I have a 2004 Ranger XLT, 4WD, 4.0L. Swapped the engine at 200K with a Ford Crate motor and Ford crate transmission at 230K. Presently 258K and was running great until last weekend, cruising at 65 and no power. Was able to drive home another 12 miles at 30 MPH, no more.

Checked the transmission fluid, pink and not burnt. Replaced the fuel filter and air filter, air box was clean. Cleaned the MAF sensor, with no joy. Scanner is not picking up any codes, or pending codes.

My son threw out the possibility that it could be a clogged CAT, this make sense?

Thanks in advance for any insights.

 

Sure, partially blocked exhaust limits RPM and power
Any engine is basically a self powered AIR PUMP, so if you limit air in or air out you limit RPM/power

You can test for that with Vacuum gauge on the engine, vacuum gauges are $30 and can diagnose many engine running issues, good tool to have
Or just have your hand over tail pipe while some one REVs the engine