableSlayer]

No I haven’t, I was going to test vaccum with a harbor freight vaccum gauge. But I can look into smoke test. The app is dash command. I have a more traditional scanner that shows fuel trim I’ll try that. Thank you for your help and your time

I use Dash command also. Did you purchase the extra pods for your truck that Dash command has available?

I would like to see what your other scanner shows for fuel trim readings. The pictures you posted from it last week tell me that you need to do the intake gaskets. Like another person says they are suspect and are known to go out frequent on the 350 vortec.

 

[SableSlayer]

No I haven’t, I was going to test vaccum with a harbor freight vaccum gauge. But I can look into smoke test. The app is dash command. I have a more traditional scanner that shows fuel trim I’ll try that. Thank you for your help and your time

You can do a smoke test really easy with a cheap cigar.