that pic was from a different thread where someone was trying to access the blend door from the engine bay, ignore the blue circle, you said the engine bay configuration is different?? that pic was missing alot of parts as i had to pull everything off the passenger fenderwell, Here is a pic of a completed, stock, 4.3 with a 2003 Block and California Emissions, Notice the only difference on top of the motor is an extra vacuum line that runs to a diverter actuator.

You mentioned a valve job, was any performance modifications done? either higher valve lift, ported heads/intake, or anything at all that would make it run differently, the PCM knows how a stock 4.3 should run and what it should see from its sensors, and if anything is done to make it run differently from stock, the PCM will pick it up and throw any number of codes, including the mystical P0300.

 

No modifications, but I bought the car "as is" with a chromed air intake, not stock. Cannot find a stock air intake anywhere, so far. I suspect that the previous owner may have tried to tune it at some time, just a hunch, though. I may go ahead with both the check valves, popped the P0440 code again today.

 

can you take a picture of the underhood of your truck? similar to the shot i had posted above.

 

Here are the photos of the engine bay, as requested!

2001 Chevy Blazer LS 4.3L engine bay

2001 Chevy Blazer LS 4.3L engine bay

 

. it has a 411 PCM??
thought those were a model year 2003 and forward thing.
You mentioned the previous owner may have tried to tune it, have any way of verifying it?
and lots of exposed wiring...

 

No way to verify the "tune" or not. It is a "411", though! Thanks, again for your expertise!

 

man model year changeovers are weird, dont make much sense either since GM didnt switch S10s to the new Serial bus until 2003+

 

I exposed the wiring because "rats" had eaten, a lot. This was painstaking, but, I had to find the shorts, exposed copper, etc. The ecu has been a question in my head, since I bought the car. I even ordered a new (refurbished) one, by a supposed reputable company, that ended up screwing me over. Anyway, stayed with the old one! Blazer starts just like it should, runs great and all. All finish work will be done when I get it through, smog!

 

Really super closely check over all wiring everything involved in misfire/detonation detection
this includes - Knock sensor, Cam sensor, and the crank sensor

 

Plugs, wires Dist Cap, knock sensor, crank sensor, all new and fresh. Relearns all done when needed...
Wiring still going over. I feel there may be a spot I didn't see or detect. This has been ongoing. It seems I've performed every detection procedure, My main focus has been wiring, from first seeing those eaten wires.