Why do you need to upgrade your fuel pump?
While a fuel pump might seem like an upgrade only for fully built cars with huge turbos, even those of us pushing the limits of stock frame turbos may have something to gain. Fuel pumps, like all fluid pumps, have a maximum flow capacity and an optimal efficiency window. Ideally you want to choose a fuel pump that never has to operate outside of its efficiency range on your particular setup. The stock fuel pump on most FWD Volvos will support an absolute maximum of somewhere around 300 bhp. This means that even a tuned car with a stock turbo may be experiencing the effects of a fuel pump operating outside of its optimal efficiency window.
A fuel pump pushed to its limit will not be able to sustain fuel pressure which will result in poor atomization of fuel leaving the injectors as well as high AFRs. Because the engine relies on the atomized fuel charge for cooling, this situation can lead to high cylinder temps, detonation, and engine damage. In an attempt to combat a maxed out fuel pump, the ECU may increase injector duty cycle which will only further decrease fuel pressure and atomization quality. In extreme situations, one would notice injector duty cycle spiking accompanied by AFRs continuing to rise.
We recently ran into this situation while tuning a 2.3 T5 with a TD05H-16G turbo. AFRs at redline were higher than ideal so we re-curved the map several times. However, AFRs stayed at around 12.0:1. All evidence pointed toward a severely maxed out fuel pump. We installed an ARD 340 LPH fuel pump and data logged the car again with no changes to the tuning. Where we previously were seeing AFRs of 12.0:1, we were now seeing AFRs of 10.0:1, a full two point difference. Injector duty cycle was 0.8% lower, and boost was 0.4 PSI higher.
With the new high flow fuel pump, we were able to properly
dial in AFRs and rest assured that the pump was operating within its efficiency
window. Take note that a small 16G compressor
wheel is only slightly larger than a 19T wheel (46.5mm inducer/60mm exducer
compared to 46mm inducer/58mm exducer).
So if a 16G at 17.3 PSI was pushing the absolute limit of the stock
pump, one can reason that a properly tuned 19T or 18T can run the stock fuel
pump close to its limit.