If you are planning on dropping a 2003 motor into your '99, the PCM of the '99 may not like it. If you do this, I would recommend pulling the PCM and engine wiring harness from the donor vehicle to put into yours. Reason being is that the 2002+ engines do not have an external EGR valve like the 2001-older engines do. That and I believe some of the other emissions equipement may have changed. Look over both engines very closely and note the differences. I think you'll be surprised.

But then again, if you use your upper intake on the donor long block, you should be ok.

 

the w motor is the more poweful engine, The 1994 w engine is the most powerful stock engine they made in the 4.3 liter. it probably has to do with the CPI injection (spider), its got like an extra 5 horsepower over all the other years of engines even the newer ones, so of course they decreased the hp in later years

 

If I may pose a very similar question...

I just found this board and am sure it will be very helpful in my decision.

I'm debating on a 99 Blazer 4x4 4D for my wife. I've got a 97 2D tahoe, but she prefers the Blazer and the two extra doors

Anyway, I came across a 99 with a blown motor. However, I have a 2000 Astro with the 4.3 that's been wrecked.
Are the motors interchangable? If not, are they at least the same block? According to the owner of the 99 Blazer, the "bottom of the motor needs to be rebuilt." I'm not too sure what he means, I'm waiting for a call back to get the rest of the details.

What do you guys think?

Thanks for the help. I'm looking forward to getting started

-Justin

 

The engine is basically the same. Teh differences come in the form of sensors and fuel injection systems. Swap the sensors from your engine to the new engine, and swap the intake manifold from your engine to the new engine and everything will work just fine.

The Astro engine may have the sensors on the opposite side of the engine from yours, however the ports should still be in the block for the sensors to match your engine. Take the plug out , put your sensor in, take out the other sensor, and put the plug in.