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. 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 hp with no load, 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 take longer for the pump to wind down 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 for P/S Schematic


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

 

Brilliant!

 

Great stuff! I still need to get Jeff@SPMS to do this for me.

-Charles

 

Hell yeah Im next in line for this set up!! Tight work!!!

 

Excellent work. Anyone want to buy my 92-95 mr2 setup? lol...

 

best thread of 2009, i gotta get me one of these pumps.

 

I am interested

 

Don't know how I missed this. Great job on the write up

This is on my growing to do list.

 

I believe kommon's conversion has the pump mounted in the same place as mine. However, it wouldn't be hard to mount it somewhere else in the bay.

Thanks for the compliments everyone.

 

so i was really interested in getting this going i call the toyota yard and they are out of the 91-95 pumps, (just like 98specR said), and they have the newer pumps (again just like he said).

The price was 275 for the newer motor.

98specR how much did you pay for yours?

 

I would definitely keep calling around. I purchased my 2005 pump for $150 shipped plus $20 for the pressure line. In my experience the older pumps go for between $75-$250 and the newer ones go for between $100-$250. Most of the junkyards I called wanted no more than $200 shipped for the 00-05 pump.

Don't forget to ask for the pigtail!

 

there are a few on car-part.com for under 100bux

 

Great setup, definatily going to consider this one. Also looking into eps systems at the moment..

 

way out there, but a lot ofhondas are starting to use electric pumps, correct? if so, why not use a honda pump considering there are probably a greater quantity than MR2 spyders in the junkyard.. just a thought..

 

No, the new Hondas all use electric racks. No fluid involved.

 

AH!!! that would be why. thanks for the clarification. carry on!

 

Where go B2 "Speed Signal" ?


Note : I Paid my pump 255 us + shipping on ebay

 

Guys, ran across this post after doing a google search.

I have recently completed a PS conversion using the toyota pump from a 2000-2005 MR2. I am not using the stock lines, just AN 6 lines. I was wondering if you guys knew if the pump lines have a restrictor in them?

When turning the wheel quickly, it feels as though the pump cant keep up. I wasnt sure if the pump is running out of volume or pressure, or if its the lack of a restrictor. Im using a mustang GT rack in a FFR GTM.



Does anyone have any specifics on the pump, such as pressure, and flow the pump is capable of?

BTW, I have a friend that has developed a controller that interfaces with this pump and which can take a signal off an ABS wheel sensor that is configurable to allow boost based on speed. The other option is the boost can be controled with a dial/pot... so you can dial in the boost with a simple dial. I can update you guys on the progress if you like.

I just installed the controller this weekend and it works great... I will be getting the controller that has the dial/pot option in a few days so can report on that as well.

David

 

With our Hondas we can just use the electronic speed sensor that sends signal to the odometer.

 

Do any of you guys know the flow rate of the 2000-2005 Toyota pump?

David

 

This sounds sweet, but I'm not seeing any pictures and the links do not work?

 

Very nice!

 

^^^^^^^^^^^^^^^^^
kart much?

 

Beware using an6 lines on the pump. The pressure is typically in the 1,000-1,200 psi range. I'm surprised that you have not blown a line yet.

I'd be very interested in more info about the speed based controller. I have the older style 92-95 MR2 electric pump, and I'm missing an integral part of the system to have the full blown speed/load based control of the pump. However, the older pump is known to draw upwards of 70 amps at times, so I'd need to know that this controller can handle that kind of current.

 

I know the pump's maximum output pressure is about 1200 psi; however, I'm not sure of the flow rate.

No leaks or blown lines here. I used all factory lines (MR2 p/s pressure line from the pump fitted with a piece of Honda pressure line to the rack). The 6-AN to 5-AN reducer, tube nuts, and tube sleeves are all steel. I believe they are rated up to 3000 psi.

On a side note, I know Kiwi used aluminum AN fittings on his EHPS conversion in his write-up without any problems.