pcmhacking.net

kojab wrote:Putting it simply the fuel reg still regulates but at a different pressure if the fuel pump output is changed. We all know it changes with different engine vacuum and this is why it is not easily noticed unless someone is looking for it.

As the actress said to the bishop, "it is all about size!".

The regulator will maintain an an fuel rail accurate pressure referenced to the manifold absolute pressure, but if the pump can push twice the fuel that the regulator can handle it if the return line is too small then rail pressure will rise independent of the regulator's efforts.

Simon

There is a table in MAP ECUs (not sure about MAF PCMs) to compensate for fuel pump flow changing with respect to battery voltage, its a minor change but a change nonetheless. It corrects for low voltages by increasing PWs and higher voltages by reducing the PW. It is not RPM referenced so does not compensate for a restriction in the return line at light loads. The voltage changes pump speed which in turn changes the fuel flow through the system, if the vac referenced fuel reg was a perfect device then there would be no pressure change with varying the voltage until the fuel use exceeded the fuel flow. But GM added a table to correct for pump speed

Yeah but then to complicate things even more in the L67's they added the module to be activated by a bit flag for the dual speed controlled by pulse width modulation I believe, but the 18% it was out when cool once driving it for more than 10 minutes in this car in particular needed another 10% added back in, so it wasn't that far out just needs a coolant correction factor tweak but not sure whats best there?

Yes, the dual speed fan module. The PCM checks the required fuel mass to achieve the target AFR based on the mass airflow rate. If it exceeds a threshold then the pump increases in speed via the PWM signal commanding 100% instead of the slow 33% DC (I think it is). Would be interesting to log fuel pressure and the pump DC.

Sounds like a code mod for 11P The Fuel pump is a PWM output so with a solid state relay can have the same control.

Ahh yeah it would be if I had the car for longer & had a solid state relay, but will talk the customer into it for future & try & get a descent solid state relay (any ideas?).

I wasnt suggesting a solid state relay for this car, was thinking out loud that 11P could also have the option of fuel pump speed control.

Yeah nah thats cool, so something like this could do the job...
http://www.ebay.com.au/itm/PCB-Mount-So ... 486144a01d

It's list as 12v but reading on the top of it saying 5v 2amp?

your neede something that could handle a decent amount of amps to drive the pump properly!