Congratulations! It looks like your truck still has all of the original equipment in place. Including the original "feedback" carburetor and thermostatic air cleaner. That is very rare for a 30 year old truck. Do not remove anything. These trucks run very well when all of the correct components are in place and working.

Like Franklin said, the next step is to pull the codes. Since you have a complete truck with EEC-IV, you should be able to get your truck to run great again without too much trouble.

 

A test light works well, just count blinks.

The EEC-IV connector might be red and might be near the battery area.

There are some youtube videos of guys pulling codes and counting blinks of the check-engine light, you might look at those as it's the same kind of blinking you'll see if you use a test light (or sweeps of a meter).

 

The 1980 - 1986 trucks did not have a CHECK ENGINE light. These models had an EMISSIONS light instead, located at the far left of the brow-mounted dash lights.

 

Correct, they don't have that; first year of those was 1988.

The videos I'm referring to are all of 1990s-gen models, there seem to be lots more videos of guys doing *that* than there are using a testlight or meter (althoug I've come across *one* of those but couldn't find it again last night).

 

[QUOTE=FrankOXO;16588599]I went to the site you suggested, the one above. My truck does not have a check engine light. Where do I find the multi-pin plug so I can use a meter to check for codes?[/QUOTE]

Look on the inner fender on the passenger side near the battery. It is either red or orange in color.

Oops! I see that ctubutis beat me to the punch.

 

Zero EEC-IV specific knowledge on my part (as proved in other posts), but here is some advice applicable to nearly any engine that won't pass emissions. This is in addition to the excellent advice already given:

Get new spark plugs. You mentioned cleaning them, but don't waste your time. They are cheap. Replace the distributor cap, rotor, and plug wires, too. I never feel bad suggesting normal tuneup parts. You need the ignition system in top shape and all these parts have a finite life span.

Definitely replace the O2 sensor. Even if there are no related fault codes, get a name-brand replacement. The bulk of the computer's decisions are based on this normal wear and tear part. It is very common for the sensor's accuracy to drift with age. You'll never know there's a problem until you run a tailpipe sniffer test.

The catalytic converter may also be suspect, especially if original. It's very easy to test. Beg, borrow, or steal a non-contact infrared thermometer. Even a cheap $30 unit will work fine. Take the truck for a test drive and get the engine to normal operating temperature. At idle, compare the converter temperature at the inlet and outlet ends. The outlet should be at least 100 degrees F hotter than the inlet. Run this test as quick as you can after a test drive, before it can cool off. If you see less than 100 degrees temp rise, the converter isn't working.

Please note this test isn't 100% conclusive. If you do see 100+ temp rise, it's still possible the converter isn't properly cleaning up the exhaust. However, if less than 100 temp rise with a warm engine, the converter is toast.