Locked-Up Bimmer

Aug. 4, 2017
This bulletin released by BMW addresses the issue of potential engine hydraulic lock caused by a fuel injector that is stuck in the open position, where the engine will mo longer turn over due to liquid fuel trapped in the cylinder.

This bulletin released by BMW addresses the issue of potential engine hydraulic lock caused by a fuel injector that is stuck in the open position, where the engine will mo longer turn over due to liquid fuel trapped in the cylinder.

If a vehicle is towed into the shop with a suspected hydraulic lock condition, the following repair tips should be applied:

  • Remove the spark plugs and rotate the crankshaft manually. Do not crank the engine with the starter. Fire hazard is possible.
  • Check the compression on all cylinders.

Testing conditions:

The battery must be in perfect condition. The engine should be warm, with coolant temperature at a maximum of 95 degrees Fahrenheit. The accelerator pedal should be fully depressed when cranking the engine.

Crank the engine until the compressor gauge indicator stops rising. The compression pressures should be approximately equal for all cylinders, at 143-256 psi. If the compression pressures are all within specification, check the engine oil for fuel dilution and change oil and filter if needed.

If compression is below 143 psi in the cylinder in which a stuck-open injector has been diagnosed, that cylinder’s piston/connecting rod may have been damaged due to the force applied by the hydraulic lock.

Remove all fuel injectors and check the leakage rate. Further engine tear-down should be carried out to determine the cause of low compression in the affected cylinder.

The starter drive and ring gear should also be checked for damage such as missing or stripped teeth.

Sponsored Recommendations

Cam & Crank Sensor Training Series

Today's advanced engines depend on accurate and consistent information from cam and crank sensors for performance, fuel economy and emissions, and not all cam and crank sensors...

Buying Your Next Diagnostic Tablet

When you last invested in a diagnostic tablet for your shop, did you consider it a potential gateway to increased revenue? Probably not. It’s likely you viewed it as a necessary...

Access Carside OEM Repair Data with MOTOR TruSpeed

Now available on all Autel MaxiSYS Ultra Series tools, MOTOR TruSpeed Repair delivers expanded OEM service and repair data within days of being published by

ADAS Case Study: From 10 Calibrations a Month to Over 10 A Day

Originally published by Vehicle Service Pros, March 26, 2024

Voice Your Opinion!

To join the conversation, and become an exclusive member of Vehicle Service Pros, create an account today!