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Old 06-03-2009, 11:24 AM   #1
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Engine Management System - SDS (Simple Digital Systems) EM-6E
As installed on Honda 2.7 litre engine in 1989 Acura Legend

A few notes to start off:

SDS is a stand-alone engine management system. This unit controls both fuel management and ignition timing. It replaces the factory PCM/ECU, so it may not be street legal in your state/county. This system will not control EVAP, EGR, 2-Stage intake/induction systems, etc. It will not use any factory sensors for inputs, except for the TPS (Throttle Position Sensor).

Injectors - IMPORTANT! - The factory injectors on my '89 Coupe were low-impedance (low resistance) injectors. If upgrading your injectors, you have the choice of high or low impedance. SDS makes their systems for either type so make sure you specify. I recommend LOW impedance, and no larger than 750 cc/min (roughly 70 lbs/hr).

The SDS “E” model is designed to work with aftermarket spark boxes like MSD and Crane. I suggest using the MSD. I don’t think you can control timing with SDS without using an aftermarket spark box, so be prepared for the extra cost for the MSD system. Also, see my other DIY on wiring an MSD box to a factory coil.

THIS IS NOT A COMPLETE MANUAL! This D.I.Y. will show the tasks that need to be performed for the Honda 2.7 Litre V6 to run on this particular engine management system. It will not go into detail as to the specific wiring of each component/sensor, because this is thoroughly covered in the installation manual that comes with the system. This D.I.Y. will show you the basic "hardware" modifications required, so you can get a good idea of what to expect if attempting this installation.

You need to have a good understanding of electrical wiring, such as wiring a relay, reading wiring diagrams, etc. Do not attempt this unless you are confident in your skills. There are a lot of things to wire up, and you have to get them all correct before you can even start the engine and see if you’re right.

Once this system is installed, it has to be programmed. Unless you’re going to take it to a professional who is familiar with the system and has a dyno, then you are going to need a good set of gauges to aid in tuning. The SDS will come with a small LED fuel mixture meter, but I suggest a digital wideband meter. Also, you’ll need a vacuum/boost gauge to help with tuning in part-throttle conditions. If boosting, get an AEM fuel pressure regulator for an NSX, and hook up a fuel pressure gauge. SDS cannot compensate for fuel that is not delivered by the fuel pump, so get the gauge to keep an eye on it to avoid melting your pistons. Gauges are very important when street tuning a stand-alone system, so don’t be cheap.


The ignition timing is fully controlled through the SDS. The only input the SDS "sees" for detecting crank/piston position is the Hall Effect Sensor, which is a magnetic pickup device. Tiny magnets are placed into holes in the crank pulley as "triggers" for this sensor.

You need tools for very precise measurements, as well as a drill press, and some sort of metal-working lathe. A lathe for machining brakes will work, as long as the crank pulley can slide onto the shaft, and be accurately centered.

The first task is to determine the position that the Hall sensor will be located. The placement of the first timing magnet is crucial, and depends solely on the position of the Hall sensor in relation to the crank pulley when cylinder #1 is at TDC (Top Dead Center). The best spot I found to mount the Hall sensor is directly underneath the crank pulley, with the sensor facing out so that it picks up the magnets mounted to the INSIDE lip of the pulley.

As you can see, an "L" bracket of thick steel will work fine. This piece needs to be very sturdy once mounted. You are only going to have about 2mm clearance between the sensor and the tips of the magnets, so any vibration could be destructive. Make it to where you can adjust to get the clearance right using shims/washers. Also, use thread-lock. You really don't want those oil pan bolts we are using to back out.

Now that we have our spot for the Hall sensor, it's time to mark holes.

With the Hall sensor mounted, place the engine crank to where cylinder #1 is at TDC. (This should be when the single mark on the pulley lines up with the pointer on the timing cover. Also, the keyway on the pulley/crankshaft points straight up in this position.) Place a good mark where the Hall sensor is while the engine is in this position. Mark the inside lip, where the magnets will be. This mark is not the location of the first magnet, so don't start drilling.

Remove your pulley, lay it down on the bench with the INSIDE lip facing up toward you. The first magnet position needs to be 80 degrees ADVANCED of the mark you made with the pulley mounted. So looking at the inside lip, follow the edge COUNTER-clockwise 80 degrees. This is the location of the first magnet.

Next, you need to scribe a perfect circle around the lip of the pulley to serve as a reference for drilling. All three holes need to be exactly the same distance from the pulley's center, so scribing this line will give you a good groove to start your pilot holes. The final hole will be 1/8", so keep your circle far enough from the edges to where you will not drill into the belt grooves, and you will have enough metal around the hole to have a good sturdy setting for the magnets. This is especially difficult if using the brass pulley, like the one shown in the next picture. Don't run the motor on the lathe, but just turn it by hand. You only are making a slight groove.

I suggest marking all three hole locations before drilling. They need to be an even 120 degrees apart, perfectly. Once you have them marked, re-check using the triangle method - all three sides of the triangle need to be the exact same length. When you start drilling, use a drill press. You cannot afford to make mistakes here. Drill each pilot hole one at a time, measuring again between each drill. I cannot stress enough the importance of accuracy in this procedure.

The holes should be only deep enough to leave 1.5mm of magnet sticking out from the surface of the pulley, and they all need to have the same amount of stick-out, exactly. When fitting the magnets to the holes, use 5-minute epoxy, naturally the kind formulated for metals, not plastic.

There is a procedure that will need to be done once the system is installed, and the engine is idling. The procedure calibrates the first magnet position to what the computer actually "sees", due to varying clearances, and slight changes that may take place when you remove/reinstall the Hall sensor. It's important to do this procedure as shown in the manual before you start tuning the ignition timing.


First of all, the large black box on the firewall with all the solenoids, vacuum lines, sensors, and junk will no longer be used, so take it all out. You will have only three vacuum lines coming from the intake manifold once the install is done - brake booster line, fuel pressure regulator, and one going to the new MAP sensor. If you want a boost/vacuum gauge, use a "T" fitting to hook to the MAP sensor line, so that you see the exact same reading as the MAP sensor. This will aid in fuel tuning. All other ports on the intake for vacuum lines should be plugged.

Continued on next post...

Last edited by sam o nela; 01-18-2010 at 09:42 AM.
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Old 01-18-2010, 09:17 AM   #2
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All EGR ports on the intake manifold, cylinder heads, and exhaust manifolds have to be plugged. You can make plates from thick steel to block these openings, or weld them shut. I would not recommend welding on the heads, though. The following pictures are of the intake manifold. All EGR ports are welded shut, as well as idle passages that will no longer be used. The only passage to leave open is the where the idle valve bolts to the very top of the manifold, and there are two round holes which will serve as the passages for fast idle operation (Seen in the second picture below, upper RH corner). Fast idle is an option on the SDS system, so weld them shut if you're not going to get the option. NOTE: Make sure you have a throttle stop-screw on your TB (Throttle Body). This will be used to adjust normal idle when the installation is complete.

If installing a fast idle valve, just tap the two holes to accept a 1/8" NPT thread barbed fitting each, and attach hoses from the fittings to the valve. One of the holes goes to the intake manifold, and the other goes to the TB just before the throttle plate. When the fast idle valve is open, it will allow additional air to bypass the TB. There is another hole inside the TB that runs to the manifold, which is originally used as the idle port. I recommend not using this hole for idle air, but use the throttle plate stop-screw instead. I separated the TB from the manifold and filled the old idle port with epoxy to seal it.
NOTE: You CAN make it idle using the old idle port, but with the 2-stage induction taken out, the idle won't be as stable as using the throttle plate angle to regulate idle air.

On the cylinder heads there are 2 holes to block. They are both on the front head. Make plates, and use the factory gaskets to seal them off.

Speaking of the 2-stage induction system, remove it. Separate the two halves of the intake manifold and remove the section with all those little butterflies in it (see picture below). Bolt the manifold back together with new gaskets, but you need to either use shorter bolts, or several washers with the old bolts. The old bolts as-is will bottom out before the head seats.
NOTE: This will cause the TB to sit slightly higher than normal, so make sure it clears your hood. It worked fine with mine.


Water Temp Sensor: Installs to cylinder head on front of engine. Specify the "GM" sensor when ordering from SDS. It threads right in with no modification.

Air Temp Sensor: Needs to be installed close to and just before the TB. Easiest install is with cold-air intake pipe. Tap a hole, and lightly screw it in using RTV sealant. Weld a boss on if boosting, but for N/A this will be fine.

MAP Sensor: Best place for this is on the firewall. You need to make a bracket so that the vacuum port is going out of the bottom.

Oxygen Sensor: Only one is used with the system. Specify the single-wire type. Install as normal, with new wiring to SDS.

Throttle Position Sensor: This sensor is hard to replace, modify, or even break! They last forever, and the factory one will work with the SDS unit. Do the ohms tests in the manual to figure out which wires to connect. Do not wire it incorrectly, or you can fry the SDS unit. Just cut the factory connector from the harness, wire them up, then plug it in.


The main relay has to be supplied with two grounds in order for the fuel pump to come on. The SDS has an option for fuel pump activation, and you should definitely get it. The two grounds for the main relay are supplied by the PCM, so after the installation there will be no circuit to activate the relay, and you would have to wire a manual switch to turn it on, which is not track-legal.

Wire colors vary with different models, but on my ’89 coupe there is a black wire and a green/black wire that have to be supplied with the ground provided by the SDS unit. This is the cheapest and easiest way to wire up the factory fuel pump, and still be street/track legal. (SDS deactivates the ground and turns off the fuel pump if the engine stops running, as a safety measure.)


Ignition timing is a term that refers to exact time that the spark plug produces a spark in relation to cylinder position. It is always expressed in degrees BTDC (Before Top Dead Center) or degrees ATDC (After TDC). The spark usually NEVER fires ATDC, always BTDC.

To advance timing = More degrees BTDC
To retard timing = Less degrees BTDC

When programming the SDS system, there are two parameters to adjust timing:

RPM Timing – Values for base RPM based timing curve. As RPM increases, you need to advance timing more and more.

Timing ADV/RET Load – Values to adjust timing for engine load. Vacuum or pressure readings correspond to additional advance or retard commands.

When you run at WOT (Wide open throttle), the SDS uses only the RPM timing curve. The MAP sensor is seeing “0”. No pressure, no vacuum. Atmospheric pressure is “0”.

At part-throttle conditions, the timing needs to advance more to make the engine run smoothly and increase fuel mileage. The more you can advance the better, for fuel economy and performance alike. However, you can only advance so far before you start to get spark knock, which can cause damage if not corrected.

For best ignition tuning, get to a dyno tuner. It’s hard to “feel” the difference, and there’s no gauge that’ll tell you when it’s right. I’ve included this picture to show what a decent timing chart for this engine should look like.

The gray bar across the middle shows the base RPM timing curve. The trick is to make the timing match the numbers in all of the other boxes when you duplicate the corresponding load/pressure conditions. This is fun.


There are two basic fuel curve parameters on the SDS:

RPM Fuel – Base values that represent a number which the computer will look at to determine injector pulse-width. Values are changeable in 250 RPM increments.

Manifold Pressure (MAP) – Values that represent a number that the computer will compare to the RPM fuel values to determine actual pulse-width given for the current load condition. Values are changeable on a 64-point graph ranging from 30 inches of Mercury to 30 psi.

Other parameters that affect fuel include:

Engine temp – Increases or decreases fuel amount to slightly to compensate for slight changes in engine temperature.

Start – Cold start enrichment. 32-point graph corresponding to cold-start temperatures.

Fuel tuning can be quite aggravating without a dyno. Always try to stay a little on the rich side at first to be safe. The SDS comes with a mixture knob, which allows you to quickly change the injector pulse-width while you are trying to duplicate load conditions, doing WOT runs, etc. The knob is a great tool, but use it wisely. If the engine is running poorly, go rich first to see if it gets better, then go leaner if it doesn’t.

I hope this helps to see what all is involved with installation of a system like this. Good luck to anyone who takes it on!

Last edited by sam o nela; 01-18-2010 at 09:43 AM.
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