I have swapped to a walbro on numerous cars without affecting AFRs. If the pump is worn or old or running at 100% duty cycle, changing to a new pump will affect the tune and fueling.

 

your right well spotted

 

Ive probably done a 100 of them now and every single one has needed the AFR retuned.



-Em

 

Only makes sense if you are close to maxing out the stock fuel pump, right?

When I was on the stock fuel pump, and switched to a walbro I noticed it definitely went a little richer.

 

I was wondering, Is it that safe to be running at 13.0 - 13.3 AFR?

 

Mechanical pressure regulators reduce pressure from their inlet to their outlet. They are not capable of producing a higher outlet pressure than their inlet. By design, they compensate for higher pressures, but if the inlet pressure drops below the outlet set pressure, there is nothing a regulator can do about it.

The issue you see with an aftermarket pump and AFR issues is intrinsic to mechanical non-adjustable regulators.

One of the springs in the regulator is pre-loaded to deliver a specific pressure at its outlet. This outlet pressure varies within a range based on the inlet pressure and down stream restrictions during dynamic conditions. With an adjustable pressure regulator, you are able to dial in the pre-load on this spring.

Extremely high performance regulators are capable of maintaining very close to their set outlet pressure even as inlet pressures climb. It's no wonder, however, that most automotive FPRs are not "extremely high performance."

So, as the inlet pressure increases, so too will the outlet pressure to some degree, since the pre-load on the regulator spring has not varied in relation to the inlet pressure.