Just got my swap done. 5.3 with ls1 intake 4l60e. My prob is it seems to idle great but when i get on the road under load it stumbles horribly under any throttle range, but if i floor it full throttle its like you flip a switch and it pulls hard and smooth as long as i am wot. Im not getting any codes. Any ideas i am dying to drive this truck.
It's probably something in the tune. When you floor it, it goes into PE mode and the fueling is different, hence the better running. Get it to a tuner, unless you do your own tuning.
__________________ 85 Monte Carlo SS, 5.3/4L60E Daily driver--traded
84 Monte Carlo SS, LS3 418, 248/254 615/595 with XER and XE lobes. AFR 225, 1 7/8 Hedman headers from BRP. 200-4R. 9" Ford, 3:50 gears.
Sounds like mine the first time I ran it. Make sure the o2s are plugged in the correct sides. My car didn't throw any codes either and I got lucky watching the data and the O2s were reading wierd. I had written left and right on the plug when I did the harness so when I checked my theory was confirmed, swapped connectors and runs 100% now.
the oxygen sensors have 4 wires going to them, of the 4, one will be purple. The sensor on the DRIVERS side should have a purple with white stripe, and sensor on PASSENGER side will be solid purple.
Are you using the truck mass airflow sensor?
Are you using the LS1 injectors? If so, which part#? (3 of them from 99 to 02)
What are you using for fuel pressure regulator. (vacuum referenced?)
All that info is very important when it comes to getting the computer programmed for your setup. If you did not provide, or were not asked that info, it could be incorrect and causing your drive ability concerns.
I had the excact same issue. idled great, part throttle stumble/ miss ,at WOT it pulled like crazy. I got in contact with the guy who done my computer and he told me my 02 sensor wires were crossed. swapped them around it its a whole new car ,runs great. check into what Busta said on your 02 sensors he was the one that done my computer. unplug one of your 02 sensors at the plug and look at the harness wires there if the drivers side has a purple wire with a whit stripe then the 02 wiring is right if it has a solid purple they are on the wrong side.