epeterson

Hey guys, I'll make a long story short. I've got a 2004 Chevrolet Silverado 2500 with the 6.0/4L80.

Original engine started rod knocking a few weeks ago (other than the obvious knocking it had no drivability issues). I found a replacement similar year 6.0 for sale from a gentleman who had it rigged to an engine test stand. I got to hear his 6.0 run and verify oil pressure.

Got the old engine out and new one swapped in over the past few days and now the new engine runs and idles smooth. But when I drive down the round about 2500-3500 rpm the check engine light starts flashing and it throws a P0300 code for misfire. The plugs and wires are new, so I was thinking maybe I got a bad coil with this used engine. I took the coils from my old engine (that ran great a few weeks ago, no misfire) and put them on the new engine, same issues. Go down the road and check engine light starts flashing, but the truck does not act any differently and without that light I would have no idea it was missing.

Any ideas where I should turn next? The guy I got the engine from did the new plugs and wires so maybe I pull them out and verify gap/replace aftermarket wires with AC delcos? I'm at a loss, any insight would be appreciated!

Thank you

01CamaroSSTx

iTrader: (3)

Having the same issue on my 03 Silverado 1500 HD. Ran a compression test and all the cylinders but No.6 are berween 180 and 190 psi. with No. 6@175psi. I replaced the plugs with some No.7 heat range plugs that I had from the SS and I'm now in the process of checking for ignition. So far I've checked bank 2 and all cylinders are firing and No.1 is firing. I'm sure I'm going to find that they're all firing. After that I'll be checking for intake manifold or exhaust leaks. I can see there's at leat 2 or 3 exhaust manifold bolts where the head of the bolts are broke off. Motor has 356K miles and is in need of attention. The wires are MSD Super conductors and farely new so I may just buy some TR6's and see if that helps. It's a flashing SES light and the engine certainly doesn't owe me anything.

Rick Dorion

iTrader: (1)

Try a crank sensor relearn. Easy to do with the right scanner ( I bought a chinese knockoff XTOOL D7 and did it myself). Scanner needs to be bi-directional.

I've fixed that issue twice on my 6.0's after doing the usual tuneups, etc.

Kjduvall

if your o2s are super old (like you cant evan remember last time you changed em) that will do some weird stuff, heck ive seen it evan not throw a code . also seen a stuck iac on throttle body act like that to. and the intake gaskets aint a bad idea if there old as dirt too.

wlink14

My dads suburban had fake AC Delco spark plugs(PO installed) that were causing a similar issue. Make sure you have good spark plugs not from amazon(make sure someone didn't return fakes to your local parts store as well) there are videos online of what real vs fake plugs look like.

01CamaroSSTx

iTrader: (3)

Getting spark on all cylinders.. Just replaced the plugs with TR5's and P0300 with the dreaded flashing check engine light remains.. It's misfiring for sure and has a rough idle and I'll know more once I pull the intake to clean it. Upon inspection of the plugs I can tell she's burning some oil so I'm sure the valve seals need replacing there's most likely a buildup of gunk inside the ports and on the valves as well. The injectors probably have some gunk on them too which could also contribute to this.

Kjduvall

totally agree with you. seen it first hand on some amazon ac delco plugs ,have heard about amazon walbro pumps lately as well. although i dont think thats whats going on here.