1999 5.7 350 vortec P0304 cylinder 4 misfire

[socal k1500]

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.

Yes I did purchase the GM specific pid stuff, any particular you wanna see? I have cigars around I can do a smoke test like that.

 

[socal k1500]

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.

They look way more normal with my regular scanner.

 

[SableSlayer]

Yes I did purchase the GM specific pid stuff, any particular you wanna see? I have cigars around I can do a smoke test like that.

Those ft numbers should still be closer to zero. Do you know how to do the test with a cigar?

 

[socal k1500]

Those ft numbers should still be closer to zero. Do you know how to do the test with a cigar?

Yeah just blow the smoke into one of the vacuum lines with the truck off , where is a good spot on this truck?

 

[SableSlayer]

Yes I did purchase the GM specific pid stuff, any particular you wanna see? I have cigars around I can do a smoke test like that.

You should delete the extra banks in dash command that are showing fuel trims. You only need them for banks 1 and 2 short term and long term.

 

[SableSlayer]

Yeah just blow the smoke into one of the vacuum lines with the truck off , where is a good spot on this truck?

You need to block off the air filter when you do it. I would pull the clamp on a intake hose closest to the air filter then take a plastic bag and put it in between the hose and the piping on the air filter so it's tight like Saran wrap that put the hose back on and tighten the clamp. Then locate the Ambien Air temperature sensor on the air intake ducting and pop it out then stick a hose into that and blow the smoke into that hose

 

[socal k1500]

You need to block off the air filter when you do it. I would pull the clamp on a intake hose closest to the air filter then take a plastic bag and put it in between the hose and the piping on the air filter so it's tight like Saran wrap that put the hose back on and tighten the clamp. Then locate the Ambien Air temperature sensor on the air intake ducting and pop it out then stick a hose into that and blow the smoke into that hose

Vaccum gauge holds at 20 at idle , idles rough tho and scanner shows random misfires happening during idle

 

[Schurkey]

You're never going to see a small vacuum leak with a cheap dampened gauge.

You MIGHT see the effect of a small vacuum leak using electronic vacuum sensors. Maybe. The one on my 'scope can match intake-valve-open vacuum pulses to the correct cylinder creating it; but I've never used that to confirm an intake gasket leak.

Years ago, they were selling ultrasonic microphones for detecting vacuum leaks and window-seal air leaks. But you'd likely have to cram the microphone inside the intake runner, or work it in from under the manifold. Totally impractical.

A smoke-test can often confirm very small leaks. If the gasket is leaking on the bottom-side, you'll have to blow enough smoke in there to fill the crankcase before the smoke will come out the oil-fill cap opening after you remove the "710" cap.

If you don't know how old the intake gaskets are...time to pull the intake manifold. The Vortec engines had tremendous problems with intake gaskets when they were new. I thought the gasket was "improved" to solve that issue; but I'm hearing on this forum that it was never "really" dealt with--better, but still not "fixed".

I've lost track--have we completely ruled-out injector and ignition problems? Valve springs, cam lobes good?

 

[socal k1500]

You're never going to see a small vacuum leak with a cheap dampened gauge.

You MIGHT see the effect of a small vacuum leak using electronic vacuum sensors. Maybe. The one on my 'scope can match intake-valve-open vacuum pulses to the correct cylinder creating it; but I've never used that to confirm an intake gasket leak.

Years ago, they were selling ultrasonic microphones for detecting vacuum leaks and window-seal air leaks. But you'd likely have to cram the microphone inside the intake runner, or work it in from under the manifold. Totally impractical.

A smoke-test can often confirm very small leaks. If the gasket is leaking on the bottom-side, you'll have to blow enough smoke in there to fill the crankcase before the smoke will come out the oil-fill cap opening after you remove the "710" cap.

If you don't know how old the intake gaskets are...time to pull the intake manifold. The Vortec engines had tremendous problems with intake gaskets when they were new. I thought the gasket was "improved" to solve that issue; but I'm hearing on this forum that it was never "really" dealt with--better, but still not "fixed".

I've lost track--have we completely ruled-out injector and ignition problems? Valve springs, cam lobes good?

Isn’t my intake supposed to be sealed tight on the throttle body ? I did my smoke test and right away smoked started pouring out of the here ?

 

[Schurkey]

Coming out of the air-intake hat where it seals to the airhorn? Or coming out farther below and I just don't see it?

A new gasket/seal between the hat and the throttle body airhorn would resolve that leak--or maybe just tightening the fasteners.