SL ECU Major Differences or Why NOT to Use an SL ECU

[99 vr4]

SL ECU Major Differences or Why NOT to Use an SL ECU

As some of you know, I have been working with a team of people for almost a year trying to find a low cost solution for a flashable ECU on the 3000GT platform.

I have tried many different "donor" ECUs from other V6 platforms, Mitsubishi, Hyundai, and Mazda (yes Mitsu makes thier ECUs). I have had to reverese engineer circuits that are critical for the ability of the ECU to correctly manage the engine with out harm.

I know that some of you have bought or are buying SL ECUs thinking that this will work. Let me tell you that it is not a 100% solution. In fact, it is not even a 90% solution. It is a bad idea. Why?

Here are a few of the issues that have been identified, not in any particular order.

1. No stock boost gauge. Simple fix, replace your now non-functioning boost gauge with and aftermarket boost gauge.

2. No stock two speed fuel pump control - Fuel pump stuck on HI. No biggie you think, right? Wrong . . . see the next item.

3. No stock fuel pressure solenoid control. Oh Oh. The stock ECU controls the pressure of the fuel being delivered through a two stage system. First you have the two stage fuel pump (above). Then you have a Fuel Pressure Regulator on the end of the rail. And lastely you have the fuel pressure requlator controlled through a selonoid. This selonoid controls the amount of boost pressure that the FPR sees on the boost compensation port. If this is controlled incorrectly or not at all you can have either to high pressure (no big deal) or not enough pressure (big deal). How do you fix this issue? Install an aftermarket fuel pressure regulator. Solves both problems.

4. No wastegate control. Mitsubishi controls the amount of boost that the wastegate sees through a selonoid. The SL ECU does not have this circuitry on the board. How do you fix this issue? Install an aftermarket boost controller.

5. Knock Sensor! Ok, because of the design of the engine, Mitsubishi handles the knock sensor input differently. Although the knock sensor it self is used on many platforms, the twin turbo has a different hardware controlled circuit. There are significant hardware differences between the turbo and non-turbo ECUs which results in both "phantom" knock and the inability for the ECU to see "real" knock. What this means is when the ECU sees phantom knock, it pulls time reducing performance. When the ECU fails to see real knock, the knock continues and will slowly trash your bearings until such time the knock is loud enough that you can hear it and say "oh shit" or your bearings let you know what is up - then you join the spun bearing club. What can cause this knock? Lack of fuel caused by bad fuel pressure, or a bad tune are two of the many culprits. How do you fix it? You don't. The ECU needs to be modified.

[Jesters Deadd]

SL ECU Major Differences or Why NOT to Use an SL ECU

As some of you know, I have been working with a team of people for almost a year trying to find a low cost solution for a flashable ECU on the 3000GT platform.

I have tried many different "donor" ECUs from other V6 platforms, Mitsubishi, Hyundai, and Mazda (yes Mitsu makes thier ECUs). I have had to reverese engineer circuits that are critical for the ability of the ECU to correctly manage the engine with out harm.

I know that some of you have bought or are buying SL ECUs thinking that this will work. Let me tell you that it is not a 100% solution. In fact, it is not even a 90% solution. It is a bad idea. Why?

Here are a few of the issues that have been identified, not in any particular order.

1. No stock boost gauge. Simple fix, replace your now non-functioning boost gauge with and aftermarket boost gauge.

2. No stock two speed fuel pump control - Fuel pump stuck on HI. No biggie you think, right? Wrong . . . see the next item.

3. No stock fuel pressure solenoid control. Oh Oh. The stock ECU controls the pressure of the fuel being delivered through a two stage system. First you have the two stage fuel pump (above). Then you have a Fuel Pressure Regulator on the end of the rail. And lastely you have the fuel pressure requlator controlled through a selonoid. This selonoid controls the amount of boost pressure that the FPR sees on the boost compensation port. If this is controlled incorrectly or not at all you can have either to high pressure (no big deal) or not enough pressure (big deal). How do you fix this issue? Install an aftermarket fuel pressure regulator. Solves both problems.

4. No wastegate control. Mitsubishi controls the amount of boost that the wastegate sees through a selonoid. The SL ECU does not have this circuitry on the board. How do you fix this issue? Install an aftermarket boost controller.

5. Knock Sensor! Ok, because of the design of the engine, Mitsubishi handles the knock sensor input differently. Although the knock sensor it self is used on many platforms, the twin turbo has a different hardware controlled circuit. There are significant hardware differences between the turbo and non-turbo ECUs which results in both "phantom" knock and the inability for the ECU to see "real" knock. What this means is when the ECU sees phantom knock, it pulls time reducing performance. When the ECU fails to see real knock, the knock continues and will slowly trash your bearings until such time the knock is loud enough that you can hear it and say "oh shit" or your bearings let you know what is up - then you join the spun bearing club. What can cause this knock? Lack of fuel caused by bad fuel pressure, or a bad tune are two of the many culprits. How do you fix it? You don't. The ECU needs to be modified.

What!??? A bad idea? really? Having an inexpensive completely tuneable ECU that is nearly plug and play with an adaptor harness is a bad idea?
I have tested it on my car and IT WORKS GREAT!

1. No stock boost gauge... the stock boost gauge doesn't even measure boost, you should have a real boost guage anyway!

2. No stock two speed fuel pump control... hotwired fuel pump. This is like stage one upgrade stuff.

3. No stock fuel pressure solenoid control...Install an aftermarket fuel pressure regulator and hook up the vacuum from the intake. The fuel pressure solenoid only cuts vacuum to the fuel pressure regulator during hot starts. Most people have already disconnected this with no noticable affect.

4. No wastegate control... install a manual boost controller or a better one truboost etc.. Again this is stage one upgrade stuff.

5. Knock Sensor!... I tested this on my VR4 and got the same amount of knock on the same program as my 99VR4 ecu at the same locations... it wasn't 100% scientific but it was very repeatable...

Basically have a boost gauge, hotwired fuel pump with an adjustable fuel pressure regulator and a boost controller and you are set with an 98/99 SL ECU. This is all stuff you will need for stage one upgrades. You will have all the tuning ability of the 98/99VR4 for much cheaper than a 99VR4 ECU. Just ask questions and know what you are doing before you do it.

[99 vr4]

Trust me when I say the knock sensor circuits are COMPLETELY different. Obviously for an experienced tuner such as yourself this is a non-issue. But for the majority of DIY types that are not experienced tuners . . . you should not "play".

The best way to explain this in normal non technical terms is like this. The knock sensor is a piezo element which produces electrical "noise" in response to physical vibrations. Very much like a microphone produces electrical signals from a sound wave. The hardware on the circuit board consists of filter circuits and amplifier circuits. Very much like an audio amplifier. Now lets say you just bought a new 300 watt sub amp for you car audio. It can drive a subwoofer from 20 hz to 140 hz. But your subwoofer is only rated at 20 hz to 100 hz. So you put a band pass filter in line with the speaker. But you miscalculate and your band pass filter only allows 100 hz to 140 hz through. Will it work? Yes. Will it work well? No. Will you blow your speaker . . . time will tell.

[Drummer]

So I can just replace the few circuits with the correct value resistors and cap and the knock will read correctly? I hope!

[Jesters Deadd]

So I can just replace the few circuits with the correct value resistors and cap and the knock will read correctly? I hope!

That would be hard to do... you need the correct values and you would need to be able to solder surface mount components...

[Jesters Deadd]

Just FYI to keep info together...

Jester, from what I can see is that the knock issue with the Diamante and Montero ECU's seems to affect some people more than others. Some people swear they don't get knock, and others get all sorts of issues with these ECUs. Knock itself is not always able to be duplicated. Lets say some guy in NY is getting knock. I could load his tune and not get any knock. There is so much more here than just the tune and fuel delivery.

You have to take into account fuel formulations. Not all gas is equal. And even if you buy Amoco Gold here in St. Louis you can bet it is not formulated the same as Amoco Gold in Florida or New York. Although the EPA mandates RFG vs CG in high polution areas, they also limit the Reed Vapor Pressure (basically the rate of boil off) so RFG will be formulated differently in the winter vs. summer vs. elevation for each major area. Frequent Questions | Reformulated Gasoline | US EPA Then you have to take into count air temperature, density, barometric pressure (elevation), and humidity. Throw all of this into the mix with your tune and thats how you might not get knock or you might get knock.

So although I am sure that your real world test yielded no additional knock, its not 100% because there are more variables. As far as the filter circuits are concerned, I am sure that Mitsubishi, if they could have cut corners (and cost) by using the same knock sensor circuits, they would have. Even though we are talking a small handful of parts, the engineers designed it, tested it, specified it, and signed off on it. It is there for a reason.

As far as working the math for the filter circuits, I hate laplace transforms and I don't see myself working out that math any time soon.

Interesting information per the 99 service manual...
"The knock sensor generates a voltage proportional to the magnitude of cylinder block vibration due to knocking and inputs it to the engine control module. Based on this signal, the engine control module provides retard control of the ignition timing."
So maybe it doesn't need Laplace transforms just a little V=IR.

[Drummer]

That would be hard to do... you need the correct values and you would need to be able to solder surface mount components...

Thats fine. The values and locations are known, and surface mounted soldering is not a problem.

[Drummer]

Trust me when I say the knock sensor circuits are COMPLETELY different. Obviously for an experienced tuner such as yourself this is a non-issue. But for the majority of DIY types that are not experienced tuners . . . you should not "play".

The best way to explain this in normal non technical terms is like this. The knock sensor is a piezo element which produces electrical "noise" in response to physical vibrations. Very much like a microphone produces electrical signals from a sound wave. The hardware on the circuit board consists of filter circuits and amplifier circuits. Very much like an audio amplifier. Now lets say you just bought a new 300 watt sub amp for you car audio. It can drive a subwoofer from 20 hz to 140 hz. But your subwoofer is only rated at 20 hz to 100 hz. So you put a band pass filter in line with the speaker. But you miscalculate and your band pass filter only allows 100 hz to 140 hz through. Will it work? Yes. Will it work well? No. Will you blow your speaker . . . time will tell.

That sub would last forever cause its getting higher frequencies and not working as hard as it could ;-) J/K lol But yea, someone was saying that the SL ecu has a slightly more sensetive knock circuit and could produce fantom knock. I have not opened up the 98 SL's I have yet, nor do I have a reference VR4 ECU.

[green-lantern]

IDK, I wish this would get resolved because I've been told by a very reliable source that the circuitry is exactly the same.

[Monster Stealth]

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