fuel pump pressure is within factory spec when key on and with engine running and when shut down

ok, when was the last time you had the injectors cleaned?? not an additive, they never work, but done professionally??? makes a huge difference.

Roy

I haven't. Another thing is when the engine begins to load up at idle there is smoke coming from tailpipe, but, when the engine clears up the smoke disappears

My question at the time: I have a 94 ranger 4.0 5 speed trans. I'm having with the engine's performance. When I am driving and there is no load on engine it acts as if there is a breakdown in the ignition, but when it is at full throttle it runs great. I hooked up my scanner and ran KOEO and got codes 538,411,412,121. KOER codes: cylinder 6,21,15,38,25,14,41. The expert suggested I have the fuel injectors cleaned. Hell, what about the other problems.

Greetings

Those codes are almost always a result of operator error during the KOER test. You likely missed pushing the brake pedal after engine id was output and missed the dynamic response test (aka goose test) just before the codes are output. Try testing again and let me know what you get.

As far as the other codes, I suggested the injector cleaning as a start. one problem can cause many others to come up.

I would use this as a starting point before moving forward. You said you did not have it done. I would get it done, have the regulator checked and then we move forward eliminating this as a possible failure.

Roy