The Bosch MW is proof that a nameplate can be shorter than the research needed to repair the pump correctly. Customers across the country can use our mail-in inquiry process to determine available testing, repair, rebuilding and calibration options for the exact unit.
What is the Bosch MW system?
Bosch MW refers to an in-line mechanical injection pump family used in various diesel applications. The family name alone does not establish its governor style, delivery setting, mounting, or usable service parts. A photograph of the governor end can be as useful as a clear picture of the nameplate.
Common symptoms and what else to check
Sticking controls, leaks, poor response, smoke and hard starting warrant a structured examination, but fuel-feed and engine concerns should also be checked before removal.
How to investigate a suspected MW pump problem
A technician needs the full Bosch number, equipment and engine data, and any history of previous adjustments. Matching that information to the correct calibration procedure is especially important on older in-line systems.
Repair, rebuild or replacement: making the right call
The right repair may range from addressing a local defect to a broader rebuild with applicable bench adjustments, provided parts and procedures remain available.
Other names and numbers to look for
The most useful search terms for this family include: Bosch MW; Bosch MW injection pump; MW in-line diesel pump.
BOSCH MW design, applications and diagnosis
How the Bosch MW Works
Picture five small syringes in a row, pressed in turn by one camshaft, each aimed at a single cylinder.
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A feed pump on the side of the MW, with a hand primer, pulls fuel from the tank.
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The pump camshaft pushes each plunger in firing order.
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A control rack rotates the plungers to set how much fuel each stroke delivers. A flyweight governor moves the rack as rpm changes.
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Delivery valves snap shut after every shot.
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Turn the key off and engine vacuum pulls the rack to no-fuel. That’s the shutoff.
Shop Talk: ALDA is the boost-sensing diaphragm on top of a turbo MW. Until the turbo supplies air, it holds back the extra fuel, so the car doesn’t blow a black cloud at every stoplight.
What It Fits
| Make and model | Engine | Years | Notes |
|---|---|---|---|
| Mercedes 300D and 300CD (W123) | OM617 | 1977-85 | Non-turbo early, turbo later |
| Mercedes 300TD wagon (W123) | OM617 | Check the tag | |
| Mercedes 300SD (W116) | OM617 turbo | 1978-80 | North America only |
| Mercedes 300SD (W126) | OM617 turbo | 1981-85 | US cars |
| US Army M939A2 trucks | Cummins 6CTA 8.3 | Per owner forums |
Did You Know? The 1978 300SD was the world’s first production turbodiesel sedan, sold only in North America. When Bosch moved OM617s elsewhere to the newer M pump in late 1980, US and Canadian cars kept the MW.
Part Numbers We See
The tag carries a Bosch number and type code, and many pumps carry a Mercedes number too. Pumps differ by market and turbo, so photograph every number. Your engine number helps as well: it starts with the 617 code, such as 617.912 for non-turbo or 617.952 for the W123 turbo.
Why MW Pumps Fail and the Symptoms
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Seals: hardened O-rings weep, often at the delivery valve holders on top.
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Worn elements: tired plungers and delivery valves deliver weak or uneven fuel.
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Governor and rack wear: the idle hunts and response gets vague.
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ALDA trouble: a torn diaphragm or an enthusiastic adjustment brings smoke or sluggishness.
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Water: rust on precision parts.
Symptoms:
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Fuel weeping at the top of the pump
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Hard starting, especially hot
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Black smoke or slow acceleration
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Rough or hunting idle
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Won’t shut off with the key
Owner’s Tip: Won’t shut off? The shutoff runs on vacuum, so check the vacuum lines before you blame the pump. Change both fuel filters while you’re at it.
Details that make a bosch mw inquiry useful
On a Bosch MW, the Mercedes engine type, pump code and installed governor arrangement are particularly helpful. Explain whether the complaint involves leakage, rough running, poor starting or a governor that does not respond correctly. Photograph any linkage and modifications before removal, since an older engine may have received adjustments or replacement components during decades of service.
Frequently asked questions
Can a Bosch MW injection pump be rebuilt?
The repair options for Bosch MW can range from an isolated defect to extensive inspection and rebuilding, depending on mechanical wear, governor condition, correct parts and the original calibration specification. Before replacement or adjustment, check whether the engine-side fuel supply and installation timing have been properly assessed. Learn about mechanical pump service.
Will a MW pump from another engine fit mine?
Bosch MW compatibility: Similar mounting flanges do not prove matching fuel delivery, governor behavior or application rating. Matching the exact build and engine requirements matters more than external appearance. Record the drive and control details along with the complete pump tag before removing or comparing units. Start with the pump directory.
Request Bosch MW Service Information: Start your repair inquiry
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