1999 5.7 350 vortec P0304 cylinder 4 misfire

[socal k1500]

Misfires up hills under load

replaced
Plugs, wires
fuel pump
fuel filter
ignition coil,
distributor including cap and rotor and verified using scan tool cam retard is within spec.
cleaned maf and verified its working correctly.


Is there a way to see if its my injectors going bad before i replace them?
here is freeze frame

You must be registered for see images attach

 

[Schurkey]

What is the fuel pressure? You're +15 and +14% on the long-term fuel trims.

I wouldn't expect 70% throttle to go 44 mph and 38% load.

What are the O2 sensor readings?

Any misfire counts for the other cylinders?

 

[socal k1500]

What is the fuel pressure? You're +15 and +14% on the long-term fuel trims.

I wouldn't expect 70% throttle to go 44 mph and 38% load.

What are the O2 sensor readings?

Any misfire counts for the other cylinders?

Ok, so I haven't checked fuel pressure, Ill add that to the list. Can you elobrate on what im looking for in the fuel trim numbers? I'm a noob at diagnostics Im trying to learn as much as i can

I was WOT going up a hill trying to trigger the CEL so i could collect some data on it.

at idle o2 sensors appear to be in working order. Based on voltage readings in OB2

misfire counts are high in cylinder 4, but also present in cylinder 7. Not enough to trigger a code

 

[boy&hisdogs]

Sounds a lot like what my truck was doing about a year ago.

I had my injectors go bad AND a bunch of little electronic parts that I had already recently replaced so I was chasing my tail for a long time.

Look up how to do and injector pressure drop test. It's not fool proof but if you have an injector that's totally dead it will be obvious.

 

[socal k1500]

Sounds a lot like what my truck was doing about a year ago.

I had my injectors go bad AND a bunch of little electronic parts that I had already recently replaced so I was chasing my tail for a long time.

Look up how to do and injector pressure drop test. It's not fool proof but if you have an injector that's totally dead it will be obvious.

my truck is at 123k miles on stock injectors so im thinking its them

 

[boy&hisdogs]

my truck is at 123k miles on stock injectors so im thinking its them

I forget the exact mileage that mine started acting up, but i'd start suspecting them around that mileage. It's not a very difficult or invasive test so it's worth doing. It might not tell the whole story though, you might have injectors that spray the proper amount of gas (and look normal in the test) but in a bad spray pattern that might not run quite like it should still.

But my truck had one injector that was totally dead, no sound and no gas sprayed at all and another that was spraying inconsistent amounts of gas so I had a pretty good idea it needed to be replaced regardless of what else might be wrong with the truck.

 

[socal k1500]

I forget the exact mileage that mine started acting up, but i'd start suspecting them around that mileage. It's not a very difficult or invasive test so it's worth doing. It might not tell the whole story though, you might have injectors that spray the proper amount of gas (and look normal in the test) but in a bad spray pattern that might not run quite like it should still.

But my truck had one injector that was totally dead, no sound and no gas sprayed at all and another that was spraying inconsistent amounts of gas so I had a pretty good idea it needed to be replaced regardless of what else might be wrong with the truck.

did you do the injector upgrade to the newer version? Does it run way better after the upgrade?

 

[boy&hisdogs]

did you do the injector upgrade to the newer version? Does it run way better after the upgrade?

Actually mine already had the upgrade and those went bad. But I also did a lot of other tune up type work along with them so it's hard to say exactly what did it but yes it runs super smooth now.

 

[SableSlayer]

I chased this same problem on my truck the past 3 years. Start with your fuel pressure test and a smoke test. The smoke test is up make sure it's not a vacuum leak. Your fuel pressure should be somewhere from 50-60psi.

On my truck I replaced the injectors multiple times as well as fuel pump, distributor, Cap n rotor, wires, multiple sensors, etc... What it ended up being was the lower intake gaskets causing an internal vacuum leak. Upon replacing the gasket I found a missing bolt in the intake above cylinder 8. After getting the gasket done and replacing the bolt the truck got a rod knock on cylinder 8 a week later so had to do the bearings as well. I'm pretty sure the knock was due to there not being a bolt in that spot of the intake for 10 years. Anyways here I am a month later and finally no misfires at all.
My truck was missing on cylinder 4 on hills, freeway around 75, and anytime I was towing

 

[SableSlayer]

Due to your fuel trim readings being around 15 percent I'm leaning towards your intake manifold gasket. I'd check fuel pressure and smoke test before though.