JB4 Fuel Wires, what exactly are they doing?

[Mr. Tech]

As the title says, I'm wondering what exactly the fuel wires are doing. My understanding is that they measure the AFR (air fuel ratio) from the O2 sensors, then, somehow, trick the ECU into running leaner.

With access to only the MAP and TMAP sensors, is the JB4 just telling the ECU, through the TMAP sensor, that the IAT (intake air temperature) is hotter than it actually is?

And if the JB4 detects a "too lean" situation, I'm assuming it'll tell the ECU that the IATs are lower, to increase fuel (decrease AFR)?

Perhaps I've answered my own question, but I'd appreciate some confirmation.

 

[Adamdan]

It tricks the o2 sensor so the jb4 can change the air fuel mixture. It leans out the afr and makes around a extra 30hp if I remember right.

 

[Terry@BMS]

If you search around you'll find previous discussions on it. Might be in the long n54tech thread.

 

[Mr. Tech]

If you search around you'll find previous discussions on it. Might be in the long n54tech thread.

Well, just spent a couple hours researching it on the n54tech forum. Even read through every post with the words "fuel wires" in it based on a search and no one explains how it changes the AFR. Is it literally just adjusting what it sends as the charge pipe temperature through the TMAP sensor?

I suppose, at the end of the day, it doesn't really matter how it's doing this, but as an engineer, I can't help but want to know exactly what's going on. Hence why I've watched a bunch of tuning videos and spent time learning how exactly the turbos work, what the wastegates and diverter valves are doing, etc. This is my first high performance car and I want to make sure I monitor all the correct things to make sure this vehicle lasts a while, while at the same time, maximizing performance without going too crazy with mods.

Regardless, thanks for all your help so far through email, this forum, and the n54tech forum.

 

[Adamdan]

I think the wire that taps into the o2 sends a signal and the ecu sees that signal and tricks the ecu into changing the afr.

 

[Terry@BMS]

Hmm strange I'm sure we've been through it before. Well here is the 20 second version:

The JB4 monitors the lambda signal in each bank via CANbus and using an internal PID system to target a specific air/fuel ratio adjusts the o2 sensor signal dynamically so actual AFR in each bank is at the desired target.

 

[oddball]

The fuel wires tap into the O2 sensor harness itself. I haven't bothered to actually verify, but it appears they tap into the Ip (+12V power) wire, which doesn't make much sense.
Anyway, my assumption is they snag either the calibration wire or the actual signal return wire and either throw extra current at it or draw current away to modify the ECU's reading of the O2 sensor. The CAL wire makes the most sense (should require the least current), but don't know if they could get as much adjustment as they want out of that. The signal wire also makes sense, but seems that would require more current than the JB4 could safely sink/source.
But, I'm just totally guessing here.
The whole point is much like the MAP/TMAP sensor bypass main harness. JB4 influences what the ECU reads. So as far as the ECU is concerned, the engine is still running around 10:1 at WOT like it wants, but in reality it's leaner.

 

[ecko04]

Hmm strange I'm sure we've been through it before. Well here is the 20 second version...

Definitely been there before. Every couple of months there’s a “what do the fuel wires do...” type of thread. Given that the fuel wires existed before the Stinger platform, and the work the same way with other JB4 implementations, it has been addressed several times. Just add this thread to archives.

 

[Mr. Tech]

Hmm strange I'm sure we've been through it before. Well here is the 20 second version:

The JB4 monitors the lambda signal in each bank via CANbus and using an internal PID system to target a specific air/fuel ratio adjusts the o2 sensor signal dynamically so actual AFR in each bank is at the desired target.

Well, I'm sure glad I did a bunch of research on tuning before you gave me this answer because all of that made complete sense haha. Thanks for a short and sweet breakdown!

But now my thought is, if you're monitoring lambda, which comes from the O2 sensors, how do you know what the new lambda is once you start altering the O2 sensor outputs? Do you just have a look up table that says "this is how an average Stinger's AFR looks like based on all these other CANbus parameters, so use this value for AFR, at this moment? Then you just guard band it so that Stingers that tend to run lean for some reason, won't run too lean? So in theory, while that would protect some Stingers from running too lean, it could leave some power on the table for other Stingers?

 

[Mr. Tech]

Definitely been there before. Every couple of months there’s a “what do the fuel wires do...” type of thread. Given that the fuel wires existed before the Stinger platform, and the work the same way with other JB4 implementations, it has been addressed several times. Just add this thread to archives.

Then I'm definitely looking in all the wrong places or the search features is broken haha.

Edit: to be fair, I saw at least a dozen posts of people asking what the fuel wire do. To which the response was always something to the effect of "they allow the JB4 to change your AFR so you run a bit leaner to make more power" (see attached image). I'm looking to find out how they change the AFR.

 

[Mr. Tech]

The fuel wires tap into the O2 sensor harness itself. I haven't bothered to actually verify, but it appears they tap into the Ip (+12V power) wire, which doesn't make much sense.
Anyway, my assumption is they snag either the calibration wire or the actual signal return wire and either throw extra current at it or draw current away to modify the ECU's reading of the O2 sensor. The CAL wire makes the most sense (should require the least current), but don't know if they could get as much adjustment as they want out of that. The signal wire also makes sense, but seems that would require more current than the JB4 could safely sink/source.
But, I'm just totally guessing here.
The whole point is much like the MAP/TMAP sensor bypass main harness. JB4 influences what the ECU reads. So as far as the ECU is concerned, the engine is still running around 10:1 at WOT like it wants, but in reality it's leaner.

Sounds about right to me. The signal wire won't require much current to override since it's voltage is being generated by the O2 sensor. The JB4 uses DACs capable of +/-25mA output per pin. That said, they are likely just applying a voltage and letting the DAC sink/source whatever it needs to achieve that voltage. That'll get much more reliable results

 

[ecko04]

Then I'm definitely looking in all the wrong places or the search features is broken haha.

Edit: to be fair, I saw at least a dozen posts of people asking what the fuel wire do. To which the response was always something to the effect of "they allow the JB4 to change your AFR so you run a bit leaner to make more power" (see attached image). I'm looking to find out how they change the AFR.

Before the fuel wires became the norm there was a lengthy thread on N54 where Terry described exactly what they were doing and how it was being done. Once again, fuel wires aren’t a new phenomenon at this point.

Many inquisitive minds have come along and asked the exact same question.

 

[Mr. Tech]

Before the fuel wires became the norm there was a lengthy thread on N54 where Terry described exactly what they were doing and how it was being done. Once again, fuel wires aren’t a new phenomenon at this point.

Many inquisitive minds have come along and asked the exact same question.

Ah, I think that's where my problem was. I was looking in the Stinger/Hyundai section of the N54 forum. I'll have to do a search from the top page of the forum and see if I can find it there. Thanks!

 

[Terry@BMS]

Well, I'm sure glad I did a bunch of research on tuning before you gave me this answer because all of that made complete sense haha. Thanks for a short and sweet breakdown!

But now my thought is, if you're monitoring lambda, which comes from the O2 sensors, how do you know what the new lambda is once you start altering the O2 sensor outputs? Do you just have a look up table that says "this is how an average Stinger's AFR looks like based on all these other CANbus parameters, so use this value for AFR, at this moment? Then you just guard band it so that Stingers that tend to run lean for some reason, won't run too lean? So in theory, while that would protect some Stingers from running too lean, it could leave some power on the table for other Stingers?

The sensor has a specification sheet that dictates what the positive or negative current flow at any lambda represents. Otherwise, how would the ECU know the air/fuel ratio?

 

[Mr. Tech]

The sensor has a specification sheet that dictates what the positive or negative current flow at any lambda represents. Otherwise, how would the ECU know the air/fuel ratio?

But if you're overriding the current flow with the JB4 to trick the ECU, you can't also sample that current flow, because... wait... are you also monitoring the voltage required to override the O2 sensor's output one way or the other? I suppose that would give you the actual AFR since you could do some basic math to subtract out the JB4's alterations. Very clever

Basically, I just want to confirm that the JB4 is still able to monitor the AFR, while altering it. Verses running open loop and adjusting the O2 output based on pre-determined look-up tables (which is still legitimate if properly guard banded).

 

[Terry@BMS]

The ECU samples the current which the JB4 reads via CANbus, the JB4 knows how much current it's adding or subtracting. Just basic math from there.

 

[Whiteybird]

I suppose, at the end of the day, it doesn't really matter how it's doing this, but as an engineer, I can't help but want to know exactly what's going on.

Why am I not surprised at the amount of questions going on in this thread, that are in no way controlled by the end user lol. Other that wanting to know "why X does this".

 

[Mr. Tech]

The ECU samples the current which the JB4 reads via CANbus, the JB4 knows how much current it's adding or subtracting. Just basic math from there.

Awesome! Thanks for the explanation and patience with all the questions, Terry!

 

[Mr. Tech]

Why am I not surprised at the amount of questions going on in this thread, that are in no way controlled by the end user lol. Other that wanting to know "why X does this".

The "why/how" matters when you want to protect your investment. If Terry told me that they just run open loop and use a look-up table based on what their test Stinger did at WOT, without double checking the AFR in real-time, I wouldn't install the fuel wires because the extra performance isn't worth the risk of running way too lean with no checks.

Fortunately, after my many questions, I've found that Terry has put a lot of time and consideration into making his tune as safe as it is fast.

Unfortunately, there are a LOT of tuners out there who don't put this much consideration into safety. You'll never know which ones are legit until you ask these types of questions. Guys saying, "I ran xyz tune for 10k miles with no issues" only goes so far, especially on a brand new platform with zero long term data.

Knowing exactly how everything works allows me to make an educated decision on what's safe for my $50k car instead of taking it on blind faith and just crossing my fingers.

 

[turboAWD]

Agreed - Terry seems, as far as I can tell, to work on cars the way I would want to, if I had the time, the knowledge and ability, etc..

Now if we could just persuade him to try his hand at ECU tuning