When replacing the ignition or to check while troubleshooting we have to check for correct base timing.
The ignition used on the VIN Z, (TBI) version of this engine has something particular to it when it comes to setting the base timing.

We have to disconnect the adjustment wire from the distributor in order to be on the basic mechanical timing.

Now on the 4x4 version where is this f*****g wire?

The manual states a brown black wire near the firewall but does not state where exactly. Only the electrical and diagnostic manual will give a hint as now you can see that it is on the passenger side of the firewall and not the engine side.

You may have to remove one of the covers under the dash in the foot room of the passenger side. Or you are able to pull the carpet down easily. If not possible better to remove the cover (couple screws) instead of cutting the carpet because a couple of cables run below the carpet. Below the dash under the carpet we will find the ominous black and brown cable and - oh wonder - even a connector which can be pulled apart easily.

Now adjust your timing and your Blazer should be running fine again.

NOTES
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You can actually set a base timing with the cable connected but then you will have the following symptoms:

- Starts just fine every time either cold or hot (no issue there)
- Accelerates just fine when very cold
- Won't accelerate when starting to warm up and will feel like having 50 HP instead of 165 HP.
- Low rpm will deliver lousy performance but will eventually take you places
- Fuel economy is terrible (consumption is up by about 25 - 30 %)
- Shifting feels like it shifts down earlier as one is used to (needs more fuel at same rpm and sluggish acceleration makes you push accelerator even more which makes it shift down at some point).
- Will have near normal power at high rpm

TECH
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Despite having a distributor we are dealing with an electronic ignition controlled by the ECU. Only on start-up the ignition module controls spark and delivers it according to a basic mapping until passing 400 rpm at which point the TACH signal from the distributor makes the ECU take over advance control from the distributor. As we need to know the zero point we have to adjust the distributor which is the only source of the correct mechanical happenings on these engines for the ECU. But we have electronics interfering with this so we have to tell the IC on the distributor to stop messing with our timing and go into basic mechanical mode. This is done by disconnecting the brown-black wire.

Now we can set the basic timing using a timing light on #1 cylinder spark plug.

The difference is about 8° where, when done wrongly, at least the ignition is late (safe side) but makes an awful ride.

Trying to find my pics and when I find them I'll post them as well.