4.8 to 5.3 Swap. Engine in but I need troubleshooting help.

[RedHeartbeat]

Sounds like you have a vacuum leak somewhere or the IAC motor needs to relearn. First off I would start with getting the tune corrected before you kill this engine, too. You made too drastic of a change to keep running the same tune even limping it around. You say it's overheating too? Definitely get the tune done since it could be doing all kinds of strange things causing overheat issues. Have you removed the air bleed hose that goes from the heads up to the TB and make sure you have a good stream of coolant coming out? If air is trapped in there you will overheat. Make sure those lines flow. If you added headers and didn't have them before you undoubtedly moved the 02 sensors. If they don't warm up properly you won't get a good reading from them. The most common fix for 02 issues on trucks with headers is getting the after cat 02 sensor from about a 2002 Corvette and wire them in instead of the truck 02s. They are made to read at cooler exhuast temps. An alternative is to wrap your headers with exhaust wrap to help keep the heat in the airstream.

[trunknuts]

Sounds like you have a vacuum leak somewhere or the IAC motor needs to relearn. First off I would start with getting the tune corrected before you kill this engine, too. You made too drastic of a change to keep running the same tune even limping it around. You say it's overheating too? Definitely get the tune done since it could be doing all kinds of strange things causing overheat issues. Have you removed the air bleed hose that goes from the heads up to the TB and make sure you have a good stream of coolant coming out? If air is trapped in there you will overheat. Make sure those lines flow. If you added headers and didn't have them before you undoubtedly moved the 02 sensors. If they don't warm up properly you won't get a good reading from them. The most common fix for 02 issues on trucks with headers is getting the after cat 02 sensor from about a 2002 Corvette and wire them in instead of the truck 02s. They are made to read at cooler exhuast temps. An alternative is to wrap your headers with exhaust wrap to help keep the heat in the airstream.

Okay, sorry. I meant to say the engine 'doesn't' overheat. I don't have heating issues. I did remove the air bleed hose and it is flowing well. As far as the headers go, the original 4.8 had the headers installed and I retained all four 02 sensors. I did check for vacuum leaks, but found nothing wrong. How do I get the Idle Air Control Valve to relearn?

I'm sending out an extra 4.8 computer that I have and having it reflashed for the 5.3 tune. I guess I'll wait for that and see where it gets me. Thanks for your response.

[zebra]

well, if the tune you're running is programmed for the 42# injectors (or whatever they are), don't put the smaller ones in there.
you sure there ain't any vacuum leaks? i just installed my headers last night & the first start surged to about there & promptly died. thats when i remembered i forgot to plug the hole from the EGR delete

[trunknuts]

Okay. So I made a few changes. I now have a 5.3 block, with the 4.8 intake manifold, cable operated throttle body, original 5.3's injectors, and a properly tuned ECM. The idle is now at about 2,000 RPM! I've checked for vacuum leaks, with a gauge this time, and it's showing normal at about 20. I cannot think of any other issues. Any ideas? Can anyone tell me how to make the IAC motor relearn?

[mopower440]

you ever figure out the problem?

[yellowbu]

mine was doing something similar. I replaced the iac, went thru the idle learn procedure. Replaced the maf sensor. still had the prob. I had a ver slight vacuum leak at the intake gaskets. Replaced the intake gaskets and it idles smooth as new.