LS 6.2L tech

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    LS 6.2L tech

    I have an 08 Yukon with a 6.2 in it, about a year ago while driving up I70 into the mountains it shut off while coasting down a hill, it started back up after pulling off to the side and hadnt had an issue since.
    Today while pulling up I70 to the Eisenhower tunnel it died again while coasting to a stop, went to push on the gas and nothing, just dead. This time it would not restart, so CDOT pulled me off to the side where I pulled relays fuses and pounded on the fuel tank thinking it was the fuel pump, and popped the gas cap on and off just out of habit.
    It would crank and ever so slightly kick, but not take off. I then pushed in on one of the shrader valves on the fuel rail and had plenty of fuel coming out, making me believe the fuel pump was ok.
    After sitting for about 45 minutes it started to try a little harder to start and after 10 or so attempts finally started and ran fine.
    I drove it 100 miles home with no issues until I got of the highways, whenever you would slow down and come to a stop for a light it would pull down below 500rpm and nearly stall, then have very poor throttle response until it got above 1000rpm. I started popping it into N at lights and keeping the revs above 1500rpm which seemed to keep it alive.
    When I got home I came to a stop and it about died when getting into the garage so I popped it in N and just let it try to idle thinking something in the trans was the issue, but it just surged around 4-500rpm, when I gave it some throttle it stumlbed really hard and struggled to climb about 1000rpm, but once it did it ran fine.
    There were no active or stored codes on it. I was thinking fuel pump or pressure regulator, but I am not very convinced thats my issue. After sitting for a few hours at home it runs fine now and I cant repeat any of it.

    #2
    Everything you say sounds like fuel pressure. Put a gauge on it and run it out the hood so you can watch it while driving under load.

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      #3
      Originally posted by larboc View Post
      Everything you say sounds like fuel pressure. Put a gauge on it and run it out the hood so you can watch it while driving under load.
      I was thinking fuel pump, but it runs fine under load. Only has issues at idle. Would that be a sticking pressure regulator?
      Its a very annoying issue, I went out and drove it for 20 minutes with HPtuners hooked up and couldnt get it to trip up at all

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        #4
        From my googling looks like several people have similar issues, and no fix for it.
        I doubt its anything with the trans, as that wouldnt make sense for no restart.
        https://www.tahoeyukonforum.com/thre...l.26430/page-3

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          #5
          Is the oil pressure ok? A buddy just did a swap with a 6.2 and had a oil pressure problem. Research showed low oil pressure can cause a "limp mode" issue.

          Apparently the pickup screen can get clogged or the o-ring on the pickup tube can get damaged and cause issues.

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            #6
            The big underhood fuse/relay box goes bad on GM vehicles and cause similar symptoms. Next time it happens, smack the relay box or put ice on it to see if it changes.

            Also, that thing needs 60 psi to start. If it didn’t get in your eyes or at least on your shirt when you pushed The schrader valve, it may have been a fuel pressure issue.

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              #7
              Clean the throttle body. I know it sounds stupid but I had the same issue on two different trucks. The problem won’t throw a code but what was happening:

              oil deposits built up around the butterfly and the plate couldn’t calibrate properly so when I let off the throttle the TB would operate at say 10% but because of the gunk inside the TB it would completely close and stall the engine only when coming to a stop or coasting. I had to do the same thing put it in neutral and keep the revs up. First I thought it was an alternator because I was seeing the voltage drop coming to a stop.

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                #8
                Originally posted by Baconator View Post

                I was thinking fuel pump, but it runs fine under load. Only has issues at idle. Would that be a sticking pressure regulator?
                Its a very annoying issue, I went out and drove it for 20 minutes with HPtuners hooked up and couldnt get it to trip up at all
                Maf signal look plausible? K N airfilter?

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                  #9
                  I second the throttle body or IAC. Similar problem on a car I have was caused by junk build up in the idle air control. I'm sure it's a different set-up in your engine than mine but it probably has something to perform the same function.
                  Last edited by WHATAHEEP; 06-22-2020, 08:51 AM.

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                    #10
                    Originally posted by WHATAHEEP View Post
                    I second the throttle body or IAC. Similar problem on a car I have was caused by junk build up in the idle air control. I'm sure it's a different set-up in your engine than mine but it probably has something to perform the same function.
                    No iac, but the TB issue is a tsb for those engines so it sounds likely. I would have thought that would throw a code though.

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                      #11
                      Does it have a factory Intake? I had a 6.2L Silverado that had a AEM intake, the filter kept falling off the Intake tube in the filter box and it wouldn't throw a code, but I had all sorts of drivability issues.
                      88 Ford F-turd50 IDI Crawler

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                        #12
                        Sounds to me like intake gaskets. Perhaps the ECU is reading something different than what is actually happening.

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                          #13
                          I cleaned the TB, made no difference. I replaced it just to rule it out and made no difference either.
                          It died on me today in an intersection, I bled the fuel from the rail and it tried starting a few times then finally took off and ran fine the rest of my trip. I pulled it into the garage an it started to choke a bit, I let it sit there in Drive to see what it would do and just stumbled around 500rpm, I gave it a little throttle and it recovered and idled fine.

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                            #14
                            Sounds like a fuel pressure problem. I've got that engine in my buggy and it requirsr really high pressure to run properly.

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                              #15
                              At this point, you need to have a scanner that can read real time values plugged in so it can record wtf is going on the next time it happens.

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