took old motor out of my 2001 Chevy Blazer 4x4 which is 4,3L v6 vortec and put another motor out of a 98 chevy tahoe but wasn;t the original motor that came out of the tahoe and motor look the same. Went to start it Blazer will crank but not start. throws a P1638 code. there was a few things like motor mount different fan sets up a bit higher, help please. is there a difference in motor or wire harness? can send picture if needed

 

so took the scpi from engine that came out put it on one i put in the blazer leaking gas out of exhaust and in spark plugs. acts like it wants to start but unhooked the fuel pump fuse drained out gas by manually turning fly wheel only code it throws is a p1638. also says it has Fed / California Emission. Not understanding why it wont start...

 

Swapping engines over several model years is a major undertaking.

To correctly understand what you did:

The engine comes out of your 2001
The engine from a 1998 Tahoe (i guess the same old 4.3 V6) comes out of that donor car
You put that 1998 Tahoe engine into your 2001 Blazer

What has been swapped along with the engine?

The manufacturer makes a package of a car with a specific engine and ECU which goes along with that.
This ECU controls far more than the engine but is also integrated into the electrical system of the car, the transmission, transfer case etc.

What we normally see on successful engine swaps is to swap the mechanical part of the engines but keep the original setup for air-intake, fuel injection and sensors. This keeps the ECU happy and may work. In other success cases the engine was swapped together with the full harness and ECU but I doubt that this would work with a 2001. Especially not with swapping an older model engine into a newer car. (Apart from legal issues which may arise, depending on the state you live in.)

Maybe some members will chime in which have done such swaps.

In the meantime I would suggest, you search for "engine swap" in the forum. Lot's of information there.

 

Correct on the motor except that the donor motor from the '98 Tahoe was a donor to the Tahoe so therefore I do not know where or what it came out originally out of, but the casting number on but engine is 14099090W. and both say 4.3L 6 SGI.anged the intake and it dumped gas in the spark plugs. still wont start. could it be something to do with the key fob or theftlock deterrent feature on the 2001 blazer.

 

Yes this could be an issue. But if using the correct FOB and it is correctly paired to the Blazer it should work.

Have you swapped the engine harness or used the 2001 Blazer OEM harness?