engine cylinder head has dual quench-type combus-
tion chambers that create turbulence and fast burn-
ing of the air/fuel mixture. This results in good fuel
economy.

The cylinders are numbered 1 through 6 from front

to rear. The firing order is 1-5-3-6-2-4 (Fig. 1).

The crankshaft rotation is clockwise, when viewed

from the front of the engine. The crankshaft rotates
within seven main bearings. The camshaft rotates
within four bearings.

BUILD DATE CODE
The engine Build Date Code is located on a

machined surface on the right side of the cylinder
block between the No.2 and No.3 cylinders (Fig. 2).

The digits of the code identify:
• 1st Digit—The year (8 = 1998).

• 2nd & 3rd Digits—The month (01 - 12).

• 4th & 5th Digits—The engine type/fuel system/

compression ratio (MX = A 4.0 Liter (242 CID) 8.7:1
compression ratio engine with a multi-point fuel
injection system).

• 6th & 7th Digits—The day of engine build (01 -

31).

(1)

FOR EXAMPLE: Code * 801MX12 * identi-

fies a 4.0 Liter (242 CID) engine with a multi-point
fuel injection system, 8.7:1 compression ratio and
built on January 12, 1998.

LUBRICATION SYSTEM

DESCRIPTION

gear—type

positive

displacement

pump

mounted at the underside of the block opposite the
No. 4 main bearing.

OPERATION

The pump draws oil through the screen and inlet

tube from the sump at the rear of the oil pan. The oil
is driven between the drive and idler gears and
pump body, then forced through the outlet to the
block. An oil gallery in the block channels the oil to
the inlet side of the full flow oil filter. After passing
through the filter element, the oil passes from the
center outlet of the filter through an oil gallery that
channels the oil up to the main gallery which
extends the entire length of the block.

Galleries extend downward from the main oil gal-

lery to the upper shell of each main bearing. The
crankshaft is drilled internally to pass oil from the
main bearing journals (except number 4 main bear-
ing journal) to the connecting rod journals. Each con-
necting rod bearing cap has a small squirt hole, oil
passes through the squirt hole and is thrown off as
the rod rotates. This oil throwoff lubricates the cam-
shaft lobes, distributor drive gear, cylinder walls, and
piston pins.

The hydraulic valve tappets receive oil directly

from the main oil gallery. Oil is provided to the cam-
shaft bearing through galleries. The front camshaft
bearing journal passes oil through the camshaft

Fig. 1 Engine Firing Order

Fig. 2 Build Date Code Location

1 – YEAR
2 – MONTH
3 – DAY

9 - 62

4.0L ENGINE

sprocket to the timing chain. Oil drains back to the
oil pan under the number one main bearing cap.

The oil supply for the rocker arms and bridged

pivot assemblies is provided by the hydraulic valve
tappets which pass oil through hollow push rods to a

hole in the corresponding rocker arm. Oil from the
rocker arm lubricates the valve train components,
then passes down through the push rod guide holes
in the cylinder head past the valve tappet area, and
returns to the oil pan.

4.0L ENGINE

9 - 63

DESCRIPTION AND OPERATION (Continued)

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