GTC505m Engine Ignition Analyzer

Finding dead or malfunctioning coils and plugs can be hard work. The GTC505 makes ignition troubleshooting quick, easy, and painless. It’ll help you, and the people depending on you, get moving again!

The GTC505 is the product of 20 years of work (by GTC) on ignition diagnostics. This tool will tell you exactly what’s going on with any spark ignition system as soon as you put its sensor by your coil (or spark plug wire). Swapping coils and other components in and out until you figure out what’s wrong is slow, tedious, and wasteful. The GTC505 will take the guesswork out, so you can be confident that the problem will be solved on your first try.


Who it’s For:

  • Marine outboard mechanics
  • Gasoline inboard mechanics
  • Small engine repair shops doing fault diagnostics
  • Motorcycle technicians doing diagnostics or aftermarket modification
  • Automotive technicians looking for a GTC505 with all the extras

What it Does:

Quickly and easily detects engine RPM and spark parameters. Useful for checking for ignition system faults and misfires, or for tuning and aftermarket modifications.

How it Works:

  1. Connect the appropriate sensor
  2. Turn the unit on
  3. Position the sensor near the ignition module or wire
  4. Check the engine RPM, spark peak voltage, burn time, and dwell angle/ramp time. The digital view gives you a quick look at the average, and the chart view will show you any misfires.

Warranty & Support:

Covered by our standard 1-year warranty, and supported for much longer. Replacement parts and accessories are generally available for 10+ years.

  Proposition 65 Warning

This product can expose you to chemicals including Styrene, which is known to the State of California to cause cancer, and Bisphenol A (BPA), which is known to the State of California to cause birth defects or other reproductive harm. For more information go to


  • GTC505
  • Flexible probe
  • Extension cable
  • Coil on plug (COP) active sensor
  • Spark plug wire (SPW) shielded capacitive sensor
  • USB micro cable and AC charger adapter
  • Protective rubber holster
  • Hard padded case for carrying and storage
  • User’s manual
  • 1 year parts and labor warranty


Small Engines

    Small engines without alternators use magneto ignition systems. The engines with alternators usually use distributor or capacitive discharge ignition systems.
General Technologies recommends using either the TA100 or GTC505 when working with small engines. The TA100 is economical and easy-to-use; it helps you set idles, and check for major spark issues. The GTC505 can help you find issues at particular RPMs, and gives you more information on how the ignition system responds to loads. The GTC505 is also good if you want a tool that will work on larger (automotive or marine) engines.

Motorcycle Engines

    Modern motorcycle engines generally use coil-on-plug ignition systems (, often pencil-type modules). Older motorcycles used distributors or magnetos depending on their size and number of cylinders.
General Technologies recommends the TA100 for people who are only working on vintage motorcycles, and the GTC505 for those who want to work on all kinds of bike. The TA100 is economical, and good for setting idles or checking for fouled plugs on magneto or distributor-type systems. The GTC505 works on all kinds of systems, and can help you diagnose complicated problems.

Marine Engines

    Small marine engines (<25hp) generally use magneto ignition systems. Large, old marine engines use distributor ignition systems. Since 2015, larger marine engines have started to use coil-on-plug ignition systems.
General Technologies recommends that marine engine technicians working on newer engines use the TA500 or GTC505. The GTC505 is best for technicians looking to do in-depth diagnostics, such as finding occasional misfires. The TA500 is good for less detailed work, like setting idle speeds and checking for fouled plugs.

Automotive Engines

    Modern (gasoline) automotive engines are coil-on-plug based. Most cars manufactured before 2005 use distributor ignition systems, though there are also a few that used capacitive discharge systems.General Technologies recommends using a GTC505 for these applications, because it is compatible with COPs, and can help you diagnose occasional misfires


  • Display waveforms in real time
  • Detect and display dwell angle (in high voltage sparkplug-wire systems), and ramp time (for COP systems)
  • Graph burn time, spark plug voltage, dwell/ramp time, and RPM for each spark, allowing for detection of misfires
  • Compare readings between cylinders with a “candlestick” graph that displays maximum, minimum, and average readings for each cylinder
  • Display everything on a 3.5″ color TFT LCD screen
  • Rechargeable Li-Ion battery provide 6+ hours of working time
  • Pass the rigorous “MIL-STD-810” drop test
  • Multiple sensors and hook-up options:
  • All specially designed for use with the GTC505
  • 2 m (74”) shielded coaxial cable with BNC and sensor connector
  • 30 cm (12”) shielded flexible goosneck with BNC and sensor connector
  • Cable and flexible gooseneck can be use with any sensor
  • Electrically shielded clip-on and spark plug wire sensors fit up to 8 mm diameter wires
  • Active coil on plug (COP) sensor for optimal signal detection and rejection of interferance from other ignition modules
  • Automatic detection and configuration of the sensors
  • Compatible with the 2 m (74”) shielded coaxial clip-on spark plug wire sensor P/N: GTC505-CSC

Sensor Specs

TA100 sensor TA500 sensor GTC505 coil-on-plug sensor GTC505 spark plug wire sensor
Sensor Type capacitive capacitive capacitive & inductive capacitive & inductive
Works on Capacitive Discharge Systems
Works on Distributor Systems
Works on Magneto System
Works on Coil-On-Plug Systems

Analyzer Specs

TA100 TA500 GTC505
Measures Engine RPM
Measures Peak Spark Voltage
Measures Spark Burn Time
Measures Dwell Angle
Measures Ramp Time


What is the difference between the GTC505, the GTC505m, and the GTC505-CSC?

The GTC505 is an engine ignition analyzer. The most basic kit it comes in: with a flexible probe, extension cable, cop sensor, spw sensor, USB micro cable and AC charger adapter, user’s manual, 1 year warranty, and hard padded carrying case.

The GTC505m is an upgraded version of the GTC505 kit – it comes with everything in the GTC505 kit, but with the GTC505-CSC accessory, and a larger hard padded carrying case to accommodate the extra accessory.

The GTC505-CSC can be purchased separately (here), or together with the analyzer in the GCT505m kit.

GTC505-CSC GTC505 GTC505m
Engine Ignition Analyzer
Flexible Probe
Coil on plug (COP) active sensor
Spark plug wire (SPW) shielded capacitive sensor
Clip-on spark plug wire capacitive sensor
Extension cable with BNC and sensor connector
USB micro cable and AC charger adapter
Protective rubber holster
Hard padded case for carrying and storage
User’s manual
1 year parts and labor warranty


Brochure: GTC505M-BREN
Manual: GTC505-MNEN

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