1986 Chevrolet Truck ENGINE WONT RUN RIGHT

Usually, you just go with the basics. I saw what you replaced, did you do any testing, before hand?

If it cranks good but won't start, have a helper crank it while you visually check for spark at the spark plugs. If spark everywhere, check fuel pressure and injector pulse where applicable. If your TBI fuel injection, 5 psi won't run a v8. You might get it started with a lot of cranking, but, it will run poorly and die quickly.

Another thought is to check timing, valve/spark.

If your computer controlled, check trouble codes. You should be able to check OBD1 codes, yourself.

Let us know what you find?

All "crank, no start" conditions are approached in the same way. Every engine requires certain functions to be able to run. Some of these functions rely on specific components to work and some components are part of more than one function so it is important to see the whole picture to be able to conclude anything about what may have failed. Also, these functions can ONLY be tested during the failure. Any other time and they will simply test good because the problem isn't present at the moment.
If you approach this in any other way, you are merely guessing and that only serves to replace unnecessary parts and wastes money.

Every engine requires spark, fuel and compression to run. That's what we have to look for.

These are the basics that need to be tested and will give us the info required to isolate a cause.

1) Test for spark at the plug end of the wire using a spark tester. If none found, check for power supply on the + terminal of the coil with the key on.

2) Test for injector pulse using a small bulb called a noid light. If none found, check for power supply at one side of the injector with the key on.

3) Use a fuel pressure gauge to test for correct fuel pressure, also noticing if the pressure holds when key is shut off.

4) If all of these things check good, then you would need to do a complete compression test.

Once you have determined which of these functions has dropped out,
you will know which system is having the problem.