Fuel System

What does a 'fuel/fueling system' do?

It injects fuel into the air that is being sucked into the engine. Even though the carburetor is virtually non-existent anymore in the Astro/Safari world, I'm going to include it here.

It's the entire system of a tank(to hold the fuel), pump(to create flow), filters(to keep crap from plugging the injectors), regulators(to create/maintain a restriction to build proper pressure), injectors(meter fuel to the engine), supply/return lines(to move the fuel around), etc, all working together.

What type of fueling systems are there on Astro/Safari vans?

Carbs, TBIs, CPI/CPFI, SCPI, MPFI types are described below.

Engine Codes:

The engine code is the 8th character of the VIN number: https://service.gm.com/dealerworld/vincards/ or this link for when that site goes down: https://web.archive.org/web/20170609202619/https://service.gm.com/dealerworld/vincards/

Go by the VIN to be sure.

• 1985-1990 VIN E = 2.5L4 = TBI single injector

• 1990-1991 VIN B = 4.3V6 = TBI dual injector

• 1985 only VIN N = 4.3V6 = Carb

• 1986-1994 VIN Z = 4.3V6 = TBI dual injector

• 1992-1995 VIN W = 4.3V6 = CPI poppet valves

• 1996–2001 VIN W = 4.3V6 = SCPI poppet valves All of the 96-2001 can be upgraded to MPFI using the proper kit/spider. https://amzn.to/3rafCmf

• 2002-2005 VIN X = 4.3V6 =LU3 = MPFI individual injectors

2.5L inline 4

• 1985-1990 TBI 98 hp (73 kW)@ whatever rpm 2.5 L

4.3L v6

• 1985 CARB 155 hp (116 kW) @ 4000 rpm 230 lb·ft (312 N·m) @ 2400 rpm 4-BBL 9.3:1 LB1

• 1986 TBI 160 hp (120 kW) @ 4000 rpm 235 lb·ft (319 N·m) @ 2400 rpm TBI 9.3:1 LB4

• 1987–1992 TBI 160 hp (120 kW) @ 4000 rpm 235 lb·ft (319 N·m) @ 2400 rpm TBI 9.1:1 LB4

• 1987–1992 TBI 160 hp (120 kW) @ 4000 rpm 235 lb·ft (319 N·m) @ 2400 rpm TBI 9.1:1 LB4

• 1987–1992 TBI 160 hp (120 kW) @ 4000 rpm 235 lb·ft (319 N·m) @ 2400 rpm TBI 9.1:1 LB4

• 1992–1994 CPI 200 hp (150 kW) at 4,500 rpm 260 lb·ft (353 N·m) at 3,600 rpm CPI 9.1:1 L35 (standard on AWD, optional on RWD, internal balance shaft)

• 1995 CPI 190 hp (140 kW) at 4,500 rpm 260 lb·ft (353 N·m) at 3,400 rpm CPI 9.1:1 L35

• 1996–2001 SCPI 190 hp (140 kW) at 4,400 rpm 250 lb·ft (339 N·m) at 2,800 rpm SCPI 9.2:1 L35

• 2002–2005 MPFI 190 hp (140 kW) at 4,400 rpm 250 lb·ft (339 N·m) at 2,800 rpm MPFI 9.2:1 LU3

The higher the fuel system pressure, the quicker the pump wears out. The TBI units(9-14psi) and even older carburetors(4-6.5psi) are low pressure systems, where as the newer port injection systems(55-66psi) operate at a much higher pressure. Great for mixing fuel but harder on the pump.

Fuel pressure requirements:

• Carburated 4-6.5psi Running

• All years TBI pressure should be ~9-14psi Running

  • All other injection types MPFI and SCPI should be ~55-66 psi Key On Engine Off(KOEO) Note: Actual specs have varied slightly over the years, some examples are given below. You can also do the throttle blip test once the engine is up to normal operating temperature by quickly opening the throttle which should cause the fuel pressure to jump to ~61-64psi

    • 2002-2005 (MPFI) 55-62psi (from FSM)

    • 1996-2001 (SCPI) 60-66psi (from FSM)

Fuel Pressure Leakdown: If the fuel pressure drops off immediately after turning off the key, usually it's a regulator or a problem in the tank. Build pressure in the system, turn off the key and immediately pinch off the fuel supply line, if the pressure holds then the problem is in the tank, otherwise it's likely that the plenum has to come off.

Fuel and vacuum gauge for under 15psi. For carbs and TBI, but it doesn't include the TBI adapter

Fuel pressure test kit for TBI(includes TBI adapter) and all others.

Often you can borrow a fuel pressure test kit from your LAPS.

NOTE: If you are going to pinch off the return for testing, only do it with a fuel pressure gauge attached as pressure higher than 15lbs over spec can damage the fuel system components.

Fuel Pump Pulsator/Damper

Don't forget about the fuel pulsator/damper that is in the tank, it often gets eaten away by the corn(ethanol) in our fuel and then leaks. Can be replaced with another damper/pulsator or a piece of properly rated hose and clamps. Looks like 96 was the last year for these.

Fuel injection spider replacement is quite common on the ones that use the poppet valves. Poppet valves won't open at a pressure lower than 45psi and often have issues at even slightly higher PSI.

The newer 3rd Gen vans fuel injection system doesn't use poppet valves, but real injectors at the end of the spider assembly. They have made kits for the earlier 96-2001 vans that can be used to 'upgrade' the earlier SCPI fuel injection systems to MPFI, resulting in a much improved/reliable/smooth fuel injection system: https://amzn.to/3rafCmf

These were the prices the last time I looked, when this page was originally published:

1 reman injector costs $40-70 + gaskets + return shipping for core

1 new injector is about $80-110 + gaskets (no core charge)

1 reman spider is $160-200 + gaskets + return shipping for core

About $210 for a complete new assy w/shipping(no core charge) http://amzn.to/2o45wTg + gaskets

And if you are doing the upgrade from poppet injectors, if you need the bracket, they are available here: https://amzn.to/2R6lAaB or https://amzn.to/3erIOAN

If you are going to be changing the spider injector assy or replacing the regulator, you should also 100% change out the LIM gaskets if they have not already been done. https://amzn.to/3CWpN2X

Also, might as well drill out the ignition coil rivets while you are in there, replace with 2 m4 bolts that are ~25mm long. Makes replacement down the line a whole lot easier.

94 CPI reman injector spider https://amzn.to/3y64St3 and fuel lines aka nut kit: https://amzn.to/3Dzf4vn