2000 silverado 5.3 4x4 p0300

[bentstraight]

My 2000 silverado was running fine but the transmission had issues . Took the tranny out 4l60e and did a installation . Got the truck back together and when i tried to run it it had code p0300 and ran like crap . It has 4 new o2 sensors . What would make a vehicle go from running good to barely running after a tranny swap only ? There are no other codes at all coming up on the obd2 ??

[CamGTP]

Did you miss a ground wire when putting things back together?

[bentstraight]

A ground wire such as ? There really isnt a lot to do with grounding when doing a tanny sawp . Just assembled everything as per procedure , checked the fluids , new gaskets for the exhaust , new o2 sensors , and it ran fine when the tranny went . Im thinking maybe bad gas in the tank . 

[richard wysong]

There are ground straps on the rear of the engine which may or may not be on the bell housing bolts, Even if bolted to the engine they may have broken when the trans was hanging. Is the crank sensor on the flywheel on that? Any other codes? should be a 300 code indicating which cylinder(s) are misfiring, also check for a vacuum leak, did the hose get disconnected from the brake booster?

[bentstraight]

thats the weird thing there are no other codes beyond p0300 . That is what makes no sense ? There should be something specific showing a sensor code . or injector/cylinder , or anything more than p0300 . I drained the gas tank and added some injector cleaner into a high octane fuel and added it into the tank. The truck started and mellowed out a fair bit , and the idle was much smoother . Then when i felt i had it the check engine lit up and not long after began flashing. I tried a mode 6 scan but its a 2000 and to old . Im thinking maybe crank sensor as its location sucks and was questionable but i went with it . 

 When the truck was initially parked it ran fine. The tranny was done . So it sat a while then had a trans installed and it ran fine but there was a issue with the flex plate and a fluid leak . So it sat for some time as I had surgery on my hand . Jump ahead a year ish and i got the tranny removed and sorted out . I installed it buttoned up the rest and it ran like crap right off the bat . It has only showed p0300 during all this ? 4 new o2 sensors . new fluids , exhaust had previously been leaking at the y pipe joints but i sealed that all up tight ( why i replaced the 4 o2 sensors ) .... ya so thats whats up ...thanks for any ideas 

[richard wysong]

Any sign of rodents? You can unplug 1 coil at a time and possibly determine which cylinders are misfiring then try moving coils around and see if the miss follows, seme with injectors