See Figures 1, 2 and 3
Your first stop in engine identification is the VIN which will supply you with a code to identify the engine with which the vehicle was originally equipped. If you believe the engine is not original equipment for your vehicle, identification can be a little more difficult. Check the labels found on about the engine compartment (radiator shroud, power steering pump reservoir, air cleaner) for more clues. Your last resort is the often difficult to interpret engine codes.
All engines will have some engine build code attached on a label and usually stamped or laser cut into a portion of the block. The 2.5L engine identification numbers are stamped on the left side of the rear engine block flange. All of the early-model (1985-89) and many of the later (1990-93) 4.3L engine identification numbers are stamped on a pad of the engine block which is located at the lower front edge of the right side cylinder head. On these vehicles the eighth digit of the serial number identifies the engine used in the vehicle.
Many of the later model engines relocated the identification numbers. On some 1990-93 4.3L engines, the number can be found at the rear left of the block, just above the oil filter adapter. The left rear location is also used on many of the 1994-96 engines covered by this guide. The balance of late-model engine codes are found on the upper right, rear of the block. On late-model 4.3L engines, the number is a 8 digit code which includes, a source code, month of build, date of build and broadcast code. See your dealer's parts department for translation of these codes.