motor breaks up at 2500 rpm at cruise
07-15-2005, 09:57 PM
#1
motor breaks up at 2500 rpm at cruise I have been working on a friends truck.
Basic specs:
2004 Controller
6.0L
LS6 heads,
2001 LS6 cam
Truck intake
Started with a 6.0L Truck cal.
6 speed manual
Motor runs and idles fine. Runs good at wide open throttle, fuel trim looks good spark looks good, truck pulls strong.
At a 2500 rpm cruise, usually 3rd 4th or 5th gear, the motor starts to misfire, P0300 codes, but roll back into the throttle, and put some more load on the engine, and it clears right up. I have to spend some time watching what spark advance is doing, but I am at a loss on this one. When I watch for the misfires per cylinder, the misfire counts go nuts, but not always on the same cylinders. It seems to jump around.
No other codes, all the coil connections are good both on the harness side and the plug wires. Injectors look good, no vacuum leaks that I can find or hear, and like I mentioned the fuel trims look decent, no more than +/- 5-7%. I have had trucks a lot further off than that and never had a steady state problem like this.
Any thoughts??
Basic specs:
2004 Controller
6.0L
LS6 heads,
2001 LS6 cam
Truck intake
Started with a 6.0L Truck cal.
6 speed manual
Motor runs and idles fine. Runs good at wide open throttle, fuel trim looks good spark looks good, truck pulls strong.
At a 2500 rpm cruise, usually 3rd 4th or 5th gear, the motor starts to misfire, P0300 codes, but roll back into the throttle, and put some more load on the engine, and it clears right up. I have to spend some time watching what spark advance is doing, but I am at a loss on this one. When I watch for the misfires per cylinder, the misfire counts go nuts, but not always on the same cylinders. It seems to jump around.
No other codes, all the coil connections are good both on the harness side and the plug wires. Injectors look good, no vacuum leaks that I can find or hear, and like I mentioned the fuel trims look decent, no more than +/- 5-7%. I have had trucks a lot further off than that and never had a steady state problem like this.
Any thoughts??
10-07-2011, 02:17 PM
#2
This is EXACTLY what my trans am is doing. Anyone know what the problem could be? Its got new plugs maybe 5k ago and just started doing this. Sorry for the necropost but im desperate!
