A Complete Collection of Troubleshooting Methods for the Fuel System

1 Precautions for maintenance of fuel system

Before disassembling the oil pipe, the pressure should be released first to prevent the higher pressure fuel from spraying out and causing a fire.

When installing oil pipe joints, for bolted pipe joints, new gaskets must be used during installation, and the joint bolts must be tightened by hand first, and then tightened to the specified torque with tools. For nut-type pipe joints, it should be noted that a thin layer of lubricating oil is first applied to the bell mouth, and the same is tightened by hand first, and then the joint is tightened to the specified torque with tools.

After the injector is removed, the O-ring cannot be reused. Lubricate the O-ring with gasoline before installing the injector. Note Do not use engine oil, gear oil or brake fluid. When installing, it must be installed while turning left and right, and it must be aligned and not skewed. Poor installation of the upper part or damage to the O-ring will cause oil leakage; poor sealing of the lower part will cause air leakage.

After the fuel system is overhauled, carefully check for oil leaks. Turn on the ignition switch, the engine does not start, connect the diagnostic seat FP and +B terminal (for Toyota models) with a jumper wire, and make the fuel pump work forcibly. Clamp the oil return pipe, the system oil pressure will rise to 400kP. Check the fuel system for oil leakage, and start the engine only after confirming that there is no oil leakage. After starting, let the engine run at idle speed, and then carefully check whether there is any oil leakage, and then close the engine cover to run normally.

2 Fuel system oil pressure release and preset

01 Release of fuel system oil pressure

In order to facilitate the next start, after the engine is turned off, there is still a high fuel pressure (residual pressure) in the fuel line. When disassembling the fuel pipeline or replacing fuel filter, electric fuel pump, fuel injector and other components, the oil pressure in the fuel pipeline should be released first, so as to avoid a large amount of pressurized fuel spraying out when the fuel pipe joint is loosened, causing personal injury or fire . To relieve fuel pressure, proceed as follows:

① Pull out the fuel pump relay or fuse, or pull out the fuel pump wire plug. Start the engine 2~3 times to ensure complete decompression (or stop the engine naturally after starting). Finally reconnect any relays, fuses or wires that were removed.

②Put cotton yarn or other oil-absorbing items under the oil pipe joint or wrap the joint nut, and then slowly loosen the joint nut, so that the gasoline is absorbed by the cotton yarn or oil-absorbing items, then remove the cotton yarn or oil-absorbing items, and finally put the pipe joint Retighten.

③ After the pressure is relieved, a small amount of fuel will leak out when inspecting the fuel pipeline or joint. At this time, cotton yarn can be used to wrap the dismantled part to absorb the leaked fuel.

02 Presetting of fuel system oil pressure

After dismantling the fuel pipe for maintenance, in order to avoid too long starting time when starting the engine for the first time because the fuel pressure in the oil circuit has not been established, the oil pressure in the fuel pipe should be preset according to the following method.

Connect all the fuel pipe connectors, use a jumper wire to short-circuit the FP terminal of the diagnostic seat and the +B terminal (for Toyota vehicles) or unplug the fuel pump relay, and short-circuit the power terminal and the fuel pump control terminal. Turn on the ignition switch to force the fuel pump to build up oil pressure.

3 Fuel tank leak check

Fuel tanks are constructed of lead-plated tin alloy steel or high-density molded polyethylene. Leakage of the fuel tank, even if it is leaking, is very dangerous. When a fuel tank is suspected of leaking, it must be checked carefully (before checking, a dry powder fire extinguisher should be prepared).

First relieve the fuel system pressure, then remove the fuel tank, install a short fuel line on the fuel tank, and plug all other outlets on the fuel tank. Fill the fuel tank with 7~10kPa compressed air through the short oil pipe. Check the suspected leak with soapy water or immersion, and replace the fuel tank if a leak is observed.

4 Detection of fuel system oil pressure

Oil pressure detection includes working oil pressure detection, maximum oil pressure and residual pressure detection.

01 Working oil pressure detection

Before testing the oil pressure of the system, firstly release the pressure, and then connect the oil pressure gauge to the oil circuit. Some systems have oil pressure taps in the lines, while others do not. If there is an oil pressure detection hole, the oil pressure gauge can be directly connected to the oil pressure detection hole; if there is no oil pressure detection hole, the oil inlet pipe can be removed, and the three-way pipe joint is connected in series to the oil inlet pipe, and then the three-way pipe Connect the oil pressure gauge.

Start the engine, the fuel pump starts to work, and observe the system oil pressure at idle speed and different speeds. Oil pressure at idle and at different revs varies slightly, but not much.

Common system oil pressure failures include high oil pressure and low oil pressure. Too high oil pressure will make the mixture too rich; too low oil pressure will make the mixture too lean.

The reason for the high oil pressure is that the oil pressure regulator is faulty or the oil return pipe is blocked. At this time, you can remove the oil return pipe of the oil pressure regulator, put a hose on the end of the oil return pipe of the oil pressure regulator, put the other end of the hose in a container, and start the engine. If the oil pressure is normal at this time, it means that the oil return pipe is blocked; Otherwise, the oil pressure regulator is faulty.

Low fuel pressure can be caused by low fuel in the fuel tank, clogged fuel pump filter, faulty fuel pump, improperly installed fuel pump outlet line, clogged fuel filter, or a faulty oil pressure regulator. Start the engine and run it at idle speed, clamp the return pipe of the oil pressure regulator and observe the indication value of the oil pressure gauge. If the oil pressure can rise above 100kPa, it means that the oil pressure regulator is faulty; if the oil pressure is still too low, check whether the fuel filter is clogged, whether there is little or too dirty fuel in the fuel tank, the installation of the oil pipe, the fuel pump filter, etc. Whether the net is blocked. If normal, replace the fuel pump.

02 Maximum oil pressure detection

Clamp the oil return pipe to stop the oil return pipe from returning oil. At this time, the indicated oil pressure of the pressure gauge should be 2~3 times higher than that without clamping the oil return pipe; otherwise, the performance of the fuel pump is reduced, and the pump oil pressure is insufficient, so it should be replaced fuel pump.

03 residual pressure detection

After the engine is stopped, a certain residual oil pressure should be maintained in the pipeline of the multi-point injection system to facilitate restarting. If the residual oil pressure is very low or equal to zero after the engine is stopped, it will cause a failure that is difficult or impossible to start.

The reason why the system residual pressure is very low or zero is that the check valve of the fuel pump is not closed tightly, the oil pressure regulator leaks, the fuel injector leaks oil or the fuel system pipeline leaks oil. The inspection steps are as follows:

First visually check whether there is oil leakage in the fuel system pipeline. Then start the engine and run at idle speed, clamp the return pipe of the oil pressure regulator, turn off the engine, and observe the pressure indicated by the oil pressure gauge. If the oil pressure does not drop, it means that the oil pressure regulator is leaking; if the oil pressure still drops, start the engine again and run at idle speed, clamp the oil inlet pipe and the oil return pipe of the oil pressure regulator at the same time, turn off the engine, and observe the change of oil pressure after 10 minutes. If the oil pressure drops slowly, it means that the fuel injector is leaking; if the oil pressure does not drop, it means that the check valve of the fuel pump is not closed tightly, and the fuel pump should be dismantled and cleaned to check the check valve or replace the fuel pump.