Rich exhaust and smoke

There are a couple of things that will cause the engine to run extremely rich even in these older trucks.

Basically, any computer-controlled engine relies on correct sensor reading.

This means we need to know the correct amount of air that is coming in and the correct fuel pressure. The PCM uses these two things including all the temperature sensors to properly match the amount of fuel needed.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

The PCM can only control the amount of fuel so it needs to know how much air and at what temp to get the proper air fuel mixture.

Lastly it relies on the o2 sensors to tell is exactly what it is doing so that it can make adjustments based on rich or lean exhaust.

So, we need to check all these sensors and see if they are showing that the air is coming in and proper fuel pressure and temperature.

Then we need to see that the o2 sensors are seeing that the exhaust is rich. If it is not, then the o2 sensors are the issue.

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

If all this checks out, then more than likely the PCM is the issue, and it is not able to adjust things properly even though it is getting correct info.

Let's start with this and go from there. Thanks

I think we may have found the Issue. The early 1990's Ford truck put the PCM in a bad location (through the firewall under the brake booster) allowing it to be venerable to water. We removed the computer to find it extremely rusted and it looks as though it had sat in a puddle of water. We are going to go ahead and swap it out just to cover that portion.

Thank you so much. That is great info. I am attaching the location of this module for those that may need it. It is where you talked about and is actually called the EECM.

Thanks for coming back and updating us.