Please note this thread has been inactive for 90 days. For the best results, please start a new thread.
Results 1 to 25 of 25
  1. #1
    Cadet
    Join Date
    Oct 2008
    Location
    Merritt Island, FL
    Posts
    10

    Default 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. #2
    Moderator achris's Avatar
    Join Date
    May 2004
    Location
    I come from a land down-under...Perth, Australia
    Posts
    15,186

    Default 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/

  3. #3
    Cadet
    Join Date
    Oct 2008
    Location
    Merritt Island, FL
    Posts
    10

    Default 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-

  4. #4
    Honorary Moderator Emeritus Don S's Avatar
    Join Date
    Aug 2004
    Location
    Western WA.
    Posts
    62,323

    Default 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.


    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.

  5. #5
    Cadet
    Join Date
    Oct 2008
    Location
    Merritt Island, FL
    Posts
    10

    Default 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-

  6. #6
    Cadet
    Join Date
    Oct 2008
    Location
    Merritt Island, FL
    Posts
    10

    Default 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-

  7. #7
    Honorary Moderator Emeritus Don S's Avatar
    Join Date
    Aug 2004
    Location
    Western WA.
    Posts
    62,323

    Default 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.


    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.

  8. #8
    Petty Officer 2nd Class
    Join Date
    Oct 2007
    Posts
    135

    Default 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?

  9. #9
    Cadet
    Join Date
    Oct 2008
    Location
    Merritt Island, FL
    Posts
    10

    Default 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-

  10. #10
    Cadet
    Join Date
    Oct 2008
    Location
    Merritt Island, FL
    Posts
    10

    Default 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-

  11. #11
    Honorary Moderator Emeritus Don S's Avatar
    Join Date
    Aug 2004
    Location
    Western WA.
    Posts
    62,323

    Default 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.


    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.

  12. #12
    Cadet
    Join Date
    Oct 2008
    Location
    Merritt Island, FL
    Posts
    10

    Default 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-

  13. #13
    Rear Admiral Maclin's Avatar
    Join Date
    May 2007
    Location
    Argyle, Texas, United States
    Posts
    4,162

    Default 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.

  14. #14
    Moderator achris's Avatar
    Join Date
    May 2004
    Location
    I come from a land down-under...Perth, Australia
    Posts
    15,186

    Default 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/

  15. #15
    Petty Officer 2nd Class
    Join Date
    Oct 2007
    Posts
    135

    Default 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.

  16. #16
    Honorary Moderator Emeritus Don S's Avatar
    Join Date
    Aug 2004
    Location
    Western WA.
    Posts
    62,323

    Default Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

    I'm beginning to believe you have two problems. Have you changed the starter lately? It wasn't automotive and missing a terminal was it?
    With the ignition switch in the run position, you should have battery voltage (whatever it is) at the PURPLE wire on the oil pressure switch. When you have the ignition switch in the start position and the starter is cranking the engine over, you should have battery voltage at the PURPLE/Yellow wire on the oil pressure switch which goes to the D terminal in the picture below.
    NOTE: The battery voltage will be less while the engine is cranking because the starter is pulling the voltage down, but it should be 10V or above.



    Once the engine starts, and the oil pressure builds the switch should close and put power to the pump.
    BUT, you have to have power to the purple wire at all times with the ign. switch on, and the switch must close when oil pressure builds or the engine will die.
    Don S.


    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.

  17. #17
    Cadet
    Join Date
    Oct 2008
    Location
    Merritt Island, FL
    Posts
    10

    Default Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

    Starter and solenoid are original equipment. I'm the original owner as well. I've changed the alternator, water pump, manifolds, risers, oil pan and throttle linkage, but that's it. Not too bad for a 15 year old boat, I figure.

    This was the last year the 20SL was made, and I understand Wellcraft was rather infamous for slapping together odds and ends at the end of a production run. My linkage especially, was made up of 3 different brands of parts that no manual shows as being stock. Might have been the dealer too, I know. Just saying that it may be possible Wellcraft or the dealer did something a bit abnormal with this particular boat.

    Anyway, with regards to the above diagram (you're finding some excellent examples, by the way - cool!), this does look like my solenoid, alright. But mine has the battery cable, the breaker cable and the orange alternator field wire all on A, the yellow w/red stripe on B, the purple w/yellow stripe on D and an insulated strap on C going into the starter housing. No red w/purple stripe even coming out of the wrapped harness. Now, it's difficult to see for sure, especially in this afternoon's fading light, so I'll double check all that in some good light tomorrow, and try to get a picture as well.

    I'm trying to follow the pressure switch logic. I know that the pump normally runs before the engine is cranking or running. It runs for about 5-10 seconds then stops. I've used that as a signal to start cranking the engine, especially in colder weather. Unless the pressure switch holds some residual pressure, this should not be possible until the engine is cranking.

    Also I found a schematic that matches my wiring. I attached it, but I'm not sure how to insert the image like you've been doing.

    -Mike-
    Attached Images Attached Images

  18. #18
    Honorary Moderator Emeritus Don S's Avatar
    Join Date
    Aug 2004
    Location
    Western WA.
    Posts
    62,323

    Default Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

    I'm trying to follow the pressure switch logic. I know that the pump normally runs before the engine is cranking or running. It runs for about 5-10 seconds then stops.
    Is this an EFI engine? For the pump to run when you turn the key on, it has to be. The SN you gave for the engine is for a carbed engine.
    Don S.


    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.

  19. #19
    Moderator achris's Avatar
    Join Date
    May 2004
    Location
    I come from a land down-under...Perth, Australia
    Posts
    15,186

    Default Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

    Oh dear, it looks like reality is on the blink again.
    Marvin, from "The Hitch-hiker Guide to the Galaxy" by Douglas Adams.

  20. #20
    Cadet
    Join Date
    Oct 2008
    Location
    Merritt Island, FL
    Posts
    10

    Default Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

    Nope, not an EFI engine. I wish! :>)
    Carburated LX engine. I hear what you're saying, but I can guarantee that this pump has had this behavior for the last 14 years. It has been my habit since about year 3 or 4 to listen for the fuel pump to stop before I would crank the engine. Seemed to help on cold days back in Colorado.
    -Mike-

  21. #21
    Cadet
    Join Date
    Oct 2008
    Location
    Merritt Island, FL
    Posts
    10

    Default Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

    Don,
    Thinking about when I started to listen to the pump, I remember now that this pump is slightly newer than OEM. The original pump failed when the boat was about 2 years old. The dealer replaced it under warranty, probably in '97. I had forgotten all about that. Didn't the 4.3L have an EFI option by then? Perhaps the dealer used a pump for an EFI system as my replacement? I'll have to look at the part number on the pump and look it up.
    -Mike-

  22. #22
    Honorary Moderator Emeritus Don S's Avatar
    Join Date
    Aug 2004
    Location
    Western WA.
    Posts
    62,323

    Default Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

    The EFI pump and/or a carbed pump ONLY comes on when something puts power to it. It does not have a mind of it's own. The ECM on an EFI engine runs the pump for 2 seconds to build fuel rail pressure to the injectors. The ECM controls that. There is absolutely nothing that will run that pump for 2 seconds in a carbed system. Your system is identical to the wiring diagram I posted earlier.
    Don S.


    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.

  23. #23
    Petty Officer 2nd Class
    Join Date
    Oct 2007
    Posts
    135

    Default Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

    maybe noise your were hearing is when fuel line was empty and once full pump would quiet down. you said purple-yellow wire went into harness it has to come out somewhere. you can still look under dash for fuse panel and see if you see puprle-yellow wire, i'd check all fuses both sides, like you said if dealer could have done anything, i'd check purple wire on back of alternator or at solenoid for voltage. if you can use your DVM to check ohm from both ends of p-y wire you can find. other than that you could get a test light and probe wire till it wont light and that's where trouble is at, i'd do that as a last resort.

  24. #24

    Default Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

    My mechanic just changed the starter on my 4.3lx alpha1 and now he says the fuel pump its not working or it won't turn on, on your post you asked the guy with the same problem if he changed the starter lately, what could be the problem with that?

  25. #25
    Honorary Moderator Emeritus Don S's Avatar
    Join Date
    Aug 2004
    Location
    Western WA.
    Posts
    62,323

    Default Re: No power to fuel pump on 1994 4.3L V6 Mercruiser

    Welcome to iboat Lex, you need to start a new thread with your question as noted by the red warning bar at the bottom of this thread suggested.
    Don S.


    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.

Similar Threads

  1. New Engine - Mercruiser V6 4.3L
    By thrasher in forum Mercruiser I/O & Inboard Engines & Outdrives
    Replies: 14
    Last Post: October 29th, 2008, 05:53 AM
  2. No Compression 1990 V6 4.3L Mercruiser
    By swozi in forum Mercruiser I/O & Inboard Engines & Outdrives
    Replies: 6
    Last Post: April 27th, 2008, 01:46 PM
  3. Fuel filter 4,3L V6 Mercruiser 1992
    By thrasher in forum Mercruiser I/O & Inboard Engines & Outdrives
    Replies: 4
    Last Post: August 1st, 2007, 02:26 PM
  4. 4.3L Mercruiser I/O power to fuel pump
    By floridablonde1 in forum Mercruiser I/O & Inboard Engines & Outdrives
    Replies: 4
    Last Post: April 29th, 2003, 09:04 PM
  5. 4.3L Mercruiser I/O power to fuel pump
    By floridablonde1 in forum Mercury & Mariner Outboards
    Replies: 1
    Last Post: April 27th, 2003, 08:17 AM
  1. iboats Forum Directory - Over 100,000 forum posts organized by topic