M70 / M73 / M73TU Family

BMW M73
BMW M73B54 – photo by The Car Spy

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

M73

Updates

Differences from the M70:

  • Roller bearing camshaft followers

Usage

M73B54

M73TU

Updates

Differences from the M73:

  • Electronically heated catalyst
  • Variable MAP thermostat
  • Water-cooled alternator

Usage

M73TUB54