Megasquirt and Microsquirt - Spark/ignition output
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Megasquirt and Microsquirt - Spark/ignition output |
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Introduction -
Coils types -
Wiring -
Firing order -
Introduction
The following shows a simplified block diagram of the Megasquirt system.
This section of the manual will focus on the spark/ignition output and ignition coils. First we will cover the basics of coil types and then move on to wiring required to connect your ECU to these coils.
Coil types
Coils come in many shapes and sizes. The coil may be a single tower coil, dual tower wasted spark coil or multiple coils in a coilpack. The current drive may be high current inductive, logic level inductive or CDI type.
High current inductive - standard single tower coil
This style of single output coil is extremely common. In different applications various coil resistances and currents are used. Until the seventies most coils were "12V type". During the seventies it was common to use "8V" ballasted coils. With the advent of EFI, lower resistance "EFI only" coils came into use. These are usually accomodated by setting the appropriate dwell.
High current inductive - wasted spark coilpack
Shown here is an "EDIS type" coilpack from Ford. Similar style coilpacks are used by numerous manufacturers. Each of the two high current inputs produces a spark in a pair of outputs. These are wired to cylinders that need to fire 360 crank degrees apart.
Shown here is a GM two post coil. The high current inputs produces a spark in the pair of outputs. These are wired to cylinders that need to fire 360 crank degrees apart.
Bike type CDI coils
More information is needed on these coils - generally they need a CDI style driver to operate them correctly.
LS1, LS2, LS truck coils - logic level
The LS style coils are of a "coil near plug" design, they are also logic level which means they can be directly connected to the MS3X ignition output.
They are easy to obtain used (in the USA) and are available new from OEM or aftermarket. The truck coil gives the most powerful spark and is easily identified by the heatsink.
LS1 coil wiring
A dwell figure of 4.0ms is advised for LS1 coils.(was 4.5)
Note that some coils have a built-in overdwell protection feature. If given too much dwell the coil will automatically spark. This can give a dangerous
advanced spark. Be sure to strobe your timing at high revs to ensure this is not happening.
LS2 coil wiring
A dwell figure of 4.0ms is advised for LS2 coils. (was 4.5)
Note that some coils have a built-in overdwell protection feature. If given too much dwell the coil will automatically spark. This can give a dangerous
advanced spark. Be sure to strobe your timing at high revs to ensure this is not happening.
Mazda rotary coils - logic level
These coils have integral ignitors and can be controlled with a logic output.
Coil-on-plug coils (high current or logic level)
There are many different coil on plug coils used by the OEMs. Some are logic level, some require high current drivers. If a coil has two wires it is certainly high current. If a coil has four wires it is almost certainly logic level.
High current 2 wire COP (Renault)
2/3 wire COPs (without built-in ignitors)
2-wire and 3-wire COPs require an ignitor as they are simply a 'dumb' high-current ignition coil. Check your service manual to determine the pinout.
For a 2 wire COP, the two wires are :
For a 3 wire COP, the three wires are :
4/5 wire COPs (with built-in ignitors)
4-wire or 5-wire COPs have a built in amplifier (ignitor) so they can typically be
connected directly to the 0-5V low current MS3X logic level spark outputs.
Some COPs require 12V signals or more current than the MS3X outputs
Unconfirmed - some 3 wire COPs might contain a driver.
Coil input resistance check
Many logic coils are suitable for direct connection to MS3X outputs, but before use it is necessary to check the resistance to ground
on the input.
Using a multimeter set to resistance, check between the Spark Signal Input and Signal Ground.
If you have a reading of say ~1k then the MS3X outputs can be used directly.
If you measure around 120-500 ohms then you will need a buffer.
(An external buffer box may be available in the future, presently you will need to DIY. See the MS2/Extra manuals for options.)
VAG P/N 06B 905 115 COPs: as used on (VW 1.8t and may other VAG cars (2001+).)
During production these coils have changed electrically and it is necessary to perform the resistance check to confirm suitability.
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Pin 1: Connects to Pin 1 on all other coils and then to +12v ignition feed (or fuel pump relay) Pin 2: Signal ground (connect to engine block*) Pin 3: Spark Signal from ECU (from MS3X or via buffer) Pin 4: Power ground (connect to engine block) |
Earlier than 2001 coils, PN - 06B 905 115, 06B 905 115 rev B and E.
These have an input resistance of ~1k and should work ok with the MS3X outputs. Be sure to use "Going high (inverted)"
Cranking dwell = 4.0ms
Running dwell= 3.0ms
Later than 2001 coils, PN 06B 905 115 rev L and R
These have a low input resistance and require a buffer.
Avoid the earlier 'L' revision as they are reported to have reliability issues.
Cranking dwell = 4.0ms
Running dwell= 3.0ms
Ignition amplifiers
These take a 0-5V logic signal from the ECU and provides a high current ground switch suitable for driving a coil. They are also designed to withstand the high voltage kick-back from coils. Certain vehicles include similar modules as standard.
Bosch 211 module wiring
The Bosch 211 module offers a simple to use four channel coil driver, however it is an expensive option. A single module new will cost significantly more than buying a set of LS style coils used.
Generic modules
DIYautotune now offer their Quadspark four way ignition module. This is easily used to drive high-current coils from ECU logic outputs with similar wiring to the Bosch module.
Various other OEM or aftermarket coil driver modules exist that follow the same general pattern as the Bosch module.
The creative DIYer could use BIP373 or equivalent to make an external ignition module driven from the logic outputs.
Ignition output wiring
In order to correctly drive a coil it is necessary for the ECU to provide the correct signal to it.
The main types are:
Firing order
The outputs ALWAYS fire in sequence A,B,C.... so you must apply your firing order in the loom.
Firing order - coil on plug
e.g. on a 4 cyl engine with 1342 firing order SpkA = 1, SpkB = 3, SpkC = 4, SpkD = 2
on a V8 with 18436572 firing order. SpkA = 1, SpkB = 8, SpkC = 4, SpkD = 3, SpkE = 6, SpkF = 5, SpkG = 7, SpkH = 2
Firing order - wasted spark
Here, the cylinders are paired from one output and typically a double ended coilpack is used.
e.g. on a 4 cyl engine with 1342 firing order. SpkA = 1&4, SpkB = 3&2
on a V8 with 18436572 firing order. SpkA = 1&6, SpkB = 8&5, SpkC = 4&7, SpkD = 3&2
If you have a question, comment, or
suggestion for this FAQ please post it on the forum.
No part of this manual may be reproduced or changed without written permission from James Murray, Ken Culver and Philip Ringwood.