Buick 231cu. (3.8L) Engines

V6 Turbo SMPFI

The 3.8L Turbo-Charged engine was originally equipped with a Rochester 4 barrel carburator from it's first days up to the end of 1983. This engine used the VIN Code "3".

In 1984 that changed and many improvements were incorporated including a Sequential Mult-Port Fuel Injection system. These changes gave the engine a different VIN Code, VIN "9".

The F.I. was different from the earlier Analog MPFI which used a "banked" system used on some V8's that injected all four cylinders on each side of the engine, in that it used a Digital computer to inject fuel into the intake manifold one cylinder at a time just above the intake valves and just before the ignition for that cylinder. It uses sensors on the crankshaft and camshaft to send a signal to a more modern Digital computer to inject fuel into each cylinder. These same sensors also trigger a signal through the computer to fire the spark plugs through a coil system that was distributerless and had no moving parts.

This engine is not the same as the newer Buick 3800 engines used in the transverse mounted FWD cars of later years and they are not interchangeble.

Firing Order: 1-6-5-4-3-2

Distributor Rotation is Clockwise. Note: 1984-85 was a Distributerless system

Before checking the compression see this article: "Compression Testing"

• Ensure the battery is fully charged
• Remove spark plug wire from one plug and loosen the plug 1/2 turn.
• Re-install wire and repeat for each cylinder.
• Start and run the engine for a few seconds.

What this does:

• Loosens and blows any carbon on the spark plug nose out the exhaust.
• Hopefully blows debris from around the plug hole away.

Then:

• Remove all wires, keeping in order and all spark plugs.
• Perform Compression test cranking for at least 5 times/cyl.