Bosch EFAW Dwell Angle Measuring Device — Motor Tester (Used / Legacy)

Bosch · EFAW Series · Analog Ignition Diagnostic · Bench-Tested Before Ship

The Bosch EFAW is a German-built legacy motor tester from the classic EFAW series, designed for analog measurement of ignition dwell angle, battery voltage, charging-system voltage, starter-motor current draw, alternator ripple, and overall battery condition. Originally released in the 1970s–1980s, it remains a sought-after bench instrument for workshops, automotive training schools, and restorers that need to keep older contact-breaker / points-style ignition systems in service. KOEED sources vintage and hard-to-find service instruments for MRO teams and engineering classrooms that can no longer order new replacements from the OEM.

Where the modern shop floor has moved on to digital scan tools and PLC-driven test rigs from Allen-Bradley, Siemens, Mitsubishi, Omron, Fanuc, Schneider, Yaskawa, Panasonic, and KEYENCE, the EFAW still does a job that no modern scan tool can: it speaks the analog language of a 6-volt positive-ground Bosch distributor in a 1968 Mercedes, or a 12-volt Bosch coil on a vintage Volvo. KOEED tests every unit on the bench before it ships, so you can drop the EFAW onto a workbench and put it to work the day it arrives.

Key Technical Specifications & Overview

The EFAW pairs a moving-coil analog meter movement with a rotary function selector and dedicated test leads. The values below reflect the typical OEM-published envelope for the EFAW family. Individual used units may vary slightly by production year and revision; ask KOEED for the as-tested report on the specific serial number in stock.

Application Scenarios — Where It Fits

The EFAW is not a generic multimeter and it is not a modern OBD-II scan tool. It sits in a specific niche where Bosch-era analog ignition systems still have to be diagnosed by hand. Common call-outs include:

• Classic-car restoration workshops maintaining 1960s–1980s European vehicles with Bosch distributors, coils, and contact breakers.
• Automotive engineering schools and vocational training programs that teach points-style ignition theory, dwell angle, and dynamic timing on a physical bench rig.
• Engine rebuilders and pre-OBD diagnostic shops verifying charging-system voltage and starter current draw on carbureted engines.
• Museum and private-collection garages that must keep vintage vehicles in roadworthy condition without modifying the original analog electricals.
• Aftermarket test-rig builders who wire a Bosch motor tester into a PLC-driven automation cell alongside a Fanuc robot or a Yaskawa servo station for end-of-line training fixtures.
• Pre-1985 commercial-vehicle service bays (older Mercedes-Benz, MAN, Volvo, Scania) where the OEM service literature still references Bosch EFAW test points.

For modern CAN-bus, OBD-II, or PLC-driven diagnostic lines, KOEED’s active production portfolio covers Allen-Bradley, Siemens, Mitsubishi, Omron, Fanuc, Schneider, Yaskawa, Panasonic, and KEYENCE. The EFAW is the dedicated bridge for everything that predates that ecosystem.

Integration & Wiring Notes

The EFAW is a passive bench instrument — it does not need a separate AC supply, but it must be wired into the vehicle harness under test. The standard connection pattern is:

• Red lead to battery positive (+): powers the meter movement and provides the reference for voltage / charging-system measurement.
• Black lead to battery negative (−) or chassis ground: completes the measurement loop. Confirm polarity on positive-ground vehicles (pre-1970 European cars).
• Inductive pickup on the coil low-tension wire: senses the contact-breaker opening/closing to derive the dwell-angle reading. The clip should sit on the wire between the ignition coil and the distributor.
• Current clamp (optional) around the battery main lead: for starter current draw and alternator output tests. Use the Bosch-recommended clamp or a 1 mV / 1 A shunt equivalent.
• Function switch: set to Dwell for ignition measurement, V for DC voltage, A for current (with clamp), and Battery for load-test condition.

When integrating the EFAW into a data-acquisition cell or a Siemens SIMATIC training station, treat the EFAW as the human-readable analog front end; a modern PLC reads the same physical signals through its own analog input module and the EFAW sits on the bench as the reference instrument. The KOEED FAQ covers typical PLC ↔ analog-instrument wiring patterns.

Installation & Commissioning Tips

A used Bosch EFAW is a robust instrument, but a five-minute commissioning pass before the first job will protect both the meter and the vehicle harness:

• Visual inspection: check the meter glass, the rotary switch detents, the banana-jack insulation, and the case for cracks. A yellowed case is normal; a cracked meter glass is not.
• Mechanical zero: with the unit unpowered, adjust the small mechanical screw below the scale to bring the needle to exactly zero. This is the most common drift issue on a stored EFAW.
• Battery reference check: connect to a known-good 12 V battery, switch to V, and confirm the reading. A fresh alkaline cell in the on-board reference circuit keeps the meter accurate.
• Function-selector exercise: rotate the switch through every position several times to clean the contact surface; old grease on the wafer switch is a common source of intermittent readings.
• Lead continuity: buzz the red and black leads and the inductive pickup with a standard multimeter before relying on them in the bay. Replacement leads are inexpensive; a wrong reading on a vintage harness is not.
• Bench layout: mount the EFAW on a non-conductive surface, route the high-current clamp away from the low-signal pickup, and keep the unit out of direct solvent splash.

KOEED performs this exact commissioning on every EFAW we list. If you want a second opinion on a unit you already own, send the serial number and a few photos to Moritta@KOEED.COM and our team will cross-check the Bosch service-manual envelope.

Procurement, Warranty & Lead Time

Every Bosch EFAW sold by KOEED is a used / refurbished legacy instrument, sourced through our China Sourcing Company network, individually bench-tested, and graded against the OEM service-manual envelope. Because the catalog is finite and serial numbers vary, KOEED runs the EFAW on an RFQ model rather than a fixed price.

For full BOM-style sourcing (EFAW plus leads, current clamp, and storage case), or to bundle a Bosch EFAW with a modern Allen-Bradley CompactLogix / Siemens S7-1200 / Mitsubishi MELSEC / Omron CP1 training rack, use the KOEED Create a Quote form. Need help identifying an unmarked part, or cross-referencing an EFAW to a specific vehicle harness? The AI Diagnostic Tool runs 24/7 and is tuned to legacy industrial catalog codes.

Questions before you RFQ? Visit KOEED Contact Us, read the About KOEED page, or send the BOM straight to Moritta@KOEED.COM for a 24-hour quote.