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Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
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Experience:  Have owned a repair shop for 25 yrs.
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97 Chevy: 4X4..shifting..My check engine light came

Customer Question

I have a 97 Chevy 4X4 5.7 liter with 260k miles... About a month ago my truck had a slight hesitation just before shifting down from overdrive (speed anywhere between 40 to 55). My check engine light came on and off a couple of times. My mechanic stated the codes where EGR circuit and transmission solenoid. The problem began to be more and more frequent. He checked the codes again with the EGR circuit showing again. He replaced the EGR valve and gasket with screen last year, so he now thinks it just needs to be cleaned out. Either remove the EGR valve and clean that out or remove the intake and clean that out. The problem is pretty much constant now... from a high rpm take off to even interstate speeds. When driving up and down slight inclines, I have to drop down to drive/3rd gear to avoid the problem. My mechanic says there could be carbon build up coming from catalytic converter or it is just normal build up. I have recently put 4 cans of "Sea Foam" and 4 cans of another brand cleaner without improvement. Any insight would be appreciated. I can not afford to "try this"... "ok then try this" if you know what I mean. My truck is my only transportation.
Submitted: 3 years ago.
Category: Chevy
Customer: replied 3 years ago.
Relist: No answer yet.
One mechanis says it is carbon build up, the other says number three is misfiring under load... I do not know which way to go.
Expert:  Tim's Auto Repair replied 3 years ago.

hi

the first thing to do here is to check the fuel pressure,these vortec engines must have no less than 60psi at all times,the fuel pump may be weak[common]and need to be replaced.....this is where to start on your truck

thanks

 

Fuel pressure

 

Testing and Inspection

 

Description

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

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

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.
    • 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.
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 12808
Experience: Have owned a repair shop for 25 yrs.
Tim's Auto Repair and other Chevy Specialists are ready to help you
Customer: replied 2 years ago.
Thanks for the information.... but $300 later, the plug wires were my problem
Expert:  Tim's Auto Repair replied 2 years ago.

hi

i didn't want you to replace the fuel pump without testing it.......if it tested well..we would have moved on

thanks

 

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