Fuel pump not priming - car slow to start - why?

Discussion in 'Engine, Transmission and Drivetrain' started by eddyvr4, Oct 10, 2014.

  1. eddyvr4

    eddyvr4 Leaving Skid Marks

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    Hi - at some stage during my mucking around with the fuel system the fuel pump has stopped priming, so it only runs when the key is moved to the start position, and this means when starting after the car has been sitting for a few minutes, its sluggish to start as it takes a few seconds of cranking to bring up the fuel pressure. once started the car runs fine.

    Basically it needs a few seconds or sometimes more of cranking then it slowly grumbles up into life.

    is there a relay or something specific i should be looking for that controls the pre start priming? or is it the ECU that controls priming (but i havent touched the ECU...)

    apparently some of the early evos dont even have a priming circuit for the fuel pump, but this symptom has just appeared for me and i reckon its come and gone a bit in the past as well. im quite sure it used to prime.. it certainly used to bang into life much better than it is at the moment..

    any ideas??
     
  2. VOLK

    VOLK Stabbin' technique!

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    That's standard for my FL, only runs the pump at the start position. Much like yours and several others I've read of, it stumbles for a second before cold start raised idle. Even if I let it prime for a second or two before I start via clutch switch, makes little difference. Some days it starts better than others. Still drives fine, still fine under load, I've ignored it.
     
  3. Nitephyre

    Nitephyre Flaccid Member Lifetime Member

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    It's a VR4 Thing, not for us to understandâ„¢ :D

    I'm running a Stevebro pump & Tuna and it still hates cold start.
     
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  4. eddyvr4

    eddyvr4 Leaving Skid Marks

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    Hmm, for the best part over the last 5 yrs it fires up quite respectably, not like some cars, but briskly enough.... since a week ago, i did something when fiddling on the fuel side (swapping pumps back and forth, cutting into the fuel line) and now it takes a lot longer, its embarassingly slow to start once its been sitting for a while.. Apart from that it all seems good.

    I might need to redo the spot where i put in a brass T piece fitting to take off the fuel pressure guage, maybe that is not sealed well enough..i sealed the threads with Gas tape and the clamps are proper EFI clamps.. Why is it that everytime i touch something i break something else! <shakes fist at car>

    i even replaced the o ring on the end of the fuel pump with a nice new tight one.. you try and do the right thing and where does it get you! argh! :)

    <end rant>
     
    Last edited: Oct 11, 2014
  5. Kaldek

    Kaldek 2 AYC Bars Premium Member

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    Mine does this too. Walbro pump, tuned, fuel pressure gauge that shows me there is good pressure in the rail. Still on a cold start she'll stumble for a second before coming up.

    My theory is a dirty ISC that needs cleaning.
     
  6. NuffNuff

    NuffNuff 1 AYC Bar Lifetime Member

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    Mine does this too . huge stumble on first start of the day. But I have to say it didn't do it before I fitted my FMIC
     
  7. VOLK

    VOLK Stabbin' technique!

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    My hypothesis is slightly incorrect cold start afr from slower velocity intake path that bigger piping and 'cooler endows. In my case, ISCV is fine, throttle body is clean. Cold cranking enrichment duty cycle would have been set by oem for stock cooler, piping etc. Fires up fine if I let it crank but not fire, then let it start on the second attempt.
     
  8. Kaldek

    Kaldek 2 AYC Bars Premium Member

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    Well in that case, I'll just leave it be.
     
  9. whats_doing

    whats_doing QLD Events Manager Moderator

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    Either pump is on the way out or you have a leak with the o-ring sealing the pump to the harness.

    I had a similar issue. took forever to finally catch, when it did it was fine. It seemed to lose all fuel in the line which caused it to take ages to start.

    Seeing as you have taken the pump in and out a few times, it might have gotten a split in the o-ring. Hit @TME_Steve up for a new one.
     
  10. NuffNuff

    NuffNuff 1 AYC Bar Lifetime Member

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    when you started getting the fueling issue on start, did you notice any fuel issues on hard cornering too?
     
  11. whats_doing

    whats_doing QLD Events Manager Moderator

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    Can't say I noticed.
     
  12. Kaldek

    Kaldek 2 AYC Bars Premium Member

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    In my case, I can sit there and prime the rail for 10 seconds (and also see the rail pressure come up to and hold 36psi) and it will still have an initial very low idle for 2 seconds or so. I've also seen the car hold that pressure in the rail for over an hour after shutoff, so it's not that. I have a brand new pump, and new O-ring.
     
  13. jungle

    jungle 3 AYC Bars Lifetime Member

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    As above!
     
  14. jungle

    jungle 3 AYC Bars Lifetime Member

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    for the guys that have had this issue, fitting a new pump fixed it. Mine was was fixed after changing pumps
     
  15. TME_Steve

    TME_Steve 3 AYC Bars Trader

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    Or boost leak
     
  16. Kaldek

    Kaldek 2 AYC Bars Premium Member

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    On only the first engine start of the day? Surely not.
     
  17. mookers

    mookers puri puri Administrator Moderator

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    My car has always done the first-start-of-the-day stumble. Both before and after I swapped the stock intercooler and piping for x3emotorsports items, before and after the Walbro fuel pump went in, and before and after I had it tuned by TME_Steve.

    My theory is that it needs a coffee in the morning to wake up, like the owner does.
     
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  18. Kaldek

    Kaldek 2 AYC Bars Premium Member

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    Thanks mate. Nothing like some empirical evidence.
     
  19. Kaldek

    Kaldek 2 AYC Bars Premium Member

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    I do love a challenge though. I challenge myself to find a reason for the stumble that I can consistently identify and resolve!

    Only problem is I have to wait a day between each test unless I find the answer quickly. :)
     
  20. TME_Steve

    TME_Steve 3 AYC Bars Trader

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    Boost leak makes it run lean. Lean enough to stumble on start but run fine.
     
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