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Before & After - My 1993 K1500

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  • Sounds like you ruled out the IAT sensor itself and generally if the circuit is shorted or open you will get an extreme signal one way or the other (like -30 or 300).

    Next step is to verify the reference signal. Should be getting a 5 volt signal to the sensor. The PCM supplies both the 5 V and the ground.
    Not sure about the wire size causing the issue. If the IAT is reading too low that should correspond to a higher resistance, and I would expect the larger wire to have a lower resistance. Wouldn't be surprised if you are getting straight battery voltage as I think that this increase in voltage compared to the desired 5V would cause an increase in resistance that corresponds to the temp reading you are getting.

    Comment


    • Originally posted by Waffle
      http://ls1tech.com/forums/pcm-diagno...uit-input.html

      Read this link for some info and it talks about some details with the iat. Remember that last sensor you had that was grounded to chassis and not to the pcm? Maybe thats the case here or maybe a wire is open somewhere. Anyway, it talks about proper volt and ohm readings for the iat.
      The MAF was the sensor that I grounded the signal from the PCM. It was black so I tied it in with the others.

      Originally posted by blazerbrad View Post
      Sounds like you ruled out the IAT sensor itself and generally if the circuit is shorted or open you will get an extreme signal one way or the other (like -30 or 300).

      Next step is to verify the reference signal. Should be getting a 5 volt signal to the sensor. The PCM supplies both the 5 V and the ground.
      Not sure about the wire size causing the issue. If the IAT is reading too low that should correspond to a higher resistance, and I would expect the larger wire to have a lower resistance. Wouldn't be surprised if you are getting straight battery voltage as I think that this increase in voltage compared to the desired 5V would cause an increase in resistance that corresponds to the temp reading you are getting.
      I will check the voltage tonight.

      Comment


      • There are 5 wires going to the MAF. The pink wire is key on power at 16.42v
        The yellow and tan wires on both vehicles with key on, not running, MAF plug disconnected were 5.82 volts. The rest of the tests were done with them running fully warm. I checked the temp of the air filter on mine and it was 105.


        -------------------Mine-------------Wifes
        IAT temp---------73---------------93
        Yellow------------3.14-------------5.06
        Tan---------------3.09-------------1.90
        Pink
        Black
        Black/white

        Wifes car
        Click image for larger version

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        • Took the truck out for a test run and it did pretty good. It threw codes all day about the MAF low circuit, but it still ran pretty good. It needs some fine tuning. The hill in the video was difficult because you started dragged your diffs about 3/4 of the way up. Took a bunch of attempts, but I finally made it up.

          Comment


          • The concept is pretty basic as you are turning a couple solenoids on and off to just shift between the gears. The purpose of the computer is to control and adjust the shift parameters....basically up and down shift timing and shift firmness based on speed, engine rpm, load, etc...

            I believe what Kevin is talking about is if everything is working 100% properly the transmission will still upshift into 2nd gear when you reach maximum RPM even if you have the shifter pulled down into 1. In some situations that is not what you want to happen and I think the big hill climb is one of those. It would shift into 2nd and you could hear the engine bog down. It would also be nice to start from a stop in 2nd gear sometimes.

            Back to the ECM receiving a signal that the t-case it is in 4 low, I was curious if this was the case and finally got a chance to confirm there is a signal that adjusts parameters if it is low range, just as said above. If the VSS was at the output of the transfer case on the donor vehicle (which assume it was since he had to modify the transmission from the donor to get a VSS) then it is not changing the speed signal itself, but would be changing the algorithm that controls the transmission shift points (which are based on engine RPM, vehicle speed, load, etc...).

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            • The pcm will shift out of manual 1st to 2nd at the WOT setting specified in the tables. You can start in 2nd, but if stomp on it it will kick into 1st. The easiest way to solve this is to use a shift kit. http://www.summitracing.com/parts/tr...-hd2/overview/ It is exactly what I want. The last kit I did I set the shift firmness to towing so it didn't snap hard. It was fine in 2 hi, but 4 lo was was harsh at higher rpms. I might leave the firmness stock and have the firmness adjusted in the pcm. I do think hooking up the 4 lo wire will help with shifting in drive, but that's it. For now, I will hook the 4 lo wire up and deal with it. I just changed the fluid and flushed it out with Dex 6, so I'm thinking this winter I'll do something. That was like $100 in trans fluid...

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              • The wire I should've left intact. DOH!!!

                Click image for larger version

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                • I pulled the harness mostly back out so I could run the 4 lo wire and see what the deal was with the MAF sensor. I was thinking that I attached one to many black/white ground wires together. GM uses black and black/white wires for sensor wires too, not just grounds. Well, that wasn't the problem, they were all good. When I shortened the harness, I staggered the solder connections so there wasn't any next to each other and used shrink tube. For whatever reason, I didn't stagger the MAF wires. Well the shrink tube shrank too far, and a few pointy soldered wires were sticking out and touching the other wire. I fixed those and now the IAT reads within 2 degrees of the coolant temp, or room temp... I'll know tomorrow how the 4 lo wire works out.

                  Comment


                  • that has to be frustrating as hell. I am glad that you are making progress.
                    1976 CJ 5
                    1984 CJ 7
                    1993 K3500 GMC 6.5 TD

                    Comment


                    • Originally posted by tbshakie View Post
                      that has to be frustrating as hell. I am glad that you are making progress.
                      Yes, very Hopefully it will run like it should now.

                      Anyone ever run Tom woods off set u-joints? Curious to see how they hold up.
                      My front t-case joint binds some at full droop, so I bought one hoping it won't bind anymore. I usually have to service that joint after every ride.

                      ATTACH]8381[/ATTACH]
                      Attached Files

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                      • I don't know anyone that runs them. Have read they vibrate like hell at anything over crawling speed, but I do NOT have any first hand experience.
                        1976 CJ 5
                        1984 CJ 7
                        1993 K3500 GMC 6.5 TD

                        Comment


                        • Originally posted by tbshakie View Post
                          I don't know anyone that runs them. Have read they vibrate like hell at anything over crawling speed, but I do NOT have any first hand experience.




                          My front shaft is made with AG spline, so I'm sure I won't notice any extra vibrations.
                          Last edited by 93 Krawler; 08-12-2015, 08:30 AM.

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                          • I took it for a spin today, and it runs great now. IAT temps are right where they should be. The speed is now correct in 4 lo too. Looks like I'm good to go. Windrock here I come.

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                            • Out of curiosity, did you now have the VSS on the transfer case or transmission? Glad to hear it is running better now. Now it's time to tear it back out for a cam and a shift kit!

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                              • Originally posted by blazerbrad View Post
                                Out of curiosity, did you now have the VSS on the transfer case or transmission? Glad to hear it is running better now. Now it's time to tear it back out for a cam and a shift kit!


                                It's on the tcase now. There may be a cam in the future, but I'm done for a while...

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