Really strange idea of the day!!!

[jim_in_dorris]

Okay, perusing 98's fan control code gives me the output for the fuel pump, now the question is: How many amps is an EP377 fuel pump? I could use the fan relays for the fuel pump.

Next question: Would an oil pressure sensor work for closing the loop on the fuel system? The one in my truck is a 1 wire, not sure if that would work or not. The range would probably work, just have to figure out what the calibration looks like. I.E. what voltage is what pressure. I think it might not work because of sensor grounding, but I could probably ground the sensor in the T adaptor.

[RobertISaar]

i actually have a similar situation with the 1 wire oil pressure sensor... what i did was grab a spare instrument cluster, powered it up on a bench, connected the oil pressure circuit to ground through various resistances(it's a 0-~80 ohm sensor) and then used my multimeter to check the voltage between the resistor and the cluster. my results? at most, i should see around 8.2 volts or so when the sensor is pegged at 80PSI. so if a run a /2 voltage divider, i can put it into the 5 volt range of the A/D circuit in the PCM, then just tap a wire into the oil pressure sensor circuit(using a high value resistor, to prevent it from skewing the gauge).

anyways, as long as you have 1 open A/D channel that is internally connected to ground via a resistor, you can do this.

[jim_in_dorris]

Okay, now I need to find an open A/D channel. One thing nobody has mentioned is the Oil Pressure Switch that is connected electrically to the fuel pump. I don't think that it would work well if it was wired in parallel to a PWM circuit.

[EagleMark]

You can remove it. It provides power when running if relay fails. If relay fails you will have long crank starts until oil pressure switch powers fuel pump IIRC. They are not used in aftermarket wiring harness and I don't use them when rewiring a harness.

[jim_in_dorris]

Actually i was aware of that because for a long time after I bought my truck the Oil Pressure Switch was disconnected and I didn't know it. I think they are just a source of another oil leak anyways, and the rebuild will not have one. I was just throwing it out there. ;) I will probably start looking at code now as it appears that the hardware is doable. ( I still don't know how may amps the fuel pump needs, but maybe by looking at the stock fuel pump relay I can get that.) I will have to re-pin for the fuel pump. I also need to look at the Key On / Engine Off fuel pump prime logic.

[RobertISaar]

key on, engine off logic that applies to almost all OBD1 applications:

first power-up, turn on pump for 2 seconds, then shut off, to build up pressure in case it has leaked down since last startup. then so long as reference pulses keep occuring, the pump will continue running. when keying off, the pump goes off as well. if the key is still in the on position and the engine quits running(stall), the pump will run for 2 seconds, then shut off.

of course, your application may be different.

[jim_in_dorris]

Well, I spent some time looking at schematics for my truck. Then I looked at the code. I may have to disable the fuel pump voltage errors, not positive yet, still thinking on that. If I repin A1 to one of the PWM outputs, I should be able to makes some code changes and all will be good. Now is time to start thinking on what parameter I should use to set output pulse width. Would RPM be sufficient? After all, HP = Tq x RPM. Or will MAP need to be part of the equation?

Pseudo code for RPM base would probably look something like this:

If (RPM lt 2000) then
Injector constant = (61# at 15 psi)
fuel pump DC = 33%
else
If (RPM gt 3000) then
Injector constant = (61# at 34 psi)
fuel pump DC = 100%
else
Injector constant = (61# at 23 psi)
fuel pump DC = 66%
endif
endif

I still need to look at fuel pump relay to see what amp value is. The way I drive, 85 % of the time my RPM's will be below 2000. (in OD at 55 I am doing 1875 + -)