re-learn and timing retard

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  • shumro
    Junior Member
    • Dec 2016
    • 6

    re-learn and timing retard

    I have a 1996 GMC with a 305 Vortec. I am using a friends Modis and was wandering how to set up for adjusting the timing and also for a doing a crank relearn

    Thanks for any help
    Robby
  • Joe Rappa
    Snap-on DSD
    • Aug 2007
    • 2050

    #2
    If it's got a crank sensor, then you aren't going to be adjusting the timing.

    If you are talking about doing the cam position sensor offset, then:
    go to the Data Menu.
    Go to the EGR/EVAP Menu (most likely there. If not, just check the other data menus)
    Find the CMP Offset PID
    It should be 0 degrees +/- 1 degree
    If it isn't, turn the distributor a little, then rev the engine. The CMP Offset PID won't update until the RPMs are over 1500. So adjust the distributor, do a little throttle snap, recheck, etc.

    Crank Relearn is in the Functional Test Menu. Make sure you know how to do this before you mess with it. If you do it wrong, it won't learn anything.
    Why are you doing it? Did you replace the engine or PCM? If not, it's unlikely that you need to do it.

    Joe
    "You don't build a reputation on what you're going to do"
    Henry Ford

    Comment

    • shumro
      Junior Member
      • Dec 2016
      • 6

      #3
      thanks
      I will let you know how it turns out

      Robby

      Comment

      • shumro
        Junior Member
        • Dec 2016
        • 6

        #4
        no i just replaced the crank sensor, the old one had a bad o ring and leaked oil.
        Think I need to do it or not?

        Thanks
        Robby

        Comment

        • Joe Rappa
          Snap-on DSD
          • Aug 2007
          • 2050

          #5
          Originally posted by shumro
          no i just replaced the crank sensor, the old one had a bad o ring and leaked oil.
          Think I need to do it or not?

          Thanks
          Robby
          According to service procedures, Crank relearns need to be done if you replace the PCM, Reflash the PCM, Replace the crankshaft or engine.

          Unofficially, it can also be done when the scanner is showing misfires on all cylinders and the engine isn't misfiring.

          So, no. I don't think you need to do a crank relearn on that truck.

          Joe
          "You don't build a reputation on what you're going to do"
          Henry Ford

          Comment

          • shumro
            Junior Member
            • Dec 2016
            • 6

            #6
            Thanks
            The modis is showing 0 mis fires for all cylynders

            Comment

            • Joe Rappa
              Snap-on DSD
              • Aug 2007
              • 2050

              #7
              Cool. Do you CMP Offset and you're all set.

              Joe
              "You don't build a reputation on what you're going to do"
              Henry Ford

              Comment

              • shumro
                Junior Member
                • Dec 2016
                • 6

                #8
                Thanks Joe
                Just got a question on the timing.. Ive been told that the RPM's need to be above 1000 RPM and set it to "0", so after you adjust the distributor do rev it to 1500 and then drop to 1000 and re-check/

                Thanks
                Robby

                Comment

                • Flatrater
                  Junior Member
                  • Dec 2013
                  • 11

                  #9
                  Cam Offset spec is ±2° for a V8. While that is the spec, what you can get away with is much wider, more so on the positive side.

                  Once you drop more negative than about -8°, the rotor location under light cruise with the associated advanced timing (50+ °) will put the rotor too near the center of the distributor cap electrodes.

                  The PCM will need to see a little RPM before it will update the cam offset pid. Make your adjustment, raise idle speed for a moment, and then release it.

                  Originally posted by shumro
                  Thanks Joe
                  Just got a question on the timing.. Ive been told that the RPM's need to be above 1000 RPM and set it to "0", so after you adjust the distributor do rev it to 1500 and then drop to 1000 and re-check/

                  Thanks
                  Robby

                  Comment

                  • Joe Rappa
                    Snap-on DSD
                    • Aug 2007
                    • 2050

                    #10
                    Originally posted by Flatrater
                    Cam Offset spec is ±2° for a V8. While that is the spec, what you can get away with is much wider, more so on the positive side.

                    Once you drop more negative than about -8°, the rotor location under light cruise with the associated advanced timing (50+ °) will put the rotor too near the center of the distributor cap electrodes.

                    The PCM will need to see a little RPM before it will update the cam offset pid. Make your adjustment, raise idle speed for a moment, and then release it.
                    you are right about the RPMs. I mis-typed. It needs 1500 RPMs to update that PID. Not 1000 like I typed. Thanks for catching that.

                    Joe
                    "You don't build a reputation on what you're going to do"
                    Henry Ford

                    Comment

                    • shumro
                      Junior Member
                      • Dec 2016
                      • 6

                      #11
                      Joe
                      followed your instructions and the cam retard is -2 ... For a little history this is my sons truck... we replaced the heads and did the injection spider up date with the motor in the truck (what a task). I put the engine at TDC #1 during disassymbly and made three reference marks on the distributor... Cant believe I got that close on the re-install.. I wanted to tweak it to "0" but my 19 YO begged me to leave it be... he's been with out a truck for two weeks, Do you think -2 is close enough, it runs really well.

                      Thanks for your quick help with the motis, what a slick tool... wish my buddy would let me have it, I think I could make some cash... LOL

                      Thanks
                      robby

                      Comment

                      • greasybob
                        Senior Member
                        • May 2008
                        • 1590

                        #12
                        Yep, a good scan tool in the right hands is like having your own ATM machine. As far as the -2 degrees goes, it might be just a hair away from setting a P1345 code. A stubby wrench and a bump of the distributor might be all it takes to put it at Zero. Unless The rotation is already maxed out and it's up against the intake manifold.

                        Comment

                        • Joe Rappa
                          Snap-on DSD
                          • Aug 2007
                          • 2050

                          #13
                          Originally posted by shumro
                          Joe
                          followed your instructions and the cam retard is -2 ... Do you think -2 is close enough, it runs really well.

                          Thanks for your quick help with the motis, what a slick tool... wish my buddy would let me have it, I think I could make some cash... LOL

                          Thanks
                          robby
                          Flatrater posted that the spec was +/- 2 degrees for a V8. Honestly I didn't look it up. I've always set them between -1 and 1 degree regardless of the engine. I think you will be ok there, so give it a try. If it gives you trouble it will wither be the P1345 like greasybob noted, or the fishbite misfire that doesn't show up on the scanner as a misfire.
                          The cool thing about working on your own vehicles is that you can experiment and not worry about a comeback. If it gives you trouble you can fix it without a customer thinking you goofed up.

                          Glad you had fun with it. Happy Holidays!

                          Joe
                          "You don't build a reputation on what you're going to do"
                          Henry Ford

                          Comment

                          • ericsautomotive
                            Member
                            • Mar 2014
                            • 66

                            #14
                            Tech Note: Snapping the throttle gets the PCM to repost the cam retard degrees on your scan tool.
                            This makes tweaking the distributor make faster process on the GM engines...
                            Just a future thought, Eric's
                            Don't guess! Test !!

                            Comment

                            • Witsend
                              Banned
                              • Nov 2012
                              • 2942

                              #15
                              I think I would scribe a mark loosen the bolt and tweak the distributor just a hair in the opposite direction of rotation to advance it a couple degrees, If you have a new Chinese timing chain and gears , chain likely stretch a little and retard a couple more degrees and then you'll be out.
                              Better safe than sorry. Not quite like the old days where you take a point file across the sharp edge of the rubbing block of the points,NL2 lube the distributor cam and advance weights, and try to set the dwell a little on the lower side of the spec range, so as the rubbing block would wear and then the points gap get slightly smaller, the dwell would theoretically be spot on( unless of course the points eroded faster than the rubbing block.

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