Question about GMC Sonoma

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I have a 1995 GMC sonoma with a 4.3 vortec motor. I have replaced the fuel pump, cam sensor, crank sensor, and it still doesn't run. It has good spark and when I spray carburetor cleaner, she will run. HELP! Thank you.

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  • 2 more comments 
  • deb4787 Apr 28, 2010

    I checked where the oil filter is supposed to be on the block, but they have an adapter plate with two lines going to the front of the engine, where the oil filter is. I did not find any relay. Thank you

  • deb4787 May 03, 2010

    I could not find the sending unit but I took a fuel pressure reading. It said kpAx10 the gauge went all the way to 10 or on the other side it went to 7. Where do I find a diagram to find the sending unit?

  • deb4787 May 06, 2010

    I have replaced the oil sending switch and it will not start. I removed the return gas line from the back of the manifold and I have no gas coming out. HELP!

  • deb4787 May 08, 2010

    what would course the fuel not to return to the gas tank on the 1995 vortex?

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  • Master
  • 3,489 Answers

The only other thing that will cuase this issue is the ECU itself. The ground circuit is completed by this unit. You can look in the power distribution box(before replacing the ECU) and check for the fuse, relay, and the power wire. The power wire should be the same for the injectors and then driven by the ecu for ground.

Posted on May 08, 2010

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  • GMC Master
  • 17,970 Answers

Removal and installation of the fuel pump and sending unit assembly is the same on MFI/SFI vehicles as it is for TBI vehicles.

I have a 1995 GMC - 6da992f.jpg

Fig.: Exploded view of the fuel pump and related components used on TBI equipped models

1965d91.jpg

Fig.: Fuel system pressure testing


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Fig.: The fuel pump test connector is normally found in the engine compartment, on the left fender

  1. Properly relieve the fuel system pressure.
  2. If necessary for access, remove the air cleaner assembly and plug the vacuum port(s).
  3. Disconnect the flexible fuel supply line, located in the engine compartment between the fuel filter and throttle body.
  4. Install a fuel pressure gauge, such as J-29658 or equivalent, in-line between the fuel filter and throttle body unit (between the steel line and flexible hose). If necessary use an adapter or T fitting in order to connect the gauge and complete the fuel circuit.
A T fitting may be fabricated for this purpose. Depending on the fuel pressure gauge, short lengths of steel tubing, appropriately sized flare nuts and a flare nut adapter may be used.
  1. If the engine will run, start the engine and allow it to run at normal idle speed. The fuel pressure should be 9-13 psi (62-90 kPa).
  2. If the engine does not run, turn the ignition ON , but do not attempt to start the engine. Listen for the fuel pump to run. Within 2 seconds of turning the ignition ON pressure should be 9-13 psi (62-90 kPa). If necessary, cycle the ignition OFF , then ON again, in order to build up system pressure.
  3. If the fuel pump did not run or system pressure did not reach specification, locate the fuel pump test connector. The test connector is usually found on the driver's side of the engine compartment (on or near the fender), with a single wire (usually red) leading from the relay to the connector. Using a jumper wire, apply battery voltage to the test connector in order to energize and run the fuel pump. The pump should run and produce fuel pressure of 9-13 psi (62-90 kPa). If the pump does not run, check the relay and fuel pump wiring.
  4. If the pump pressure was lower than specification, first check for a restricted fuel line or filter and replace, as necessary. If no restrictions can be found, restrict the fuel supply line between the pressure gauge and the TBI unit (a flexible hose may be temporarily clamped to produce the restriction), then apply voltage to the test connector again. If pressure is now above 13 psi (90 kPa), replace the faulty pressure regulator. If pressure remains below 9 psi (62 kPa), then the problem is located in the fuel tank (the fuel pump, coupling hose or inlet filter).
  5. If during Step 7, the pressure was higher than specification, unplug the injector connector, then disconnect the fuel return line flexible hose which connects the line from the throttle body to the tank line. Attach a 5 / 16 ID flex hose to the fuel line from the throttle body and place the other end into an approved gasoline container. Cycle the ignition in order to energize the fuel pump and watch system pressure. If pressure is still higher, check for restrictions in the throttle body return line. Repair or replace the line if restrictions are found or replace the faulty pressure regulator if no other causes of high pressure are identified. If fuel pressure is normal only with the flexible hose-to-fuel tank line out of the circuit, check that line for restrictions and repair or replace, as necessary.
  6. Once the test is completed, depressurize the fuel system and remove the gauge.
  7. Secure the fuel lines and check for leaks.
  8. If removed, install the air cleaner assembly.

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Posted on May 04, 2010

  • ZJ Limited
    ZJ Limited May 08, 2010

    Fuel filter is near the back of the vehicle just forward of the
    gas tank. Just look for the fuel lines coming out of the top of
    the tank and follow them a short distance forward….. you’ll find
    the fuel filter. This filter has a plastic quick connect lock on
    one end of the filter which is almost impossible to disengage
    without the proper tool.

    The Fuel-Sending unit on your GMC Sonoma is located inside the fuel
    tank. This unit is equipped with an arm that extends down into the tank
    and connects, through a variable resistor, with the fuel gauge on your
    instrument panel. In many cases, problems with the variable resistor
    makes replacement of the sending unit necessary.

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  • GMC Master
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What is the fuel pressure, do u hear the pump running? have u checked the oil pressure activated fuel pump cutoff switch near the oil filter to see if the wiring has been come off or is burnt onto the exhaust pipe, this is a common problem, very poor design, i will bet that is where your problem is,also does the check engine light work, do u have any codes in memory, here is how to check for fault codes with a jumper wire.

http://check-engine-light-codes.blogspot.com/2006/03/gm-1983-95-vehicles-obd1-codes-self.html

Posted on Apr 28, 2010

  • 2 more comments 
  • yadayada
    yadayada Apr 29, 2010

    it is not a relay it is is an oil pressure sending unit, it is near the distributor on the top of the engine block, has an oval connector. see picture below.


  • yadayada
    yadayada May 04, 2010

    THE SENDING UNIT IS AT THE REAR OF THE INTAKE MANIFOLD, IT IS HARD TO SEE.

  • yadayada
    yadayada May 06, 2010

    do u have power to the fuel pump relay, i think u are over your head here, suggest u seek a professional shops help with troubleshooting this

  • yadayada
    yadayada May 08, 2010

    have u supplied the info i asked for? if u have not then you are not going to get any useful help.

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  • Master
  • 2,427 Answers

One of the valves (low speed valve) the the carb is messing up,, service the carb by taking it apart and claning it or do what i would and replace the carb..

Posted on May 07, 2010

  • Rishi Roshan Ali May 07, 2010

    sorry!!!! if u have fuel injection system

    1.) clean and service throttle body system
    2.) clean and service injectors...
    3.) change plugs and wires..


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My 1998 gmc snonma votec wont start it cranks and cranks and after about 20 mins it starts after that i can shout it off and it will fire back up fine then a day will go by and it dose the same thing


You have to check the fuel pump pressure to make sure it is supplying sufficient fuel pressure..Try turning the switch to on but do not start..now listen for the fuel pump to prime the system..it should run for 4-5 seconds the shut off..now try and start..if it is fully primed it should start...note although you are getting some gas dosent mean the pump is ok...sometimes it starts to go bad and then all at once it will let you down for good...have it checked out..good luck

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Problems starting a 2000 Sonoma 4.3l vortec engine


It could be a bad fuel pump located usually under the rear of the vehicle on either passenger or driver side. Or you need to replace the fuel filter may be plugged up.

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What is the fuel pump pressure for a vortec 4.3l engine on a 2000 Sonoma gmc


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Cam sensor location


If you have a 4.3 vortec the cam sensor is in the distributor. 
Hope this helps you, kee3p me posted.

May 29, 2009 | 1998 GMC Sonoma

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Installed new fuel pump on 1995 gmc sonoma, still won't crank. Will turn over but not crank. Put on new alternator also.


Check the fuel pump relay.
Check the fuel pump auto shutoff switch, push RED reset button.

Apr 09, 2009 | 1995 GMC Sonoma

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