Safer Failsafe for WMI

[Bull Run]

I currently have TUNE+ (AEM Stage 2) WMI the failsafe set up as shown by Adam: [ame="[MEDIA=youtube]r9LDKQh9Tlc[/MEDIA]"]

The way it's set up is that the TB wire going to the ECU is cut and connected to a failsafe solenoid included in the kit. Green wire from the WMI controller (applies ground when an error is detected) goes to the solenoid, creating an open circuit for the TB wire and puts the car in a limp mode when an error is detected. The limp mode, in this case, is that the car barely idles. It's good for preventing engine damage but not very safe if you are cruising at a high speed.

For example, I was on the highway cruising at around 70 MPH when the failsafe triggered (ended up being a grounding issue). The car acted as if I suddenly lifted off of the throttle. Fortunately, I was able to get to the shoulder and stop, turn off the WMI controller, and restarted the car to get off of the limp mode. I can see how this can be an issue if there wasn't a safe place to pull over.

I did some research and found the Snow Performance Boost Control Solenoid pictured below. When this solenoid triggers, it should limit the boost to whatever the spring rate is for the WGA (e.g., TS WGA with 12psi springs should fully open the WG at 12psi). This should reduce the power to a safe level but allows you to maintain reasonable speed until you can safely pull over or even drive home to troubleshoot. If you have AP, you can even switch over to the non-WMI map and turn off the WMI controller to undo the failsafe while driving.

Before I proceed with this experiment, has anyone else set up their failsafe this way? Has anyone tried disabling the factory WGA solenoid instead?

Correction: The green wire grounds on error condition, so this solenoid will be hooked up to it and a 12V source.

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[RubyRed15]

If the diagram shown here is to be believed, pin 16 of C1551E can be utilized for reducing the boost to "WGA spring pressure", which should be less brutal than the limp mode you've described. Pin 86 is "CTRL MOD. - POWERTRAIN # THROTTLE ACTUATOR CONTROL MOTOR (TACM+)"; pin 16 is "CTRL MOD. - POWERTRAIN # WASTEGATE SOLENOID (TCWRVS)"

 

[Bull Run]

If the diagram shown here is to be believed, pin 16 of C1551E can be utilized for reducing the boost to "WGA spring pressure", which should be less brutal than the limp mode you've described. Pin 86 is "CTRL MOD. - POWERTRAIN # THROTTLE ACTUATOR CONTROL MOTOR (TACM+)"; pin 16 is "CTRL MOD. - POWERTRAIN # WASTEGATE SOLENOID (TCWRVS)"

Thanks for the info! My plan is to unhook the wiring harness to the WGA solenoid to ensure that the max boost is limited to the WGA spring rate or lower (or some other limp mode that still allows for safe speeds) when I get home later. If this works, I'll reconnect the TB wire and splice into the #16 wire using the currently installed failsafe solenoid. My original plan was to splice into the wiring at the WGA soleniod location, but doing it at the ECU side should provide a cleaner look (plus I already have failsafe wires going there).

 

[RubyRed15]

Looking forward to hearing about your findings.

Where is the WGA solenoid?

 

[Bull Run]

Looking forward to hearing about your findings.

Where is the WGA solenoid?

It's in front of the turbo with three hoses going to it; From WGA, turbo outlet side (boost pressure source), turbo inlet side (bleeds off boost pressure to the WGA).

The picture below's not from a Mustang but should give you an idea on the plumbing.

 

[RubyRed15]

Yep. Found it. As you described, bolted to the corner of the block.

 

[Bull Run]

WGA bypass solenoid disablement test went as expected. Unplugged the solenoid harness as seen below and tucked it away to prevent belt contact. Surprisingly, it didn't trigger a CEL. Maximum boost was limited to little over 15 PSI, which was expected since WGA that came with VS2+ has a 17 PSI spring.

The car was boosting a little over 26 PSI before, so I felt a large power drop by being limited to 15 PSI. Otherwise the car drove fine and still accelerated decently enough, which is exactly what I wanted the failsafe to do.

Checked to see if any codes were recorded after the run and saw "P0246 - Turbocharger/Supercharger Waste Solenoid A High", which means the solenoid circuit reading does not fall within the recommended specifications due to a damaged solenoid, or faulty wiring. This was expected since removing the harness had the same effect as cutting the wiring.

ECU pin #16 is the wire that goes to the solenoid and that's the one you need to splice into the failsafe solenoid. Colors of the wire (VL/WT) is same as one of the wires on the solenoid hardness. You can also use a multimeter to check for continuity from the ECU to solenoid harness.

With everything put back together, I knew the WGA bypass solenoid was working due to the car getting over 26 PSI of boost. After the first run, I pulled into a parking lot, and while the car was running, disconnected one of the wires for the fluid level sensor to simulate running out of the water/meth mixture.

This caused the WMI controller to throw an error, verified via one blink (low fluid) of the status light every few seconds as shown below.

This triggered the failsafe solenoid, which created an open circuit for the WGA bypass solenoid. As before, it didn't throw a CEL but the car was limited to around 15 PSI of boost. I switched to the non-WMI map and switched off the WMI controller to disable the failsafe. However, it seems that the ECU kept the WGA bypass solenoid disabled as tje car was still limited to 15 PSI until I restarted the car. After restarting the car with WMI controller/failsafe off, I was able to get up to 24 PSI, which seems to be the limit for the non-WMI map.

Overall, I'm happy with this setup since I shouldn't have any issues driving home with the WGA bypass solenoid disabled. While this doesn't trigger the CEL, I can still tell that something went wrong due to limited boost and flashing status light.

 

[RubyRed15]

Outstanding!

I love love LOVE your status LED placement, btw!

 

[Bull Run]

Outstanding!

I love love LOVE your status LED placement, btw!

Thanks! The plastic piece snaps off pretty easily and there is an existing hole underneath, so plenty of space for the light.

 

[5.0yote]

Gunna be honest I have the exact same setup with the throttle cut, and its never been a problem to flip the switch power off the car and back on while rolling. While this instance would be a bit more convenient, limp mode does more than just cut your throttle, it changes your existing running map to limp mode modifying timing, fuel etc. Hence limp.

IF you had some catastrophic even with your methanol at just the wrong time say under WOT at max boost, just cutting boost can in some instances not be a proper recovery option and you may want to fuel, timing etc. pulled back as well which should happen via the ECU automatically but sometimes odd stuff happens. This may be convenient in the sense of driveability but I am not very confident it is a suitable fail safe in all situations.

 

[Blyman93]

I'll admit it's annoy8ng to have the safety go off and not immediately realize it's your methanol doing it. I've had almost half a tank of meth flip my failsafe after taking an aggressive turn lol but now that I know to turn it off and restart the car, I'm not too worried about it. Limp mode on these cars is like blowing 3 spark plugs at once.

 

[Bull Run]

Gunna be honest I have the exact same setup with the throttle cut, and its never been a problem to flip the switch power off the car and back on while rolling. While this instance would be a bit more convenient, limp mode does more than just cut your throttle, it changes your existing running map to limp mode modifying timing, fuel etc. Hence limp.

IF you had some catastrophic even with your methanol at just the wrong time say under WOT at max boost, just cutting boost can in some instances not be a proper recovery option and you may want to fuel, timing etc. pulled back as well which should happen via the ECU automatically but sometimes odd stuff happens. This may be convenient in the sense of driveability but I am not very confident it is a suitable fail safe in all situations.

You brought up some good points especially if you're using WMI for fueling. In my case, I'm using the WMI for cooling rather than fuel, so reduction of 10 PSI worth of boost should be sufficient. I believe many tuners discourage using WMI for additional fueling because so many things can go wrong with them. Considering that almost 90% of my commute is on a busy city highway, I'd rather avoid having to power cycle my car if I can avoid it.

Here's my counterpoint; most of the modders here have either stock WGA with 7 PSI springs or upgraded to TS WGA with 10 PSI springs. I don't think that any tune that's so aggressive that it can cause ecoboom with 7 to 10 PSI of boost is unsafe to use on a street car. Also, if you are using progressive setup set to start at 5 PSI and maxes out at 20 PSI, it won't be spraying much around 7 to 10 PSI anyways. Additionally, note that failsafe will not work if the controller completely dies, loses power, or if you forgot to switch it on in the first place, which is another reason to avoid using WMI to make up for fueling.

I run one tune for all seasons and during my commute, I've seen the ambient temperature drop down to high 30's during coldest days, and close to 120's during the hottest days. So a good street tune should be able to adjust to a wide range of conditions quickly.

 

[RubyRed15]

Gunna be honest I have the exact same setup with the throttle cut, and its never been a problem to flip the switch power off the car and back on while rolling. While this instance would be a bit more convenient, limp mode does more than just cut your throttle, it changes your existing running map to limp mode modifying timing, fuel etc. Hence limp.

IF you had some catastrophic even with your methanol at just the wrong time say under WOT at max boost, just cutting boost can in some instances not be a proper recovery option and you may want to fuel, timing etc. pulled back as well which should happen via the ECU automatically but sometimes odd stuff happens. This may be convenient in the sense of driveability but I am not very confident it is a suitable fail safe in all situations.

Is pin 86 really a limp mode or is it just a throttle cut? Based on the name of the pin, I'd assume the latter, in which case I'd also assume no more adjustment to timing etc. than you would get from having the wastegate drop to spring pressure, relative to the drop in power, of course.

 

[Bull Run]

Is pin 86 really a limp mode or is it just a throttle cut? Based on the name of the pin, I'd assume the latter, in which case I'd also assume no more adjustment to timing etc. than you would get from having the wastegate drop to spring pressure, relative to the drop in power, of course.

It's really a limp mode as aside from no throttle response, the car idles very rough. As Blyman93 mentioned, it feels like the engines only running on one cylinder. You might be able to simulate it by unplugging your TB harness.

 

[Cobra Jet]

Interesting thread and component.

The question I have is, even if an “error” occurs - isn’t the damage already done even if the failsafe activates?

Meaning, damage can occur seconds before that failsafe activates. Sure, the failsafe will do it’s job by cutting any other feeds to disable or shut down the engine AFTER it’s tripped.

?

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