I bought this 4X4 Ranger several months ago. It is my 4th Ranger to own.
It started and ran good. But when I emission tested it, it recorded 6X over the limit. I cleaned the fuel system out and it tested 2X the max.
I replaced the O2 sensor and Computer.
When I started it, it ran for about a minute, backfired, and has not started since. Where do I go from here.
I have pulled the TBI system off and I am cleaning it thoroughly.

 

Over the limit on what?
CO
HC
NOx

Actual numbers for these would be helpful

If it backfired your timing belt may have skipped.

High NOx numbers means EGR system is not working right, if so equipped, or you are running lean if no EGR, with either you are probably "pinging" under load.


An important part of emission output is the engine temp, that's why "they" recommend driving vehicle for 20mins prior to bringing it in for testing.
2.3l tends to run cool which is very bad for the emissions and the engine.
It should have a 195degF thermostat and engine temp on gauge should be above 1/3(just below 1/2 is best) after 5 minutes of running.
If engine stays cooler then emissions will be higher and oil will never get warm enough to burn off water(condensation) and fuel(blow-by), this will cause bearing damage if left unchanged.

Standard cold startup on fuel injected, computer controlled, engine should be like this:
Engine starts and idles at 1,000rpms, a little higher if outside temp is very cold
As engine warms up idle will slowly drop
At normal operating temp(about 5 mins) idle should be at 700rpms and stable.

If idle isn't stable and tends to go up and down, then MAP sensor on firewall may have a leak in it's vacuum line, MAP sensor is a small device with a 3 wire connector and a vacuum line connected to the intake.
The MAP(manifold absolute pressure) sensor is the main sensor the computer uses to adjust the gross fuel and air mixture, O2's are used for fine tuning, but ONLY after engine warms up, O2's need to be at a minimum of 650degF to work.
So a mis-functioning MAP will cause rich/lean problems, so emissions problems.

 

It was high in every category. That is why I replaced the ECU. And that made it worse. Now it won't start after it backfired.

 

If engine was running OK before, then problem wouldn't be the computer, these tend to fail "big" when they fail, high CO or HC wouldn't be computer, a sensor giving the computer bad info maybe, but not the computer itself.

Actual numbers would be helpful.

"The “two-way” Cat converters combined carbon monoxide (CO) with unburned hydrocarbons (HC) to produce carbon dioxide (CO2) and water (H2O). In 1981, two-way catalytic converters were rendered obsolete by “three-way” converters that also reduce oxides of nitrogen (NOx)."

So with the actual numbers you may decide that the Cat converter isn't working like it should.
If you had high HC numbers then a working cat convertor should get red hot, that is a DIY test to see if Cat is working, engine idling disconnect spark on one cylinder, this makes an exhaust with very high HC(unburned fuel) and Cat will start to heat up very quickly, if it doesn't then Cat is bad.

Cat converter's wear out, usually they rust our and collapse internally, lol, but the material in them does get used up so they simply quit cleaning up the exhaust at some point.