Fuel pressure damper defective? Fuel at the leak-off line (W116, W126)
The fuel pressure damper is one of the most unassuming components of the K-Jetronic – a yellow-chromated part next to the fuel distributor, almost always overlooked during troubleshooting. Yet it reveals its fault more clearly than any other component of the injection system: it drips. This guide shows how to check it and how to tell it apart from the warm-up regulator.
Bosch fuel pressure damper 0280161007 – unused NOS new part in the original Mercedes-Benz parts box. Clearly visible at the top: the pipe nipple for the leak-off line, where diaphragm damage shows up first.
Symptoms: how do you recognize a defective pressure damper?
The key symptom can be spotted without any tools: The leak-off line runs from the small pipe nipple on the damper. If fuel drips there, the diaphragm has failed. Because pressure escapes from the system as a result, a characteristic driving symptom appears too – the cold engine starts, dies again, and leans out when you give it gas.
| Symptom | Likely cause |
|---|---|
| Fuel drips from the leak-off line's pipe nipple, smell of fuel in the engine bay | Pressure damper – diaphragm torn |
| Cold engine starts, dies again immediately, leans out when you give it gas | Pressure damper (pressure loss through the defective diaphragm) |
| Injection system audibly runs rougher than usual, pressure in the system fluctuates | Pressure damper – the pressure pulses from the pump and valves are no longer smoothed out |
| Engine judders and surges throughout the entire warm-up phase, runs perfectly once at operating temperature, nothing drips | More likely Warm-up regulator (control-pressure regulator) |
| Poor starting only after the car has stood for a longer time, no problem after a short stop | More likely fuel accumulator |
| Fuel present in the vacuum hose, engine generally runs too rich | More likely Fuel pressure regulator |
This distinction saves money: if the nipple stays dry and the problem only occurs in the first few minutes after starting, check the warm-up regulator first.
Causes: why does the pressure damper fail after decades?
Inside, a diaphragm works against a spring. It absorbs the pressure pulses generated by the fuel pump, system pressure regulator and injection valves, and releases them again in damped form. This lets the injection system run more quietly and with more stable pressure, preventing foaming in the fuel and wear on the injector needles.
After decades in service, this very diaphragm is the wear part: it hardens and tears – the fuel then takes the path the design provides for that, namely out through the leak-off line. As long as the component stays dry, nothing shows on the outside; the damp pipe nipple is the first visible sign.
Test it yourself: 5 steps before you replace it
- Dry test at the pipe nipple (free): Place a clean white cloth under the damper next to the fuel distributor and check it after a drive. Fuel stains or a persistently damp nipple confirm the diagnosis.
- Check the leak-off line: The line at the upper nipple runs to the intake manifold or to the rubber connector of the valve cover breather, depending on the model year. Pull it off and check whether fuel is present – there should be none there. Caution: keep ignition sources away and have a catch cloth ready.
- Feel the fittings: Check the hex, thread and the fuel and control-pressure line connections for fuel discoloration and damp edges. A loose fitting can, at best, save you the replacement.
- Observe cold running: Does the engine start cold, die again immediately, and stumble when you give it gas? Combined with a damp nipple, the diagnosis is clear.
- Measure pressures (workshop step): The final confirmation comes from a test gauge. It lets you distinguish system and control pressure from Warm-up regulators and Fuel accumulators before you replace any parts.
Solution: replace with the genuine Bosch 0280161007
A repair is not possible – the housing is sealed and the diaphragm is not available separately. The only option is replacement with a genuine part bearing the Bosch number 0280161007 (Mercedes A 000 078 05 92). The component is screwed in, so the replacement is quick.
Important before buying: The suffix number is decisive – compare the number stamped on your old part exactly. The successors 0 280 161 009 and 0 280 161 012 are not directly interchangeable, nor is the D-Jetronic damper 0 280 161 002 (W108, W109, W111) from the return line, nor 0 280 161 005 and 0 280 161 024. The system pressure regulator 0280160007 is also a different component.
Both versions are in stock:
Bosch 0280161007 – NOS
New part, unused in the original box · W116, W126, R107, C107, W123, W460
289,00 €
View offer →
Bosch 0280161007 – tested
Genuine used part, tested · W116, W123, W107/R107, Porsche 928
169,00 €
View offer →
Not sure whether 0280161007 is your number?
Send us the chassis number and model year, or a photo of the Bosch stamp – we'll check it for free. Bosch 0280161007 / Mercedes A 000 078 05 92, NOS 289,00 € · tested 169,00 €.
Check fitment for free →Compatible vehicles
| Model series | Models | Model years |
|---|---|---|
| Mercedes W116 S-Class | 280 SE, 280 SEL, 350 SE, 350 SEL, 450 SE, 450 SEL, 450 SEL 6.9 | 1976–1980 |
| Mercedes W126 S-Class | 280 SE, 280 SEL, 380 SE, 380 SEL, 3.8, 500 SE, 500 SEL | 1979–1986 |
| Mercedes R107 SL | 280 SL, 350 SL, 380 SL, 450 SL, 500 SL | — |
| Mercedes C107 SLC | 280 SLC, 350 SLC, 380 SLC, 450 SLC, 450 SLC 5.0 | — |
| Mercedes W123 / C123 / S123 | 280 E, 280 CE, 280 TE | 1976–1985 |
| Mercedes W460 G-Class / Puch G | 280 GE | 1979–1993 |
| Porsche 928 Coupé | 928 4.5 (from 07/1980) · OE 928 110 231 02 | 1977–1982 |
| Rolls-Royce / Bentley | Silver Shadow II, Silver Wraith II, Camargue, Corniche, Bentley T2 · OE UE 40706 | 1980 |
Does not fit KE-Jetronic, Motronic or diesel engines. The Bosch number stamped on your old part is always decisive. More components: Fuel pressure regulators & dampers and Fuel system & injection.
FAQ
How do I recognize a defective pressure damper?
At the leak-off line's pipe nipple: if fuel drips there or the connection is persistently damp with fuel, the diaphragm has failed. This fits with a cold engine that starts, dies again, and leans out when you give it gas.
What does the pressure damper do in the K-Jetronic?
It smooths out the pressure pulses from the fuel pump, system pressure regulator and injection valves. This lets the system run more quietly and with more stable pressure, preventing foaming in the fuel and wear on the injector needles.
Can I keep driving with a defective pressure damper?
We advise against it. A torn diaphragm means fuel escaping in the hot engine bay – a safety risk. The damper is screwed in and quick to replace.
Is the pressure damper the same as the fuel accumulator or the warm-up regulator?
No, these are three different components of the K-Jetronic. The fuel accumulator (0 438 170 xxx) is significantly larger and has no leak-off line, while the warm-up regulator (0 438 140 xxx) controls the control pressure based on engine temperature. The pressure damper only dampens pressure pulsations.
Which pressure damper fits my vehicle?
What matters is the Bosch number stamped on your old part, which must match 0280161007 exactly. 0 280 161 009, 0 280 161 012, 0 280 161 002, 0 280 161 005 and 0 280 161 024 are not interchangeable. If in doubt, send us the chassis number and model year – we'll check it for free.
KFZTeile-Thot is a specialist workshop for tested and refurbished Mercedes parts with our own test benches, specializing in Mercedes classic cars and K-Jetronic components – over 1,000 eBay reviews (almost all positive). Questions about fitment? Call us: 0179 8991069 (Mon–Fri 8 am–6 pm) or use the contact form. More K-Jetronic guides: Warm-up regulator defective and Fuel accumulator defective.