I have taken the engine out of my 99 Dodge ram 1500 because the transmission went out and put the engine in my 2001 Dodge ram 1500 4x4 and it will crank but won't start? I have tried swapping the ecm from 99 with the 01 and didn't seem to help .. I did have to put the 99 wiring harness in the 01 because of different injector plugs and I noticed a sensor was on the intake manifold housing right in front of the injectors on passenger side of the engine on the 01 engine but not one on the 99 engine that I put into the truck. Not sure what it is? Could that be why it isn't starting?is the ecm not allowing it to start because of the missing sensor not communicating and if so will the 99 ecm work in the 01 truck that now has 99 engine in it?

 

Put the 01 ECM and wiring harness back into the truck, and swap the intake manifold from the 01 engine back in there as well. You are likely introducing problems, due to differences in connector pinouts.....

Also, check the crank position sensor. It is frequently a victim of engine swaps.