suburban gas eater

[ChevyTech]

The plug in the second picture is where the vacuum assisted brake booster usually gets its vacuum from.

Does the one you are working on have Hydra-boost (hydraulic booster using fluid from the power steering pump)?

Your first picture shows, there are no holes in the intake manifold for an EGR valve. This is clearly not a regular production vehicle. It most likely does not have a standard prom (chip) in the ECM (computer). You can not use service manual to diagnose or repair this problem. You will need to concentrate on fundamental causes of pining (spark knock) (pre-ignition)

Test the fuel pressure.
Test for restricted exhaust.
Consider the quality of fuel in it.
Is the engine running to hot?
Check the ignition timing. Has the timing been changed – distributor turned or removed?

Make sure Nothing rattles, clicks, ticks, knocks or is loose anywhere on or in the engine OR transmission.

Code 43 can be the hardest code to find the cause of.

I will make a separate reply with instruction on testing fuel pressure and ignition timing.