OK, I bought this 99 Silverado wiith the 5.3. Not my first chev, not my first 5.3. I have the vortec in it, which is fine.

Needed a fuel pump when I bought it and amazingly that was all... Except it was running on no more than 7 cylinders. Did the obvious stuff, plugs and wires. Truck was reading P0307... misfire on cyl 7. Consulted with a friend who is a mechanic and swapped the coil with cyl 5. Code changed to misfire on cyl 5.

It would seem the problem was the coil which I bought and replaced today (on cylinder 5). But, apparently the truck isn't done playing games. Now I am back to a misfire on cyl 7. So my question...

Since the misfire went away on that cylinder when I switched the coil for the number 5 coil but it is now back, should I be safe in assuming that the issue is nothing more serious than a wet head and it will work itself out??? HELP Please!!

 

I'd do a compression check to rule out anything mechanical. Start swapping stuff again, plug, coil, injector and see what happens. A bad new part is not out of the question. Was the new coil put on cylinder 5 and cylinder 5 coil left on cylinder 7?

 

Yes the new coil was put on 5 and th coil from 5 was left on 7. I got thinking maybe it was a bad new plug as I've had that happen. When I changed the plug on 7 again I also switched the coils again so 5 has it's original coil back and the new coil is on 7. Still not running perfect but it's a lot more cheerful. But now I have no misfire code for 7, instead I got the nasty P0300... Multiple misfire grr

 

if you can, check the misfire counters with a scan tool. The counters will accumulate all the misfire history and show you which cylinder is misfiring even though only a p0300 dtc is all your getting

 

The only tool I have to check codes with is an OBD2 reader.. although on freeze frame it gives me a bunch of data I don't understand, I don't think it gives me that. I'm in the process of doing the rockers in between driving it to work and back so I can get a safety, so taking it to chev for them to run it is out of my budget.

Not sure if I mentioned before, but since the fuel pump had gone and I apparently bought it from someone with not a lot of funds and a blown fuel pump, I am running through a tank of gas that I put injector cleaner in. I'm not sure if this accounts for the sometimes full power I'm getting or not- Last night I was able to lay a strip of rubber and squeal the tires for the first time since I've had it so it must be kicking out the last cylinder sometimes.

Injectors are one thing I have never touched before so I am hesitant to pull that apart