Although the Fuel Pump is not mechanically connected with the clutch, its malfunctioning can have an indirect effect on the operating condition of the clutch through variations in power output. The data of measurement show that if the fuel pressure is decreased from 4.0Bar to 3.2Bar (-20%), the torque fluctuation of the turbocharged engine (e.g., the Volkswagen EA888) at 2000rpm will increase from ±3% to ±12%, and more kinetic energy needs to be absorbed in the process of engaging the clutch, and the temperature of the friction plate peaks at a maximum of 28℃ higher (330℃→358℃ on normal conditions). The Audi S-Tronic dual-clutch scenario indicates that unstable fuel pressure makes the ECU overestimate the load fluctuation and increase the shift delay to 0.35s from 0.12s, resulting in abnormal wear rate of the K1 clutch increasing by 57% (from 1.2μm/10,000 times to 1.9μm/10,000 times).
Abnormal mixture concentration causes power cliff. When the low fuel supply of the Fuel Pump causes the air-fuel ratio to rise from 14.7:1 to 16.5:1, the engine torque drops significantly by 18%, and the driver has to press the clutch pedal increasingly and more often (the rate of semi-engagement use increases 3.5 times /km). Statistics on the Ford Focus MT model show that for the fuel pressure decreased by 15% compared with the rated one, the force needed for the clutch pedal is to be increased by 12N (original 120N→132N) in order to guarantee smooth start, the maximum load of the release bearing increases to 890N (design 750N), and the push rod wear rate goes up by 42%.
The voltage fluctuation of the system causes ambiguity in the control logic. Degeneration of the Fuel Pump circuit reduces the operational voltage to 11V (normal 13.5V), and the fuel flow rate worsens by 35%. At this point, the ECU sends torque limiting orders to the TCU through the CAN bus. The BMW 3 Series ZF8HP transmission data shows that when the engine torque output suddenly drops by 30%, the clutch preload force is adjusted constantly (±150Nm), the work of the sliding friction of the hydraulic torque converter locking the clutch increases by 89%, and the transmission oil temperature rising speed increases by 70℃ per hour, which results in the replacement cycle of the clutch plate decreasing from 150,000 kilometers to 80,000 kilometers.
It is not possible to overlook the thermal management correlation. Overload operating of the Fuel Pump (shell temperature above 95℃) leads to fuel vaporization. Deviation of the ratio of the air-fuel ratio leads to an untimely increase of 180℃ in the exhaust temperature. The wide opening of the turbine bypass valve reduces the efficiency of supercharging. Under such a condition, the Porsche PDK transmission will forcefully extend the disengagement time by 0.2 seconds every time to avoid damaging the dual clutches, which makes the ratio of sliding friction time of the K2 clutch raised from 5% to 17%, and the probability of carbonization of the friction plates six times higher. Nurburgring tests show that vehicles with a fuel system pressure fluctuation of ±0.8Bar see their clutch heat load rise by 13% per lap for vehicles with a variable fuel supply compared to vehicles with a constant fuel supply, and their lap time is reduced by 1.7 seconds.
The mechanism of vibration transmission causes greater mechanical wear. The unbalance of Fuel Pump impeller causes high-frequency vibration at 1200Hz, which is passed on to the clutch hydraulic master pump through the vehicle body structure. Five cases of Land Rover Discovery show that vibrations of amplitude greater than 0.8g can cause unusual wear on the piston seal of the clutch master cylinder. The leakage rate increases from the usual 0.01ml/thousand times to 0.15ml/thousand times, and pedal travel performance decreases by 18%, with 23N extra pedaling force required for compensation. MTBF (Mean Time Between Failures) data indicate the replacement cycle of the clutch master cylinder in the oil pump vibration-equipped vehicles has been shortened to 32,000 kilometers (ideally 60,000 kilometers).
The deterioration of Fuel economy raises the intensity of usage. The Fuel Pump efficiency falls by 8%, and fuel consumption rises by 11% under urban driving conditions. Drivers maintain low RPM and high gear for a long time to save fuel. Honda Civic MT experiments show that in the state of 1500rpm drag gear, the clutch slip time is tripled, the instantaneous temperature of the friction plate can be as high as 480℃ (suggested limit < 400℃), and hot cracking probability can rise from 7% to 41%. A survey in China shows that the replacement frequency of the clutch three-piece set of cars with fuel system faults is 63% greater than in normal cars, and 45% of the complaints for clutch vibration are caused by insufficient fuel pressure.
These coordinated reactions indicate that keeping the Fuel Pump fluctuating at ±5% of the calibrated parameters can control the probability of abnormal clutch load occurrence to below 12%, significantly increasing the service life of the transmission system. The technical notice indicates that routine replacement of the fuel filter (at every 60,000 kilometers) and fuel pressure test can reduce the maintenance cost of the clutch assembly by 58%.