In this article and video Ford GDI & GTDI Fuel Pressure Testing is reviewed and what to expect using a gauge verse a scan tool is shown. Each tool can display a different value. it is important to be aware of this when testing.
After performing a full vehicle scan, live data is typically the next step in isolating problems in a vehicle. Sometimes there are variances in scan data and actual measured values.
On Ford Vehicles, the base fuel system pressure will be biased about 10 PSI from the gauge reading. This is typical of the FRP (Fuel Rail Pressure) reading on non-GDI or the FLP (Fuel Low Pressure) reading on GDI engines. This is a characteristic that should be known when attempting to diagnose fuel system concerns.
When diagnosing a fuel trim issue, testing fuel pressure would be a normal test step. Variance in pressure (low) would cause in increase in fuel trims to adjust the delivery amount in the cylinder. Seeing this difference in actual verse scan tool fuel pressure data could lead to unnecessary fuel system repairs.
In this example, scan tool data shows a low pressure reading of about 87 psi.
Low pressure sensor voltage is about 3.8 volts which coincides with our DVOM reading, acquired using a backprobe at the low side fuel pressure sensor.
The gauge on our subject vehicle is displaying from 70 – 85 PSI, with normal fluctuation due to the cam driven high pressure fuel pump.
When checking base fuel pressure readings on Ford vehicles, be aware that the scan tool reading will be approximately 10 PSI higher than a mechanical gauge at idle.