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GoldStar
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Electro-Hydraulic Power Steering (EHPS) Conversion

Disclaimer
I originally got this idea from the Electrical Vehicle (EV) community and horse power information comes from Derek’s, from Hondata, write-up awhile back.
All the information is being provided so that anyone, who is interested, can perform this conversion. If you are not mechanically and electrically inclined this conversion may not be for you. However, I believe it is simple enough that anyone who can read and understand the schematics I have provided should be able to complete this conversion.
I have tested this conversion on the street daily driving and on the track at Road Atlanta, Sebring, and Virgina International Raceway. It works flawlessly.
I do not consider myself an expert and your results may vary.
ALL the information required to do this conversion has been provided. Please read the thread completely before you post any questions.


Background
Many people who swap B or K-series motors into their cars choose to leave out their mechanical power steering. Their reasons range anywhere from thinking it is too hard to retain (it’s NOT) to wanting to save that extra 5-8 hp it takes for the engine to power the mechanical p/s pump.
This conversion allows one to retain power steering while keeping power loss down to a negligible level. According to Derek at Hondata, the mechanical p/s pump on a K-series motor draws about 8.5 peak hp while in the straight position, while the B-series’ pump draws about 5 hp. The loss from an EHPS pump (depending on load) is between 0.25 and 0.75 hp, through the alternator. At less than 1 hp loss to run EHPS, it is definitely an alternative to consider.
So what’s the big deal? Power steering is important because it reduces driver fatigue and offers more precise steering while on the track. Not to mention, it is also great to have around town in stop and go traffic and while parking.
I have performed two of these EHPS conversions on my car in the past using a 92-95 MR2 power steering pump, which I have long sold. I did not like their loud high pitched whine and the fact the pumps always stayed on full blast. Being that I daily drive my car and that the 92-95 MR2 pump uses a brush DC motor, I knew that it would only be a matter of time before the brushes would eventually wear out on the already old pump and require a rebuild. Also, it would have taken too much effort to get the pump to work the way the manufactures intended, which would have required the p/s ECU, p/s driver, and steering angle sensor to be adapted. Some people have wired in a switch to turn off the pump while it is not in use. I did not want to always have to be fiddling with a switch while on the road.
This leads me to a power steering pump from the 00-05 MR2 Spider. This pump is the all-in-one solution to all your power steering needs. This aluminum pump has a stepper motor (no brushes to wear out) with integrated electronics (controller), reservoir, and rubber bushing in its mounting points. Once the pump is powered on, it winds down on its own when there is no load (steering wheel not turning). And when a speed signal is used the pump turns off at freeway speeds. These features improve the life of the motor and alternator. Additionally, because it has rubber bushings built in, it is already isolated once mounted. This makes the pump much quieter than its older counterpart.
Another thing worth noting is that the p/s pump from the 92-95 MR2 draws a lot of amps. Even the stock 75 amp relay would fail all the time on the original cars. Many people fixed this by running 75-100 hi-amp aftermarket relays. The 00-05 MR2 p/s pump only requires a 50 amp relay. It draws about 4 amps at idle and usually runs less than 40 amps at full load.

The Conversion
The pump used for this conversion can be found in a 00-05 MR2 Spider, which should make it easier to find than the 92-95 MR2 power steering pump. The hydraulics and electronics are very straight forward. The needed components to make it work can be found at most auto shops or junkyards.

The Pump


Hydraulics
Making the hydraulics work is a matter of stepping down the 10mm hardline from the pump to the 8mm hardline to the rack. I used the pressure line that came with the pump and a small piece of the pressure line from my Integra’s rack. Luckily, 10mm is very close to 6-AN and 8mm is very close to 5-AN. So all I did was mate the two using a 6-AN to 5-AN reducer and the appropriate tube nuts and sleeves. If you don’t have the proper tools to do this it may be easier/cheaper to have the line made.
The rack return line and the return on the pump’s reservoir are both 10mm. All I did was plumb the return lines to an oil cooler in front of the car using 3/8 inch heater hose.
After hooking up the pressure and return lines, 1 ½ bottles of p/s fluid, powering the pump on, and turning the steering wheel lock to lock to bleed the system I was happy to see that there were no leaks.

Pressure line


P/S Oil Cooler


Electronics
Since the pump required a 50 amp relay and fuse, I used an ABS fuse box off a 91-93 Honda Accord. This particular fuse box has all the components required to wire up the MR2 p/s pump. If you do not want to use what I used, an 8 gauge power wire and an aftermarket 50 amp relay and a 50 amp fuse should work just fine.
The pump does not require a VSS signal to operate. It just will not turn off completely at higher speeds; however, it will still wind down very low on its own when there is no load.
Also, the pump I purchased did not come with the connecting plugs so I had to make my own connectors. Try to get the pump with its plugs; it will make for a cleaner, water tight harness.
Lastly, because the system is triggered when the ignition is turned on, I wired in a switch so I could turn the system on after the motor has been started.
All the required wiring is illustrated bellow.

Pump Pin-Out Wiring
See the attached schematics for more details.
Click here to see P/S schematic


Fuse Box Pin-Out Wiring (91-93 Honda Accord ABS)
You won’t need the rest of the lower amp fuses.
Click here to see Fuse Box schematic


Photos
I designed a mount bracket for the pump using CAD (Cardboard Aided Design). :up::D:up:


I welded together pieces of 1 inch aluminum square pipe to make the mount(weighs less than 7 ounces).


Pump Installed


 

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so what size belt you using now 52.5?
 

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Nice write up! kommen_sense would love it. I like the 00-05 Spyder PS motor a lot better.
Already been trying to track one down :) It looks much smaller/lighter than my older mr2 pump as well.
 

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I've been following people's setups, but I haven't seriously looked for one yet. I've been too busy drilling holes in my car. Finally got a rollbar in the thing. Redoing my current ehps setup probably won't happen before the winter.
 

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Hi people, this is my first post here, found the forum via google when searching for some EHPS conversion.

I'm planning on doing this to my car, but I was wondering if anyone has tried other pumps?

What seems very common on new cars (at least here in europe) is a pump made by 'TRW', it has multiple harness inputs, normally 3 plugs on it with various pin connections. So I am wondering if it performs similarly to the MR2 jobby. My guess is that being a modern pump it would operate quite efficiently.

I've yet to look up specs on it, just wondering if any one else has thought about using a TRW pump or something else? This is what it looks like: http://cgi.ebay.co.uk/ELECTRIC-POWE...9|66:2|65:12|39:1|240:1318|301:0|293:1|294:50
 

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Do you know what kind of signal it requires from the speed sensor? I like this idea and am thinking it might be a nice mod to get a tad more power and a tad less weight out of a 944 I'm building for the track. Just wondering if I should expect to build a circuit to convert the speed signal from the 944's tranny to some other waveform.

~russ
 

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Cool, so just a sin wave probably. Perfect. I can just throw it on a bench and use a function generator to see what frequency it needs to see to cut off, then an osciliscope on the speed sensor from the 944 should let me know if I need to put a chip between them to change the frequency.
 
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