56.3 runs rough when cold & WOT - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**dmarty** · 08-29-2011, 08:37 PM

My '99 5.3 pops and farts when cold and WOT with a load. Starts fine and runs well when warm. Runs fine cold too if I don't open the throttle too far. Has 304k miles and is mostly original. The intake gasket was replaced at 100k when I replaced a noisy lifter. I also replaced the fuel press reg at 200k. Everything else is original including the O2 sensors. Any ideas? O2 sensors? Injectors? EGR? I just replaced the plugs, wires and fuel filter as they had 120k on them, but it didn't help. Thanks!

08-29-2011, 08:37 PM	#1
dmarty Active Member Join Date: Dec 2008 Location: Verona, WI Posts: 100	56.3 runs rough when cold & WOT My '99 5.3 pops and farts when cold and WOT with a load. Starts fine and runs well when warm. Runs fine cold too if I don't open the throttle too far. Has 304k miles and is mostly original. The intake gasket was replaced at 100k when I replaced a noisy lifter. I also replaced the fuel press reg at 200k. Everything else is original including the O2 sensors. Any ideas? O2 sensors? Injectors? EGR? I just replaced the plugs, wires and fuel filter as they had 120k on them, but it didn't help. Thanks! __________________ 72 GMC Sierra Grande SWB 402 BB A/C (Owned it since 1973) 99 Silverado 1500 LT with 315K miles (RIP) 2012 GMC Sierra SLT

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