5 questions to ask yourself before switching to a standalone ECU

By J.G. Pasterjak
Jun 27, 2022 | Shop Work, ECU, electronics, GRM+ | Posted in Shop Work , Electronics & Electrical Systems , Buyer's Guides | From the Dec. 2021 issue | Never miss an article

In the continuing quest for performance, eventually you’ll hit physical or digital barriers separating your car from that next level. When it comes to the physical barriers, those are usually pretty cut and dried: Piston engines are air pumps, ultimately, so installing those exhaust headers and an intake that increases pumping efficiency are straightforward decisions.

But when it comes to the digital side–and let’s face it, most of the engines in our world are now controlled by some sort of computer–answers are less clear. 

We faced some of these tough questions when we decided to switch our C5 Corvette project to a standalone ECU, and we’re facing them again while upgrading our 1991 Toyota MR2 Turbo–a car that existed fairly early in the timeline of factory computer-controlled performance. 

So we’ve compiled a list of questions and investigative alleys to pursue while making your decision about an aftermarket ECU. You’ll note that some of them don’t have answers, as we’re still in the process of answering them ourselves–and many of those answers aren’t universal anyway. But we think they provide a good jumping-off point to help you shop for an ECU upgrade, so here we go.

1. What problem are you trying to solve?

Do you want to produce more power? Are you switching from carburetors to fuel injection? Adding or augmenting forced induction? Compensating for different fuels or blends? Merely trying to get a handle on various engine parameters to make better decisions?

These are some of the first questions you need to answer when shopping for an ECU upgrade. 

We’ll give you a couple examples: Our Corvette race car already had a factory ECU capable of running not only the stock engine, but the LS3 that replaced it. The stock ECU was reflashable with proper software. 

However, using that computer with the new engine required lots of physical adapters and digital trickery to make it talk properly with the more modern powerplant. So, we decided to eliminate the factory computer from the engine management chain altogether and go standalone.

On our MR2, the decision process was a little different. Our engine had been upgraded to Toyota’s later Gen4 3S-GTE, with the factory computer reflashed somewhere along the line. 

However, no one really provides that service anymore due to the complexity and inflexibility of the final product. The stock computer actually compensates well for hardware changes–like increasing fuel pressure through the use of regulator adjustments or altering boost through the use of manual boost controllers–but its compensation strategy is always one of engine preservation, not ultimate power. 

We also wanted to add gauges to monitor things like oil pressure and temperature. While we could have added those gauges individually, by the time we tallied the costs, going to an aftermarket ECU and having the ability to simply monitor all those parameters via a single display unit seemed like the easiest solution. As a bonus, we also wound up with programmable engine controls. 

We feel as if we’re at the limits of the factory ECU for the MR2 project, so we’re gathering the parts for a standalone conversion–and we’ll share that install very soon.

2. How will you control your new ECU?

The ability to minutely alter every engine setting is both the advantage and the burden of aftermarket ECUs. Still, if you’re not comfortable handling some basic tuning functions, that shouldn’t be a dealbreaker.

Many devices–like the Holley Terminator that we originally used on the Corvette–offer rudimentary handheld controllers featuring simplified menus that allow the user to change common parameters without having to deal with a laptop and a full interface suite. Some more advanced systems are controlled via physical switches, meaning multiple tune files can be “hot swapped” without rebooting the system.

Want to call in an expert? That’s easy. In fact, we recommend having someone qualified perform that first tune and provide a good baseline. The viability of real-time remote tuning–where a tuner can remotely log in to a laptop connected to your car from anywhere with an internet connection–means that working with a pro doesn’t even require a shop visit. 

3. How ready is your engine for an ECU upgrade?

To control your engine functions, the ECU needs to monitor a slew of parameters from the powerplant. Crankshaft position, exhaust mixture, fuel flow, various pressures and temperatures, rates of rotation and even acoustic monitoring for preignition all factor into the final engine control scenario.

If you have a more modern car, you’re likely in luck, as your OEM computer is already monitoring most if not all those functions. Plus, there’s a good chance that many of those sensors and even their associated wiring can be repurposed for your aftermarket black box. Even if that’s not the case, at least you have existing ports and sensor access for those functions, and typically you can just substitute your OEM parts for similar parts that are compatible with your new ECU.

But if you have an older configuration–maybe you’re switching from carburetors and points to a fully modern fuel-injection and direct-ignition setup–that may require more physical accommodation for those sensors. Certainly a crank position sensor will have to be adapted, and knock sensors may have to be accommodated somehow if you plan to use those. 

Additionally, if you’re running forced induction, you’ll probably also employ some mechanical boost controller that’s controlled by the ECU. In those cases, you’ll need to make provisions for both the physical install and the plumbing and wiring. 

4. How will you monitor your engine in the car?

You still need to keep an eye on all the important operating parameters of your engine, and this is where you have a few choices. 

Traditional gauges are obviously an option, but that route may require parallel wiring or plumbing. Why not just read the signals that the ECU is already monitoring?

Luckily, the ECU folks anticipated this need, and that’s why most of them offer ready-to-go dash modules. The ECU simply passes those signals to the customizable LCD dash interface, which you can configure to monitor any parameters you like.

Some ECUs also offer Bluetooth or Wi-Fi outputs (either built in or through an outboard module) and a companion app that runs on iOS or Android tablets. So, you can output your parameters to a custom dash that runs on a tablet and use that as your dash interface.

Also, realize that on many modern cars, switching to a standalone system means that you absolutely will need to make a decision about monitoring, because your factory gauges–once driven by the stock ECU–will no longer function.

5. What else do you want your ECU to do?

The ECU functions simply: It has inputs that are looking for a range of resistances or voltages as well as outputs that send signals of specific voltages or waveforms. These inputs and outputs are typically definable within the software interface of the system. 

So, those same channels can be reconfigured to look for new signals–from things like speed sensors, accelerometers, position sensors, GPS data, and the list goes on. So long as you have available channels in the box, you can send inputs to them and get outputs from them.

Altering the characteristics of the ECU based on those sensors then simply becomes a series of conditional, if/then statements that can be defined within the software. For example, if rear wheel speed is greater than 110% of front wheel speed, then cut spark every x crankshaft rotations to reduce power. Bing, bang, boom, that’s how you get traction control. 

Yes, we realize we just explained traction control with a statement akin to “An F-22 is just an airplane,” but that fairly describes the basic path. 

Lots of ECUs are capable of more advanced functions, but many get there in different ways. More high-end, motorsport-based systems have true multi-channel capability built right in, but programming usually takes some specialized knowledge since you’ll usually be accessing a lot of the functions on a root programming level, modifying lookup tables or specific lines of code controlling the device.

Consumer-based systems typically have more channels available–or that can be added via expansion modules–than many installs will ultimately use. And the programming for these consumer-level systems tend to be more menu-based than code-based. 

Then there’s the whole can of worms of CAN bus interfaces that allow your new ECU to interface with modern CAN (Controller Area Network) automotive interface bus standards. These interfaces can control other automotive functions like lights and windows–all the other stuff a car does besides actually run–and probably deserve their own story. We’ll route this topic through our editorial department for further discussion in a follow-up piece.

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View comments on the GRM forums
Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
4/11/22 11:04 a.m.

6. Do you have emissions inspections?

Aftermarket ECUs will not return OBD-II codes, so if your car was built after 1995 and you have regular emissions checks, you should check to see if your state has alternative testing methods for cars with inoperative emissions monitoring systems. Keep resale in mind as well, the ECU will prevent you from selling your car to some states because of htis.

AndyHess New Reader
4/11/22 1:26 p.m.

"Want to call in an expert? That’s easy. In fact, we recommend having someone qualified perform that first tune and provide a good baseline. "  OK - Where do you find an actual expert?  There are so many claims on the Internet and in forums, and so many horror stories - is there an index of reliable expert tuners for OEM ECU's?

Pete. (l33t FS)
Pete. (l33t FS) GRM+ Memberand MegaDork
4/11/22 1:33 p.m.

In reply to Keith Tanner :

Not being able to connect to the computer IS an emissions fail.


You've no idea how many failed emissions I've fixed by replacing the cigarette lighter fuse, usually after digging a penny out of the receptacle.

alfadriver GRM+ Memberand MegaDork
4/11/22 2:25 p.m.
Pete. (l33t FS) said:

In reply to Keith Tanner :

Not being able to connect to the computer IS an emissions fail.


You've no idea how many failed emissions I've fixed by replacing the cigarette lighter fuse, usually after digging a penny out of the receptacle.

There's a useful trick to look for a cheap car.  

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
4/11/22 3:11 p.m.
AndyHess said:

"Want to call in an expert? That’s easy. In fact, we recommend having someone qualified perform that first tune and provide a good baseline. "  OK - Where do you find an actual expert?  There are so many claims on the Internet and in forums, and so many horror stories - is there an index of reliable expert tuners for OEM ECU's?

This article is about aftermarket ECUs and not reflashed OE ECUs, but the question is the same. Who would identify a tuner as an expert and/or reliable, and maintain the list? It's always going to have to be crowd-sourced unless there's some sort of training required by the manufacturer of the ECU (or the reflashing interface), and I don't think any manufacturers require that.

If I was looking for a local tuner of something like a Megasquirt, I'd go to the people who sold me the Megasquirt (probably DIY Autotune as they're the adults in the room) and ask for recommendations.

alfadriver GRM+ Memberand MegaDork
4/11/22 3:16 p.m.
AndyHess said:

"Want to call in an expert? That’s easy. In fact, we recommend having someone qualified perform that first tune and provide a good baseline. "  OK - Where do you find an actual expert?  There are so many claims on the Internet and in forums, and so many horror stories - is there an index of reliable expert tuners for OEM ECU's?

I didn't read this closely until Keith replied.  For OEM reflashers, there will never be a compiled list of business that do that.  Ever.  Unless every one of them wants a knock on the door from the FBI.  

Experts for that have to really be careful, especially since there is a recent crack down on OEM re-calibrate software.

Paul_VR6 (Forum Supporter)
Paul_VR6 (Forum Supporter) SuperDork
4/11/22 8:51 p.m.
Keith Tanner said:

If I was looking for a local tuner of something like a Megasquirt, I'd go to the people who sold me the Megasquirt (probably DIY Autotune as they're the adults in the room) and ask for recommendations.

There is also "Find a Tuner" on MSExtra.com, if you don't want to wade through FB groups. Also :wave:

frenchyd MegaDork
4/12/22 3:34 p.m.

In reply to JG Pasterjak :

Thank you so very much for this. I've been trying to sort all this out myself and keep running into a wall. 
 I really need a EFI for dummies  excerpt all of the books I've bought while helpful explaining things fail to walk me through step by step.  
      There is the mega squirt, here is the V12  now you can substitute this Lucas sensor  for that GM sensor by using this connector wired to the Red & green wire. 

Maybe not that linear but something close.  
My next step is to buy the cables from DIY and see if I can figure that stuff out myself. 
 I'm actually proud that I've gotten this far.  I tried the forums but wow,  a newbie really isn't welcome.   
     I follow a lot of U Tube especially with our Calvin Nelson on his 4200 Atlas. 
     But he's off and running and I'm not even in the Toddler stage. 

Paul_VR6 (Forum Supporter)
Paul_VR6 (Forum Supporter) SuperDork
4/12/22 4:13 p.m.

I can get onto teams with you and hold your hand on a per-hour basis. I include 2hr with all my pnp system sales in a similar way but limit it to getting the sw running, logging, troubleshooting as all the wiring bits are taken care of already.

frenchyd MegaDork
4/13/22 9:45 a.m.

In reply to Paul_VR6 (Forum Supporter) :

I fully intend to hire your knowledge and experience   as soon as I'm out of the Toddler stage.   Right now we are still in the building it stage. 

ShinnyGroove (Forum Supporter)
ShinnyGroove (Forum Supporter) HalfDork
4/13/22 10:19 a.m.
frenchyd MegaDork
4/13/22 11:12 a.m.

In reply to ShinnyGroove (Forum Supporter) :

Thanks,   I've got the earlier version of that but maybe  if it gets into the real nuts and bolts. (Litterly ) it will be helpful. 
I'm a,  get it at the junkyard kind of guy rather than buy new. ( the parts not a book) 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
4/13/22 12:15 p.m.

If you want to substitute junkyard parts, you need to be able to evaluate how the sensors (etc) compare, and that means learning more than just "these are the same if you swap a wire". You're going to have a hard time finding a cookbook that will tell you that without the underlying knowledge. Luckily, other than having a large number of cylinders, those V12s are pretty simple engines so you don't need a lot of data to make them work.

BTW, there are some big Echlin books that contain data on various sensors. You'll need to know how to read them, but it's a good way to find various substitutions. 

frenchyd MegaDork
4/13/22 12:43 p.m.

In reply to Keith Tanner :

I used to have the Echlin book but that was decades ago back when I was reworking distributors. Heck, maybe it's still in the cabinet? ;-) 
   Yes I know the V12s are simple engines. But open the hood of a stock one and it will scare most people.   Then once you get the Air conditioned fuel lines off, the Cajillion  miles of hoses and  vacuum off etc. suddenly they reveal  just how simple they are.   In fact they are simpler than the beloved small block Chevy.  Well 12 of things instead of 8 but that's about it. But no pushrods or rocker arms.  
   They are faster to change camshafts  than a typical V8. They even provide you with a stand to hold the cam sprocket. 
 I digress 

 Since  the Lucas  unit is fixed and only can be modified if you unsolder parts it's going away. Mega Squirt that came with the car is going in. So I'm going to change over a lot of sensors etc to GM  the injectors will all be GM.  (6.0 flex fuel )   Pretty sure I'll be using the Trailblazer injector line too (x2)  I may even use a crank trigger instead of the Hall effect crank sensor on the back side of the distributor rotor. 
*they even used SAE sizes rather than Metric. Right up to the point they were bought by that foreign car company? Ford?   

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
4/13/22 3:03 p.m.

I was thinking of the V12 as simple from a control perspective. It doesn't matter if it's OHV or OHC or what size bolts it uses from an engine management stand point. What matters is the cams don't change so there's no dealing with VVT. No throttle body control, no alternator control, maybe not even an idle speed valve. I don't know what your ignition system will be but you might even not have to deal with that if you're running a dizzy. It's basically a lawnmower engine.

That's how you have to generalize your thinking. Pushrods are irrelevant. What are your controls, and what are your required inputs?

Maybe not SAE, maybe they used those Imperial measurements that came from the UK in the first place.

Theres more than one Echlin book, I've seen them online as well. If you're looking to find out what the range of a temp sensor is, or what sensor has the right thread and measurement range, that's where you get it. 

frenchyd MegaDork
4/13/22 11:35 p.m.

In reply to Keith Tanner :

Oh, on line?  That's helpful.   I'll look for it. 
 Yeh, you're right, the v12 is very early EFI.  Just squirt some gas in a batch and let the valves sort it out. 
 Ignition? Aw, let the whirly gig in the center deal with that. 
  Since the Lucas unit doesn't have a single chip in it. It's not adjustable. Hence the Mega Squirt. 
     But I've seen countless guys attempt to work with the Megasquirt without success.  I've only found one guy who actually has it working. 
    My thinking is those Lucas sensors are all analog.  The Mega squirt was designed for a GM and thus digital so if I use GM sensors  they are at least speaking the same language. 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
4/14/22 12:34 a.m.

You'll find that most sensors are analog. A temp sensor is just a resistor that changes value with temp. TPS is usually something similar. Engine speed is likely pulses in the Jag, which is basically digital. The MS might turn these into digital information so it can work with them but they're analog coming in.

 What you're really doing is looking for sensors that are similar to the defaults, but you should be able to adjust the system to read just about anything. You just need to know what the signal looks like. 

I'd approach this by starting with "what do I need to control (fuel only, apparently) and what information do I need to do it?" Probably engine temp, air measurement and a precise engine speed with a TDC indication. You can add more but that's about the minimum. Engine temp is cake, if you have a functional electric gauge you have that. Airflow is just plumbing. Engine speed and TDC means a cam sensor or a crank and a cam sensor. Heck, I think you can get away without TDC if you do batch injection. 

goingnowherefast GRM+ Memberand Reader
4/14/22 4:16 p.m.

So I have experience tuning on Haltech, AEM Infinity, EMU Black, and Megasquirt 3. Realistically, I don't think you need a tuner that specializes in one specific unit as they all boil down to the same tables and settings just with a different UI. Select a good tuner that's reputable, has a load bearing dyno (no, you can not effectively tune on inertia rolls), and preferably has a motorsports background (as the quality and refinement of their work needs to be that much higher than someone with a street only background). 

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