5 Symptoms of Low Fuel Pressure (and Possible Causes)
Is your car hard to start, stalls, or just plain runs poorly (especially under load)? Low fuel pressure could be the culprit. As most of us know, sufficient fuel is needed for the combustion that powers your vehicle’s engine. But far fewer people know that this fuel also needs to be delivered within a certain pressure range.
Read on for the symptoms and most common causes of low fuel pressure so you can get back on the road. What does “low fuel pressure” refer to? Generally, the majority of today’s gasoline engines operate with fuel rail pressures in the 45-60 PSI range, with the higher values ​​of this range becoming more common over the past decade.
Thus, any fuel pressure below 45 PSI is highly suspicious. The lower this pressure value, the more impaired the engine’s operation will be. Older carbureted gasoline engines did not require as high fuel pressure as today’s fuel injected engines. In fact, carbureted engines rarely operate at delivery pressures above 5-8 PSI.
For this reason, low fuel pressure was not considered a likely cause of problems in a carbureted engine until the delivery pressure dropped below 5 PSI.
Diesel engines are an entirely different story. Diesel fuel is not ignited by a spark like gasoline, but by heat generated by compression. To achieve efficient combustion, the diesel must be atomized during injection. Fuel pressure in older “pump-pipe-nozzle” fuel injection systems ranged from 45 to 100 PSI, with further increases at each fuel nozzle. Today, it is not uncommon for modern “common rail” diesel engines to have fuel pressures of up to 30,000 PSI.
Symptoms of Low Fuel Pressure
Lack of proper fuel pressure commonly results in a number of secondary symptoms, many of which can negatively impact the vehicle’s drivability. Recognizing these symptoms can prove crucial in expediting diagnosis and eventual repair.
1) Poor Performance Under Load (Slow Acceleration)
One of the first symptoms many drivers notice when their vehicle experiences abnormally low fuel pressure is an overall lack of power under load. This may manifest as a general lack of throttle response, or an inability to accelerate normally.
2) Intermittent Stalling
When the engine’s fuel pressure falls below a certain limit, it can no longer sustain combustion. This often results in intermittent or without warning stalling. Such events can occur at idle or under load.
3) Starting Issues (Car makes a clicking noise when starting)
Similarly, abnormally low fuel pressure can affect the engine’s ability to start as intended. This occurs when the engine’s fuel pressure is too low to initiate combustion predictably upon startup, resulting in a “no start” condition.
4) Misfires
Another common symptom of lower than standard fuel pressure is the sudden occurrence of seemingly random misfires. These misfires occur when one or more specific cylinders do not have the necessary fuel pressure to initiate combustion, resulting in the cylinders shutting off temporarily.
5) Check Engine Light Illuminated
In most cases, a sustained period of insufficient fuel pressure will cause your vehicle’s check engine light to illuminate. This most commonly occurs when one or more of your vehicle’s downstream oxygen sensors detect a lean condition. This light will remain on until the root cause of the immediate issue is resolved.
