Help with 5.3 swap!

[Clayman]

Ok so I just got done installing a 5.3 in my 94 2500 and it will fire up but immediately dies. Any ideas?!? Ive done a little research and all I can come up with is the vats... is this a possibility or do I have other problems? Any help GREATLY appreciated!!

[blacstar]

check everything from intake leaks past the maf sensor to communication to pcm, fuel pressure, its gonna be hard for anybody to diag without lookin at it in person. Assuming the pcm was flashed, start with the basis,air+fuel+compression+ignition. something is the culprit!

[Frenchy]

My gut is leaning towards VATS.

[Clayman]

Ive got good fuel pressure... brand new pump. And its firing right up it just idles for like 2 secs and shuts off. Ive checked all the vacuum hoses and they're all connected properly. Also when I went thru the new wiring harness to marry the two together all the wires checked out continuity wise from sensors to pcm. The only thing not connected is the vss... I have to lengthen those wires because the harness was from a 2wd 4l60 and I converted the trannyonly itself to a 4wd(by swapping output shafts). Is it possible that that would cause something like this?

[Clayman]

My gut is leaning towards VATS.

I hope so...most of what ive found about these symptoms is vats related and I have to get a tune anyways so hopefully that will take care of it.

[TRPLXL2]

What year is the truck??

I did an engine swap on a 97 firebird, and I had the exact same problem. It would stay running for about three seconds and then die, mine WAS Vats. I never had a custom tune done as it wasn't necessary, so I just bypassed it by grounding the theft deterent relay and using resisters in the ignition. If you have Theftlock (newer truck) Then it is a little more complicated...

[Clayman]

its a 1994 2500...

[Frenchy]

Just get the VATS deleted in the tune. Take the easy way out.

[Clayman]

Can I do that with a handheld efilive scanner or do I have to actually get it tuned?

[Clayman]

Also another question I have is my oil pressure gage... I plugged the obs sender in the hole the nbs sender came out of... with the help of an adapter but now my oil pressure gage is pegged all the way past 80 in the dash and when I turn the key on it don't move. Any ideas?!