fuel pump only primes with laptop plugged in

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scarpa
MegaSquirt Newbie
Posts: 3
Joined: Fri May 06, 2011 12:12 pm

fuel pump only primes with laptop plugged in

Post by scarpa »

I am having issues with the MS grounding the pump. I am running MS 2 v3.0 w/tuner studio. MS is a new assembled unit from DIY. works normal with the stim hooked up. with MS plugged into engine harness and laptop fuel pump primes but no rpm signal at cranking. all sensors work, double checked wiring (OK) MS gets 12v but just seems like it is not grounding. I have 12v at FP relay. and 12v at Main relay during ign. on and cranking any info would be very helpful in getting this engine to run. thanks
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trakkies
Super Squirter
Posts: 1162
Joined: Tue Dec 30, 2008 3:06 am
Location: SW London, UK

Re: fuel pump only primes with laptop plugged in

Post by trakkies »

The pump runs at switch on to prime the system. It then needs a tach signal to run after this. So if you're not seeing a tach signal at cranking, no pump.
Dave P, London UK.
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scarpa
MegaSquirt Newbie
Posts: 3
Joined: Fri May 06, 2011 12:12 pm

Re: fuel pump only primes with laptop plugged in

Post by scarpa »

I agree, but the pump will prime with the laptop plugged in when you key on the ign. if I unplug the laptop, no prime but power to MS power to main relay power to fuel pump relay in but no power out of relay and relay works fine it seems the MS isnt providing ground is it something in the MS.
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Matt Cramer
Super Squirter
Posts: 2951
Joined: Sat Jul 03, 2004 11:35 am

Re: fuel pump only primes with laptop plugged in

Post by Matt Cramer »

Does this problem also happen on the Stim?
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scarpa
MegaSquirt Newbie
Posts: 3
Joined: Fri May 06, 2011 12:12 pm

Re: fuel pump only primes with laptop plugged in

Post by scarpa »

no when I plug in the stim pump circuit works fine I just dont get 12v at pin 30 on FP relay 12v at pin 37 at MS could it be internal? testing wiring again so far everything is per 3.0 wiring diagraham.
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Matt Cramer
Super Squirter
Posts: 2951
Joined: Sat Jul 03, 2004 11:35 am

Re: fuel pump only primes with laptop plugged in

Post by Matt Cramer »

The MS supplies ground, not power. If it's not getting power, check the wiring.
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FordTaurusGuy
MegaSquirt Newbie
Posts: 18
Joined: Thu Apr 21, 2011 6:28 pm

Re: fuel pump only primes with laptop plugged in

Post by FordTaurusGuy »

scarpa - I'm not an expert but the two issues I have had with my fuel pump have been bad grounds. Not on the MS side but on the sensors and engine side harness.

My fuel pump was not coming on at all... it was a missing ground on my TPS.

Now my fuel pump comes when I start the car but it does not prime...
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