Ford EPAS Feedback Failure?
The Electric Power Assist Steering (EPAS) is a potential problem on 2011-14 Mustangs if you modify the suspension in certain ways. We hear from customers weekly so I wrote this. I am not saying that this will happen to your 2011-14 Mustang but it happened to our 2011 GT and we've heard of this on at least 100 more cars, too.
PDF of EPAS document:
http://www.vorshlag.com/documents/Ford_EPAS.pdf
The document above talks about EPAS features to fix "Pull Drift Compensation", something most people didn't care about. Ford engineers neglected to see the negative side effects when it sees parameters outside of the OEM suspension/tires/bushings. When you take a 2011-up production Mustang and modify any of these items below you can
potentially cause the EPAS to go into an erroneous feedback loop.
Modifications that can cause EPAS Feedback Failure- Aftermarket Front Control Arms
- Aftermarket Front Control Arm Bushings
- Radical changes to front suspension geometry
- Significant tire/wheel changes (especially R-compound tires or slicks)
Our issues first occurred with lowered ride height + poly LCA bushings, on an autocross car daily driven on 265mm street tires.
This list may be incomplete, but it shows what we've seen that can cause this failure, and what some other suspension manufacturers and racers that have called and talked to us about have seen. It doesn't always happen when you change these parts, especially if you just do the mods and only daily drive the cars. Often it only takes time or circumstances - when these mods are installed, then eventually the car is driven at road course or autocross event, the feedback failure soon follows. And once it begins to happen it only takes a few circumstances (minimum speeds, a certain amount of steering input speed) for it to happen again and again. Watch the video below for how this happened on our 2011 GT after installing Energy Suspensions front LCA bushings.
Vorshlag EPAS feedback loop video.
The video above has been viewed many thousands of times. It has been sent to Ford engineers, but to my knowledge, Ford Motor Company does not have a fix for this, nor do they even acknowledge that there is a problem. The blame is quickly put onto any aftermarket suspension or wheel/tire modifications. Which is true - those changes can kick off this error, and we have not seen this happen on 100% stock Mustangs.
But... there
is an error in their programming, for this to happen so frequently with one simple bushing change. This issue
cannot be fixed with a new program upload into the EPAS computer (located within the steering rack assembly), either. All attempts to over-write theses "ones and zeros" have been rebuffed or failed. But
Ford Racing has a fix...
Vorshlag does not sell the M-3200-EPAS steering rack, but Rehagen Racing does.
We talked to Ford Racing folks, who knew all about the problem. They developed the "race rack" above for the Boss 302-R/302-S race cars, which all come with this M-3200-EPAS rack installed. It has the same hardware as the production 2011-14 racks, but just has the "auto nibble" or "Pull Drift Compensation" programming turned off. It is a simple $999 fix. They will not over-write this programming onto a used steering rack - they will only sell you a new one. We asked many times while the M-3200-EPAS unit was on backorder for several months.
So, if you have a 2011-14 Mustang and plan on doing a lot of suspension modifications, either AVOID touching the front LCA bushings or using an aftermarket control arm (or even the Boss 302-R LCA) or PLAN for this rack upgrade. The LCA bushing or arm replacement are the two most common causes of EPAS feedback failure, and doing either is almost a 100% guarantee you will see this feedback failure. But if you run a production 2011-14 Mustang in any serious track or autocross competition, you pretty much HAVE to replace these bushings, so plan on the M-3200-EPAS upgrade at the same time.
Why are these bushings imperative to replace? See for yourself. The rear-most lower bushing in the front Lower Control Arm is a HUGE chunk of soft rubber. It is the size of a 8 oz beer can. And if the rubber wasn't bad enough, it isn't even solid - there are channels or voids cast into the bushing, which are filled with hydraulic fluid. This does not make for a stable platform to mount the control arm, through which a majority of the suspension loads pass through.
Bushing Deflection Test
Do this visual bushing deflection test, as it is a real eye opener. Go in a parking lot with your S197 Mustang. Have someone prepared to drive the car while you watch. Stand a few feet beside the car and watch the front wheel. Have them reverse briskly then stop firmly. Watch the front wheel move fore-aft relative to the chassis. It will move a LOT. This is unwanted wheel movement and suspension geometry change in action, and it is very evident. The S197 Mustang is not the only car that suffers from super soft front suspension bushing deflection, as you can do this test on virtually any BMW or Subaru and any number of modern cars and see the same thing happen.
Now imagine the car braking from 100+ mph, on a road course, while turning, and the car is equipped with wider and much grippier R-compound race tires. With the stock
Beer Can-sized rubber & hydraulic bushings in place there would be a LOT of front control arm bushing deflection, which results in unwanted toe change to the front geometry. This will make the car unstable under braking. This is undesirable, of course. The fix is upgrading to firmer (polyurethane) front control arm bushings. These parts are low cost, with a
less than fun installation, but they do work to control toe change under braking. But once installed... steering rack feedback will most certainly occur. And believe me, when this Feedback Failure happens on the street it is disturbing enough, but on a road course it is downright scary. We found that the only way to stop it once it happened on a road course was to come into the pits, cycle the ignition key, reset the Traction Control system (turning it 100% off), then going back out. After about a few months of this nonsense (while waiting on the M-3200-EPAS to come off of backorder), we finally replaced the rack with the Ford Racing unit and it has never happened again. There were zero other changes or benefits to this $999 steering rack.
I'm not trying to sell folks on some bushing upgrade, or scare you into buying a steering rack we don't sell. Just warning you of a potential recipe for problems if you have one of these cars and do these mods. I don't want people reading our forum posts, buying Mustangs and mimicking our S197 suspension mods, to then blindly fall into the EPAS Feedback Failure. And overall these 2011-14 Mustang GT/Boss302 cars are the Performance Bargain of the Decade, and I highly recommend them to anyone that wants a super reliable 420+ hp V8, RWD sports coupe with outstanding brakes (optional Brembos), and a good basis to build upon - all for a really low price. Heck yes you should drive one, and you might end up buying one, just know that this is one of those potential Achilles heels, and the fix is fairly straight-forward, if a tick costly.
Note: This issue does not affect other S197 Mustangs, like the 2005-2010 models with traditional hydraulic assist power steering, and might not even affect other cars made by other car makers with electric assist steering. More and more automakers are moving from hydraulic to electric steering assist systems, and this technology has MANY benefits (costs, weight, power savings, tunable power assist). I do think these electric racks will become the norm for OEM and racing vehicles alike. Ford just has a glitch here that I think they could fix with a little programming, and they have in the $999 Ford Racing version.
Cheers,