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Hello. My son and i have just installed an aftermarket external fuel pump on his 94GT as we've just installed a 363 Dart engine with an F1 procharger.

At the rear of the car is a green wire with a yellow stripe that goes to the inertia switch and we have tapped into that one to act as a trigger for our 40amp relay and that way we still retain the inertia switch.

With key on, that wire is hot...fires the relay and the pump turns on for priming just for 'prove out'. Then that wire isn't hot.

I understand this wire comes from the CCRM (Constant Control Relay Module) and is tied into the ECM (Ours is an AEM standalone).

Anyone have any idea as to how the pump receives voltage after that green/yellow wire is deactivated?

Thanks...John
 

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Discussion Starter #2
I think i've already figured out the majority of our problem. As far as i can see the green wire is a timed positive feed to prime the pump and the pump primes. But then i noted that we lose all pressure.

Then i realized that we do not have a one way check valve off the pump on the supply line and that is the reason that after the pump primes, we lose all pressure.

If i understand it correctly after the pump primes the one way check valve keeps the pressure in the rails at the preset pressure (we have an adjustable regulator) and the pump shuts down.

Then with the lines primed the engine cranks and the
ECM sends the signal to the CCRM to the fuel pump relay and the green wire then becomes energized again.

Please feel free to chime in if you agree or disagree with my theory as i'm an old carb guy and am just trying to keep up with this injection stuff.

Regards....John
 

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That's it. So, you're piggy-backing the OEM EEC. Don't worry about the check valve. When you start cranking, the pressure will come back in just a second, however, you will lose the "priming shot" when you key-on. Again, not a biggie, and most setups won't notice. If your system does have issues, it will either be a couple extra rotations before firing as the pressure comes-up, or you may get a chuff or pop with an initial lean shot. Minor and easy to fix if you actually have symptoms.

David
 

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Discussion Starter #4
Hello PSIG. Actually this computer is a separate standalone by AEM that replaces the factory computer and is tuned with a laptop. We've ordered a one way check valve as you're right we do lose the initial prime.

While cranking, in theory we should regain fuel pressure but i think we'll have to check the program as the person who wrote the 'tune' said he turned the injector duty cycle way down for initial startup. We're running 80lb injectors.

It is a learning curve for me and my son is more up on it than i am.

Thanks....john
 

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OK, I thought you were adding the AEM on-top the EEC. Anyway, the prime pulse stops, and then the ECU waits for an RPM signal that indicates cranking to kick the pump back on. I generally do the same thing for cranking with a small prime shot (maybe 2ms) and when the engine catches and it senses rpms above a programmed threshold (faster than cranking speed indicating running), then I program fuel addition based on air and coolant temperature. With the small prime shot (or none at all) it prevents any possiblility of over-fueling or flooding on a hot start.
:tup:
David
 

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Morning PSIG:

Interesting. So what triggers the ECU as far as the signal that the engine is cranking. We're not running a crank trigger on this one just the factory distributor wired via MSD box.?

I'm assuming that once the ECU receives this rpm signal -"faster than cranking" it then turns on the relay in the CCRM for full pump operation?

Although this setup should have that one way check valve i think this engine should have fired as i ran a jumper wire from the battery to the fuel pump relay in the trunk and the pump ran full time.

Thanks ...John
 

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Your ECM gets an rpm signal - that is used as the signal the engine is cranking. So, in order:

  • Key ON gives short (~2 sec) fuel pump run and priming pulse (if programmed)
  • Key to START cranks engine and sends the first rpm signals to the ECM
  • ECM sees rpm signal and knows engine is cranking, and turns on pump (any rpm signal = pump on)
  • Engine 'catches' and the rpm signal increases indicating engine 'running'
  • Cranking fueling ends and running fueling begins based on fuel table
  • More or less fuel is added to the values in the table based on engine temps
  • Some setups also use an "afterstart enrichment' acting like a choke for some seconds after start
In the end, if your injectors are firing during cranking and your pressure is up you have fuel, and the only questions are how much and if you have spark on the correct cylinders at the right time.

David

[EDIT] PS: Your AEM ECM should be controlling the pump relay directly, with the relay trigger signal passing through the impact/inertia switch.
 

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Discussion Starter #8
Thanks Dave and awesome explanation!

Yes, the 'trigger wire' for the relay is the wire going throught the inertia switch and down to the pump.

John
 

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Discussion Starter #9
Forgot to ask you Dave, where does that rpm signal come from that signals the ecu to turn on the pump while cranking?

Key on gives it the initial prime but where does that crank signal come from?

John
 

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The RPM signal comes from wherever you wired it in. Not to sound dorky, but the ECM must have an RPM signal, and there are a dozen ways to feed it one, and I don't know what method you guys used. So, not to sound silly, but how is the engine telling the ECM what the RPMs are? It's usually tapped from a distributor sensor or output wire. How did you wire it? Finally, is the ECU also controlling the ignition or fuel only?

David
 

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Discussion Starter #11
Hello David. Not a problem.

The AEM is a direct plug and play for the Ford TM40 computer. The ford computer is out and the AEM controls everything as the ford computer did. Electric windows, fan controllers, fuel , spark ...you name it.

So i think the factory ford computer picked up the signal maybe from the distributor??? through the hall effect ? I'm not sure.

It's the same computer that my son's boss has in his 63 Acadian (
Chevy11 in the states) which has run a best of 6.97 in the quarter down in Vegas and a tickle over 7.00 up here in Canada. Both runs were on a 10.5 drag radial. So that's quite impressive.

John
 

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At the rear of the car is a green wire with a yellow stripe that goes to the inertia switch and we have tapped into that one to act as a trigger for our 40amp relay and that way we still retain the inertia switch.

With key on, that wire is hot...fires the relay and the pump turns on for priming just for 'prove out'. Then that wire isn't hot.

Thanks...John
Its been a few since setting up injection ditched it for carbs.

The factory key on engine cranking fuel pump recieves full voltage. Key on engine not running pump will come on for about 30 seconds then shut off.
Key on engine running computer controls voltage to the pump it is cut back a bit from a full 12 volts. All this power runs to the inertia switch from a relay under the hood / EEC. I think part of your issue might be using the inertia switch to run the realy you have added for the external pump. Your pump is now running or attempting to run independatly of the ECM controling it.

Now after converting to carb I wire up the system using the inertia switch to power the relay for the pump but thats different than FI.
 

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So i think the factory ford computer picked up the signal maybe from the distributor??? through the hall effect ? I'm not sure.
OK John, first - are you getting any RPM signal when cranking? Are you getting any spark? Are you running stock ignition or MSD?

Here's the skinny on Ford TFI ignition - and you need to know it to be sure your system can be controlled properly. Ford Mustangs used distributors with Hall-effect sensors that directly feed a TFI (Thick Film Ignition) module. The module can be mounted on the distributor, or may be remotely mounted. To add a good shot of confusion, there are also two versions of each - the "push start" module that controls coil dwell and is GRAY in color, and the "CCD" (Computer Controlled Dwell) version that has the EEC control coil dwell that is BLACK in color. The GRAY one is most common in the US. The most important concern is if your module is GRAY or BLACK, and you cannot interchange the two. Your ECM is designed to use one or the other, so verify which and if that's the one you have.

If all is correct there, let me know which module yours uses for specific troubleshooting steps to ensure your ECU is getting the rpm signal, and that it's also able to fire the coil.

David

TFI module types (by TMoss on veryuseful.com):
 

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Discussion Starter #14
Hello David. I'm sending you a pm....John
 
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