Has anyone successfully wired in an AEM failsafe wideband/boost gauge?

[Teck09]

So I have the AEM Wideband/boost failsafe gauge sitting here and am ready for install. Only one problem, I have no idea where to start. Has anyone done this who would be willing to give me a hand? Mainly looking for help with the Audi pinouts.

As shown below, I need an input for the failsafe function which AEM lists as the #7 blue wire but have no idea where this needs to be connected to in the car.

#9 appears to be the tach output if I am understanding correctly and I assume I tap into the back of the gauge cluster for this?

#10 is self explanatory.

#14 is obviously a ground but there are 3 different grounding options listed. Now I am assuming (a lot of assuming going on in here lol) that AEM when mentioning EMS is referring to the factory Engine Management System but have no idea if it has an analog ground input. If you notice the notes below the AEM pinouts it lists the different grounding options for #14.

Finally #15, and is what I assume to be the output that goes into the factory harness to allow for logging, etc and will go to the #4 pin of the factory green O2 plug.

How am I doing so far lol? Any help would be greatly appreciated. Just please don't tell me to go with a different setup. Good or bad this is what I have and what I am sticking with.

[Trb1]

Don’t you have to purchase the failsafe relay and such to go along with this? That’s the way zeitronix is anyways. Failsafe is what you decide you want it to be. You can cut throttle or boost easily. Just splice the power wire for one of the two and if it triggers the failsafe it will route power away from the spliced wire and ground it out. This would kill throttle or cut back to wastegate pressure. You can program the parameters too.

[S4James]

most common would be to break the n75 connection and drop boost to WG pressure.

[Teck09]

Don’t you have to purchase the failsafe relay and such to go along with this? That’s the way zeitronix is anyways. Failsafe is what you decide you want it to be. You can cut throttle or boost easily. Just splice the power wire for one of the two and if it triggers the failsafe it will route power away from the spliced wire and ground it out. This would kill throttle or cut back to wastegate pressure. You can program the parameters too.

I'm not 100% sure whether or not any additional hardware is needed. I'll look into it. I didn't anticipate buying any and figured I would wire it up along the lines of what you described. Most likely via the n75 like S4James mentioned but wasn't/still not sure if cutting throttle or ignition is a better or safer route.

Once I source some wiring diagrams I'll hopefully be able to make some real progress. Untill them I am just gathering as much info as I can. With any luck I'll hear from someone who has done this. Thanks guys.

[PwrWgn]

There is a failsafe connection on decent water-meth setups that taps into ECU pinout 104. might be comparable...

http://s4mods.com/b5-aquamist-hfs3-i...tom-meth-tank/

[Trb1]

In theory cutting throttle or ignition might be safer, but in actuality, you’ll have the car on the road and cutting your power would be dumb. I’d suggest the n75 route as well, as the only way that will fail is if you have a waste gate or signal line issue.

[Teck09]

There is a failsafe connection on decent water-meth setups that taps into ECU pinout 104. might be comparable...

http://s4mods.com/b5-aquamist-hfs3-i...tom-meth-tank/

Thank you for that. It was pretty helpful.

In theory cutting throttle or ignition might be safer, but in actuality, you’ll have the car on the road and cutting your power would be dumb. I’d suggest the n75 route as well, as the only way that will fail is if you have a waste gate or signal line issue.

In the above situation linked by PwrWgn the N75 looks like it is diverted through the AEM controller which has two wires controlling the failsafe. My gauge has only one which supplies a ground. Should i then just tap into either side of the N75 wiring effectively grounding the signal when activated? I guess I am not 100% familiar with how the N75 regulates boost pressure so understanding how the failsafe would effect it is a bit beyond me atm.

[S4James]

use a relay. wire it to disconnect the power wire to n75 when your failsafe grounds out.

[Teck09]

use a relay. wire it to disconnect the power wire to n75 when your failsafe grounds out.

If a break in the connection is what is needed, I'll do that. Like I said, I am still a bit uneducated when it comes to the N75. Thanks for the idea

[jimmer009]

So what would the point of this be??? So you don't run lean??? I mean the me7.1 has only a million reasons to put you into limp mode. And threw tuning or even a decent set up you should be ok. Not just one day start running lean. Or is it better to be safe than sorry???

[vavJETTAw36]

So what would the point of this be??? So you don't run lean??? I mean the me7.1 has only a million reasons to put you into limp mode. And threw tuning or even a decent set up you should be ok. Not just one day start running lean. Or is it better to be safe than sorry???

Essentially replicating limp mode. Puts you on WG cracking pressure when you run too lean during high boost.


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[Teck09]

So what would the point of this be??? So you don't run lean??? I mean the me7.1 has only a million reasons to put you into limp mode. And threw tuning or even a decent set up you should be ok. Not just one day start running lean. Or is it better to be safe than sorry???

Like vavJETTAw36 said but that isn't why i am running it, just an added feature. I wanted a single gauge to show AFR and Boost and this is the one I ended up with. The failsafe was just a bonus feature IMO. I'll give it a shot, if it acts up or interferes with the tuning I'll disable it and just run it as a gauge.

[jimmer009]

Ok that makes sense.

[travis_w]

When connecting this to the n75 what wire should it be tapped into?

[S4James]

interrupting the ground should be safe enough.. I don't know what the convention is. Is there one?

[Teck09]

When connecting this to the n75 what wire should it be tapped into?

According to the tutorial that PwrWgn linked it is pin #104 on the main ECU plug. Not sure if that is a ground or not though

interrupting the ground should be safe enough.. I don't know what the convention is. Is there one?

Like you said with the relay, I would imagine breaking the connection on either side would be fine. I have it opened up and am doing the wiring right now, the failsafe wire is my next step. I am going to trace the wires and see if one side of the N75 leads directly to ground.

[Teck09]

OK, one side of the N75 goes to the smaller ECU plug pin #104 as stated above, the other to the large plug pin #7 and does go to ground somewhere along the way. Given my basic electrical knowledge I do not think it is a totally open/direct ground however as I am getting 33.3k when I ohm it. All testing is being done with the ECU removed so it may change once it is installed. Given all of this #104 would be the signal, yeah?

[S4James]

id say its a safe bet. just be careful with the relay. wouldnt want to accidently send 12V up the wrong wire and fry your ECU

[Teck09]

Definitely. Somehow I have managed to misplace or discard my ecu so that won't be an issue anytime soon lol.

Just thinking out loud here, can you think of any reason intercepting and grounding the signal rather than breaking it with a relay would be bad practice? The install would certainly be easier but once again (a common theme lol) I am not educated enough to make the call either way.

[S4James]

yeah thats not how electic circuits work... you are talking about shorting the signal wire to ground. Bad idea.

[travis_w]

So from what I understand the ecu pulses ground to the n75. So if you use the ground wire and set up the failsafe with the low ground output that should send a ground to the n75 there fore making the car run on wastegate pressure. Correct me if I'm wrong.

[Teck09]

yeah thats not how electic circuits work... you are talking about shorting the signal wire to ground. Bad idea.

Yeah, I realize directly grounding a power wire is asking for trouble. The reason I asked is Trb1 seemed to elude to doing it that way. I just figured he has a better understanding of how the N75 circuitry works than I do.

.......Just splice the power wire for one of the two and if it triggers the failsafe it will route power away from the spliced wire and ground it out. This would kill throttle or cut back to wastegate pressure. You can program the parameters too.

Can you elaborate a bit? I think you were referencing how Zeitronix works but does it initiate the failsafe by sending a ground signal similar to the way the AEM gauge does?

[Teck09]

So from what I understand the ecu pulses ground to the n75. So if you use the ground wire and set up the failsafe with the low ground output that should send a ground to the n75 there fore making the car run on wastegate pressure. Correct me if I'm wrong.

That is what I initially had hoped as it would be a whole lot easier and cleaner doing it that way. But as S4James said, if it is a hot wire that would be no bueno. I believe the N75 is disabled when unplugged so wouldn't that mean once the ground was removed it was open/allowing only wastegate pressure? Counter intuitive to the way you described it, yeah? I honestly have no idea lol.

[travis_w]

I have just been trying to research it also and that is one of the things I read.

[Teck09]

Same here. It would be a whole lot easier if I was doing this on a running driving car where I could test working systems as I go but unfortunately that isn't the case. The never ending build continues......

[vavJETTAw36]

But the default state of the n75 is to bleed all pressure. I’d think you could simply open either the positive or negative to kill the n75.


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[travis_w]

So Blake just emailed me and said he believed you just ground out the signal (power) and it will do cut to wastegate pressure.

[vavJETTAw36]

So Blake just emailed me and said he believed you just ground out the signal (power) and it will do cut to wastegate pressure.

Ground out the power? I think you mean open the signal. You can open signal or open ground. Each will effectively turn off the n75 which, since the n75 is designed to fail open, will default to "wastegate cracking pressure".

[travis_w]

I think......

[vavJETTAw36]

I think......

I just checked the wiring diagram on the n75. There’s two wires: one fused 12v and the other is a signal wire. It is essentially throwing ground like the fuel injectors do. What Blake means is that the ecu is grounding the n75. Think of the wires as a water hose and the ecu as a valve for water to flow. The ecu is essentially opening that valve for the water to travel which activates the n75. Ive always referred to this as “throwing ground”.

So you can either sever the 12v source or you can ground the signal wire. Either way you’ll need to add a SPDT or SPST relay. It’s just a matter of choosing the appropriate location that’s most convenient for installation and maintenance.


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[travis_w]

So like I stated earlier the computer is sending a pulsed ground so when you supply a solid ground to the n75 it defaults to cracking pressure?

[vavJETTAw36]

So like I stated earlier the computer is sending a pulsed ground so when you supply a solid ground to the n75 it defaults to cracking pressure?

I do not know this 100%, but when you unplug the n75 it defaults to cracking pressure. Which would lead me to believe that the pulsing would actually activate the n75.


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[travis_w]

I just checked the wiring diagram on the n75. There’s two wires: one fused 12v and the other is a signal wire. It is essentially throwing ground like the fuel injectors do. What Blake means is that the ecu is grounding the n75. Think of the wires as a water hose and the ecu as a valve for water to flow. The ecu is essentially opening that valve for the water to travel which activates the n75. Ive always referred to this as “throwing ground”.

So you can either sever the 12v source or you can ground the signal wire. Either way you’ll need to add a SPDT or SPST relay. It’s just a matter of choosing the appropriate location that’s most convenient for installation and maintenance.


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Why would you need the relay. Is it for when the computer tries to not send ground.

A diy would be awesome for this.

[Teck09]

Why would you need the relay. Is it for when the computer tries to not send ground.

A diy would be awesome for this.

That's where the confusion is, for me at least. Not knowing what kind of signal is used for the n75 makes me apprehensive to apply a ground.

The way I see it the relay would only be needed if you are breaking the signal. The ground output from the gauge (failsafe wire) would then activate the relay, severing the connection.

The other way being discussed would be to just tap into the n75 signal wire with the aforementioned failsafe wire. When the gauge sends the signal it would apply a solid ground to the wire rather than severing it.

I opted for the relay method just to be 100% safe. I'll post up pictures and pin locations once I am finished.

[vavJETTAw36]

Why would you need the relay. Is it for when the computer tries to not send ground.

A diy would be awesome for this.

It would depend on how the AEM is going to operate and how the n75 actually operates. If AEM throws ground to activate fail Safe and n75 needs to be grounded to purge boost then you wouldn’t need a relay. But if polarity is going to oppose each other than you’d have to relay it.

I believe that the n75 works by throwing ground which tells the n75 to hold pressure. When it wants to purge it severs the ground. It looks like the AEM might work by throwing ground when fail Safe is activated. In this case you want to break the ground to the n75 so you’d want to introduce a relay.

When I get home I will do a quick bench test to check function on the n75




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[travis_w]

The aem has a power and a ground you can use. So either way it has both options. If you use ground you just get rid of the power and likewise the other way.

[Teck09]

The aem has a power and a ground you can use. So either way it has both options. If you use ground you just get rid of the power and likewise the other way.

Not the gauge I am installing anyways. There is one failsafe wire and it is labeled as a ground output. See the 2nd picture in my first post, it is labeled #7.

[travis_w]

Sorry. My failsafe has both but everything I'm ready is to use the ground

[Teck09]

It would depend on how the AEM is going to operate and how the n75 actually operates. If AEM throws ground to activate fail Safe and n75 needs to be grounded to purge boost then you wouldn’t need a relay. But if polarity is going to oppose each other than you’d have to relay it.

I believe that the n75 works by throwing ground which tells the n75 to hold pressure. When it wants to purge it severs the ground. It looks like the AEM might work by throwing ground when fail Safe is activated. In this case you want to break the ground to the n75 so you’d want to introduce a relay.

When I get home I will do a quick bench test to check function on the n75

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I am interested in what you find. I believe that a ground is sent to raise the boost pressure like you mentioned before. Removing the connection to the n75, which results in wastegate pressure seems to confirm this.

[Teck09]

Sorry. My failsafe has both but everything I'm ready is to use the ground

No worries, didn't mean to come off abrasive. I had to double check my instructions to make sure. If it had both I would have been severely wasting my time lol.