• If this is your first visit to the iboats.com Boating Forums, be sure to check out the FAQ. To post a question or comment, begin by signing up. To start viewing messages, select the forum that you want to visit from the selection below.
  • ALL iboats Forum Members and Guests:
    To show our appreciation for your participation in the Forums, we're offering an exclusive Forums-only discount good for an additional 5% off your iboats.com order for a limited time.
    To redeem, simply call our Customer Service Team at 800-914-1123 (Open M-F, 9am - 8pm Eastern Time) and mention the Forums 5% off discount. Offer excludes engines, trolling motors, and electronics.

Announcement

Announcement Module
Collapse

Help Tip: If you have a question that has not been answered to your satisfaction in the archives, it is always best to start a new thread of your own. By starting your own thread, you will receive the maximum number of views by forum members.

Below are some additional forum policies in hopes of all iboats members will follow, Thank you.

1. Please do not reply to old threads or hijack existing threads. Old threads of a technical nature are like a library book, Please do not write in them.

2. Old threads should be considered archives and used for reference only. Please do not reply to them.

3. Do not take over someone elseís thread (aka hijack) with your own question, even if it is similar. If you have a question that has not been covered to your satisfaction in the archives, it is always best to start a new thread of your own.

4. If you have a question for the original poster (OP) and the thread is over 30 days old, send the OP a PM, he may not even visit the forums any longer, or may not notice your question in the old thread.

5. By starting your own thread, you will receive the maximum number of views by forum helpers that may not even notice your question when itís posted at the end of someone elseís thread. And those answers will be specific to your particular issue.

6. Please do not post to threads that have been inactive for more than 3 months unless you are the original poster. We have very active forums and any thread that remains inactive for that long should be considered "dead". It is especially confusing when there is an entirely new question posted to an old thread.

7. Posting at the end of any thread is considered to be hijacking the original posters thread which in turn subjects the thread to be closed if it continues to happen thus not making it fair to the original poster in the future had for some reason he/she needed to return for additional information or provide an update of the problem solved which is always welcomed within a reasonable amount of time frame.

8. Please note that you should see a red banner pop up near the bottom of each inactive thread asking you not to reply to old threads. The Red banner will read: Please note this thread has been inactive for 90 days. For the best results, please start a new thread.

Thank you all in advance for doing your part in helping iboats run a smooth ship.

Additional forum rules linked below.
http://forums.iboats.com/forum-rules-guidelines-405/
See more
See less

No power to fuel pump on 1994 4.3L V6 Mercruiser

Page Title Module
Move Remove Collapse
X
Conversation Detail Module
Collapse
  • Filter
  • Time
  • Show
Clear All
new posts


  • No power to fuel pump on 1994 4.3L V6 Mercruiser

    I am trying to troubleshoot my starting problem. It was running fine about 2 months ago before TS Fay came through here. This is the original 1994 Mercruiser 4.3L V6/Alpha One combo in a 1994 Wellcraft Excel 20SL. Engine S/N is OF272108.

    The fuel pump will not run, the accelerator pump is dry and the fuel line above the pump is dry. I did get a fair amount of fuel from the line that runs from the tank to the bottom of the pump. The engine will crank and will fire if "hand fed" a small amount of fuel directly into the carb (I know - dangerous thing to do. I used a very small amount, and yes, I did replace the flame arrestor before cranking it over). Oh yeah, fuel tank is over 3/4 full as well.

    Using a DVM, I have checked the wiring at the pump connector. I have continuity through the black wire to ground, but no voltage through the purple w/tan stripe wire, with the ignition on. I cannot locate the other end of the purple w/tan stripe wire after it disappears into the wrapped wiring harness behind the carb.

    Electrical seems to be generally OK as the engine will run when it gets fuel as noted above. I have checked every connector and splice I could find to make sure things are seated (I did find and repair one bad connector to the bilge pump, though). Oil pressure registers on the dash gauge when it tries to run.

    Anyone have any ideas? I'm not convinced yet that it is the pump itself until I can confirm that the power is getting to the pump.

    Thanks!

    -Mike-


  • #2
    Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

    Just above the oil filter (non-remote filter) is an oil gallery fitting. There's a tee piece with the oil pressure sender and an oil pressure switch. The supply for the fuel pump is fed through that switch. It's only closed when there is oil pressure. The way the pump gets power when cranking is through a terminal on the starter solenoid.

    To test the pump without the engine running you can temporarily jumper across the oil pressure switch. Those switches have been known to be a problem with corrosion. Many 4.3 owners, not knowing the dangers, have jumpered them out permanently.

    Chris........
    The world takes on a whole new perspective when viewed from 100' below...



    1972 Bertram 'Bahia Mar' 20
    2006 Mercruiser 4.3MPI (0W617679) w/Alpha 1 Gen II (0W829301)
    **
    Please don't send service questions in private messages. That's what the forum is for. Messages of thanks, always accepted.
    **
    Member of the month - April 2013. http://www.iboats.com/blog/achris-member-of-the-month/

    Comment



    • #3
      Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

      Thanks! I didn't locate those connectors - I was focused on the top end. I'll give that a try tomorrow, and post the results here.
      -Mike-

      Comment



      • #4
        Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

        Here is the fuel pump wiring diagram. It may help you understand how and why it works.

        Don S.

        sigpic

        Please, no PM's (Private Messages) regarding boat/engine problems.
        That is what the forums are for.
        Only forum/moderator issues will be answered in PM's.

        Comment



        • #5
          Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

          Thanks, Don S! That clarifies what achris sent. I'll be checking back on these this afternoon. I'll post the results here when I return.

          -Mike-

          Comment



          • #6
            Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

            OK - first, I tried the jumper across the oil pressure switch with no change in results.

            Second, I traced all the connections in the schematic down to the terminals and found no problems with pinched wires, corrosion, loose connections, etc., other than two exceptions: 1) the red/purple wire that is supposed to feed the starter solenoid does not exist in this harness, and my solenoid does not have another post to connect anything to, either. 2) I have an additional red cable running from the battery post on the starter solenoid up to a 50A breaker mounted on a bracket on the intake manifold alongside the start slave solenoid. This cable is slightly smaller than the red battery cable, but much heavier that the other wires in the harness. The output of this breaker uses a heavy red/purple wire that disappears back into the harness and I presume feeds the red/purple common line that goes back to the alternator.

            My next thought is to use a splicing connector and tap the purple/yellow wire from the fuel pump and connect it directly to the battery to see if the pump will run.

            Any other thoughts? You guys have been great and I really appreciate the feedback. Although the solution hasn't been found yet, you've been very helpful!

            Thanks!

            -Mike-

            Comment



            • #7
              Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

              My next thought is to use a splicing connector and tap the purple/yellow wire from the fuel pump and connect it directly to the battery to see if the pump will run.
              Don't ever do that on your boats wiring. That would be the weak spot in the wire and would eventually corrode and break.
              Just unplug the connector on the pump and use a couple of jumpers from the battery to test the pump.
              You just push in on the wire on the connector to release the connector.
              Don S.

              sigpic

              Please, no PM's (Private Messages) regarding boat/engine problems.
              That is what the forums are for.
              Only forum/moderator issues will be answered in PM's.

              Comment



              • #8
                Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

                I have not seen a post on it yet but did you check all fuses?

                Comment



                • #9
                  Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

                  Yeah, I wasn't crazy about that idea, either. I've seen plenty of wires corrode internally from that kind of break in the insulation. I was going to hit it with some anti-corrosion goop I have and wrap it with some high-heat electrical tape. Better not to do it at all, though.

                  I'm off to the garage to build a couple of jumpers....

                  Thanks!

                  -Mike-

                  Comment



                  • #10
                    Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

                    Funny, now that you mention it, I haven't even seen a fuse. No fuse block or inline fuses, either. Just the one master 50A breaker. Interesting.....

                    Thanks!

                    -Mike-

                    Comment



                    • #11
                      Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

                      The only fuse you will have is one under the instrument panel. But, if it blew, you wouldn't have spark either. Since it will run if you get gas to it, you have spark.
                      When you check the pump, if it doesn't run, DO NOT start beating on it or holding the power to it for long periods of time. It may just be locked/gummed up from sitting.
                      Don S.

                      sigpic

                      Please, no PM's (Private Messages) regarding boat/engine problems.
                      That is what the forums are for.
                      Only forum/moderator issues will be answered in PM's.

                      Comment



                      • #12
                        Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

                        OK, the pump works!

                        I ran jumpers straight to the battery and to ground and got a solid flow of fuel from the pump. I had the fuel line disconnected and in a can so I could be sure there was fuel instead of just hearing the pump run. Pulled the jumpers off and re-connected the fuel line and the connector to the pump and turned the key on. No noise from the pump. I cranked the engine and it started right up and ran for about a minute at idle, then stalled and would not restart. Just used up the fuel in the line, I'm sure. Repeated the experiment and got the same results. Pumps with jumpers. Engine runs for a minute after re-connecting it all, then stalls. No noise from the pump while connected to the harness.

                        Also jumpered the connectors for the oil pressure switch one more time to be sure and still no noise from the pump, so I believe it's not a bad pressure switch. Actually, if I look at the schematic, I don't think the pump relies on the pressure switch for power anyway, and I seem to remember the pump running as soon as I turn the key to "ON" (but not to "START") and then it would stop in about 5-10 seconds, presumably because it reached adequate fuel line pressure to start the engine and keep the float bowl full.

                        So, I'm back to the wiring harness. How much voltage should I be able to read at the pump connector? A full 12v or something less? I'm going to do as many continuity checks and voltage checks as I can before I give up and call my mechanic. I'm just going to hate it if I have to pay him $250 to find a $20 part has gone bad. :>)

                        Many thanks again!

                        -Mike-

                        Comment



                        • #13
                          Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

                          The pump will get a full 12 volts under the proper circumstances. If it is carbed then the pump should not turn on with the key. The pump will only get 12 volts when the key is in the START position during cranking or when the engine is running and the oil pressure safety switch sees oil pressure and turns "on". This is how it works if wired correctly. You should be able to read the wiring diagram and see how it all connects.

                          You will never have power at the pump with just the key in the ON position (engine not running). However there should be 12 volts on one of the oil pressure safety switch terminals in this condition (key ON and engine not running). If there is power at the oil pressure switch then jumpering across those terminals should give 12 volts to the pump and it would start pumping (this could indicate a bad oil pressure safety switch). If there is not 12 volts at the oil pressure safety switch on either terminal then the problem is between the oil pressure switch and the 12 volt source.

                          The pump receives a full 12 voilts with the key in START position thru a bypass circuit. If the pump does not run when cranking then the problem is between the key and starter/solenoid or starter/solenoid and the pump.
                          1991 HydroSwift 2200 Cuddy Volvo Penta 570/DP
                          1980 Glastron SSV167 90HP Mariner

                          Comment



                          • #14
                            Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

                            With the key ON, you should get volts (all 12) at one of the terminals (purple wire) on the oil pressure switch. If you have that, then put your temporary jumper in place and see if it's still there. I'd be looking for a bad connection somewhere that has 12 volts there without load, but when the load comes on, the voltage drops away.

                            Check voltage at oil pressure switch without the switch jumpered, and then with the switch jumpered. If you don't have voltage there any time, then start working back towards the purple wire.

                            Chris...........
                            The world takes on a whole new perspective when viewed from 100' below...



                            1972 Bertram 'Bahia Mar' 20
                            2006 Mercruiser 4.3MPI (0W617679) w/Alpha 1 Gen II (0W829301)
                            **
                            Please don't send service questions in private messages. That's what the forum is for. Messages of thanks, always accepted.
                            **
                            Member of the month - April 2013. http://www.iboats.com/blog/achris-member-of-the-month/

                            Comment



                            • #15
                              Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

                              make sure your connecting a water supply if letting engine run, so you dont end up with a second problem.

                              Comment

                              Working...
                              X