Tom Wilson
July 1, 2003

Horse Sense:
Knuckle-dragging 5.0s are sure to benefit from AEM's powerful new engine manager immediately, and soon, so will 4.6s. By the time this makes print, the EEC V version of the AEM computer should be only a month or two away from availability.

We Ford enthusiasts have been alternately blessed and plagued by Ford's Electronic Engine Control IV engine-management system. Powerful-and in its mass air version, highly adaptable-EEC IV has been all the engine management most owners could want.

On the other hand, EEC IV is likely the most mule-headed and secretive management system ever in widespread use. Its complex inner workings are for all practical applications a secret of Ford's, and when the blowers and turbos go underhood, adapting EEC IV to seamlessly meet the engine's new demands becomes impossible. So, while electronic aids have evolved from intercept-and-patch strategies to rather complex add-on boxes, complete control has been offered via replacement engine-management systems. These so-called stand-alone systems do not work with EEC IV-they replace it.

The advantage of replacing EEC IV is not that the stand-alone systems are better-nearly all are far inferior in complexity and often in sampling rate and response speed-but rather that they are designed to be tuned and are thus responsive to input. To date, such systems have been race-oriented, so the complexities of EGR function or air conditioning have simply been discarded. This has made such systems poor choices for streetable cars.

When the computer does all the work, there doesn't have to be much stuff in the sales box. Thus the AEM Plug & Play Programmable Engine Management System easily fits into a small carton. As expected, the support information is on a CD ROM, so there's a bare minimum of paperwork to get the system up and running.

Furthermore, stand-alone systems have been built around their maker's vision of sensors and wiring. To fit these stand-alone systems to a Mustang originally carrying EEC IV management, nearly every vestige of EEC IV must be removed and replaced with the new system. Thus the Ford computer, wiring harness, and sensors had to be ash-canned in favor of new bits. This is a lot of work, expensive, and plain-old inefficient, as much of the hardware being tossed is of high quality.

But not anymore. We just took a quick look at an entirely new concept in stand-alone engine-management systems offered by AEM. "Oh, an import company," you say. Well, yes, AEM's corporate history does run strongly through the sport-compact world (all the way back to an association with Redline and Weber carburetors if you want to continue that line of thought). This sport-tuning background hasn't hurt AEM in an engine-management sense, as making sequentially turbocharged, double-overhead-cam sewing machine engines run in the eights is at least as difficult as getting our adequately-sized units to do the same. Furthermore, AEM is not a couple of 20-somethings squinting under a droplight in their mom's garage at whatever they can pilfer from a RadioShack dumpster. Thanks to sales of various bolt-on and management bits, AEM has the resources to hire qualified engineers and to support an R&D facility to prove its designs.

What makes AEM's Plug & Play engine-management system different is the company's philosophy of keeping the entire host car's sensors and wiring, and changing only the computer itself. This means you can basically put away your soldering gun and wire crimpers, as there is precious little wiring to string. That also means the excellent factory wire connections are not broken, the stock connectors are retained, and dependability stays at the gravity and sunrise levels of consistency of the factory system. The underhood cosmetics even remain stock, if that's your thing.

It's also worth noting that a comprehensive system such as this is ultimately less expensive than going the usual piecemeal route. With the AEM computer there is no need to buy a separate boost retard, a separate datalogger, a separate two-step timing control, and so on. All those functions are incorporated into the AEM ECU.

The RES232 communication cable from the laptop plugs into this jack on the side of the AEM box. The computer has to be out of the kick panel to access the connection.

Also, AEM notes that on a primary level there is little difference between tuning a lawn mower's 311/42hp Tecumseh and a 2,000hp Pro 5.0 engine. Both are four-cycle gasoline engines that require the fuel and spark to show up at the right time. Thus, while pride in ownership may be strongly varied to the nut behind the wheel, to a computer, getting a Mustang, Camaro, or Civic engine to strut its stuff is the same task. There is no reason to reinvent the core properties of an engine-management system-and AEM doesn't bother. Instead, the company has focused its energy on customizing the interface between the basic engine-management portion of its computer and the host vehicle's wiring harness, sensors, and other details. Thus the AEM box has two basic parts, one generic to all AEM ECU's and the other specific to a vehicle.

It's this customizing to the vehicle that makes the AEM system so easy to install, and it's where the Plug & Play name originated. All that's required is to remove the stock EEC IV computer and plug in the AEM box. AEM has essentially duplicated Ford's engine-management tuning as the default programming, so the Mustang will run just as it did stock from the first twist of the key.

Turning the Knobs
So far so easy, but what about tuning? The sky's the limit, really. To get right down to it, you name the function and the AEM computer allows you to display it in almost any table, graph, or 3D modeling you can imagine, datalog it, and best of all, modify it. And when AEM says nearly any function, it means all the way down to the esoteric stuff such as EGR valve function.

To be more specific, in the EEC IV version of the AEM computer there are 434 functions that can be logged and modified. All factory inputs and outputs are accepted, so it's like having a completely adjustable EEC IV box-in other words, a lot more than simply fuel and spark.

You'll know where the Plug & Play name came from after installing the AEM computer. It simply replaces the stock ECU in the passenger footwell.

Furthermore, AEM has installed several upgrade paths. The ignition, for example, is defaulted to the specific input on which the EEC IV system runs, but there is also provision for a four-coil ignition in case you decide to run a distributorless system. Other options include the ability to run mass air or speed density, or your choice of batch or sequential fire on the injectors (you'll have to do some wiring to batch-fire the injectors, however, as the stock harness is set up to run sequentially).

Other important upgrade paths support forced induction. Examples of this are the two channels of boost control, so you don't need an external boost controller. And that boost controller can be triggered off nearly anything: rpm, road speed, coolant temperature-you name it.

Because tuners are always adding hardware Ford never dreamed of, and that hardware needs controlling as well, AEM has provided its computer with 16 additional programmable outputs. These can be anything the tuner wishes to wire up-examples would be radiator fan controls, shift lights, and various solenoids (such as an entire nitrous system). These are all individually controlled, and again, you can trigger them off nearly any parameter, such as water temperature, throttle position, boost, rpm, vehicle speed, and so on. In practice, these programmable outputs are best handled by running 12 volts to the actuator, then having the computer switch the ground circuit. But it can be wired the other way around, if desired.

What's more, in the support software, AEM provides a map of the pin callouts in the wiring harness-to-computer connector. These are in a chart showing what Ford calls each pin, what AEM calls that pin, and whether that pin is Dedicated, Available, or Plug & Play.

Sitting in the car and tapping through windows, tables, and charts is what modern performance tuning looks like. Here Scott Armish, the EMS applications engineer at AEM who did the development work on the Mustang Plug & Play application, leans Max Sigwart's '92 LX for another 30 hp.

If the pin is Dedicated, that means even though you can move it using the AEM controls, don't touch it! Examples of these are the power source, the ground wire, and the unique signal from the speed pickup on the TFI module. Available means that pin is unused by the stock computer, so it's open for any use the tuner may wish to assign it. Plug & Play denotes pins used by Ford, but that are OK to change via the AEM software. Most of the time you'll leave the pins alone, of course, but sometimes it's nice to have the ability. A good example would be if the EGR was removed. Then you could redesignate that original EGR pin in the harness and use the circuit for something else.

The more AEM explained the programming possibilities of its computer, the more we could see the real propeller heads falling into the adjustability abyss. AEM calls it the "science project" effect, and it doesn't take much imagination to visualize some techno-junkie clacking away at his keyboard in order to monitor his IAC valve voltage in real time. A perhaps more real-world example of this is the tuner can define which oxygen sensor affects which bank of cylinders (not something on which many people would need to change the default setting). In addition, a knock sensor can be added, the tuner can define what is the background noise threshold in both type and volume for the knock sensors, and then he can define what he wants the ECU to do about it. Pull timing? Add fuel? How much timing? How much fuel? For how long? This could take all night.

Logging In
Having all the adjustability in the world is fairly academic if you don't know what the computer is doing in the first place. Datalogging is the tuner's window onto the computer's whirling gears, governor, and steam whistle, and interpreting what's been datalogged is the art of engine management. The AEM computer has powerful tools to help with both jobs.

The AEM datalogger has a half-megabyte of capacity and the afore-mentioned 434 parameters it can log. This includes any calculation the computer figures, and it leads to some esoteric logging capabilities, should you really want them. There aren't many times you'd want to log the air/fuel ratio correction due to air temperature, but you can. The logging list goes on and on-barometer, air temperature, knock from a left-hand knock sensor, ditto the right sensor, throttle, rpm, boost, and more.

The target audience for the AEM computer is professional tuners who can offer both the Plug & Play kit and their tuning services to customers. Access to a chassis dyno-preferably a load/inertia unit that can do part-throttle driveability work-is a must for getting all the AEM computer has to offer.

The logging rate is 250 samples per second per channel, over seven channels. There is an eighth channel, which multiplexes an additional eight inputs. Because it's sampling more data than the other channels, it samples at a lower rate, 31 samples per second.

Add all this up and the logger is capable of 2,000 samples per second system-wide. That's a lot of data.

Once the datalogger is full, you can program it to either stop recording or start recording over the already gath-ered data. If set to do the latter, it starts recording over from the beginning, so you'll always have the last half-megabyte of recorded data. It does not erase the memory entirely and start over.

If a half-megabyte of recording is not enough, you can hook up a laptop PC and record until the hard drive bursts at the seams. Under these conditions the logging rates are adjustable, so you don't have to wade through a zillion data points on the water temperature, for example. Also, you can have one channel set on a slow sampling rate and others at fast rates. Thus, the relatively stable water temperature could be logged slowly and knock or rpm data recorded much more quickly.

A typical arrangement would be four channels of datalogging to a laptop at 200 samples per second. This is IndyCar-quality datalogging.

One strong point of AEM's data presentation is the variety of ways it can be viewed. Graphs, charts, and 3D models are all possible. This is a graph and 3D chart of a fuel map. It happens to be in metric units (Load versus kPa), but it could be displayed in standard units with about three keystrokes. Just the same, there's plenty of tuning lingo to learn with computer controls, and the AEM system doesn't dumb down to "more fuel" and "less fuel" inputs. It uses "milliseconds of pulse width."

Furthermore, the datalogging channels can be based off another parameter. Say you want to know what's happening only above 5,500 rpm or only after 75 mph. The datalogger would then record only on the specified channels once that rpm or speed has been obtained. This is like having a built-in datalogger switch that you don't have to remember to turn on.

Once all the data is logged, there's a log analysis program to help decipher what all those numbers mean. Different logged data can be overlayed on graphs, with four overlays possible. Adjustable filters allow you to quickly zero in on the area of most interest. One possibility could be the air/fuel ratio, but only between 5,500 and 6,500 rpm. With all the data sampling parameters adjustable, it shouldn't take long to find out what's going on in a race car. The log analysis program is updated occasionally, with the updates available free over the Web.

For the real slide-rule jocks there are math channels, which can be created. You could take the derivative of rpm and some other factor to get the rate of change (per second, say) after you program the box to give this to you.

One suggestion AEM had was to log interesting chassis information, such as shock deflection. You'd have to rig and wire a sensor to measure shock height, but once that was done, and you did some measuring in the shop to plot how much weight it takes to compress that shock, then you could calculate the loads the shock is seeing. Take the idea further yet and the AEM datalogger could become a g-meter and, by extension, a virtual engine dyno.

Auto Tune
Should all this data and adjustability prove overwhelming, AEM's magic box has a way-trick automatic-tuning algorithm that sounds as if it could just pos-sibly make heros out of chronic double-left-footers such as magazine editors. Called Auto Tune, this wizardry requires a wide-band oxygen sensor (not what Ford puts on Mustangs and not cheap). Tech Edge, Motec, and others have the necessary unit.

Here's another way of looking at the logged data. This is an ignition map, along with a set of parameters in chart form on the right. Besides being able to select what parameters you want listed, you can rotate, roll, and yaw the 3D map into any attitude. This can really reveal where the dips and valleys are in a map.

Once the wide-band oxygen sensor is in place, it can detail the ECU on what is coming out of the combustion chambers. From there Auto Tune will build a 357-point air/fuel ratio map on which to run the engine. AEM cautions that the mapping-running the engine in order to build the A/F table-must be done under carefully controlled conditions, but the whole idea sounds as if it could save your bacon should you get lost in the numbers.

Enough Already
As you can see, in a short article such as this, we can only scratch the surface of what AEM's Plug & Play computer is capable of. Clearly it takes an intelligent tuner to use this powerful tool, and that's precisely who this computer is aimed at. Joe Sixpack doesn't stand a chance with this thing, even though he can figure out how to plug it in. But a savvy tuner can have the box installed in a heartbeat and be on his way to dialing in a recalcitrant turbo or blower motor for himself or a customer. The dreaded cold-start driveability mapping ought to be easier too with all the datalogging. For outright power, elite tuners can use the AEM box to step up to the next level at the track, all while saving themselves hours of wiring and the almost given problem of resulting loose connections, cracked solder joints, and so on.

How Much?
The folks at AEM say the list price on the Plug & Play Programmable Engine Management System is $2,038. In nearly the same breath they note no one pays list in this market, but they declined to speculate on what the real-world mail-order or discount price might be. That's a smart move designed to allow AEM's dealers to set the real retail price. Our expectation is somewhere around 20 percent off list will do the trick.

Whatever the final figure, what you'll get is the computer, a cable to hook it to a laptop, and a CD with the owner's guide, analysis software, and documentation. The EEC IV system for Mustangs is available now; the EEC V system for '96-and-later cars should go on sale in a couple of months.

We Tune, Sort Of
Part of our plan in introducing the AEM computer was to obtain a suitable 5.0 Mustang and see what sort of power and driveability we could achieve with it. A call to Eric Cheney at Xtreme Mustang Performance in Aliso Viejo, California, set us up with Max Sigwart, who volunteered his '92 LX for the job, and a day later we were off to AEM's in-house Mustang Dyno rollers.

Max's car appeared to be a good candidate because it was supercharged, cammed, and generally tuned up with '90's state-of-the-art hardware that put just shy of 400 hp to the rear tires. The package included a 0.030-inch overbored 302 with 8.5:1 compression, World Products Windsor iron heads, an E303 cam, 1.6 roller rockers, a GT-40 intake, and a Vortech S-Trim pullied for 12 pounds with the stock Vortech Fuel Management Unit (the boost-activated diaphragm unit that pinches off the return line to raise fuel pressure). Max also had a Hypertech chip and an old Crane Interceptor II installed. The chip was there for performance, while the Interceptor was for datalogging only. Actually, Max was using the Interceptor to read various outputs in real time, so he was more "data reading" than "datalogging."

Also typical of the now-aging Fox fleet, Max's odometer has rolled over twice, if you can believe that, and the current engine already had 114,000 miles on it. The original had already long gone to the great scrapyard in the sky.

Scott Armish, AEM's EMS Applications Engineer, did the honors. His first move was to install a wide-band oxygen sensor in the exhaust system so the AEM datalogger could see just what the air/fuel ratio was doing. This requires fitting one wire into a spare pin on the wiring loom, so technically it wasn't a pure plug-and-forget connection. Then it was up on the rollers to start tuning.

Right away it was clear Max's car had some issues. It was deadly rich (9:1) in the midrange, then leaned to merely rich (11:1) at the power peak. This is precisely what mechanical FMUs do on centrifugally supercharged cars, so no surprise there, other than the chip wasn't doing anything about that. Other issues were excessive blow-by and a weak voltage.

Leaning the air/fuel ratio was child's play for Scott, who keystroked away the excess fuel using a handful of dyno pulls to verify his changes. But the blow-by and battery issues were dif-ferent stories. Not wanting to scatter Max's engine in his dyno cell via repeated full-throttle blasts, Scott ultimately decided discretion was the better part of valor, and with our deadlines looming, our tuning session was over before it really began.

Just the same, Scott pulled well over 30 hp and matching torque out of the hat for Max simply by selectively leaning the A/F ratio across the rpm range. We also learned another detail when discussing the low voltage/battery condition with Scott. He says a weak battery (especially with underdrive pulleys) can help cause a hunting idle, as when the rpm drops to idle and the alternator falls off-line, the voltage drops because the battery isn't there to take up the slack, which drops the fuel pump voltage, which means a slightly lean A/F ratio, which means the idle drops a bit of rpm, which triggers the computer to add rpm. Of course, then the idle soars too high, so the computer backs off the rpm, the idle falls, and the cycle is repeated.

We suppose fiddling with the AEM computer could have made the idle better, but, of course, the real cure was either a fresh battery or up-to-snuff alternator, so we didn't try any electronic heroics.

Stock or lightly modified cars really can't benefit from the Plug & Play computer, but forced induction hot rods such as Max Sigwart's are prime candidates. Scott found 30 hp just by leaning the fuel curve provided by the crude Fuel Management Unit used on these Fox blower kits. With the AEM computer and a bit of mapping, the old FMU could be removed and a much more efficient air/fuel ratio map can be drawn. That means one less widget under the hood.

We talked to Scott about this voltage condition-he figured it was simply a case of a tired battery-and that led us to yet another example of the AEM computer's capability. There is something called a Battery Offset Table in the AEM computer (and in the EEC IV too). This is a fudge factor to account for low voltage, and hence lazy injector opening. As voltage drops, it takes more time for the injector to lift off its seat, and the mixture leans. The Battery Offset Table thus lengthens the injector dwell time in response to low voltage. The difference is, in EEC IV you can't even know such a table exists, much less modify it. With the AEM computer, it's completely adjustable.

Ford Discovery
As AEM has developed its EEC IV and EEC V replacement computers, it has received a heavy dose of Ford engine-management know-how. The company's main comment was how there were lots of dead pins on the harness-to-computer connector with EEC IV, but not so with the EEC V. As John Romero put it, EEC V "comes close to tapping out the motherboard."

Ford's EGR strategy was touchy on the Mustang systems too. "Ford must have one EGR [valve] for the entire company, and it's huge," John says. "The programming on this is critical because it's so large."

Who Are the Brains?
Works of this magnitude are rarely the result of one person's efforts. At AEM everyone from the owners on down had a hand in making the Plug & Play engine management come to life, but chief of these were AEM's Chief Engineer, John Concialdi, and John Romero, the EMS group manager who brought his hands-on knowledge of Honda's IndyCar electronics to the table. Down in the trenches, Scott Armish, EMS applications engineer previously with Gale Banks and Textron Lycoming, logged the dyno hours to get the EEC IV Mustang version sorted out.

Just the Facts
Wordy descriptions of electronic devices can be mind-numbing. Here are a few facts to remember.

* Plug & Play means no wiring to perform. Just unplug the stock computer and plug in the AEM replacement computer.
* The Plug & Play computer can be removed and the stocker replaced just as quickly as it was installed. This makes moving the computer from one project car to another a breeze.
* Each AEM computer is designed to work with a specific car. The EEC IV version currently available fits '86-'95 V-8 Mustangs. EEC V versions are coming; none of the computers can be interchanged.
* The Plug & Play concept is not totally new. It has been available from AEM for Honda and other sport compact applications for more than a year.
* AEM's computer is not CARB exempted, nor is it emissions or street legal.
* Plug & Play is a godsend to modified cars. But by itself it will gain no power and is a waste of money to install on a stock car.
* Plug & Play is easy to install but requires a knowledgeable tuner to adjust it.
* AEM offers a certification program for tuners who can come to AEM's Hawthorne, California, shop. Held on weekends, the hands-on program uses AEM's Mustang chassis dyno in both inertia and load configurations to teach Plug & Play's capabilities.
* Plug & Play owners become members on AEM's Web site forum where tuners can exchange ideas and solutions.
* AEM says all upgrades are free to its customers.