saphunt2r

I have a big power loss above 3500 rpm's pinging and engine light starts flashing, I just put a 5.3 h.o in the truck it had a 4.8 they both acted this way, parts from the 4.8 on the 5.3 are TB, fuel rail, oil sensor and flex plate that’s it, new parts so far fuel filter and mass air, and updated to a 02 vcm, So all help would be greatly appreciated..

Modern_Muscle

iTrader: (11)

what do you mean by updated?
is it tuned?

what mods are on the engine, or is it stock?

Mine will do that on cold starts, because of me not being tuned with my cam, but works itself out.

If its something really serious, the engine will go into a limp-home mode.


as I told the last guy...check your coolant temp plug on the front of the drivers side head to see if its securely plugged in.
This will cause your problem too.

have any of the threads on the spark plugs been crossthreaded or stripped? that leaks compression and will stumble and studder, and throw an engine light quickly.

is the maf in the air tube correctly, with no leaks?
It sounds like once you start hitting the power band, it has a problem.

saphunt2r

Yes it’s tuned with a 02 vcm, no mod’s both cold or hot, will check the coolant plug, but like I said the 4.8 did the same thing…your right once the motors hit the power band they both stumbled pinged the engine light starts to flash, no power back get out of the throttle runs great to 3000 rpm’s light stops flashing and go’s off…

Modern_Muscle

iTrader: (11)

sounds like a tuning problem, like it is dumping fuel at 3500, or the tables are off.

check for air leaks anywhere, and that the maf is secure in the tube. Its thinking its getting a LOT more air than it really is.

Are you noticing a fuel smell out of your exhaust, or any little black soot deposits?

dirt track racer 81

iTrader: (45)

You say its pinging once it gets to 3500 and falls on it face?? Id check fuel pressure to make sure you have plenty to the rails. did you take the injectors off the rails when you installed the new motor? Ive seen them plugged up with black crud before.. for it to ping you either have not enough fuel or too much timing. How good is the tune? If its running too much timing its going to knock and pull timing and run like a turd

saphunt2r

I would say more like lay right there, and so did the stock 4.8 before the motor change, this problem developed when the old motor was in and the timing was never messed with, so I am going to rule out the tune.. No fuel smell out of exhaust and no black soot deposits

saphunt2r

just cleared codes and it set the P0300 - Engine Misfire around 3500 rpm's and C0281 - Brake Switch Circuit (History) came on right away..

ForcedTQ

iTrader: (1)

Scan the computer for DTC's and let us know what comes up. Could be a few bad ignition coils since you said it exhibited the same behavior on the 4.8. WOT below 3500 RPM does ok? Part throttle above 3500 RPM exhibits the same behavior? Try doing a scan of the ECM while accelerating and post the recording.

dirt track racer 81

iTrader: (45)

if the pressure is dropping there aint going to be no fuel smell..First thing i would do is check fuel pressure.

Truckshop

iTrader: (17)

loosen the y-pipe at the manifolds and take it down the street. sounds like a stopped up exhaust.