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Beer and Cheese
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Discussion Starter #1
I've been asking around for a while, but no one has given me a clear answer. Any help would be greatly appreciated.

Since the earlier Fords are equipped with a CCRM (Constant Control Relay Module) which controls the fuel pump, PCM power, A/C clutch and engine cooling fan. The problem is load can be drawn away from the fuel pump by these other systems loosing fuel pressure and could happen during WOT that might cause a dangerous lean condition if the pump is not operating at a consistent 12 volts. In order to correct this problem you can run a relay to the trunk and provide the fuel pump a consistent 12 volts during normal and WOT driving.

Where I'm confused is, where do you tap in the relay to the wires?

I've read to run a 10 gauge wire from the battery to a relay in the trunk. Using a Bosch 30; 85; 86; 87 pin relay the power would go to the 30 pin and the 85 would be a ground. Where would I tap the 86 and 87?




In this basic wiring diagram, it shows a red wire being the power wire for the pump. Correct me if I'm wrong, I see a Green/Yellow wire is used to power the fuel pump? Would I connect 86 to the Green/Yellow wire from the CCRM and connect 87 going to the Green/Yellow wire to the pump so I get the consistent 12 volts? Also what kind of fuse would you use for a single 255 lph and duel 255 lph pumps?

Thank you in advance for any help,
 

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Your fuel pump only runs at 12 volts when you turn the key to the run position - normally it runs on Battery voltage which can range from 13.5-14.5 volts.

The wiring diagram looks correct .. you would want to use the original power wire from the pump on the control side of the relay - it will draw minimal amperage on that circuit, just to turn on the relay to direct power directly from the battery to the fuel pump through the relay. So you would want to run the 10 gauge wire directly from the battery, to the relay and then another 10 gauge directly to the fuel pump itself so it will be able to deliver the correct amount of amperage. Any wire can support 12 volts or higher, but its ability to pull amerage is determined by the size of the wiring itself.

I would tap into the fuel pump's original wiring after the inertia switch in the trunk - the switch will cut power if you were to get in an accident as a safety precaution. Fuse should be sized to about 70% of the amperage actually drawn by the pump itself. I think the last Ford I checked fuel pump amperage on was a stock Ford Fusion but it was somewhere around 5 amps average - the fuel pump amperage is drawn every time the commutator inside the pump motor turns to the next one - usually they are segmented into 8 pieces so if you were to watch the amp on a graphing multimeter you would see 8 amp spikes for every 1 rotation of the fuel pump motor. An inductive amp meter would be used to determine actual amperage.
 

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While it is indeed true that a fuel pump can deliver more fuel with higher voltages, the entire premise for this modification is flawed. There is no problem. There is only a problem if your fuel pump cannot supply enough fuel @12V, in which case the person relying on a couple of extra volts to supply an insignificant amount of fuel on a performance car is the real problem. The PCM has built in control for fuel delivery based on battery voltage. If your OEM fuel pump supply wire has a significant voltage drop when the other relays in the CCRM, you have other issues.
 

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Beer and Cheese
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Discussion Starter #4
Do I have it wrong on why guys are doing the relay mod? Would there be another reason to do this.:confused:
 

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Do I have it wrong on why guys are doing the relay mod? Would there be another reason to do this.:confused:
if you are indeed going to run a dual 255lph pump, then yes, the inertia switch will likely not be able to support high enough power demand to keep the voltage up. But a single pump will not be affected all that much. Unless of course your wires going into the intertia switch are corroded and contributing to the voltage loss (that is where the actual power for the pump comes from, right?). A single 255 will draw about 8.2A.

 

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Beer and Cheese
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Discussion Starter #6
Ok yes, correct duel 255 pumps. According to the Bosch wiring diagram (^^^) and what SCTbird1994 said, I'm basically connecting into the Green/Yellow wire on the control side of the relay and after the inertia switch in the trunk. I'm not sure but I think that green/yellow wire is a 10 gauge to the pump, I'll have to check. What size amp fuse should I go with? 15A? I remember my Lightning had duel 255 and I was running a 20A fuse.
 

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30-40 to be safe
 

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Beer and Cheese
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Discussion Starter #10
So I should run a ground wire from the relay (85 pin) to the battery?

Thanks again for your help!
 

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It doesent need to go to battery there is a ground back there use it
 

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Beer and Cheese
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Discussion Starter #12
That's what I was thinking, just tap into a ground wire that's already in the trunk.
 

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It's not true ground unless you have ZERO resistance/voltage drop from that point to the neg battery terminal. Dare ya to check :) You're doing all this work to try to get the most into the pump, well guess what wherever you see a +POS terminal, there's always a -NEG terminal that should be connected to a point of reference that is identical to the battery's negative terminal. Otherwise, you're not getting the most out of the positive side.
 

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The Parts Guy
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So I should run a ground wire from the relay (85 pin) to the battery?

Thanks again for your help!
That one won't matter. Pins 85 and 86 are low current; it's just a coil. What GM is getting at is that if you're upgrading the +12V supply to the pump, you should also upgrade the ground to the pump.
 

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We'll I don't know of any cobra guys that run a ground to the trunk, nor did I, u may be right gm
 

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I betcha its why all them high power cars need a lot more fuel pump than what their engines actually require---because no matter how beefed up the supply line is, if you have the electrical equivalent of a drinking straw on the exit, you're still limiting the pump from what it can really accomplish.

That's just my theory anyway. Could be easily verified though by simply looking at the voltage drop across the pump (or equivalently amperage) with a stock ground, and then with a beefed up ground (at least 8awg) routed directly back to the battery.
 

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The Parts Guy
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We'll I don't know of any cobra guys that run a ground to the trunk, nor did I, u may be right gm
That's because at least 95% of the "car guys" out there don't have a real grasp on wiring/electricity. Everybody always wants to run big power wires to their amp/headlights/fuel pump/etc., but they almost always neglect the equally important ground path.
 

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Guys, with a good connection at the battery, and at the bolt in the shock tower I used as a ground, I was seeing several volts drop with my car stereo using the unibody as ground.

This was ~50 amps, but it's comparable.

It even shifted when I hit hard bumps, lol. :facepalm:

Personally, I would establish a good ground point in the trunk for whatever you want to run big power, not just the dual fuel pumps.

I used 2/0 rope-lay cable for both power and ground to the trunk, but that's me. And it worked... :)

The relay hookup GM labelled out is the way I would go.

Wiring a bypass to the inertial relay/crmm for race only might be an option, but having the inertial switch is a good thing, imho. :) But if you're having issues, it could eliminate a marginal component.

I think 3Gs off the line would probably trip one... :)
 

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We'll I checked voltage about a year of so ago and I didn't see much loss at the back of the car if any, I went thru all kinds of crap, gm stock hose will support tons of hp, if u don't believe me test it, I can tell u straight up the issue is the fuel filter cause it necks way down,
 
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