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Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 15966
Experience:  Have owned a repair shop for 25 yrs.
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98 z71 4x4 that won,t start..few seconds..diagnostic equipment

Resolved Question:

i have a 98 z71 4x4 that won,t start, fuel pump is putting fuel out at good pressure, new fuel filter. only starts and runs for a few seconds if i pour fuel in thottel body. i dont have any diagnostic equipment, i need help thanks. [email protected],ca
Submitted: 8 years ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 8 years ago.

you need to get the fuel presure tested..these muust gave no less bthen 58psi at all may have a bad fuel is common to have a weak fuel pump in these


Testing and Inspection


Diagnostic Chart
Diagnostic Chart
Diagnostic Chart
Diagnostic Chart
Diagnostic Chart
Diagnostic Chart

Circuit Description

When you turn ON the ignition switch, the Vehicle Control Module (VCM) turns ON the in-tank fuel pump. The pump remains ON as long as the engine is cranking or running and the VCM is receiving reference pulses. If there are no reference pulses, the VCM shuts the fuel pump OFF within 2 seconds after you turn the ON the ignition or if the engine stops.

An electric fuel pump pumps the fuel through an in-line filter to the Central SFI unit. The pump is attached to the fuel level meter assembly inside of the fuel tank. The pump is designed in order to provide fuel at a pressure above the regulated pressure needed by the injectors. The pressure regulator keeps the fuel available to the injector at a regulated pressure. Unused fuel is returned to the fuel tank by a separate line.

Diagnostic Aids

Tools Required


  • J 34730-E Fuel Pressure Gauge.
  • J 34730-1A Fuel Pressure Gauge with J 34730-250 Fuel Pressure Adapter Kit.
  • d 42873-1 3/8 Fuel Feed Pipe Shutoff Valve and the J 42873-2 5/16 Fuel Return Pipe Shutoff Valve.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Wrap a shop towel around the fuel pressure connection to absorb any small amount of fuel leakage that may occur when installing the fuel pressure gauge. Turn ON the ignition leaving the engine OFF, the fuel pressure should be 415-455 kPa (60-66 psi). This pressure is controlled by a spring pressure within the regulator assembly.
  1. The fuel pressure that continues to fall is caused by one of the following items:
    • The in-tank modular fuel sender is not holding pressure.
    • The fuel pressure regulator valve is leaking.
    • A Central SFI injector is leaking.
    • Fuel line is leaking.
  1. When the engine is idling, the manifold pressure is low (high vacuum) and is applied to the fuel pressure regulator diaphragm. This will offset the spring and result in a lower fuel pressure. This idle pressure will vary somewhat depending on the barometric pressure; however, the pressure at idle should be less indicating the pressure regulator control.
  1. If the fuel pressure is less than 415 kPa (60 psi), it falls into the following 3 areas:
    • The pressure is regulated but less than 415 kPa (60 psi).The amount of fuel reaching the injector is sufficient, but the pressure is too low. The system will run lean, hard starting cold, no start, overall poor performance, and may set a DTC. Refer to Engine Cranks but Does Not Run.
    • A restricted flow causing pressure drop-Normally, a vehicle with a fuel pressure of less than 300 kPa (44 psi) at idle is inoperable. However, it the pressure drop occurs only while driving, the engine will normally surge then stop running as the pressure begins to drop rapidly. This is most likely caused by a restricted fuel line or plugged filter.
    • A leaking or contaminated pressure regulator valve or seat interface may not allow the regulated pressure to be achieved.

Notice: Do not allow the fuel pressure to exceed 517 kPa (75 psi). Excessive pressure may damage the fuel pressure regulator.

  1. Restricting the fuel return line allows the fuel pressure to build above regulated pressure. With the battery voltage applied to the fuel pump test terminal, the pressure should rise above 455 kPa (66 psi), as the valve in the return line is partially closed.
Customer: replied 8 years ago.
i don,t have a fuel pressure gauge, but i do know that there is lots of pressure, engine does not start.
Customer: replied 8 years ago.
is there a sensor or a solinoid that is stopping the fuel from getting to throttle body, engine was running great,i shut it off and went to start it 10 min. latter and now it won,t start. thankyou for your input. Customer
Expert:  Tim's Auto Repair replied 8 years ago.


these dont feed fuel through the throttle does it through the injectors under the will be hard to fix with out you haveing some testing will need to check a few things...first see if you have fire on the plug wires..if not it may be the icm


Description and Operation

All IC and Bypass functions are controlled by the VCM software. This reduces the number of circuits outside the controller and ultimately reduces the possibility for shorts or opens in those circuits that could result in driveability complaints or diagnostic trouble codes

Component Locations
Engine, RH Side
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Customer: replied 8 years ago.
tim, thanks for your feedback. your right i dont have the tools, wife has those too,ha ha. going to exept , truck starts and runs for 5 seconds if i pour fuel in the throttle body. i,d rather have an older chev that isn,t so complicated. thanks Customer