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Old 05-21-2012, 04:45 PM   #1
Snubba
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Drives: '09 silver 5-door
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Steering wander, adjusting EPS assist

Hi folks, you might remember me from such threads as "Is steering wander caused by caster?"

I have been disappointed with my Liftback cruising because it gives a disconnected feel when cruising at 65mph. It wanders down the road and needs constant steering correction to keep it straight. This is different from other cars where you can just sit there with one hand the wheel while resting it on your leg and correct the steering with less mental effort. Driving the Yaris long distance takes more mental energy to drive than other cars.

So I recently found this link by etimago (thanks!):
http://www.autospeed.com.au/A_111532/cms/article.html

So I did the same basic principle as the article and placed resistors in line of one of the steering torque sensor's wires (TRQ2, the yellow one, it comes right out of the bottom of the EPS assembly). If I installed too much resistance, the EPS would fail just the like article said. So I found a good number that wouldn't shut off the EPS when I jerked the wheel from side to side while parked on asphalt. It was 267 Ohms. I used one 220 Ohm and another 47 Ohm resistor in series to add up to 267. I THINK it made the steering effort decrease but whenever I think something made a difference, its safe to call the experiment inconclusive (because I tend to see "improvements" when none were there). An interesting thing, when I used 470 Ohms, it wouldn't fail until I jerked the wheel from left to right when parked on asphalt.

So the article mentions a "torsion bar" in the system. It is used by the steering torque sensor. So I took a big crescent wrench and put it on the steering shaft at the universal joint next to the firewall and held the shaft in place. I then turned the wheel and found SPRINGYNESS! It would move about 1/4" at the seam between the column cover and steering wheel cover before it stopped like it hit a block.

So I think this is part of the problem or maybe the whole problem. Maybe its this torsion bar and castor combined. The thing is that hydraulic power steering systems use a torsion bar too yet they feel fine.

What say ye?
Does anybody have experience with a direct-drive steering shaft in the Yaris?
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Old 05-21-2012, 07:22 PM   #2
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I have never noticed the wander issue with my 09, but I have done quite a bit of experimentation with overrides for the EPS and in the process have calibrated the torque sensor zero point with my TechStream tool a few times. Perhaps those, like yourself, having the wander issue are in need of a calibration of the EPS.
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Old 05-21-2012, 07:50 PM   #3
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I have a layman's question on this topic...

What happens if you disconnect the electric power steering? Will the car still steer safely? The reason I asked is that I positively hate power steering. When I bought a new Tacoma, none of them came without power steering so I removed the pump, capped off the hoses, and drove it manually.
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Old 05-21-2012, 08:05 PM   #4
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Quote:
Originally Posted by tooter View Post
I have a layman's question on this topic...

What happens if you disconnect the electric power steering? Will the car still steer safely? The reason I asked is that I positively hate power steering. When I bought a new Tacoma, none of them came without power steering so I removed the pump, capped off the hoses, and drove it manually.
You can pull the EPS fuse to try it out. At speed it feels about the same, but from a standstill you feel like you are steering an old truck.
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Old 05-21-2012, 08:16 PM   #5
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Thanks, I'll give that a try...

...and I already steer an old truck as my Tacoma is 16 years old.
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Old 05-21-2012, 10:07 PM   #6
Snubba
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CTScott, calibration, eh? I'll have to try that out. I have an '09 Liftback.

Tooter, funny name, in the past when I removed the fuse, it was too difficult to steer. So this afternoon I removed the fuse and the steering motor and it is easier to steer like other people have mentioned. Its a tad more difficult to steer than my '90 Honda CRX was. I like it so much that I'm going to have the Mrs. drive it and see if she'll put up with it. But its still spongy.

I did a steering comparison with my '96 Ford Crown Victoria and noted steering finesse while cruising it. Then I went back and put the wrench on the Yaris' steering shaft and used the same effort on the steering wheel and found it twists a little. I'm positive this spongyness makes for the suck characteristics. Maybe a calibration will fix it!

By the way, I took apart the steering motor assembly where it connects to the column and found the torque sensor. And sho' 'nuff, it twists there.

Here's a pic:
http://techno-fandom.org/~hobbit/car...ng/800/eps.jpg

The circled part is where I saw twisting taking place.
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Old 05-22-2012, 05:39 PM   #7
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Here's a test I just discovered to see how springy the steering wheel twists before it hits a stop:

Car off/EPS off, key in ignition so the steering wheel will move.
Jerk the wheel one way as fast and hard as you can.

You will twist the steering wheel and then feel a solid knock. This is the limit of the amount that the spring will twist until it hits a physical stop.
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