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BMW M70 / M73 / M73TU Family
Table of Contents
All Engines
Problems
- Distributor caps and rotor arms should be checked at 80k miles – if they’re worn, the engine will be down on power and get poor fuel economy
- Rubber couplers between the intake manifolds and heads can spring vacuum leaks and it’s a big job to replace them
- Oil spray bar banjo bolts can slacken and cause problems
- Throttle stepper motors can cause EML faults
- Oil can leak from the upper timing cover
M70
This engine is, in essence, two M20B25 six-cylinder engines slapped together (albeit with some differences). It has two distributors, two throttle bodies, two fuel pumps, two fuel rails, two MAF sensors, two crank position sensors, two coolant temperature sensors, and two engine computers. This makes troubleshooting issues a challenge, as it predates OBD2.
Usage
M70B50
- BMW 750i, 750iL (E32)
- BMW 850i (E31)
M73
Updates
Differences from the M70:
- Roller bearing camshaft followers
Usage
M73B54
- BMW 750i, 750iL (E38)
- BMW 850Ci (E31)
M73TU
Updates
Differences from the M73:
- Electronically heated catalyst
- Variable MAP thermostat
- Water-cooled alternator
Usage
M73TUB54
- BMW 750i, 750iL (E38)
- Rolls Royce Silver Seraph