Engine Running 12V Source

CMac89

Registered User
Are there any good sources that don't have anything to do with the EEC? I'm trying to power a pump, but I don't want it running during key-on.
 
I don't think you will get that without going thru the eec. Maybe one of the electric nerds can set you up a circuit that can trigger a relay from a crank or cam sensor input.
 
For a engine on switch I re-purposed the oil pressure sending unit, it supplies ground to a relay once 7psi is reached in the oil.

For Key On position, Tap A2 on the Ignition switch (Gray/Yellow wire), need to double check that one.
 
For a engine on switch I re-purposed the oil pressure sending unit, it supplies ground to a relay once 7psi is reached in the oil.

For Key On position, Tap A2 on the Ignition switch (Gray/Yellow wire), need to double check that one.

Hey now thats pretty good.:cool:
 
there should be switched power off the power relay. That runs into the power distribution box for some of the circuits.

Look at the load of the pump. If significant, you can get a power relay kit from painless good for 40amp and run your own battery connection. Between coolant pump, auxiliary cooling fans, fog lights, line locks, and meth pump, I added an auxiliary fuse box which had switched and always on circuits. I pulled power for it right off the battery, and the switch came off of switched power in the power distribution box. The switching of the auxiliary circuits is handled in the auxiliary panel.

remoteBatteryOverview1jpg_Thumbnail1.jpg
 
How many Amps?

For a engine on switch I re-purposed the oil pressure sending unit, it supplies ground to a relay once 7psi is reached in the oil.

It's up to 30 amps under a load. That's interesting about the oil pressure sending unit. I may have to do something like that.

The ECU I have uses grounds to trigger a relay to power units, but it isn't simple to do that in my case.

It's for an electric power steering pump. Here's how the relay is wired with a switched 12V trigger.
 

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It's up to 30 amps under a load. That's interesting about the oil pressure sending unit. I may have to do something like that.

The ECU I have uses grounds to trigger a relay to power units, but it isn't simple to do that in my case.

It's for an electric power steering pump. Here's how the relay is wired with a switched 12V trigger.

Can't you just use the ECU to trigger a relay and use that to switch always-on 12v for the 12V Ignition on the drawing?

RwP
 
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Casey, there is not a circuit that I know of that is hot only when the car is actually running. All circuits (except possibly some OUTPUTS from the EEC) that are "hot in run" are really "hot when ignition is in the on position".

There are many ways to handle what you need to do...I like both the oil-pressure relay trigger idea and toggle-switching a "hot in run" circuit. "hot in run" can be had without being "hot in start" if that is your concern.

Only thing about the oil pressure switch...what if the car dies/loses oil pressure for some reason....you also lose power steering. It would probably be safest to just run a relay off a "hot in run" ckt and throw a toggle switch in the relay trigger (coil) ckt. That way, if you need to have the ignition on, but don't want the power steering pump running, all you have to do is flip the switch. Otherwise, the pump will just run whenever the ignition is "on". Just make sure that you don't get a "hot in run & start" circuit off the ignition switch...if you do, you'll be taking power from the starter and the car may not have the juice to start (best case!)
 
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Fuel Pump only runs continously when the ECU sees a running engine. There is the 3 second prime and then it will run when cranking. You may not want that additional 50 amp load during crank time.

Will the ECU signal to the fuel pump relay handle the additional load of a second relay coil? Use the 12V feed from the fuel pump relay to drive the coil of the relay for the PS pump. Just looked and typical coil load on a 50 Amp automotive relay is .25 of an amp. An additional .25 amp on the fuel pump circuit should have minimal effect on voltage drop to the fuel pump.
 
Fuel Pump only runs continously when the ECU sees a running engine. There is the 3 second prime and then it will run when cranking. You may not want that additional 50 amp load during crank time.

Will the ECU signal to the fuel pump relay handle the additional load of a second relay coil? Use the 12V feed from the fuel pump relay to drive the coil of the relay for the PS pump. Just looked and typical coil load on a 50 Amp automotive relay is .25 of an amp. An additional .25 amp on the fuel pump circuit should have minimal effect on voltage drop to the fuel pump.

The fuel pump relay is controlled by the factory EEC, which I am assuming is totally gone from K-C's car, since he has an aftermarket ECU. Maybe the aftermarket unit has this function though?

I had considered the fuel pump circuitry earlier, but with the HP and fuel demand levels he will surely be at, I wouldn't want ANY voltage drop to the fuel pump - especially if it could vary over time. Triggering the fuel pump RELAY (might be what you were trying to say in the first place!:eek:) might be okay, as long as the ECU can handle the extra load of the PS pump relay coil. This would not affect the fuel pump supply voltage.
 
But isn't that what happens on a stock vehicle? If the engine ain't spinnin either is the PS pump.;)

Truuuue..... :) at least with the motor dying...loss of oil pressure due to a mechanical failure (assuming the motor keeps running) on a belt-driven pump would still give you assist while you got it off the road/track in the rare case of that happening.

I had pictured the wheels being even harder to turn w/the electric pump...I might be totally off-base though. I don't know much about the electric PS pump systems really.
 
Truuuue..... :) at least with the motor dying...loss of oil pressure due to a mechanical failure (assuming the motor keeps running) on a belt-driven pump would still give you assist while you got it off the road/track in the rare case of that happening.

I had pictured the wheels being even harder to turn w/the electric pump...I might be totally off-base though. I don't know much about the electric PS pump systems really.

Yeah I wanna check it out. Sounds like something I might do one of these days.
 
Having operated a MN-12 with a dead motor 0RPM and speed ~20-30mph, I can say as long as the wheels are turning steering is not too bad (the moment of inertia has been over come). Car was in tow with blown motor.

If you need/want on in case of a hard fault (I don't see a need) can set up the sending unit to trigger a 555 that keeps relay closed for ~1 min, need to also tap the Red/Green wire (hot in RUN/start); use the sending unit to arm the circuit. That way if the sending unit signal is dropped but you maintain power on Red/Green (color in engine bay) the circuit engages but not if both drop (turning car off).
 
The fuel pump relay is controlled by the factory EEC, which I am assuming is totally gone from K-C's car, since he has an aftermarket ECU. Maybe the aftermarket unit has this function though?

I had considered the fuel pump circuitry earlier, but with the HP and fuel demand levels he will surely be at, I wouldn't want ANY voltage drop to the fuel pump - especially if it could vary over time. Triggering the fuel pump RELAY (might be what you were trying to say in the first place!:eek:) might be okay, as long as the ECU can handle the extra load of the PS pump relay coil. This would not affect the fuel pump supply voltage.

How about this - instead of the ECU firing the fuel pump relay, it fires the relay that the OP wants, and the fuel pump relay is off of THAT? Reverse of what you described.

That ought to fix the voltage drop.

Or better, a "sensitive" 12v relay that then switches both the OTHER relays on.

RwP
 
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