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Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 12788
Experience:  Have owned a repair shop for 25 yrs.
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1999 Tahoe: cranks..fuel pump..the throttle body and it runs fine

Customer Question

1999 Tahoe cranks and then shuts off like something is interrupting the fuel. Tried replacing the fuel pump and that didn't work. I can dump gas down the throttle body and it runs fine. Could the security system have something to do with it ?
Submitted: 2 years ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 2 years ago.

hi

1-when and how did this problem begin?

2-does the security light stay on or flash?

3-does the engine light stay on?if so,can you give me the computer codes?

4-does the security light stay on or flash?

tell me all you can

thanks

Customer: replied 2 years ago.

Ran fine Tuesday. Went out Weds morning to start it and it cranked several times but died each time after about 2 seconds.

 

At this point, I've now run the battery down trying to figure it out so I can't check the security and engine lights. I'll have to put a new battery tomorrow to check those lights and I'm bringing a scanner home tomorrow to hook up to it.

 

The weird thing about the security is, we've had this Tahoe for about 7 years. The first 2 years we had to do the security dance where we had to push buttons before turning key but at some point, it would start without us doing the song and dance so we have been starting it just by key cranking for about 5 years now.

Expert:  Tim's Auto Repair replied 2 years ago.

ok

you will need to check a few things here

1-scan it and get the computer codes,these will give a clue to the problem

2-check the fuel pressure,these must have no less than 60psi at all times,a weak fuel pump can cause this problem

3-if the security light is on,you may need to do the passlock auto relearn procedure to get it to start

thanks

Please ACCEPT my answer so I can get credit for my work.i don't receive commission unless you do ..I'm not always going to be giving you good news,so please don't let this stand in the way of you accepting my answer.it does not cost you more money.we will still be able to communicate.. Bonuses and positive feedback are appreciated!if you are not satisfied with my answer,please do not leave bad feed back,i will gladly opt out and let another expert handle the question.if i have sent any diagrams,please print them.they will only stay on here for an hour or so.PLEASE ASK IF YOU NEED MORE HELP

 

The following is the Auto Learn Procedure:

  1. Insure the ignition key is in the ON position.
  2. Clear all EVO/PASSLOCK(TM) module and VCM/PCM DTCs.
  3. Momentarily rotate the ignition key to the CRANK position (Do NOT start the vehicle), then release it to the RUN position (Do NOT key OFF in the process).
  4. Wait 10 minutes . Observe the SECURITY indicator.
    • If the PASSLOCK(TM) sensor was replaced the SECURITY indicator will flash for the 10 minutes duration.
    • If the EVO/PASSLOCK(TM) module was replaced, the SECURITY indicator will flash for a few seconds and then remain ON for the remainder of the 10 minutes duration.
    • If the VCM/PCM was replaced with a new programmed VCM/PCM and connected to the vehicle for the first time, the vehicle will start and this procedure may not be necessary.
    • If the replacement VCM/PCM was connected to any vehicle at any other time, even momentarily, the SECURITY indicator will flash for a few seconds and then remain ON for the 10 minutes duration.
  1. The SECURITY indicator will transition from flashing to ON briefly to OFF after 10 minutes if remaining in the ignition ON position.
  2. Turn the ignition switch to the OFF position and wait for 10 seconds .
  3. Repeat steps 3-6 two more times. The new security code is ready to be communicated among the PASSLOCK sensor, EVO/PASSLOCK module and VCM/PCM. The new password XXXXX XXXXX on the next ignition lock cylinder cycle from OFF to CRANK to ON (start attempt).

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.
Engine Cranks, But Will Not Run

 

Diagnostic Chart
Enhanced Ignition System

Circuit Description

This table assumes that the battery condition and the engine cranking speed are OK, as well as having adequate fuel in the tank.

Diagnostic Aids

If no trouble is found in the fuel pump circuit or the ignition system and the cause of an Engine Cranks But Will Not Run has not been found, check for the following conditions:

 

  • Fouled spark plugs
  • An EGR valve stuck open
  • Low fuel pressure. Refer to Fuel System Diagnosis (System Check). See: Component Tests and General Diagnostics\System Check
  • Water or foreign material in the fuel system
  • A grounded Ignition Control (IC) signal circuit may cause a No Stan or a Start then Stall condition
  • Basic engine problem

The Vehicle Control Module (VCM) has integrated IC circuits that are fault protected; therefore, if a circuit has failed, the integrated IC may not be damaged. If that is the case, the IC will keep the circuit open until the fault in the circuit has been corrected.

When the fault has been corrected, reinstall the VCM and check the circuit. Replace the VCM only if the circuit is still inoperative.

Test Description

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

  1. If the signal is over 2.5 volts, the engine may be in the clear flood mode which will cause starting problems.
  2. If the engine coolant sensor is below -30°C, the VCM provides fuel for this extremely cold temperature which will severely flood the engine.
  1. Use the injector test lamp J 34730-350 in order to test the injector circuit. A blinking lamp indicates that the VCM is controlling the injector.
  2. Voltage at the spark plug is checked using the spark plug tester tool J 26792. No spark indicates a basic ignition problem.
  3. This test will determines if there is fuel pressure at the fuel injection unit and holding steady.
Please ACCEPT my answer so I can get credit for my work.i don't receive commission unless you do ..I'm not always going to be giving you good news,so please don't let this stand in the way of you accepting my answer.it does not cost you more money.we will still be able to communicate.. Bonuses and positive feedback are appreciated!if you are not satisfied with my answer,please do not leave bad feed back,i will gladly opt out and let another expert handle the question.if i have sent any diagrams,please print them.they will only stay on here for an hour or so.PLEASE ASK IF YOU NEED MORE HELP
Customer: replied 2 years ago.

 

When I dumped gas down the throttle body it squirted out good from the schraeder valve. I also already checked all the fuses with a test light & replaced fuel pump relay. It's 10:45 pm here. I'll tackle it again tomorrow after work and let you know what I get. I'm a just a hard working white boy from Texas.....been a mechanic for 30 years/ASE certified so you won't have to get real detailed for me...just throw me ideas and I'll run with them. I work on a fleet of dodge buses for a living......the Tahoe is my wife's vehicle. I'll chat with you tomorrow night to let you know what did or didn't work with further testing.

Expert:  Tim's Auto Repair replied 2 years ago.

ok

it doesn't matter how much fuel comes out of the shrader valve,,,,40psi will shoot a stream,,but,it isn't enough pressure to push the fuel through the poppet injectors,,,so,check the pressure with a test gage

thanks

Customer: replied 2 years ago.

schraeder valve reads 60 psi

engine light doesn't come on

security light stays on

no codes came up on scanner

??

Expert:  Tim's Auto Repair replied 2 years ago.

ok

sense the security light does stay on...did you try the auto relearn procedure?

thanks

 

30 Minute Re-Learn Procedure

  1. Turn ON the ignition, with the engine OFF.
  2. Attempt to start the engine, then release the key to ON (vehicle will not start).
  3. Observe the SECURITY telltale, after approximately 10 minutes the telltale will turn OFF.
  4. Turn OFF the ignition, and wait 5 seconds .
  5. Repeat steps 1 through 4 two more times for a total of 3 cycles/30 minutes (the vehicle is now ready to relearn the Passlock(TM) Sensor Data Code and/or passwords on the next ignition switch transition from OFF to CRANK). IMPORTANT: The vehicle learns the Passlock(TM) Sensor Data Code and/or password XXXXX the next ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.
  6. Start the engine (the vehicle has now learned the Passlock(TM) Sensor Data Code and/or password).
  7. With a scan tool, clear any DTCs if needed (history DTCs will self clear after 100 ignition cycles).
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 12788
Experience: Have owned a repair shop for 25 yrs.
Tim's Auto Repair and 6 other Chevy Specialists are ready to help you
Customer: replied 2 years ago.
already did that. didn't change the security light. checked connectors...pulled on wires. still the same.
Expert:  Tim's Auto Repair replied 2 years ago.

ok

i will opt out,maybe one of the other guys has an idea of what is going on here,,,someone will be right with you

thanks

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