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This article was first published in 2003.
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When you've treated your car a few breathing mods you'll invariably encounter
someone telling you to "make engine management changes". But what exactly does
this mean? Do they mean fit an interceptor, a piggyback ECU or a stand-alone
aftermarket management system? In this article we'll look into some of the pros
and cons of each approach.
Interceptors
Interceptors are gaining popularity as many current-generation cars are
becoming increasingly difficult to reprogram or convert to stand-alone
programmable management. An interceptor is a computer that is wired between the
engine and ECU. The interceptor alters various inputs and outputs from
the ECU. Depending on the particular unit, an interceptor typically gives laptop
programmable control over mixtures, ignition timing and boost pressure.
David Alexander from Sydney's Silverwater Automotive says, "An interceptor is
a relatively simple way around typical problems. If you want to run a bit more
boost, clamp the boost cut and trim fuel numbers without touching anything else,
they can be great."
"The disadvantage of an interceptor," he says, "is you can't adjust rev
limit, idle strategies or any of the functions that don't rely on the load
sensor or crank sensor.
"You can move the crank sensor input to change timing
and, depending on the specifics of the engine, the window of adjustment can be
quite large.
"Trying to do fuel adjustment by modifying the load input or a
temperature input limits you to the factory tabling. Sometimes that's fine, but
not if the engine has a lot of modification.
"If, say, you've changed the camshaft and compression ratio, you really do
need to access the more discreet functions like idle control strategies, the
point when you want it to go into closed loop, lean burn and knock sensor
control adjustment."
David Alexander suggests that you can do all of those things inside factory Holden Delco software.
Stand-Alone Programmable Management
As mentioned, stand-alone programmable systems are becoming increasingly
difficult to fit into current-generation vehicles. This is because body
circuitry (security systems, etc) are often
integrated into a single management computer. This integration means the
previous trend of ripping out the factory ECU is no longer an option.
Stand-alone programmable systems give terrific tuning flexibility -
particularly the high-end models. Stand-alone systems allow the tuner to alter
the amount of fuelling and timing at adjustable rpm and load points, change the
rev limit, adjust cam timing, idle speed, boost pressure, set various outputs
(for shift lights, extra injectors, etc) and more.
But David Alexander points out that many aftermarket programmable systems do not
have knock control.
"This can be a concern for a streetcar," he says.
"Manufacturers employ quite active knock control, which add and subtract timing
almost like closed-loop fuel control. If the driver puts a crappy batch of fuel
into the tank or the engine condition is not covered by the parameters in the
management program, knock sensing is a great safeguard to save the engine.
"There are some aftermarket management systems with knock sensing. Link has
had it for some time, allowing you to pull timing out when it sees a
predetermined amount of knock. It's not a bad idea - it's certainly a lot better
than breaking an engine. The Link will pull timing out and when you turn the key
off and start it again, it will go back to your original map - it won't save the
changes.
"Most of the people that want their car to perform put good fuel in their
engine. Ninety-nine percent of our customers understand that because they want
it tuned closer to the edge - so I don't think the absence of knock control in
some programmable systems is so much of an issue," says David.
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The Piggyback Approach
A piggyback computer is a fully programmable computer that works in tandem
with the factory ECU, but in a very different way to an interceptor. Instead of
modifying the inputs and output signals from the ECU, a piggyback arrangement
typically involves fitting a programmable computer to control only the injectors
and ignition system - power steering compensation, idle control and all other
functions are left to the factory ECU. This configuration allows the tuner to
adjust vital fuelling and ignition without interfering with the integrated
security system etc.
But there are limitations.
A piggyback ECU cannot work together with a stability or traction control
system (like the Ford BA XR6T). Furthermore you'll lose the operation of the
trip computer fitted to some cars.
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Remapping the Factory ECU
A remap of the factory ECU is the most elegant approach to engine
modification. It allows 100 percent of the factory ECU functionality to be
retained without the fitment of any aftermarket products. But there are varying
limits to what you can achieve...
Depending on the complexity of an ECU and how much effort has been put into
'cracking' it, only a small number of maps may be able to be accessed by the tuner. This
limits tuning flexibility and compromises the end result - in other words, stay
away from re-maps where the tuner has minimal access to the factory program.
On the other hand, some tuners have access to the whole management
program.
If you own a late-model Subaru WRX, a Gen 3 Holden Commodore or a Delco
managed vehicle (such as a VN-onward Holden Commodore or JE Camira) you're
fortunate enough that the entire program inside the factory ECU has been
reverse-engineered. This enables the tuner to access timing data upon knock,
alter the rev limit, closed-loop changeover and more. Taking into account cost,
the stealth nature of the modification, tuning access and the potential for an
excellent end result, this approach is extremely attractive. However, few cars
are lucky enough to have their factory ECU fully reverse-engineered.
Summary
As David Alexander points out, interceptors are a relatively simple way
around typical problems. They are ideal for making tweaks to go along with mild
mechanical changes. "There's no question interceptors will become more popular
as factory systems become harder to work with," he says.
Stand-alone programmable systems remain there for the most hard-core modified
engines that require extensive mapping modification. A programmable ECU fitted
as a piggyback means easier installation and more factory features are retained,
but you'll lose traction and stability control systems as well as trip computer
functions. This may not be an issue in some vehicles.
Due the huge variation in
tuning ability from vehicle to vehicle, factory ECU remaps cannot be put into one basket. If access to the factory program is
minimal, you can expect the end result to be poor. Fully reverse-engineered ECUs
have the potential to perform brilliantly.
"The skills of the tuner are vitally
important, whatever the approach you take," says David.
Contacts:
SAS
Silverwater Automotive Services
02 9748 1300
info@silverwaterauto.com.au
www.dynotuning.com.au
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