'99 5.3L sputtering/misfire ????

First of all thank you for letting me be a part of this forum.

Now, I have a 99 chev Z71 w/ a 5.3 that has some issues. It starts and idles fine but after about a mile of in town driving it begins to misfire badly. I will smash the throttle to the floor and it will rev up fine but when it goes back to lower rpm it begins to misfire again. And after a while it will suddenly stop misfiring and run fine. It is throwing the P300 random misfire code, and after it begins to run bad the P0152? O2 sensor bank 2 sensor 1, and also P302 cylinder #2 misfire.

New parts in the last 2 weeks:

EGR Valve
AC spark plugs
New Spark Plug wires
New O2 sensor (bank 1 sensor 2) it was coding all the time. The other one only codes when it acts up.

I have had it on computer multiple times most of my misfires are coming from the even numbered cylinders. Knowing this we thought it was the right cat. So we tried to beat the guts out of it but it still did it's thing.

does anyone know of a solution??

Thanks in advance for all your help.

Intake gaskets... Sounds like it to me anyway.

Is there a way to check the intake gasket? I sprayed the base of it with carb cleaner but it did not change the way it was running.

I also unplugged the wires that go to the EGR valve and that made no changes in the way it ran.

I then unplugged the vaccum line that goes to the fuel press. regulator no changes in the way it ran. I think that was the pressure regulator anyway

Check fuel pressure. You need 60-65, then focus on # 2 cylinder ,could be the injector spider or something mechanical, if the miss is constant at low speed confirm compression and if nothing else pops up pull that valve cover and check the valve train.

Take a look at this thread for some more ideas. The fix was something that opened my thought train.

http://www.automotiveforums.com/vbulletin/showthread.php?t=898010

Hi, The thread stickman is referring to is on a suburban with the 5.7 litre. You stated yours is the 5.3 so this is what happened to my 99' with the 5.3 litre. I kept getting the ses light and the code read was # 7 cylinder mis-fire. After much testing:runaround:, it was not a "fire" problem at all. It was a # 7 fuel injector that was clogged. I found the fuel rail had a lot of fine rust-like sediment in it also. After cleaning it and all four injectors on that side, it has ran fine. The computer only reads that there is a problem and sets a "generalized" code. My truck was idling terribly but only was noticed missing at speed when I was towing a trailer. It had just over 144,000 mi. on it when this happened.

does anyone know of a solution??

Thanks in advance for all your help.[/quote]



check for restricted exhaust.......

If the misfires are always on the even side, could it be a bad ground to the coil pack or injectors? Is the fuel pressure regulator on that side? Pull the vacuum hose and see if there is fuel in the hose.

//2000CAYukon

There is no fuel in the vaccum line. Where would the ground wire be located for those components?