boat electric fuel pump circuit at hot idle fluctuates on and off

Discussion in 'General Electronics Chat' started by sdowney717, Sep 21, 2012.

  1. sdowney717

    Thread Starter Member

    Jul 18, 2012
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    I have an older boat which has an electric gasoline pump wired so that for safety reasons the pump is only on when the engine has oil pressure and if the oil pressure drops it turns off the pump.
    The pump is controlled by a standard bosch type 5 pin automotive relay.

    The problem is with the boat motor at hot idle, the oil pressure fluctuates up and down rapidly. from perhaps 5 to 15 PSI on the manual gauge.
    This causes the oil pressure switch to open and close which causes the relay to also open and close rapidly which causes the pump to turn on and off and the pump indicator run light to flash and the buzzer beeps on and off.
    I put a restriction in the oil line feed to the pressure switch which helps a little.

    How can I electrically keep the relay on for the short time the oil pressure drops ?

    This is a wiring diagram I found on the web showing the basic idea of how the boat pump works.
    Mine has an added manual priming button I added to show the entire existing circuit.
    [​IMG]
     
  2. cork_ie

    Member

    Oct 8, 2011
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    You have 3 options.
    1) Check oil pressure on your gauge and if switch is dropping out at a pressure higher than rated closing pressure, change the switch.

    2) Rewire your circuit so that Ue alternator warning light circuit operates your relay instead. Verify that pump stops when engine is stopped & charge light lit.

    3) Bosch had a standalone relay on the K-Jetronic system that relied on an ignition pulse to remain closed. It is the perfect option as it comes on for 3 seconds when ignition is initially switched, to prime the system. After that it only closed in the presence of an ignition pulse, far more reliable than using an oil pressure switch. I am sure they are still available . They were fitted in several old (1980's -> early 1990's) Volvo, VW & Mercedes vehicles and I am sure you would get a good one at a car dismantlers.
     
  3. lightingman

    Senior Member

    Apr 19, 2007
    374
    22
    You just need a small delay/reset circuit.

    Whilst all is ok, the circuit is reset and holds the pump on. I the oil pressure drops, it starts the delay. If in the meantime the oil pressure rises again, it just resets the circuit. Only if the oil pressure is low for a certain amount of time will the pump cut out.

    You could do this with a monostable as a missing pulse detector. A 555 or a CD4047 and a transistor to drive the relay should do the trick.

    A delay of around 5 to 10 seconds should not damage the engine if the oil pressure drops.

    Dan.
     
  4. debe

    Well-Known Member

    Sep 21, 2010
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    184
    This is another way of doing it. Its a Gas safety switch that senses Ign pulses to stay on. It also stays on at switch on for a few seconds to prime fuel. This circuit is used as a safety device on LPG systems on cars.
     
  5. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    It is perhaps not that simple. As we have two situations. At hot idle then oil pressure fluctuate and then the oil pressure is normal.
     
  6. sdowney717

    Thread Starter Member

    Jul 18, 2012
    385
    13
    Looking at the schematic for ignition pulse, the 63v capacitor is that 2.2uf ?
    The capacitor after the zener says 104k 100v? what is that?
    ok, I see thanks. http://www.mikesarcade.com/arcade/components.html

    The switch at idle is fluctuating about 3 times a second

    I tried an AC Delco oil switch and a Standard Motor Products and both very similar.

    My oil pressure is above 40psi when running over 2000rpm
    The reason the oil pressure fluctuates at hot idle is due to the oil flow design of the camshaft opens a channel to the head on and off as it spins, this design is a known issue in the IH series of v8 engines when they get older.
     
  7. Dyslexicbloke

    Active Member

    Sep 4, 2010
    420
    19
    Sounds to me like n ideal project for a pre-built uP board.
    Arduino Nano for example, although there are many to chose from.

    Obviously you don't get all the fun of building logic and timers but if a quick flexible solution is what you are looking for then a single board uP, PSU and relay is quick readily available and cheep and can be simply programmed to do whatever you need.
    you could even sense the engine temperature and modify the low oil time threshold.

    Al
     
  8. sdowney717

    Thread Starter Member

    Jul 18, 2012
    385
    13
    Can you show me something I can buy in a link?
     
  9. cork_ie

    Member

    Oct 8, 2011
    348
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  10. cork_ie

    Member

    Oct 8, 2011
    348
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  11. Dyslexicbloke

    Active Member

    Sep 4, 2010
    420
    19
    Here is the link to Arduino hardware.
    http://arduino.cc/en/Main/Hardware

    It is all open source including the software boot-loader and assembler.
    There is genuine and compatible kit available all over the planet and as usual China will be the cheapest option, if not the most convenient of best quality.
    Check out Fleebay for want of a better place to start.

    The Nano and Mini are cheap and would do what you need, the Nano has an onboard USB/Serial port for programming making ti the simplest option.

    I have no vested interest in pushing Arduino and no links to the company, I just think it is a good product / concept.

    You could do what I am suggesting just as easily with most uP systems, at least those that have a simplified programming IDE so that you don't need to get into chip level embedded instructions.
    See ... Basic stamp, PIC and many others.

    Hope this helps
    Al
     
  12. sdowney717

    Thread Starter Member

    Jul 18, 2012
    385
    13
    Can someone please look at the schematic on the fuel injection relay here for a 1986 volvo and tell me how the wires will attach.
    If cork_ie is right this should work.
    His listing shows a relay with different pin configuration. this relay has the same pin numbers in different positions.

    [​IMG]

    This is from an EBAY listing and the price is reasonable.

    Just found this description any thing else ?
    he does not mention 87b, on a bosch auto 5 lug relay that 87b is off when pin 87 pin is on, here it looks like 87b is on if 87 is on?
    http://forums.pelicanparts.com/porsche-928-technical-forum/626810-wiring-fuel-pump-relay.html
     
    Last edited: Sep 21, 2012
  13. cork_ie

    Member

    Oct 8, 2011
    348
    58
    30= Battery +
    31= Ground
    15 = Ignition +
    31b = Ignition pulse from "Points" side of ignition coil.
    87 = Positive supply to pump
    87b = Spare ( you can join it to 87 if you wish to share the load, or alternatively us it to power something else < 10A)

    These numbers are common DIN standard as frequently used on European vehicles.
    Don't forget an inline fuse somewhere
     
  14. sdowney717

    Thread Starter Member

    Jul 18, 2012
    385
    13
  15. stanman11

    Member

    Nov 23, 2010
    230
    4
    Why not just use a toggle switch and a fuse to the battery?
     
  16. sdowney717

    Thread Starter Member

    Jul 18, 2012
    385
    13
    purely for safety reasons.
    You want the pump to turn off if the motor is not running, otherwise if you have a carb failure, etc..., fuel may overflow out of the engine and blow up the boat. It happened to me one time., we had a fire and I got burned.

    I am glad I was shown this fuel relay all in one package idea. I think it will solve the issue I have.
     
  17. cork_ie

    Member

    Oct 8, 2011
    348
    58
    Yes either one will work fine.
    Might be a good idea to put a freewheel diode or 0.1μF capacitor between terminals 87 & 30 to increase contact life on the relay contacts as gas pumps are highly inductive.
     
  18. sdowney717

    Thread Starter Member

    Jul 18, 2012
    385
    13
    I got the relays came nicely sealed in a bag named 'vollig'
    You can see in the prior pic the connections are all various widths, some too wide to slide on a connector, some to narrow, the coil pulse connector.

    I am thinking of soldering on wires to the connectors with a terminating ring terminal at the other end to attach to the electrical screw strip.
    As long as the solder tip wont overheat anything, this seems to be a good way to do it.

    Any other ideas? I doubt a proper plug is easy to find.
     
  19. cork_ie

    Member

    Oct 8, 2011
    348
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    You should have no issues soldering but obviously use your discretion.

    Connectors are readily available for all the sizes on this relay.

    The small pin (31b) connector is commonly used for speaker connections.
     
  20. sdowney717

    Thread Starter Member

    Jul 18, 2012
    385
    13
    Thanks, I did find a site selling the wide Volkswagen 3/8 spade connectors
    http://www.repairconnector.com/prod...-Connector-12-%2d-10-AWG-Yellow-25--Pack.html

    Not happy spending so much on these odd connectors.
    So what I did was drill out the center hole and will use a small bolt and nut on the wide lug.
    I soldered the nut to the backside but even that is not needed and could be a problem if you melt the plastic holding the metal lug. I dont recommend soldering the lugs.

    Small nuts and bolts that you might have can come from old style PC serial port connectors used to bolt into the old style AT cases. Those bolts are a chromed brass so dont tighten too much. Good idea would be goto hardware store and buy some tiny SS nuts and bolts.

    Found 3/8 width connectors at Autozone so will use them.

    I had to repair one of the relays. When I soldered on a nut, the lug is soldered into a lug board which holds all the lug connectors. It loosened and become a cold solder joint. Then getting the relay apart, I broke the circuit board loose from the lug board, so had to fix that. Lug board joins circuit board at a right angle. Dont solder on the lugs.

    It ripped the copper traces right off the lug board, the fix was to take a file and grind small notches in the circuit board in the 5 places where the lugs were wired to the copper traces on the lug board. Then use wires to connect the circuit board back onto the lug board. The notches allowed the wires to fit flush to the board so it could fit back in its black case. I used small speaker wire for the signal wires and larger wire for the relay connections. The circuit board looks pretty fancy.

    Anyway so far got one relay hooked up and it s working nicely.

    The relay does not do a key on prime of the pump for a second which I thought it would.
    It does run the pump when the engine cranks.
    I still have the manual priming button, that is very helpful when starting if the carb is dry or you have air in the fuel system.

    Only one of the relays like this does prime the pump
    so if you want that feature you need Kracker, 24.1400.30, Kraftstoffpumpenrelais, 12v Made in Germany
    So these various makers do not make them work the same.
     
    Last edited: Sep 28, 2012
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