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Pre-heater for Cummins 6BT-gctid378004

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    Pre-heater for Cummins 6BT-gctid378004

    Port side pre-heaters are not lighting up on my 3988. The "ready light" winks once when the key is turned on and then the light shuts off without going thru its 20 second cycle. Previously this was an intermittent problem which has now become permanent.The troubleshooting section of the manual provides a few system checks for this symptom which I am going thru. So far the thermistor looks ok. Reference is made to check a resistor and the manual provides pin numbers to check but does not indicate where this is. I pulled the wire harness plug off the top of the ECM and found a group of pins, but none that are numbered. Can someone shed some light on this? It should be a simple fix if it is only a resistor to replace if I knew where it was. ......this has not been a very productive day!

    #2
    There is a fuse located in the general area of the fuel filter. It is mixd in amoung a number of white wires in the area.

    Tom

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      #3
      Had similar issue on mine. The wires to the circuit breaker (small red button) at the rear of the engine had come loose.

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        #4
        The relays are just behind the starter on the right side of each engine. I'm betting they are shot. Its not that unusual, and because of the weak ground (from the heater box which contains the resistors (air intake, downstream of your aftercooler)) they end up burning out.

        To check, i would check voltage at the preheater connections at the intake, with the ignition switch turned on. If no voltage, next check at the relays. Bet you find they need replacing. The good news - Cummins in Surrey has a supply and they are relativly cheap. I think about $30 each. Beef up your ground wire and you should be able to not only fix the symptoms, but also the cause.

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          #5
          I had the same issue on my Cummins 270's. Easy way to check is to swap out unit that is in your other engine and see if that lights up . I found my sending unit was bad that way.Easy fix to swap out.

          Mike

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            #6
            You will know it is working even if the light isn't by listening to the change the voltage makes to the engine alarm or by watching the volt meter. If that tells you the relay works without seeing the light there is no major reason to change anything.
            1989 26' then 1994 32' now 2001 39'

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              #7
              Some good advice here folks.

              Tom - I will check around for fuses in that nest of wires.

              Superior Diver - will check the cicuit breaker wire.

              John - I have not checked the heaters yet, but assume the resistor referenced in the manual is in the heater box, and will check that today and beef up the ground wire as well. I think relays are available locally, and should probably pick some up for spares anyway.

              Uncle Bob - I can confirm that the circuit is not working- no change in light intensity or alarm sound.

              Thanks all - I will post the results of the next round of investigation.

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                #8
                The element in the heater box is a giant resistor - its like a small toaster in there.

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                  #9
                  I have now concluded the saga of the non performing pre-heaters on my port engine. But first let me relate some of the diagnostic details following the excellent advice provided in this thread.

                  - The Port side pre-heaters have failed somewhat intermittently over the past year, and have failed consistently since the last pull out a couple of weeks ago.

                  -Consulted the Cummins manual which has a fairly good diagnostic section for this item. It took a little effort to locate and identify some of the key elements of the pre-heat system, particularly the pin numbering sequence in the wiring bundle plug that connects to the ECM unit (computer). Man, those numbers are so small and hard to find, but they are there. For example, if the "ready light" winks once and then goes out you need to check, besides the thermistor, pin numbers 2 and 16 for a resistance of 15K ohms, and that resistance between pins 4 and 5 to be "not 0".

                  -Once the pins numbers were confirmed, the test was relatively easy. (They tested OK).

                  -Tested the thermistor per the manual (tested ok)

                  -Next, tested the heaters for conductivity as suggested in the manual. (Heaters checked OK).

                  -In case of a pooched solenoid, I bought a new one and installed it under desparation. (new solenoid still would not engage).

                  -Next, checked voltage from starter to the solenoid = 12.25v which looked to be in the range.

                  - Hmmm - it better not be the ECM (=$1700 replacement cost), but Cummins parts guy said he never heard of ECM gone bad.

                  - At that point it occured to me that although the house batteries had been on float charge all winter, the engine start batteries had not. After turning the battery charger on for the start batteries for a few minutes, and trying the pre-heat circuit again, the solution became clear. The solenoids were not getting enough voltage. SOUND FAMILIAR?

                  So upon reflection, I suspect that there are a combination of things to consider here, taking some advice from earlier comments in this thread:

                  -Make sure start batteries are fully charged.

                  -Check all battery connections (especially ground connection)

                  -Increase size of the ground wire to the heaters (as recommended earlier in the thread)

                  -Consult the manual, and take time to think things through logically, reflecting on things with a fine cigar or good quality scotch will help

                  -Conduct diagnostics methodically

                  -Remember, if things are not going well, it will all work out in the end, and if they are not working out, it is obviously not the end.

                  I now have a spare solenoid.

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                    #10
                    Bob, thanks for the great thread. When I had a problem, with other issues, my "toaster" did not go out. What do you think the problem may be, Sorry I am away from the boat, so yes a bit of a lazy question, hope you dont mind.

                    Cheers

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                      #11
                      Peter W wrote:
                      Bob, thanks for the great thread. When I had a problem, with other issues, my "toaster" did not go out. What do you think the problem may be, Sorry I am away from the boat, so yes a bit of a lazy question, hope you dont mind.

                      Cheers
                      Interesting problem, and potentially serious. I have heard of this as a cause of an electrical fire in the engine room. Several things come to mind. If the thermistor has failed in pre-heat mode, it could send a signal to the ECM that temp is below 35 deg. but the ECM should shut it off after 20 sec. After pre-heat cucle, the ECM goes into post - heat mode if rpm is under 1000 rpm, telling to toaster to cycle on and off.

                      To evaluate this situation we need more information: Is the toaster staying on at start-up, or is this condition showing up while under way in post - heat mode? Does it quit once you are up to speed (> 1000rpm?)

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                        #12
                        Hi Bob, thanks for your questions. I do not want to hijack the thread, however as we are in such a warm climate, we just disconnected, as we were short on time. We had run the engines for some time, and the port side had gone out. We did not have metres etc with us at the time to try to trouble shoot. Its still that way, and has not caused problems. Its on the to do list, however well down the line.

                        cheers

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                          #13
                          Peter W wrote:
                          Hi Bob, thanks for your questions. I do not want to hijack the thread, however as we are in such a warm climate, we just disconnected, as we were short on time. We had run the engines for some time, and the port side had gone out. We did not have metres etc with us at the time to try to trouble shoot. Its still that way, and has not caused problems. Its on the to do list, however well down the line.

                          cheers
                          Disconnecting them is probably best. If you are in a warm climate, it should make little difference on starting, especially if you have wolverine heaters. The post heaters are really a PITA anyway IMO.

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                            #14
                            Which Cummins manual did you use to troubleshoot the pre-heat problem?

                            I have the Operation and Maintenance manual and there is nothing in there covering the pre-heater circuits.

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                              #15
                              Here's another thought for those with pre-heat problems.

                              The ECM on the standard 4BT/6BT will not reliably operate below 10.5 volts. In some Bayliners, the wiring through ignition switches, two stop buttons, and multiple connectors may mean that the voltage drops below that level by the time it gets to the ECM. The wiring is undersized for the actual length, and, connections degrade over time.

                              In my boat, I had to run a new wire directly from the ignition switches to the ECM on each engine as I was only seeing about 9v there. The solenoids are fed directly from the battery, and don't pass through all of the switches.

                              The wiring diagram for the bulk of the later models is located in the model specific owner's manual.

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