# Megasquirt II no fuel pump when cranking



## water_wetter (Jun 2, 2006)

Heres my scenario.

The problem is that the car is hard to start.

Key on, pump primes

Start, no fuel pump

Running, pump runs

Pump is relayed to specs.

This is in an 84 jetta 16v.

Any suggestions?


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## ps2375 (Aug 13, 2003)

I'd check FPR and the check valve at pump. I don't think it is supposed to run when cranking.


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## bomberbob (Sep 19, 2004)

I may be wrong, but I think you want the fuel pump to run while cranking. If the fuel pump just runs a second or two and then shuts off, how much pressure will build up? And then no matter how much you let it crank, you get no more fuel pressure (till you cycle the key)? 
This caused us lots of problems, having injectors and other items on a power source that went dead during the cranking sequence. When we found a place in the fusebox that had power during cranking, starting problems went away.


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## ijcameron (May 17, 2001)

That's a good answer - the 1-2 second pulse just "primes the pump" - the pump also needs to run when cranking. I used the 12v hot wire that supplies the ignition coil to "power up" my fuel pump relay, since this remains hot any time the key is turned on.


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## ps2375 (Aug 13, 2003)

I am still using the stock fuel pump relay in it's stock location, with it stock wiring. I don't know if it supplies power to the pump when cranking or not. And I have not seen anything in my MS documentation to indicate how MS is supposed to act during this time period.


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## ijcameron (May 17, 2001)

ps2375 said:


> I am still using the stock fuel pump relay in it's stock location, with it stock wiring. I don't know if it supplies power to the pump when cranking or not. And I have not seen anything in my MS documentation to indicate how MS is supposed to act during this time period.


The difference is that with the key turned to "Accessories" the MS pump will prime for~2 seconds then shut off, whereas the totally stock VW FP relay will make the pump run constantly.

IIRC the argument for the MS system is that there is a lower risk of fire.

To the original poster - just curious - are you getting a consistent RPM signal when cranking?


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## ps2375 (Aug 13, 2003)

ijcameron said:


> The difference is that with the key turned to "Accessories" the MS pump will prime for~2 seconds then shut off, whereas the totally stock VW FP relay will make the pump run constantly.


I don't think so, the stock relay works pretty much the same way, primes the pump, then if it doesn't see an rpm signal, it will stop the pump. A mandated way for the FP relay to work incase of an accident, so the pump doesn't continue to run if the motor stalls. Thus not pumping fuel if fuel lines happen to get cut.


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## water_wetter (Jun 2, 2006)

I'm running a walbro 255 so i can hear that it isn't on when cranking. I adjusted the cranking pulse width settings, and now it starts ok. I'd say it takes twice the norm, but it manageable. I'm sure i could get it better with some time.

And, yes i do get rpm signal when cranking.

This was just the first time i used the megasquirts pump control. Usually i just hook it to the same fuse block as the ECU, separately fused of course.

My verdict is my CPW are just a little too rich, as the motor would tend to flood before. It would start fine if i held the pedal to Flood/Clear. But now its ok.


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## need_a_VR6 (May 19, 1999)

Make sure the power/coil power going to the relay are hot on crank and not on load reduction. If the fuel pump relay works for prime/run the issue is likely to be outside the ms.


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## ValveCoverGasket (Mar 20, 2002)

i assume you are getting rpm to the MS during cranking?
the pump wont run again (after the prime) until the MS sees an rpm input...


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