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Fuel injector test 535I E28

Symptoms of bad fuel injectors

  • The engine starts hard or fails to start when cold
  • Engine misses and hesitates under load
  • Poor fuel economy
  • Vehicle idles jump around

Learning context

The fuel injectors are a necessary engine component that injects and atomizes fuel into the combustion chamber. A poor-performing or bad fuel injector will affect the quality of the air-fuel ratio causing poor combustion in the engine and reducing its efficiency.

why am I testing the injectors?

I am testing the injectors to confirm that they are working properly and rule them out as the cause of excessive fuel consumption in my E28. You want to first test that the injector is working properly while on the vehicle and then remove them if you choose to rebuild or replace them.

Summary

  1. Check injectors are clicking at idle
  2. Check injectors resistance
    • 318(1984 and 1985 ONLY)= 14.5-17.5Ω
    • 325E and 325ES(UP TO 9/1984)= 14.5-17.5Ω
    • 325, 325E, 325ES(10/1984 AND ON)= 2-3Ω
    • 325i, 325is, 325iC= 14.5-17.5Ω
    • 528E(1982 THROUGH 3/1987)= 2-3Ω
    • 528E(4/1987 AND ON)= 14.5-17.5Ω
    • 533i= 2-3Ω
    • 535i(1983 THROUGH 1/1986)= 14.5-17.5Ω
    • 535i(2/1986 AND ON)= 14.5-17.5Ω
    • 525i(MOTRONIC 1.1)= 14.5-17.5Ω
    • NOTE* Although the resistance readings are the same as the early 535i models, injector part numbers are different for the later style injectors.
  3. Check for voltage at the injector electrical connector
  4. check for any damaged wires related to the injector harness
  5. replace any injector that fails any of the tests mentioned.
  6. Tools required
    • Stethoscope or screwdriver
    • voltmeter
    • Power Probe
    • Injectors- Part# 13641706176
    • 13MM socket and rachet

Warning

Gasoline is extremely flammable, take proper precautions when working on any part of the fuel system. Don’t smoke, allow open flame, or use bare light bulbs near the area exposed to fuel. If you spill fuel on your skin, rinse immediately with soap and water, wear safety glasses, and have a class B fire extinguisher on hand.

Procedure

  1. Start your vehicle and touch each injector with a stethoscope and check for a steady clicking sound from each injector. If you do not have a stethoscope you can use a long screwdriver, and place the tip on the injector and the handle to your ear. You should hear the clicking of the injector.
E28 injectors location under the fuel rail.
Use a screwdriver if you do not have a stethoscope
Using a screw driver to check injector clicking
Always wear your PPE when working on your vehicle.

2. Increase the RPM and the clicking of the injector will increase as well. Check this on all injectors. If an injector fails either of these tests replace them, and test again.

Testing the clicking of the Injectors

3. To get access to all six Injectors, I removed the intake tubbing and electrical connections from the thermostat housing.

4. To disconnect the injectors I advise using a pick to pull the secure clips off of the electrical connections.

E28 injector clips
Using a pick to remove secure clip-off injectors.

5. Unplug each injector and check the resistance across the pins. The resistance reading for my E28 is 14.5-17.5Ω.

Injector readings= Injector 1-2.4Ω Injector 2- 16.4Ω Injector 3- 16.4Ω Injector 4- 16.6Ω Injector 5- 16.7Ω Injector 6- 16.6Ω

6. Replace any injectors that fail any of these tests, and make sure that all of the secure clips are on the electrical connections

E28 all back together
E28 is all back together

Conclusion

Testing the injectors while on the vehicle allows you to identify if any of your injectors are working poorly or not working at all. After testing my injectors, injector 1 failed the resistance test, and will be replacing it. If your injectors pass the tests above the next step is to test if your injectors are atomizing fuel properly, if they fail that test you can rebuild them or replace them.

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