How to enable FP output

[jb007]

I'm using the 'Fuel Pump & Pressure' control feature and using PWM using the Nitrous 1 as the 'Fuel Pump Output'. I still want the Fuel Pump output 'FP' to turn on when the ECU powers up s it can power a relay that provides +12V to the PWM Motor Controller, which is driven by the 'Nitrous 1' output.

Can it be done? If not what alternatives do I have?

Jim

Have a MS3 with MS3x.

[jb007]

Bump... can anyone help?

[jsmcortina]

The only way to use the FP output is through the fuel pump system.

James

[jb007]

Thanks James. I'll connect my pwm controller +12V to a switched input then... can you see any issues problems with this arrangement?

Jim

[BigLou240sx]

If all you want to do is activate the PWM controller power supply based on when a normal fuel pump would be controlled by the FP pin, then you can send the FP pin to the control/coil side of the PWM controller power relay with +12v (or switched +12v) on the other side.

That way the PWM controller would only have power when a normal return-style fuel pump would run based on the output of the FP pin. Not sure if that's a recommended approach or not though since I haven't dabbled with PWM fuel pump.

ETA: probably wrong... see entire thread.

[jb007]

If all you want to do is activate the PWM controller power supply based on when a normal fuel pump would be controlled by the FP pin, then you can send the FP pin to the control/coil side of the PWM controller power relay with +12v (or switched +12v) on the other side.

That way the PWM controller would only have power when a normal return-style fuel pump would run based on the output of the FP pin. Not sure if that's a recommended approach or not though since I haven't dabbled with PWM fuel pump.

Thanks BigLou... that's what I'll do. I'll connect the FP pin as the PWM controlling O/P and wire +12v from a switched supply to the PWM controller or SSR which ever I use.

I think I'll also look at a fuel cutout inertia switch just in case I ever have an accident.

Cheers
Jim

[BigLou240sx]

On second thought (and this may be wrong)... is the fuel pump wired in such a way that the fuel pump receives +12v without going through the PWM controller or SSR? I would think the fuel pump +12v is fed by a standard automotive relay, and the ground side of the fuel pump is driven by the combination of MS3/PWM controller (or SSR).

If that's the case, I would instead wire the FP pin to the relay that provides the constant +12v to the fuel pump (and I think you probably already have a relay for this), and leave the PWM controller on switched 12v alone.

Fuel pump power supply relay: 85/86 to MS3 FP/+12v (constant/switched, don't think it matters), 30 to constant +12v, 87 to fuel pump supply. This would shut off the power to the fuel pump when there is no crank signal from your MS3. It would leave power on at the PWM controller, but don't believe that would harm anything.

OR if it is wired in such a way that the PWM controller provides the power to the pump as well:

I would use the MS3 FP pin to control the "ignition switch relay" in the picture above (and may be used in combination with a switched 12v line as well).

btw, what is "PWM controlling O/P". Not sure I understand where you are going to wire the FP pin to in your last post

and this all assumes that using the 'Fuel Pump & Pressure' control feature of MS3 does not disable the normal FP pin behavior (on briefly at key on, on only when crank signal available)

ETA: probably wrong... read entire thread

[jb007]

Hi BigLou.

Sorry I've no diagramming software handy at the moment.

The way it will connect is:

From the MegaSquirt: Pin FP Output will be the PWM output... it connects to the negative input of a fast Solid State Relay.

From the switched +12v to the Output of the SSR, I might put the +12V via a relay... not sure yet.

Since the fuel pump is in my petrol tank and its negative is permanently tide to the chassis, the SSR will under control of the FP pin switch the +12v in/out.

The 30PSI (my system is a low pressure system @12PSI) fuel sensor is a input to the MegaSquirt and is part of the feedback loop.

I originally wanted to use the FP O/P to control the relay that powers the SSR, and another Pin say Nitrous 1 to be the PWM. As James has stated and I have found, the FP pin can only be used for control of the Fuel Pump.

Hence this revised method, which I hope will be OK safety wise. I've had the MS connected to my JimStim bench testing various things including the RealTime clock, Engine Knock sensor, PWM control for the thermatic fan and the PWM fuel pressure. I'ts interesting to see it all work on my oscilloscope! I've written a little bit about it on my blog...

Thanks for your help.

Jim

[BigLou240sx]

Ok, so I think I had a general misunderstanding of what the Fuel Pump output on MS3 does when you enable PWM control of the fuel pump. This being the case, please disregard mostly everything I've said about it

I envisioned that you would use another (not FP) output of MS3 to control the PWM of the fuel pump. I assumed that the FP output on MS3 behaved the same as a return-style fuel pump setup, so that it is grounded on key on and when a crank signal is received at MS3. From the looks of it, you have found that this is not the case.

If the PWM control of the fuel pump utilizes the FP output, then it is possible/probable that the same safeguards are in place such that allow the fuel pump to only run when there is a crank signal (engine stalls, fuel pump turns off).

Apologies for the confusion, at least I learned something!

[jb007]

No problems at all BigLou. I'm learning daily... which is a good thing as when I stop learning, it means my brain has atrophied!