So i have a 2003 ford ranger. Was driving one day and i heard a loud pop. Car lost speed and would not pass 50mph. I went home and tought it is the transmission. I bought. A used transmission to try and fix the truck. Now truck struggles to keep speed above 60mph. I dont know if it is an issue with the transmission or if it is another issue. Can someone guide me on this.

 

What engine, 2.3l, 3.0l or 4.0l?
What transmission, manual or automatic?

Does the engine idle smooth or rough?

 

3.0 automatic. Does not run smooth at all. Actually with the “new” transmission it idles worse than the original one

 

Use a vacuum gauge to test engine while idling, expected is 18-21", it will jump around if idle is rough, but should see above 18" average vacuum
Raise RPMs and watch vacuum, hold RPMs steady at 2,500 or so, vacuum will drop and then come back to 17-20"
If it stays lower then you have a clogged exhaust system
Disconnect exhaust again, at the manifolds, had to do this to remove trans, and try test again, and see if engine runs smoother

If engine is still rough then I would do a Compression test
Cold engine
Remove all spark plugs first
Test each cylinder and write down results
3.0l should be about 155psi average, but depends on the gauge

Any low cylinders probably have burnt exhaust valves