When it gives you trouble otherwise, leave it alone.
I have a 2002 Blazer with the 4.3L engine and 3.73 differential gear ratio, it gives me 17 mpg on average.
on ebay search for NEW STARTER CHEVY 4.3L S10 BLAZER, C SERIES TRUCK 99 00 01 02 03 04 & ASTRO VAN this gives you an image.
The labor guide book gives 4 1/2 hrs. for a well trained mechanic to do. It has to be done right, are you will be doing it over again.
You should find a sticker under the hood, in the engine compartment that gives you that information.
The side door speakers are usually six inch, at least they are in my 95 blazer. If you buy one of those repair books based on a complete rebuild, it gives detailed instructions on how to take off door panels, replace speakers, etc.
Top, rear drivers side of engine, below the distributor. Removing the distributor gives you room to R&R the oil pressure sending unit.
I couldn't find any information that far back but here is a page that has 85 vehicles, pick the one closest to your vehicle and go the page that gives the mileage. http://www.fueleconomy.gov/feg/bymodel/1985_Chevrolet_Blazer.shtml
try changing the coolant temperature sensor that gives the computer it readings , it's located on the thermostat houseing and cost about 10 -15 dollars.
You cant unless you have access to a factory service manual that gives you the pin tests to test the ohm and voltage loads through it. Just replace it if you think it is bad. THen you have no question. Usually they are less than ten bucks. Usually.
That word is 'one'