Electrohydraulic Power Steering

[t vago]

As the title hints, I think I will pursue installing one of these critters into my Dakota. I have a 2001-2005 Toyota MR2 power steering pump module (a combined electric motor, pump, reservoir, and controller), and I found these nice instructions over here at DIYElectricCar.com.

I should be able to re-install the stock crank pulley (I swapped it with an underdrive pulley a few weeks ago and saw a whopping 1% improvement in FE), and once I do that, I should be able to get a shorter serpentine belt that would bypass the factory power steering pump altogether.

I am looking to get more than a 1% FE improvement. Specifically, I am looking at a target of around 3%, which would raise my average FE from around 20 MPG right now, to around 20.5 MPG. Not much, to be sure, but I already have most of the needed equipment floating around already in my garage - 60 amp rated relay, 4-gauge fuse holder, 4-gauge wires, electrical connectors of all sorts (crimp+solder and Weatherpak) 18-gauge wires, power steering return line, factory service manual, and (of course) the pump unit itself. I just need a pressure hose with a 16mm x 1.5 inverted flare fitting on one end and a 18mm x 1.5 o-ring fitting on the other end, a custom-made mounting bracket (and a mounting point), and a shorter (~82 inch) serpentine belt.

The big challenge I am seeing right now is where to install this thing. It's not very small, and of course the engine bay is a little crowded.



Not quite my engine bay, but similar enough so that you can see what I'm dealing with.

[Tygen1]

Very nice, keep us up to date!

[ConnClark]

looks like your a prime candidate to use George and I's alternator improvement circuit

[oil pan 4]

If you are having too much difficulty finding room to stuff the electro hydraulic unit in there, here is what I would like to put in my car:
Hydraulicstore.com - 877.778.3533 -
Notice the replacement pump clutch section.

[Frank Lee]

Were I do to something like that, I'd disconnect the pump and loop the lines to the box. Or get a manual box if there's one that'll bolt in.

[t vago]

I think I have found a good spot for the electric pump module ("good" meaning that it'll actually fit and be oriented correctly). However, there are a couple of caveats.

First, the stock power steering pump, reservoir, and PS fluid cooler will have to be removed as a unit. I will not be able to keep the stock unit in the engine bay and have the electric pump installed at the same time.

Second, the pump will very likely sit low in the engine bay, which will make checking the power steering fluid level somewhat of a challenge.

I think I can live with both of these caveats. I will make some mounting brackets to mount the electric pump module on the truck chassis, and then wire it up.

After some digging around, I could find the input and output pins on the pump module itself.

A1 - high amperage +12VDC
A2 - high amperage ground

B1 - idle up output to Toyota ECM (active high or active low?)
B2 - 4 pulse/rev speed sensor input
B3 - "TC" diagnostic connector
B4 - N/C
B5 - EHPS relay control (active low)
B6 - WOT cutout input from Toyota ECM (possibly active low)
B7 - "TS" diagnostic connector
B8 - N/C

C1 - switched ignition +12VDC
C2 - "SIL" diagnostic connector
C3 - N/C
C4 - warning lamp output (possibly active high)

So, it should be a simple matter to come up with a T flip-flop to interface my truck's VSS output (8 pulse/rev) to the input of the pump. I will probably rig up a small relay that switches a ground signal, controlled by the idle-up signal, that would be fed as the power steering pressure switch signal into my truck's engine computer. I'll probably end up using some sort of comparator circuit, taking its input from the throttle position sensor, which would provide the WOT cutout input for the pump module. Wiring up the warning light ought to be pretty simple, too.

[mwebb]

you have not made mention of the steering angle sensor input , to the power steering computer / controller / black box

on VW Audi this is a critical input delivered by the network to the steering rack which has the PS pump built in

key work here is
network -
no doubt the partial toyota network that may exist in the p/s unit does not communicate with the dodge network .

it may function anyway as the VW PS systems will function even if the system codeing is set incorrectly so that the system looks for the steering angle sensor in the wrong location -
but - those systems set DTCs - every where

the WOT cutout can be sampled at the AC compressor as it has a WOT cutout as well , the TPS is not a good choice for this input .

[t vago]

Originally Posted by mwebb

you have not made mention of the steering angle sensor input , to the power steering computer / controller / black box

I have not made mention of such a sensor, because this particular module does not require such a sensor. It uses an internal hydraulic pressure sensor to sense demand. The older MR2 EHPS used several modules and sensors, including what you're describing. This one is from a newer MR2, and is almost completely self-contained.

Originally Posted by mwebb

no doubt the partial toyota network that may exist in the p/s unit does not communicate with the dodge network .

it may function anyway as the VW PS systems will function even if the system codeing is set incorrectly so that the system looks for the steering angle sensor in the wrong location -
but - those systems set DTCs - every where

You're right. However, this is not a concern. This module was not designed to be smart enough to require a network for operation - CANBUS, ISO, J-1853, CCD, or otherwise.

The pump will still operate, regardless of whether or not I hook up the WOT cutout wire and idle up command wire. Those two wires are "nice-to-have" wires, but they're not strictly necessary for operation.

The speed signal wire is the most important signal wire, because it will allow the module to determine when to reduce its output power. The warning lamp signal is the second most important signal wire, because that will tell me if something's wrong.

The diagnostic wires are not going to be hooked to anything, since they only went to a diagnostic connector on the MR2 to begin with. This module was never interfaced with the MR2 network.

Originally Posted by mwebb

the WOT cutout can be sampled at the AC compressor as it has a WOT cutout as well , the TPS is not a good choice for this input .

Not entirely sure how this would work. Do you mean that I should tap the wiring that drives the A/C compressor clutch?

[t vago]

*cough* *cough* *cough*

Wow! This old thread sure gathered a lot of dust! Hope I don't catch a cold from all of this dust I knocked off of it!

Anyhoo, basically gave up on trying to attach an air conditioning clutch to my existing power steering pump, and am re-pursuing this MR2 pump option. I think I found a good spot, too. I'm going to attach the pump to right below where the battery sits. With the existing power steering pump removed, the MR2 EHPS fits right in. I have to get an 82 inch length drivebelt.

Had to order some Summit Racing fittings to construct a supply hose, and the parts should get in by Thursday.

Thinking of programming an Arduino to control the IDUP B1 pin to my truck's PCM, the EFI enabling signal B6 pin to the EHPS, do the necessary divide-by-two of the VSS signal, and drive an LED based off the warning lamp WL C4 pin. The Arduino would also get signals from the transmission control module and the brake lamp switch, so it could turn off the EHPS whenever the truck was in Park, or the brake pedal was pressed.

[t vago]

Some progress... Got the mount fabricated and bolted together. The mount will be attached to the battery brace. I had to remove the front bumper and the left fender for an unrelated reason, and the battery brace was right there for the taking. The stock power steering pump has been removed, and the serpentine belt has been replaced with an 82 inch length one.

The mount is made of aluminum square tubing, 1 in x 1 in, with a thickness of 1/8 inch. The bolts used are 5/16 in 304 stainless steel.

(click on picture for larger view)

Fiat Dakota with left front fender, bumper, grille removed


Front inner view of mount, off of vehicle


Rear inner view of mount, off of vehicle


Installed, inner rear view looking outboard


Installed, inner rear view looking outboard


Installed, inner front view looking outboard, next to coolant recovery tank