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Mercedes 280e k-jetronic troubleshooting?
Fix Your Damn K-Jetronic
Fits the Mercedes 280 E (W123) sold in North America. Not a VIN lookup.
Hard hot starts, rough idle, stumbles? Test the sensor plate, find vacuum leaks and read the four K-Jet pressures against Mercedes factory specs.
Free on this page. Match the row, then stop. Illustrated steps, torque and the job card stay in the PDF.
What you see Won't start hot, fine cold
Points to Residual pressure bleeding off, or plate sticking
What you see Won't start cold, OK hot
Points to Cold-start valve, thermo-time switch or cold control pressure
What you see Hunts or stumbles at idle
Points to Vacuum leak after the sensor plate
What you see Sluggish, flat off idle
Points to Plate binding or low system pressure
What you see Rough cold, smooths when warm
Points to Warm-up regulator out of spec
What you see Long crank, no start
Points to Pump, filter or relay
What you see Black smoke, fuel smell, fouled plugs
Points to Too rich: WUR, plate rest position, leaking injector or cold-start valve
What you see Sat for months, won't run
Points to Varnished plunger, old fuel, clogged filter
What you see Plate won't move at all
Points to Plunger seized in the distributor
What you see Poor mileage, runs OK
Points to Mixture out, cold-start valve dribble
General information for the vehicles this guide covers. You do the work at your own risk; follow the vehicle maker's service information and the emissions and roadworthiness rules where your vehicle is registered.
A 30–60 second clip from the Repair Guider channel. The illustrated steps stay in the PDF.
Four previews. Torque specs and the printable job card stay in the PDF.
The sensor plate test.
Job card
Is this your problem? This guide is for you if you're asking:
Not quite your problem? Request a guide, and requested guides jump to the front of the line.
Test the sensor plate first, seal vacuum leaks, then read the four pressures with the gauge between distributor and control-pressure line: valve open for control pressure, closed for system pressure. Replace only what fails, and set CO with an analyzer to the emission label.
Tools have exact part numbers; wear parts are matched by VIN or the old part. Borrow what you can.
General information for the vehicles this guide covers. You do the work at your own risk; follow the vehicle maker's service information and the emissions and roadworthiness rules where your vehicle is registered.
Chapters that say when to stop:
Illustrated steps, torque specs and the one-page job card are in the download.
With the gauge between the fuel distributor and the control-pressure line, the valve open reads control pressure and the valve closed reads system pressure (5.0–5.6 bar on the US 280 E).
Usually residual pressure bleeding off after shutdown: the accumulator, a pump check valve, the pressure regulator or a dribbling cold-start valve. It should hold at least 2.5 bar after 30 minutes.
General information for the vehicles this guide covers. You do the work at your own risk; follow the vehicle maker's service information and the emissions and roadworthiness rules where your vehicle is registered. Car guide terms · Edition 1.0 · 2026-10-07
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