when does the fuel pump drop voltage. at an rpm range? or a reading via the tps (foot off pedal)? if an rpm range, what range is it, and can foot be on the gas while in this range. car that idles + voltage meter = answer.. but i dont have a car that idles. someone plzzzz answer. hailers?

 

It should have but about 9volts until you put a load on the engine. It's a combination of afm reading/boost sensor/rpms.....we think.

If your sitting in the driveway and reving the engine, I think all you'll see is approx 9volts. I believe you have to drive the car and put it under load for the voltage to go up to 12 plus volts.

The way the question was asked was as if you think the voltage is 12v plus until you reach a certain rpm. Nope. Works just the opposite. I probably misunderstood.

It's pin 3D on the ECU that determines if you see approx 9 volts or see 12plus volts. It maintains a ground signal on the fuel pump resistor/relay which causes a low voltage output to the pump. When you put a load on the engine by driving it and boosting the engine, the ground signal is taken off pin 3D and the resistor is taken out of the circuit and the voltage goes from approx 9v to whatever the alternator is putting out i.e.12plus volts.

 

has this been tested? sitting in my driveway i should absolutely never see 12v? unless i had ac on or something? its kinda important that i know.. i wanna test this on my car and make sure its acting right but i cant get it to idle.. thus i have to have my foot on the gas.

 

No. In your driveway you can rev to your hearts desire and the voltage will stay at approx 9volts. A/C,lights etc have nothing to do with it. The word LOAD was in reference to driving the car and applying the throttle pedal in large amounts.

 

thank u very much hailers.

 

The fuel pump should see full battery voltage during cranking and for ~10 seconds after starting, and then any time the engine is under high load. In my testing this was at ~3psi boost, but I think it's a particular airflow reading that triggers it as opposed to a boost reading. That airflow reading just happens to be at ~3psi on my car.

 

well i found my problem.. AFM is jacked.. you barely open the door like a milimeter and you get a read of 0 ohms instantly. i guess then, the ecu was thinking the flapper door was pegged open all the time, thus flooding my car with fuel and cause a crappy condition. hopefully thats why my car kept flooding.

 

I doubt it. If the circuit was*OPEN* when the door was at rest...that's good. Moving it a fraction and the circuit *MAKING* is ....good/normal/the way it was meant to be.
Cranking the engine should be enough to just crack the afm vane and *MAKE* the fuel pump circuit.

For grins I disabled the part of the Circuit Opening Relay that *MAKES* the fuel pump circuit thru the action of holding the key to START. I find that the car starts up just fine with the vane in the afm making the fuel pump circuit (by airflow pulling it during starting).

 

Also take note of what the Kiwi mentioned. When the key is held to START, the fuel pump is engaged in spite of anything the afm is doing i.e. broken switch/not broken switch. Look a the schematic and you'll see the *extra* coil in the Circuit Opening Relay that pulls in the fuel pump circuit when the key is HELD to START.

 

it was the section of the AFM that the flapper goes slowly to 0 with the moving of the door, not instantly.. it was definitely bad.

 

Wouldn't the ECU store a code for the AFM if it's "jacked"?
Did you try and scan for error codes?
I don't think the AFM is your problem - the AFM does pulse several times when you check resistance, and I think it's normal.


-Ted

 

The switch in the AFM that controls the fuel pump is either open (flap completely closed) or closed (flap not completely closed). The potentiometer in the AFM that measures airflow has no effect on fuel pump operation.

 

I noticed that too, Ted..When checking resistances with the thing off the car, as the door was being slowly opened, the resistances would cycle back & forth between 2K and 6K ohms, or something in that ballpark, kinda like a sine wave. Yet when you reinstall it in the car and take her for a drive while watching the AFM input at the ECU, it's a nice linear voltage increase in direct proportion to throttle...Doesn't make sense at face value, something's going on we haven't figured out yet, & I would imagine that "something" is internal of the ECU...

That's what I was thinking, too, NZ, that imloggedin was reading the door switch...Because you should never see 0 ohms off the wiper or potentiometer circuits of the door...

 

im at work.. without having the fsm or afm to look at i couldnt tell u wich ones i tested to find out it was bad.. but its the one that changes with the door movement. and it was all screwed up. yes it was bad, theres no doubt. i got a new one and tested the same thing and it was good. put it on and my car idled.. so.. yes it was bad.. the FSM was right and the end.