Fuel pump runs as soon as the battery cable is hooked up! PLEASE HELP

ttocs · Jun 9, 2016

stupid question I am sure i missed it, did we check the inertia switch in the trunk?

rz5.0 · Jun 9, 2016

https://sites.google.com/site/sn95mustangs/tech-info/94-95-ccrm

mcglsr2 · Jun 9, 2016

rz5.0 said:
340 has become quiet popular.. I would not use a high pressure 255 over 450 my self.. But that's just me.. I just saying the 255 would not support FI 600 hp wheel or crank..maybe NA

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And OP is pushing 600+ HP with his current setup? I'm sure it is popular - it's reasonably priced and look what it flows! Of course, you probably won't get that flow on your stock OEM wires, thus making you re-wire your stuff. For a drop-in. When you start talking about that kind of power, you need to replumb your fuel lines because I'm sure the stock sizes will hold you back on flow. There's a lot more that needs to change besides just the pump at those power levels. The OP treating this as just a "drop-in" makes me form a certain impression of the situation.

At any rate, this is irrelevant to the issue at hand. I have nothing against the Stealth. It's a nice pump.

rz5.0 · Jun 9, 2016

No but on one one your previous post you said to use a 255 for around 600

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rz5.0 · Jun 9, 2016

mcglsr2 said:
Also, just as a side question, how much HP you thinking of making anyway? That pump is HUGE. On a FI application, it will flow enough to support 800 HP. If your HP goals are less lofty, like say around 600 HP, then a drop-in 255LPH would most likely work just fine, as will your stock OEM wires. The best, of course, is to run a new, larger AWG wire. But if you just don't want to, then I have to ask - why such a huge fuel pump?

/\/\ that's what i was talking about

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mcglsr2 · Jun 9, 2016

rz5.0 said:
/\/\ that's what i was talking about

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Okay, I stand corrected.

Edit: And for what it's worth, I was pretty close. Ball park.

Fuel pump comparison tests: link

You'll notice that the Walbro 255lb, on an FI application, with 25 psi of boost, will support about 575 HP. But! Not the 600 I said. So I still stand corrected (though at 20 psi of boost, it will support 603HP). Now, the other pumps are obviously better. But then again, how many of those are drop-ins using OEM wires? Like I said. 340 LPH is HUGE.

And pulling this conclusion out of the article, specifically about the Walbro 255lph (font color change my emphasis):

THIS PUMP IS EASILY THE MOST POPULAR FUEL PUMP IN THE TUNER COMMUNITY BY FAR, AND HAS BEEN FOR YEARS. IT HAS DONE WELL BY VERY MANY PEOPLE OVER THE YEARS, AND IS PERFECTLY SUITABLE FOR THE MAJORITY OF THE MASSES MODIFYING THEIR CARS. YOUR AVERAGE ENTHUSIAST DOES NOT EXCEED 600HP AT 20PSI OF BOOST, OR 700HP ALL MOTOR. THE AMPERAGE CHARACTERISTICS ARE THE LOWEST OF THE GROUP GIVING IT THE LEAST IMPACT ON YOUR ELECTRICAL SYSTEM'S RESOURCES. ITS ALSO THE LEAST EXPENSIVE OF THE GROUP, WHICH FREES UP MONEY FOR OTHER FUEL SYSTEM COMPONENTS LIKE INJECTORS.

rz5.0 · Jun 9, 2016

I get carried away sometimes.. Wasn't trying to be a dick about it

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mcglsr2 · Jun 9, 2016

rz5.0 said:
I get carried away sometimes.. Wasn't trying to be a dick about it

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No worries my dude

BigSkySN95 · Jun 9, 2016

Pulled the fuel pump fuse and the pump still runs

rz5.0 · Jun 9, 2016

Was any of the wiring spliced at any time?

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rz5.0 · Jun 9, 2016

Where you from?

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BigSkySN95 · Jun 9, 2016

No. I'm in MT

rz5.0 · Jun 9, 2016

I'm real curious.. That's to far for me to take a look..

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rz5.0 · Jun 10, 2016

The only thing now is checking wires..

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BigSkySN95 · Jun 10, 2016

Unplugged the wire harness just before the inertia switch, now the pump doesn't run

BigSkySN95 · Jun 10, 2016

Checked the dark green/yellow wire and not getting any voltage with the battery hooked up and the harness to the tank out of the loop

mcglsr2 · Jun 10, 2016

Okay, so this is how the fuel pump is wired in my 95 5.0 - I imagine yours is similar, if not the same.

Batt --> Fuel Pump Fuse --> CCRM Fuel Pump Relay. The CCRM Fuel Pump Relay is normally open, unless the PCM (EEC) energizes the relay (the pin on the EEC is 22). Once the EEC energizes the CCRM Fuel Pump Relay via pin 22, it closes the relay, so then CCRM Fuel Pump Relay --> Inertia Cut Off --> Fuel Pump.

So. If you connect the battery and Fuel Pump comes on, then the issue is 1 of 3 things (or perhaps some combination) - and to troubleshoot, keep the harness to the Inertia cutoff unplugged so that your pump doesn't run:

1) The CCRM is bad, the Fuel Pump Relay has failed Closed - only possible if the contacts inside have "welded" themselves together
-- You can check this by connecting the battery and probing pin 5 on the CCRM - if you have voltage, that means the CCRM Fuel Pump Relay is closed, and passing voltage from the battery. If you get voltage, also check #2 below

2) The PCM (EEC) is bad - it's sending power on pin 22 when it shouldn't.
-- You can check this by checking pin #22 on the PCM (or, pin #18 on the CCRM). If there is voltage, then the EEC is sending the signal to the CCRM Fuel Pump Relay to close.

3) You have a short in your wires. The short will either be between the PCM (pin #22) and the CCRM (pin #18), tricking the CCRM into energizing the fuel pump; AND/OR between the CCRM (pin #5) and the Inertia cutoff switch.
-- You can use a multimeter to test

BONUS: there's also one more pin on the PCM to check, pin #8 - this is the fuel pump monitor. When the CCRM Relay is closed and passing voltage to the pump, this pin will also have voltage. It's possible that if the PCM energizes this pin as well, it will run your pump.

Your problem is in one or more of the places I listed. There is no where else it could be, if your wires truly are stock. If someone has run different wires without your knowledge (like a previous owner), then it's a different ball game.

Edit: this is based on my 95 GT. I don't know what you have, but if it's a 94/95 GT 5.0 then it will be the same for you. If you have a different year, it might be slightly different - but probably similar.

JerZeyStangz · Jun 10, 2016

I'm now running the pump on my 96 GT. I know the is overkill for my stock setup (bolt-ons) but I bought it for room to upgrade/grow when I do a H/C/I conversion, and lastly a Forced Induction setup as the last iteration. The pump is very quiet that when I turn the key to accessory I can barely hear it run. I drove it home no problem....now carry on..lol

ttocs · Jun 10, 2016

mcglsr2 said:
Okay, so this is how the fuel pump is wired in my 95 5.0 - I imagine yours is similar, if not the same.

Batt --> Fuel Pump Fuse --> CCRM Fuel Pump Relay. The CCRM Fuel Pump Relay is normally open, unless the PCM (EEC) energizes the relay (the pin on the EEC is 22). Once the EEC energizes the CCRM Fuel Pump Relay via pin 22, it closes the relay, so then CCRM Fuel Pump Relay --> Inertia Cut Off --> Fuel Pump.

So. If you connect the battery and Fuel Pump comes on, then the issue is 1 of 3 things (or perhaps some combination) - and to troubleshoot, keep the harness to the Inertia cutoff unplugged so that your pump doesn't run:

1) The CCRM is bad, the Fuel Pump Relay has failed Closed - only possible if the contacts inside have "welded" themselves together
-- You can check this by connecting the battery and probing pin 5 on the CCRM - if you have voltage, that means the CCRM Fuel Pump Relay is closed, and passing voltage from the battery. If you get voltage, also check #2 below

2) The PCM (EEC) is bad - it's sending power on pin 22 when it shouldn't.
-- You can check this by checking pin #22 on the PCM (or, pin #18 on the CCRM). If there is voltage, then the EEC is sending the signal to the CCRM Fuel Pump Relay to close.

3) You have a short in your wires. The short will either be between the PCM (pin #22) and the CCRM (pin #18), tricking the CCRM into energizing the fuel pump; AND/OR between the CCRM (pin #5) and the Inertia cutoff switch.
-- You can use a multimeter to test

BONUS: there's also one more pin on the PCM to check, pin #8 - this is the fuel pump monitor. When the CCRM Relay is closed and passing voltage to the pump, this pin will also have voltage. It's possible that if the PCM energizes this pin as well, it will run your pump.

Your problem is in one or more of the places I listed. There is no where else it could be, if your wires truly are stock. If someone has run different wires without your knowledge (like a previous owner), then it's a different ball game.

Edit: this is based on my 95 GT. I don't know what you have, but if it's a 94/95 GT 5.0 then it will be the same for you. If you have a different year, it might be slightly different - but probably similar.

Where does the fuel cut off/inertia switch come int on the schematic? Is it the very last thing before the pump?

Test for power at the fuse, and at the inertia switch.

ttocs · Jun 10, 2016

BigSkySN95 said:
Unplugged the wire harness just before the inertia switch, now the pump doesn't run

this would cut all power all the time to it. Its just a switch, power in and then if its good power out. With it plugged in and working correctly there should be power on the two wires going to it