Hello,
So i have a 91 f150 custom 4.9l that i purchased non running. So far i replaced the tanks, pumps, fuel filter, cap, rotor, plugs, injectors, egr and tube, vc gasket, rc gasket, list goes on. Anyways this truck is running great, however, every time i pull it into drive and start moving i would say anywhere within 10 seconds- about 2min my CEL would illuminate. I ran the test and keep getting a 542 code. I have checked all my grounds (cleaned and re tightened) and even replaced the Fuel Pump Relay and still have the issue.

If anyone has ever had this issue or know what else i should test please LMK. thanks