I have replaced all plugs, wires, and the coil pack. I've done a compression test on 3 and replaced the injector. The fuel pressure at the rail is right at 55psi which is where it should be for the flex fuel v6. I did a vacuum test, its a little low at 14 inches but i dont believe thats enough to cause a dead miss on 2 cylinders. IAC seems fine, checked it by unplugging it while running. Started running much worse and then engine died. Cleaned EGR and checked it by applying a vacuum to it and watching to see if it opened, seemed to open and close fine. Checked MAF sensor by reading airflow from the OBD2, it reads within range at all rpms so I believe it is alright. Thought about possibly a backpressure issue so i took off the cats with no change. Still have a completely dead miss on 3 and 4. My truck has nearly no acceleration, which i assume is from the fact it is only running on 67% power. No clue whats causing the misses, any ideas would be very appreciated.

 

Have you checked the wiring/voltage to the injectors themselves? Noid light/volt meter. A WAG could be ECM.

 

Palm Coast, Florida ?

31' elevation, you should have 19 - 20 inches vacuum at that elevation, but the 2 cylinders not firing may cause the low vacuum.

3 and 4 use the same coil, something is causing that coil not to fire, one of the 4 power/control wires could be broke.

 

I have yet to check the voltage to the injectors, I'll be sure to do that later today. Not really sure what WAG means? I have spark at both the spark plugs, checked that last night so I dont believe there is a problem with the coil not firing. Also maybe should mention it's running very lean, not sure if that is caused by the misfire or if it's causing the misfire.

 

14" of vacuum is VERY LOW at any elevation, lol, you have bad compression or clogged exhaust..........or a bad vacuum gauge, lol

1999 3.0l Vulcan engine runs 9.3:1 compression ratio so expected static compression would be 160-165psi
You tested one cylinder, what was it?
Under 120psi would cause running misfire, static compression(cranking) is 40% higher than running compression

Better to remove all spark plugs and then test all 6 cylinders at one time, that will give you the value of a compression test and average
Testing one cylinder doesn't tell you much unless it comes up as 0psi or close to 0psi, lol

"Lean" codes are caused by misfires not the other way around, just FYI
If an engine is pinging/knocking then its actually running lean
Lean and Rich codes don't mean engine is "running" Lean or Rich they reference computers calculated air/fuel mix being lean or rich so computer has had to adjust its calculations

O2 sensors only see Oxygen, not fuel, high oxygen is lean, low oxygen is rich
If a cylinder misfires no oxygen is used/burned up, so O2 sees high oxygen, computer sets lean code

 

Alright I got a compression test kit and tested all cylinders, cylinder 3 is at 130psi, all the others are at 145psi except for cylinder 4. I got cylinder 4 at 75psi. I read somewhere to spray oil into the cylinder and run the test again, and if the compression gets better its the piston rings, if it doesnt get better its something else. Well i sprayed oil and ran it again, getting 150psi. so is that a sure fact that its the piston rings? or could it still be somthing else? cylinder 3 compression is a little lower than the rest, but arent they all really low?

 

Compression will ALWAYS GO UP when you add oil to a cylinder, so maybe you misread that part
How much it goes up can tell you if its rings or valves that are leaking

145psi to 150psi is a small jump so not rings, if it went up to 165psi then it would be rings
130psi to 150psi would be a ring issue
130psi to 140psi would be leaking valves or head gasket, not rings

75psi is a burnt exhaust valve, not rings
130psi is also likely to be valve and not head gasket

But your over all compression is low for the 3.0l Vulcan, but new gauge may not be calibrated