8.1 fuel pumps running after fuel rail pressurised

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by juggernaut1, Aug 3, 2016.

  1. juggernaut1

    juggernaut1 Active Member PLATINUM Sponsor

    701
    Apr 19, 2015
    Perth, Western Australia
    2006 38 Sundancer
    8.1S / ZF 63V Drives
    Correct, assuming it's not another issue such as fuel pump relay, wiring etc. So eliminate other possibilities first. However, Jeff Tiller at Whipple was able to test and confirm it was the PCM prior to making the fix.
     
    Last edited: Feb 9, 2017
  2. PlayDate

    PlayDate Well-Known Member SILVER Sponsor

    Dec 25, 2006
    Washington DC
    1994 370 Express Cruiser
    454 Mercruisers
    Sorry for being late to this but this sounds like a PCM programming bug from the start. As noted for most applications the PCM energizes the fuel pump from 3-5 seconds. The intention behind the short interval is to charge the fuel rail and avoid the pump continuing to run. Practically the pump could run all day because it is designed to do that.....the only thing that stops the pump after the interval is the PCM because it does not sense the engine has started. A supercharger requires a different software load in the PCM. The fuel curves are different at idle and at speed. In marine racing engines, we disable (software update) the interval since it serves no real purpose and other safety's are in place to cut all power to the engine in the event of a failure.

    So for clarity....this is not something that is related to the age of the PCM or is an indication that the PCM is failing. In all likelihood, it worked this way when it shipped from the factory.
     
  3. rondds

    rondds Well-Known Member SILVER Sponsor

    Oct 3, 2006
    Jersey Shore
    2001 380DA
    Merc 8.1s (2008)...Hurth ZF 63 V-drives...WB 7.0 BCGD (2013), Garmin 8208 & 740 MFDs, GMR 24xHD dome
    Jug, if you don't mind my asking, what did that cost and did they do any tweaking for improved performance or economy? Glad that worked. Must be a great relief for you.
     
  4. juggernaut1

    juggernaut1 Active Member PLATINUM Sponsor

    701
    Apr 19, 2015
    Perth, Western Australia
    2006 38 Sundancer
    8.1S / ZF 63V Drives
    rondds,

    Cost is US$600 - as per this website link plus freight. As you can see the fuel pump staying on seems to be a common problem along with some other known issues.

    https://whipplesuperchargers.com/index.php?dispatch=products.view&product_id=73

    No tweaking was done - although it can be - see this link

    https://whipplesuperchargers.com/index.php?dispatch=products.view&product_id=52

    I was enquiring about the stage 2 calibration which requires 91 octane or better. Your 91 MON is roughly equivalent to our 95 RON. Whist I use 95 RON fuel I wasn't sure how much octane the fuel would lose between tank fillups. I suppose I could have used an additive to maintain the octane but decided not to go down that path. From the email response I got from Dustin Whipple, they tweak the timing advance as the standard curve is very lazy, adjust the dwell and slightly increase the rpm limit. I propose to instead put the funds towards some new Veem props.

    PlayDate,

    I don't believe its a programming bug. Jeff Tiller advised the chip/chips go bad and need replacing. Refer to the first link above and you'll see that there is a list of problems with the PCM. The other reason I don't believe its a programming bug is because the Merc tech working on my boat bought it to my attention that it was not normal. Moreover, I was able to get the fuel pump to shut off on one of the motors by trying different fuel pump relays.

    As you've mentioned - whether the pumps turn off or not is probably not an issue provided you start the motors soon afterwards. However, if the pumps are left to run (say accidentally) without starting the motors, the fuel in which the pumps are submersed would soon warm up as their would be no cooling raw water running through the cool fuel module. In this situation the pumps may overheat and fail sooner rather then later. A leaky injector may also be problematic again if the pumps were left to run.
     
  5. rondds

    rondds Well-Known Member SILVER Sponsor

    Oct 3, 2006
    Jersey Shore
    2001 380DA
    Merc 8.1s (2008)...Hurth ZF 63 V-drives...WB 7.0 BCGD (2013), Garmin 8208 & 740 MFDs, GMR 24xHD dome
    Thanks Jug. Great info for future reference!
     
  6. PlayDate

    PlayDate Well-Known Member SILVER Sponsor

    Dec 25, 2006
    Washington DC
    1994 370 Express Cruiser
    454 Mercruisers
    I'm ok with it being a chip to be replaced but it is a software setting in the EPROM. The PCM energizes the fuel pump relays based on a series of conditions. Insofar as a chip going bad.....it's possible but I don't think they are replacing the actual EPROM on the main board. More likely they are replacing a solid state relay chip (which signals the fuel pump relays) that seized closed. Did they tell you what they replaced?
     
  7. juggernaut1

    juggernaut1 Active Member PLATINUM Sponsor

    701
    Apr 19, 2015
    Perth, Western Australia
    2006 38 Sundancer
    8.1S / ZF 63V Drives
    In my last email from Jeff, he said "they have fixed the fuel pump circuit". In an earlier email he mentioned the chip/chips go bad.
     
  8. superwa

    superwa Member

    50
    Jul 27, 2013
    Rhode Island
    2001 Sea Ray Sundancer 380
    Mercruiser horizon 8.1S
    Hi everyone, kind of a similar issue. In my case it’s my starboard 8.1s horizon engine. The fuel pump goes on for the usual time and shuts off, then it happens again a while later, then it happens again maybe an hour later. I can’t figure out the issue. Tried swapping fuel pump relays with the port engine and the problem didn’t change. Also it happens just by turning on the batteries, without turning the ignition keys or the ignition buttons. Any thoughts? May need a new wiring harness? One time I started the engine and it would not shut off, even after I turned the keys off.
     

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