Electro-Hydraulic Power Steering (EHPS) Conversion
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.
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 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.
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.
P/S Oil Cooler
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
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).