M104 Intake Rebuild

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This article is a reference for rebuilding the air intake on an M104 engine NOT powered by KE-Jetronic (3.0L M104.98x). There may be slight variations due to differences between specific model years and modifications or annotations to the article to support changes should be made as they are discovered.

Overview

Time 2 hours
Cost $$
Difficulty Medium
Parts required Intake manifold gaskets (104 141 1080, requires 6)
Long lower intake hose (104 094 35 82)
Short lower intake hose (104 094 36 82)
Fuel injector seal (019 997 13 48, requires 12)
Applicable models All M104 engines, excluding M104.98x

Procedure

Remove air intake pipe

  1. Unclip retaining hooks at air box behind right headlight and remove upper lid
  2. Unplug both sensors along the intake pipe
  3. Remove valve cover screws
  4. Loosen upper hose clamp at throttle body boot
  5. Pull up on air intake pipe and remove

Remove fuel rail

  1. Remove black plastic engine wiring harness cover
  2. Remove fuel pressure bleed cap located towards the center of the fuel rail
  3. Bleed excess fuel pressure by pressing schrader valve with a tool like a small screwdriver and replace the cap
  4. Disconnect fuel inlet and return hoses from fuel rail
    1. Make note of which hose goes where
  5. Remove fuel pressure regulator vacuum line
  6. Unbolt dipstick for clearance by removing 5mm allen bolt
  7. Unplug fuel injectors from engine harness by pinching connectors and pulling
    1. Metal clips may not bend all the way and a thin screwdriver can be used to gently bend the metal clips for clearance
  8. Unbolt fuel rail and pull to remove. There are 5x 6mm allen bolts holding it in place.

Remove intake manifold

  1. Unbolt remaining bolts holding intake manifold to cylinder head
  2. Loosen both hose clamps connecting the upper and lower intake manifolds together. Located underneath the upper intake manifold
  3. Disconnect wire to throttle body
  4. Disconnect air hoses near oil dipstick mounting bracket
  5. Lift up and remove air intake manifold

Rebuild

  1. Replace all vacuum lines
  2. Clean parts
    1. Intake manifold seat on cylinder head
    2. Intake manifold
    3. Throttle body boot if not replacing
    4. Intake boots if not replacing
  3. Parts to replace
    1. Intake manifold gaskets (104 141 1080, requires 6)
    2. Long lower intake hose (104 094 35 82)
    3. Short lower intake hose (104 094 36 82)
    4. Fuel injector seal (019 997 13 48, requires 12)