4.8L Isuzu Fuel Filter Replacement

How to Replace the Fuel Filter on an Isuzu 4.8L NPQ/NPR & Drain the Fuel Water Separator

Applicable Models:

1998 - 2004 Isuzu NPR/NPQ
1999 - 2004 Chevrolet/GMC W3500, W4500, W5500

Applicable Engines:

Isuzu 4.8L 4HE1 I-4 turbodiesel

Service Intervals:

Drain fuel-water separator and replace fuel filter every 13,000 miles/12 months or anytime there is an indication that there is a substantial amount of water in the separator bowl


Part Description

Part Number(s)


Fuel filter

Baldwin BF719
Wix 33382


Fuel water separator assembly

Isuzu 8-97188-042-1


Isuzu 4.8L NPR/NPQ Fuel Filter Service Procedures

Click any thumbnail to view fullsize, detailed image

fuel water separator location

• Locate the fuel-water-separator. On this Isuzu NQR, the fuel-water-separator is located just behind the drivers side door mounted on the outer frame rail.

draining fuel water separator

• Place a suitable drain container beneath the fuel-water-separator drain valve.

• Loosen the petcock (drain valve) on the fuel-water-separator and allow it to drain completely.

• Tighten the fuel-water-separator petcock after it has drained completely.

fuel filter location, 4.8L Isuzu

• Locate the fuel filter mounted on top of and towards the rear of the engine.

• Place several rags beneath the fuel filter canister to collect fuel that leaks out when the filter is loosened.

• Remove the fuel filter from the mount by rotating counterclockwise looking from the bottom of the filter into the threads on the mount (clockwise if looking from the top of the fuel filter mount downwards towards the engine).

fuel filter removed

• Verify that the fuel filter gasket was removed with the filter canister and is not stuck to the flange of the mount.

• Clean the fuel filter mounting flange with a clean, lint free cloth/shop rag.

lubricating gasket on new fuel filter

• Fill the replacement fuel filter with CLEAN diesel fuel. If no diesel fuel is available, a diesel fuel additive can be substituted. Do not add diesel fuel from the old fuel filter.

• Thoroughly lubricate the fuel filter gasket using clean diesel fuel or clean engine oil (engine oil is preferred).

replacement fuel filter installed

• Install the new fuel filter in reverse order. Tighten snug by hand; do not use tools to tighten the filter canister as overtightening may compromise the gasket seal.

fuel filter bleed valve location, 4.8L Isuzu

• Locate the fuel filter bleed orifice at the top of the filter mount.

• Loosen the fuel filter bleed orifice several turns (typically 22 mm wrench/socket).

• Place a shop towel/rag over the bleed orifice as it will seep fuel in subsequent steps.

fuel water separator bleed valve location

Optional step - fill the fuel-water-separator with clean diesel fuel or diesel fuel additive. Doing so may help the engine gain and maintain its fuel system prime following subsequent steps.

fuel prime plunger

• Locate the mechanical fuel pump mounted next to the high pressure injection pump on the drivers side of the engine.

fuel prime plunger ejected

• Loosen the black plunger affixed to the fuel pump until it ejects upwards.

• Operate the plunger by pressing down and subsequently allowing it to travel back upwards. Repeat until fuel begins to seep from the bleed orifice on the top of the fuel filter mount. This typically takes 30 seconds to a few minutes of pumping the plunger.

• Once fuel begins to flow from the bleed orifice on the fuel filter mount, tighten the bolt snug.

fuel system bled

• Push the plunger downwards into its bore and tighten. Do not attempt to run the engine with the plunger unscrewed and upwards in the operating position.

• Start the engine and allow it to run for several minutes. Check for fuel leaks at the fuel filter and fuel-water-separator. The engine is likely to run rough for up to several minutes and may stall several times until full fuel prime is obtained - this is normal.

• If engine will not start (i.e. lack of fuel prime), loosen the bleed orifice bolt, loosen the fuel pump plunger, and repeat the aforementioned bleeding procedures.