Engine - Hydraulic Lock

9232bmw02

Group 11
Engine


Bulletin Number
11 01 92 (3484)


Woodcliff Lake, NJ
January 1992
Product Engineering


SUBJECT:
Engine Hydraulic Lock

Engines:
All

Situation:
A fuel injector which is subject to a mechanical malfunction and remains stuck in the open position may cause an engine hydraulic lock condition, i.e. the engine will no longer turn over due to the noncompressible liquid fuel which is trapped in the cylinder.

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

- Remove the spark plugs and rotate the engine manually.

Caution: Do not crank engine over with the starter. Fire hazard due to possible liquid fuel in a cylinder.

- Check the compression of all cylinders.

Testing conditions:

Battery in perfect condition.

Engine warm - coolant temperature maximum of 95~F (35~C). Accelerator pedal fully depressed when cranking engine.

See appropriate Repair Manual (Group 11) for further information regarding main/fuel pump relay(s) which must be removed to disable the ignition system and fuel pump(s) before cranking and also special tools/ adaptors used for the compression check.

Crank the engine until the compressor gauge indicator stops rising.

The compression pressures should be approx. equal for all cylinders (10-11 bar/143-156 psi). If the compression pressures are all within specification, check the engine oil for fuel dilution and replace if necessary.

Note:
If the compression is lower i.e. < 10 bar (143 psi) in the cylinder in which a "stuck open" injector has been diagnosed, that piston/ connecting rod may have been damaged due to the hydraulic lock.


- Remove all of the fuel injectors and check the leakage rate as outlined in S.I. 13 08 90 (3096).

- Further engine tear down should be carried out to determine the cause of low compression in the affected cylinder, i.e. bent connecting red, damaged piston, etc. as outlined in the repair manual.

- The starter drive and ring gear should also be checked for damage, i.e. missing or stripped teeth.

Warranty
Status:
Information only.