Ignition management without distributor with cam sensor
This type of system is similar to the “wasted spark” system in that it is distributor less and multiple coil, it has a cam phase sensor in addition to the crank sensor which allows the EMS to determine where in the engines cycle each individual cylinder is. There is a discrete coil per cylinder and the EMS is then able to fire the appropriate coil.
The cam phase sensor can also be used by the injection system to provide proper sequential injection, the Rover MEMS as fitted to the VVC engine uses this kind of system, but just uses two coils as per the wasted spark set-up. The cam phase sensor is also used by the EMS to help drive the VVC mechanism. The EMS on the Subaru Imprezza uses this type of system.
How it works.
The EMS is aware of the TDC position from the crank sensor and by counting teeth can tell exactly where the engine position is at any time. It is also aware of the engines cycle position from the cam phase sensor. It uses this information together with the information from the throttle position sensor/MAP sensor to look up the appropriate ignition timing settings from the ignition map. Using the crank and cam position sensors it is then able to determine exactly when to fire each individual coil since it knows which cylinder is at the firing position of the cycle. Each cylinders individual coil is fired once per engine cycle at exactly the appropriate time. The spark is routed directly to the appropriate cylinder.
In the normal course of events with the engine operating at the correct temperature in defined conditions the EMS will use load and engine speed to derive the correct ignition timing from the map, however there are circumstances under which the EMS may need to vary the ignition timing. These normally boil down to four circumstances, engine / coolant temperature, air temperature, knocking and start-up.
When the coolant temperature is low the burn times within the cylinders are longer than with a fully warmed up engine and the ignition timing will normally need to be advanced a little to adjust. The EMS usually has a small map of ignition timing adjustments graded by coolant temperature that are added to the base timing figures.
When air temperature varies so does burn time of the inducted mixture since it is less dense, again a small map of ignition adjustments graded by air temperature are added to the base timing figures.
There may be times during the operation of the engine, even after adjustments have been applied when the timing calculated does not meet the engines requirements. Sometimes this may result in “pinking” (AKA “knocking” or “pinging”) where the mixture burns so fast that it meets the piston just before TDC while it is still on the compression stroke rather than meeting the piston just after TDC on the power stroke. This is very harmful to the engine. Some EMS systems have an acoustic sensor called a “knock sensor” which listens for knocking and will inform the EMS when this occurs. The EMS is then able to make adjustments to the timing to prevent engine knock from occurring.
Visual knock warning
Knock tuning tool
Start-up or cranking.
When starting an engine its effective RPM is quite low, around 200RPM or so. If the ignition timing used at idle is set to around 25 degrees (which is about average for a mapped engine) the chances are that the piston will hit the ignited mixture while still on the compression stroke. This will have the effect of pushing the piston down against its normal rotation, effectively this is “knocking” at cranking speeds. This is known as “kicking back” and is normally characterized by the starter motor “straining” and slowing right down, this makes the engine difficult to start and can easily destroy a starter motor in short order.
This is a common problem on engines equipped with mechanical ignition systems and more extreme cams since the engine needs plenty of ignition advance at idle to run properly. Unfortunately this extra advance can also cause “kick back” and there is no way with a mechanical system to differentiate the timing between cranking and idle.
EMS based systems solve this problem by having a separate timing value for cranking/ start-up which is normally set to around 5-8 degrees. This is low enough to prevent kickback but is high enough to start the engine; the moment the engine fires the appropriate ignition setting from the base map is used.
2D and non-mapped systems Vs 3D mapped systems.
After-market mapped ignition systems are now quite common, you may wonder what advantages they offer over a conventional ignition system. A conventional ignition system is a 2D system that only takes into account engine speed and not load on the engine; it gives a constant timing that is dependent on engine RPM only. At full throttle this is acceptable, however on part throttle economy and drive ability are seriously affected. In another vein with some performance engines the required advance may not alter in a linear manner, there may be places in the engines speed range where required advance can fall even though RPM is rising.
Some 2D systems go part of the way towards varying the ignition timing for load by fitting a vacuum advance device which advances the ignition when vacuum in the inlet manifold is high, E.G. when load on the engine is low but this will be crude at best. A mapped system can give precisely the right ignition advance whatever the engine speed or load. This improves the tractability of the engine dramatically as well as giving far better economy.
To appreciate the difference between a 2D and a 3D mapped ignition system you have to understand a little about combustion within your engine. When a fuel and air mixture ignites within the combustion chamber, the burning of the charge starts at the sparking plug and spreads throughout the mixture from that point. It takes a given amount of time for the whole charge in the chamber to burn, expand, and hence force the piston down the bore. This is why we have to start the ignition process before the piston reaches top dead centre. This lead-time is called “ignition advance”.
It follows that as engine revs rise and the engine turns faster there is less time for the charge in the chamber to burn hence the need to increase the ignition advance with increasing engine speed. Before the age of sophisticated electronics the ignition advance was always controlled mechanically, in the very early days by a lever, mounted on the steering wheel or handlebars of the machine. The driver, or rider, altered the advance according to his best guess, going on the “feel” of the engine – not always too successfully
What followed was a mechanical advance system based on a centrifugal system of weights located in a distributor. As engine speed increased the centrifugal force acting on the weights increased and caused them to move outwards, against the resistance of a couple of clockwork springs and in doing so advancing the ignition. The springs pulled the weights back as the engine slowed again reducing the advance. A series of stops and different tension springs allowed the ignition advance progress to be controlled, or altered from one engine to another, dependent on engine speed.
But there is another factor effecting advance that needs to be taken into account – cylinder filling. The speed at which the mixture in the combustion chamber burns varies with the amount of compression that the charge is under. This in turn depends on how full the cylinder is before compression takes place. For example: on a small throttle opening at higher rpm, the cylinder will only partially fill, compared to wide-open throttle at the same engine speed. It follows that you need different ignition timings for the same engine speed, but dependent on throttle position or engine load.
With the centrifugal distributor advance systems manufacturers often fit a vacuum advance unit. This pulls the timing to more advance when there was a high vacuum present in the inlet manifold (throttle closed or nearly so). The problem with these mechanical systems was that they were crude in operation and movement of the distributor base plate at high rpm caused timing scatter. For this reason most performance engines had the vacuum advance removed and the base plates welded up.
An EMS can control the ignition with very few moving parts; all it needs is a trigger and a load sensor of some kind. The EMS knows the load on the engine as well as the engine RPM. Since the ignition timing is mapped for each engine speed and load the timing is at the optimum for the engine for each load condition including part throttle. This gives the best possible performance and economy whatever the throttle position. In addition since the triggering systems invariably have no physical wear points the timing stays set correctly more or less indefinitely and is maintenance free. There are other spin-offs such as rev-limiting, shift light, accurate tacho driving and telltale as well as the certainty that the timing is never likely to ‘go off’.
The benefits from a mapped system have to be experienced to be appreciated, throttle response is razor sharp, economy is improved and tractability (especially with more radical cams) is amazing. In my own experience an engine converted from a centrifugal advance type of system to a mapped system undergoes a transformation.
Conversion of ignition from a non-mapped system.
To convert from a normal distributor based system to a mapped system is not as difficult as you might think. In addition to the EMS/Mapped ignition unit you will need a throttle potentiometer to measure throttle angle (and therefore load) which needs to be attached to your throttle spindle and a distributor with no advance mechanism in place of you existing distributor. Most of the existing ignition system, coil, leads, plugs, distributor cap and rotor arm can usually be retained.
As an alternative to replacing the distributor the existing one can have the advance mechanism locked to ensure that it gives a constant signal to the EMS. This can be done by drilling through the weights and base plate and inserting a self-tapper or by brazing/’MIG’ing the advance mechanism solid.
The EMS will require an electronic signal from the distributor so a points based distributor will not do. Most post 1980 engines have electronic ignition so if your engine doesn’t have an electronic distributor it is usually possible to find a later distributor for your engine that has a magnetic reluctor or Hall effect trigger. Some later versions of your engine may well have a factory fitted EMS system that uses a Hall effect or reluctor triggered distributor that may also not have an advance mechanism, if so this is ideal. If you cannot find a suitable replacement then a Lumenition eye fitted in place of the points will do the trick.
The EMS will require some fairly straightforward wiring in and obviously will require a mapping session on a rolling road, most EMS suppliers have example maps available which are “safe” and will get you up and running for your trip to the rolling road.
Generally mapping of an engine takes place in a controlled environment where engine temperature and air temperature can be controlled or at least measured. On after-market systems the mapping is normally done using a laptop PC that is connected to the EMS via a serial cable. Software supplied by the EMS manufacturer usually allows re-mapping of the fuel and ignition requirements with various degrees of flexibility and ease of use.
The EMS is normally able to relay back to the PC all the relevant information about the engine telemetry; coolant and air temperature, RPM, load site, current timing, current fueling, Lambda reading etc. while the engine is running. For a manufacturer an engine will be installed on a test rig which can exactly control and monitor the engines performance and environment.
For an already installed engine mapping is usually done on a rolling road which has a “pegging” facility that can hold the rollers at a fixed speed regardless of input torque. A rolling road is a set of rollers on which a vehicle can simulate driving. The rollers are attached to a “brake” that can measure the turning force applied to them and the roller speed. Using these two pieces of information the power applied to the rollers by the cars driven wheels can be measured. Generally an engine will produce maximum torque for any given speed and load when the fueling and timing are at their optimum
When there is no existing map the first trick is to get the engine started. The ignition is set to 20 degrees or so at speed sites 0 and 1 at load site 0. Fuel is added at these sites by increasing the fuel number in the map dynamically as the engine is cranked until the engine fires. If the engine temperature is very low then a degree of correction is applied to the map to enable the engine to start, once started the engine is allowed to warm up using only the first load and speed positions.
If the engine starts to die the fueling is altered to “clean up” the running, it may be that the throttle and balance need adjusting for the engine to run, this is generally done before mapping commences. By the time the engine is hot, the fueling at that load/speed site will be trimmed to almost correct. This fuel setting can then be used as a basis for all the speed sites at that particular engine load, this will be sufficient as a starting point and will allow the engine to run at those engine speeds.
The next step is to trim the idle fueling and ignition until the idle is at the desired engine speed and is reasonably clean. This is because mapping involves a lot of stopping and starting of the engine, if the idle settings are wrong the battery will be quickly flattened. Quite often the timing at the speed site just above idle is set to a very low figure which stops the engine from racing when at idle. If the engine speed rises the timing drops back and causes the speed to drop again, similarly at the speed site below idle the timing is set quite high to “kick” the engine if the idle speed drops. Once this is done the mapping can start in earnest.
The mapping process.
The rolling road is set to hold at a particular RPM by driving the car on the rollers in a high gear until that RPM is reached and “pegging” the rollers. By applying the throttle the operator can hold the engine against the rollers pegged position so that the engine speed and throttle position is constant. At this point the fueling is adjusted until the Lambda reading indicates that the mixture is stoichiometric (chemically correct).
If at any stage during this adjustment pinking is heard then the operator will back off the timing. Then the operator will adjust the timing until the rollers indicate maximum torque while listening carefully for pinking. If the torque starts to fall or the operator can hear pinking then the engine is over-advanced and the operator will retard the timing.
At the point of maximum torque the operator will back off the timing until just before torque starts to fall. This means the engine will be set at the minimum advance for maximum efficiency or minimum best timing.
Use of this technique minimizes the possibility of pinging or engine detonation in operation. Once a particular engine speed and load site has been mapped in this way the fueling and ignition values can be extrapolated to all successive speed sites for this particular engine load as a starting point. Even though these will not be correct they will be near enough to allow the engine to run. The operator will then continue for every load site at this engine speed.
This process is repeated for each successive speed and load site (or at least those which can be reached) until the mapping process is complete. Once the overall mapping is done attention can be paid to the adjustments or corrections to the map, namely cranking, acceleration/deceleration fueling and cold start adjustment. The most difficult of these to gauge is the cold-start adjustment since the engine will now be stinking hot. Often the owner will need to adjust these to give the best starting although the operator can usually supply some reasonable estimates for the cold start adjustment. It is important to make sure that the maps that have just been constructed are saved onto the hard disk, it is the operator’s responsibility to make sure that the map is extracted from the EMS and then saved.
It is during this mapping that the quality of the software has a part to play, ease of use and intuitive display of information is critical if the mapping is to proceed safely and in a timely manner.
When the engine has been mapped it is quite interesting to examine the maps. Normally the map information (after a little massaging) can be imported into Excel or similar and plotted as a surface contour. Some EMS systems (such as the Emerald M3D and GEMS system) have a graphical display built in to allow the maps to be viewed as a surface contour or wire-frame graph. Visualizing the maps in this way gives a much better and clearer picture of the engines fuel requirements and helps to iron out any “glitches” in the maps.
Generally fuel values are very small on part throttle and grow considerably when the throttle is opened (since more air is inducted to the engine). The peaks on the fuel map are usually where the peaks in the torque curve are and in most cases fuel drops off above peak torque even though horsepower may be rising. This is because cylinder filling or Volumetric Efficiency is lower past peak torque. Although the engine is consuming more fuel, it is using less per revolution since it consuming less air per revolution.
Often the operator will provide a no fuel position at the maximum load site at speed site zero, this is provided to clear out a flooded engine. Then to clear the engine of fuel it is necessary to open the throttle to its maximum and then crank. Since cold start and cranking fueling adjustments are percentage corrections to the fuel map, when applied to a zero fuel setting they will also be zero.
Ignition timing maps look rather different, at part throttle ignition timing is generally much higher often reaching more than 45 degrees since partially full cylinders burn much more slowly and require more advance. It is this part throttle mapping which is critical to the flexibility of the engine, especially when off cam. Around idle the timing numbers will be quite large to sustain a rock steady idle and will fall back rapidly above idle to stop the engine from racing. Peak timing at wide open throttle is normally reached at around 3500-4000RPM and depending on engine type a further small increase may be required above 7500RPM.
Conversion to throttle bodies/management from carburetors.
Conversion of an existing carburetor based installation is relatively straightforward provided that you fully understand what is required for the installation, if you are replacing carbs then you will need the following parts
A baffled fuel tank
A high pressure injection fuel pump
A fuel pressure regulator
Some injectors of the right capacity
The appropriate “snap on” connectors for the injectors wiring
A configuration of throttle bodies (optionally with manifold)
A throttle linkage
A throttle position sensor (usually supplied with the EMS)
A coolant temperature sensor (usually supplied with the EMS)
An air temperature sensor (usually supplied with the EMS)
A fuel rail (often included with the TBs)
Air horns and air filter
Plenty of high pressure rubber fuel hose and clips
Some 8mm fuel pipe.
If you are converting from an existing plenum based injection system then you may not need to convert your fuel tank and can usually retain the fuel pump, injectors, fuel rail and pressure regulator. Quite often the throttle pot and coolant sensor are also re-usable
The main factor to consider when converting from carburetors to injection is the fuel delivery system. The fuel tank is the first link in the fuel delivery chain. A normal un-baffled fuel tank is not suitable for an injected engine since under the influence of the various “G” forces encountered in a moving vehicle, the fuel can move away from the tank pickup and cause the fuel pump to suck air. With a carburetor based system the carb has a float chamber from which the fuel can be drawn if the pump supply dries up. An injection system on the other hand has no such reservoir; if the supply of fuel to the pump dries up then the engine will cutout due to lack of fuel. This is exacerbated by the fact that the fuel pump runs all the time with an injection system with surplus fuel being diverted back to the tank via the pressure regulator.
There are two ways of counteracting this fuel starvation. One way is to compartmentalize the tank, I.E. build a compartment around the pumps outlet which is fluid tight and use one way valves that allow fuel in to the compartment but not out again, this keeps the fuel in the area of the pump outlet. This can be supplemented by fitting a small conventional auxiliary pump that can shunt fuel from the opposite end of the tank to counteract the affects of fuel surge. The other way is to use a fuel reservoir or surge-pot that holds a liter or so of fuel that supplies the pump regardless of the fuel situation in the tank. This is fed by a small pump from the tank or by gravity and is sufficient for several seconds of engine activity. Ensuring that the fuel returned from the pressure regulator is directed at the pump outlet can also minimize the effects of surge in the fuel tank.
You cannot convert to injection and not pay attention to your fuel tank; it absolutely must be baffled and compartmentalized, or fitted with a surge-pot.
Fuel Pump, lines and regulator.
An injection fuel pump is very different to a conventional fuel pump used to supply carburetors; firstly it runs all the time and does not “stall” as a conventional pump does when the float chambers are full. It also supplies fuel at a much higher pressure than a normal pump around 80-100PSI compared with 5-6PSI. It is also essential that the pump be fed by gravity, since an injection pump is designed as a ‘blow’ pump rather than a “suck” pump. The requirement to gravity feed the pump normally means that it has to be mounted underneath and adjacent to the fuel tank, so a fused power supply is required to be run into that area. Since the fuel is continuously delivered and returned to the tank, two fuel pipes are required, a supply pipe and a return pipe. Normally the existing fuel line can be used as the return pipe with a new line laid in for the supply. When plumbing in the pump it is absolutely essential that high-pressure fuel pipe is used, normal rubber hose will not do, it will burst and cause a fire hazard, ensure that you only use properly rated hose capable of withstanding in excess of 60PSI. The inlet to the pump is normally 12mm internal size so the spur from the tank must be this size also. The remainder of the fuel pipe can be 8mm copper or steel tubing. Ensure the ends of the tube are “flared” to help the integrity of any joins.
Injection pumps are noisy so make sure that you mount your pump in a cradle of some kind suspended by rubber cotton reels or wrap it in some sound deadening material before mounting. Don’t take chances with the pump, it must be properly insulated and leak free.
Injection pumps require that the fuel be filtered before it reaches the pump, in some cases this is not easy to arrange, however any dirt or rubbish entering the pump can and will cause it to lock solid and render it permanently inoperable or damaged. Where space is limited a fine wire mesh screen can be used in the inlet to the pump provided that it is fitted in such a way that it cannot enter the pump, this will screen any reasonably sized particles. If you are using this method ensure you clean/change the screen regularly and fit a proper fuel filter following the pump.
There are plenty of injection pumps to be found in the scrap yards, most vehicles post 1989 are fitted with injection systems and are a good source of pumps and injectors. If you select a vehicle with a suitably sized engine then the pump should be up to the job, its likely that the injectors wont be far out either. It is quite possible that the fuel pressure regulator might be suitable assuming that it is not integrated with the fuel rail. My pump injectors and pressure regulator came from a broken Sierra Cosworth. Alternatively you can source the pump from a motor factor or specialized supplier.
If you already have twin Weber’s or Dellortos fitted to your engine then the obvious choice of induction system is a flange compatible throttle body kit such as the TB throttle bodies from Jenvey. These will bolt on directly in place of the similar styled DCOEs or DHLAs. If you have IDA or IDF Webers then the TF bodies are flange compatible. If your engine is not already equipped with dual side draft/down draft carbs them you must make the appropriate selection of either dual or single throttle bodies with an appropriate manifold and air-horns/filters. I have had some success having back-plates made to take the dual ITG filter on the end of a set of air-horns attached to either dual or single throttle bodies, this make a nice neat installation. If you are using the parts retained from a carburetor set-up them you can re-use the filters and back-plates. If you cannot obtain a suitable manifold for your engine then it is possible to fabricate one.
If you are upgrading from a plenum based system then you may find that you can re-use the fuel rail, injectors, pressure regulator and throttle position sensor, this will save money and aggravation. Some ingenuity may be required in the fabrication of brackets to attach the OEM components to the new throttle bodies but it is not a difficult task.
When buying the throttle bodies you must also purchase a throttle linkage since the type used on twin side-draft carburetors is not suitable and cannot be used. Generally throttle body kits come complete with fuel rails that are designed to take the standard Bosch type of injector.
Air-horns are generally necessary and the main determining factor for length is the space available on the inlet side of the engine, measure carefully here to ensure that what you are buying will fit.
The throttle potentiometer is normally fitted to the end of the spindle on one of the throttle bodies, ensure that it is fitted so that it is opening and not closing, E.G. against the spring tension.
After running the fuel line as close as possible to the end of the fuel rail the plumbing in is a simple task, if you a retaining an existing fuel rail arrangement then it should simply be a matter of bolting on the rail and connecting as before. When fitting a new rail it is important to ensure that the injectors are properly clipped to the rail and that the rail when fitted holds the injectors firmly into their position in the inlet manifold or throttle body pockets. The fuel supply should be connected to one end of the fuel rail with the pressure regulator connected to the other; the outlet of the pressure regulator is then connected to the fuel tank return pipe. The return pipe should dump its fuel as close as possible to the pump outlet in the tank.
Generally the only things to connect are the fuel pump which requires a fused supply which is switched by the ignition, the throttle potentiometer which is connected to the EMS, the coolant and air temperature senders that are again connected to the EMS and the injectors themselves. Finding a place for the coolant temperature sender is not always easy but often it is possible to drill and tap an existing boss somewhere on the engine which must be then engine side of the thermostat, preferably in the head. The air temperature sender should be mounted as near the inlet trumpets as possible.
Depending on the type of injection, batched, grouped or sequential the injectors may be wired in parallel or in series, follow the instruction which come with the EMS to make sure that you do this correctly. If you need the snap on connectors for the injectors a trip to the scrap yard is called for, make sure you get plenty of wire with the connectors and while you are there look for the connectors which clip onto the coolant temperature sender as well.
It is a good idea to bolt the throttle bodies to a dummy manifold (a piece of angle iron suitably drilled with a few correctly spaced holes will do) in order to make the injector loom and fit and adapt the throttle linkage and other ancillaries. Doing this while the bodies are not attached to the car is much more convenient as it makes the set-up more accessible. Any problems that arise can be much more easily solved.
Depending on resistance some injectors will need a resistor in series in order for the EMS to fire them correctly, ensure that this is mounted and connected correctly.
When this has all been fitted satisfactorily all that remains is to power on the pump and ensure that is circulating fuel before starting the mapping process.
Surface map contours for injection/ignition.
Below are a sample ignition and injection map from my EMS presented as surface contours, when visualized
in this way it is much clearer what is going on.
Note the relatively high advance at idle which is used to give a rock steady tick-over and the dip in timing following the idle position which causes the engine to dip back if the idle gets too fast. Note also the extra advance on part throttle throughout the range and the small dip in the timing at 3500RPM where although the RPM is higher the timing is less than at 2500 and 3000 RPM