i have a 4.8 running in my car. but recently i bought a used 5.3 engine. i was trying to bench run it to check the oil pressure and see if it run ok. i put the 4.8 ecu on and the engine flood at first. then when i got the engine running it had high idle and it surging , it also has hard starts.

 

To many variables to consider, Injectors my be different maf/map sensors may be different. In simple terms your lucky it ran at all.

 

you have another issue if its factory.

have turned on plenty of 5.3s with 4.8 files and have ran perfectly fine.

 

Agree with subeone. If its a factory swap, 4.8 to 5.3 it will run. Have had tons of customers swap out 4.8's and 5.3's for 6.0 and drive them to us for a tune. Now if you changed camshafts, injectors, maf's, intakes etc. it could be a tuning issue.

 

Be more specific on what years 4.8 and 5.3 you are talking about. And what year PCM.