Summary

One of the problems we often encounter in the process of car maintenance is the large fuel return. There are many reasons for the large fuel return of the car. The failure of the fuel pump, fuel rail, or even the fuel injector will cause this phenomenon. This article will briefly introduce the reasons for the large fuel return of the injector from the perspective of the failure of the injector and how to repair the failure of the common rail injector.

 

First, the fuel injector failed.

For a two-valve engine with an external fuel intake, we can easily measure the fuel return volume of a single injector. For a four-valve engine installed with a high-pressure ejector rod for internal fuel intake, the total fuel return volume of the injector is usually tested, and then the fuel return volume of a single injector is tested by mechanically disconnecting cylinders (blocking the fuel outlet of the fuel rail) one by one. The following are typical fuel return totals for different engines:

1) Internal fuel-intake four-valve six-cylinder engine

-Engine dragging (175-250 rpm): 30-90 ml fuel return in 1 minute;

- Low idle speed (500-650 rpm): 30-100 ml fuel return in 1 minute;

- High idle speed (1500 rpm): 60-250 ml fuel return in 1 minute;

- High speed (2300 rpm): 80-350 ml of fuel returned in 1 minute.

2) Internal fuel-intake four-valve four-cylinder engine

-Engine dragging (175-250 rpm): 20-60 ml fuel return in 1 minute;

- Low idle speed (500-650 rpm): 20-70 ml fuel return in 1 minute;

- High idle speed (1500 rpm): 20-170 ml fuel return in 1 minute;

- High speed (2300 rpm): 50-240 ml of fuel returned in 1 minute.

So specifically, which components inside the injector will cause a large amount of fuel return? Possible reasons include the following six:

1. Leakage of the valve seat surface
2. The sealing ring is damaged and leaked
3. Valve stem guide wear
4. Guide wear of the nozzle needle valve
5. Damage to the support surface of the valve seat and injector body
6. The sealing end face of the needle valve body of the fuel nozzle is damaged

When encountering a large amount of fuel return from the injector, do not only check the failure of the valve assembly or the fuel injector but conduct a detailed investigation based on the above six points to find out the cause of the failure.

 

One point is also worth noting: the injector was installed incorrectly. For a four-valve engine with an internal fuel inlet and high-pressure ejector rod installation, the correct installation of the injector is very important. If the installation is not in place or the installation is incorrect, it may cause damage to the sealing head of the high-pressure ejector rod. In severe cases, the sealing surface of the fuel inlet port of the injector body will also be damaged, resulting in poor sealing and excessive fuel return.

 

Secondly, how should the common rail injector be repaired if it fails?

In the process of installing the injector on the engine cylinder head, the common rail system has standard installation steps and methods:

1. Insert the fuel injector into the cylinder head, and install and pre-tighten the compression block, The recommended pre-tightening force is 1kN-2kN, and the purpose is to eliminate the residual stress in the cylinder head
2. Completely loosen the pressing block so that the fuel injector is not subject to any pressing force and is positioned correctly
3. Pre-tighten the high-pressure ejector rod with a force of 3.5kN-8kN (equivalent to tightening the M22x1.5 nut with a force of 15Nm-20Nm)
4. Tighten the fuel injector, the force of the fuel injector is not allowed to exceed 15kN
5. Tighten the high-pressure ejector rod, and the sealing pressure is 12kN-22kN (equivalent to tightening the M22x1.5 nut with a force of 50Nm-55Nm).

When your fuel injector fails and cannot be repaired and needs to be replaced, how to replace it?

For details, please refer to my previous article：

https://hpinjection.com/blogs/news/how-to-change-your-fuel-injectors

 

 

Summarize

The above content is the analysis of the possible reasons for the large fuel return failure of the injector. What needs to be reminded is that there are many reasons for the large fuel return. When performing maintenance, professional testing equipment must be used. 

If you know you have an injector problem with your vehicle or have questions about injector replacement kits, hpinjection.com has the answers and products you need!

You can also view and purchase the aftermarket injectors online catalog via the links below.

https://hpinjection.com/collections/fuel-injectors

 

Related reading：https://hpinjection.com/blogs/news/how-many-fuel-injectors-does-a-diesel-engine-have