Fuel Sending unit/Evap Canister/Fuel gauge issues

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    Fuel Sending unit/Evap Canister/Fuel gauge issues

    Vehicle Details:
    2002 Suburban 2500 8.1L 4x4 LT with 167K on the clock. If it matters, it does not have the robust fuel system (K53)

    Scenario:
    I bought this burb in February of 2019, and ever since, there are times when refueling, the pump will shut off multiple times long before the tank is full, and when removing the cap, there is a prolonged and quite voluminous sucking noise. No sweat, evap/vent issue, I'll get around to it.
    last Wednesday, I was headed out of town on a 2000 Mile round trip when about 500 miles into the trip, the fuel gauge goes from 0.5 tank to Empty and the low fuel light pops on. Drive another 100 miles or so, and it jumps back to 0.5 tank and holds there. This happened with nearly every tank on the trip and at about the same 0.5 tank mark on the gauge. When I would fill up, the gauge would jump to full.

    I got back to the house Saturday and started dropping the tanks (two tanks, two pumps, two senders). I know that the primary pump had been replaced at some point by a previous owner, but the aux pump is OEM. When dropping the tanks, I also noticed that they seem to have been under quite a vacuum as both poly tanks were a bit collapsed in. They seem to have returned to shape sitting on the shop floor, but that is a helluva vacuum to collapse those right? Everything else in the system looked good, but I only want to do this work once and I would like to fix the vent/evap issues while I am here.

    Question:
    I plan to replace both pumps, fuel filter, evap canister, evap solenoid (the weird part about my solenoid is there is no connector to it...just a vent?), and fuel cap.. Am i missing anything that may be contributing to the described issues?

    Any advice will be appreciated. (well, most )

    Sorry for the long post, thank you in advance.

    #2
    Well, the crickets in this thread have unanimously told me to charge ahead with my plan so, we will see how it all goes together this weekend.

    Comment


      #3
      I changed the front pump and "sensors" as GM calls them in my 07 and athing is right with the world.

      Try the front first if you have more than one tank.

      Keep in mind my year and most likely yours as well the gauge in the cluster works off both sensors to get an aggregate fuel level (i didnt see if you had more than one tank.)

      Comment


        #4
        Thank you for chiming in. Yes two tanks (front primary and rear aux). The front had been replaced at some point with a Delphi, so I am sure it is still good. The rear is original. I am going to replace them both just to be sure. Now is the time with both tanks dropped.

        Were you encountering the same venting issues too? My evap system is unlike others I have seen. There does not appear to be any active components in the whole system. Just vent tubes, canister and "solenoid" with filter. I use the ""'s because there is actually no connector routed to or located on the Solenoid. It has the connector location on the body, but there are no pins where they should be. There is also no connector available from the chassis harness nearby.

        Best guess I have is that passive solenoid is not allowing air into the system thus building a large vacuum.

        Thanks again.

        Comment


          #5
          On my 06 the dealer said they replaced the vent valve solenoid and that cured my fueling issue.

          Not sure if the ‘99-‘02’s had the same parts though.

          Comment


            #6
            I suppose I might be lately I need to check codes but not getting the same symptoms you are.

            My code reader is a real low budget pos.

            Ill check the codes and edit in the numbers but one was a evaporate leak.

            The others in the order they arrived..

            PO300.
            PO335 OR 355.
            And the large evap code. PO455


            Originally posted by backchat View Post
            Thank you for chiming in. Yes two tanks (front primary and rear aux). The front had been replaced at some point with a Delphi, so I am sure it is still good. The rear is original. I am going to replace them both just to be sure. Now is the time with both tanks dropped.

            Were you encountering the same venting issues too? My evap system is unlike others I have seen. There does not appear to be any active components in the whole system. Just vent tubes, canister and "solenoid" with filter. I use the ""'s because there is actually no connector routed to or located on the Solenoid. It has the connector location on the body, but there are no pins where they should be. There is also no connector available from the chassis harness nearby.

            Best guess I have is that passive solenoid is not allowing air into the system thus building a large vacuum.

            Thanks again.
            Last edited by PAE; 06-23-2020, 10:21 PM.

            Comment


              #7
              Sorry, should have mentioned: no codes and no pending codes

              Comment


                #8
                I had a fuel level sensor go bad on a 2010 2500. It mounted to the side of the fuel pump on that truck. The fuel garage did a very similar thing to what you’re describing. That being said, I didn’t have any issue with the tank being under a strong vacuum.

                Comment


                  #9
                  I used to work on a lot of yukon/tahoes/burbs but they were soccer mom 1500s with single tank. Usually the refueling problem was the vent valve. They are mounted underneath and are exposed to all the road grime dust and mud.

                  But the operation of the system should be the same for dual or single tank. Vacuum from the engine sucks the vapors from the tank when the purge valve opens. When the system wants to check itself for leaks, it opens the purge valve to put the system under vacuum and closes the vent valve to seal it off, then monitors vacuum pressure loss. The vent valve is normally open for refueling.

                  So ill bet your vent valve is stuck or clogged causing both of your problems. That would explain your refueling issue with the nozzle clicking off, and the fudl gauge reading erratically. The vent valve wont open (or tries to open but cant) then you go to refuel, there is no path for the displaced gasses to escape. And they are sucked flat because when the purge valve opens, it puts the tanks under vacuum, but if the vent valve never opens there is constant vacuum. Your fuel level sender is likely getting jammed inside the tank because the tank is deformed when it gets sucked flat and the lever arm is catching on something in there.

                  It may not be setting a fault because it is a basic system and only checks for leaks. If the tank is sucked flat, it sounds like it is sealed pretty well!

                  Comment


                    #10
                    You described what I was thinking the problem may be very well. I have worked on a handful of these as well, Though usually 1500's, but I have never seen a slenoid without a connector. Is there another valve/purge I should be looking for?

                    Thanks for the feedback

                    Comment


                      #11
                      1000 Click image for larger version
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                        #12
                        Post a pic of what you are talking about. There should be a vacuum diagram on the under hood emssions label (if it still has factory hood). Take a pic of that too

                        Comment


                          #13
                          Yeah thats it.

                          Comment


                            #14
                            Well, I'll be, you learn something new every day. What are the odds the engine side purge valve is an issue?Click image for larger version
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                              #15
                              Boo, the diagram dont give us a location of components. Oh well.

                              Im still putting my money on the vent valve. A faulty purge valve is more likely to set a fault code. But I suppose if you want to go down the rabbit hole, it is possible to have both a bad purge and a bad vent. And If the vent clogged first, and was never fixed, it 'could' mask the purge valve problem. A stuck open/not sealing purge valve would also suck the tank flat, but it may not set a fault code for a leak if that vent is also stuck or clogged. Sometimes you will get a p0141/p0142 lean running fault because a stuck open purge valve is basically a large intake vacuum leak. But if that vent is clogged, it seals the leak, thus no lean running fault (but the tank sucked flat).

                              You should be able to hear or feel the purge valve clicking with the engine running (not going to be on all the time, only when computer thinks it is a good time to purge). Obviously you have vacuum at the tanks so you know the valve is at least opening. If it was not closing or sealing you would likely set a fault code for a leak or lean running condition.

                              Just an interesting tidbit, on that purge valve is a green cap. That cap is the test port for smoke testing the system to find a leak. There is a schraeder valve in there that you remove, and you connect your smoke generator there.. and if i remember correctly that schraeder is left hand threads, and the only way to get a new schraeder valve is to replace that whole line. Dont ask how I know

                              Comment

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