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Discussion Starter · #1 · (Edited)
I have installed the VMAX quick-ratio steering pinion in my 91 MR2. The steering gets very heavy (not enough assist) in sharper corners after braking hard. This is apparent on the street, but an even bigger issue on auto-x courses. This is caused by the EHPS ECU not recognizing the drop in speed quickly enough to bring up the pump power level. Even unmodified cars have this problem, but it is less noticeable with the stock ratio rack.

Toyota addressed this issue in later model years, beginning in 94 (or possibly 93). IIRC, the EHPS updates also reduced the assist at high speed.

In my car, I installed a 94 EHPS ECU & pump motor. I no longer have problems with heavy steering as described above. The steering works great. This is not a complete plug-n-play solution, as Toyota changed the wiring slightly between 91 and 94. The wiring diagram pic below shows what needs to be done. Cut one wire and repin one wire on the ECU connector. The "MTL" wire moves from pin 21 to pin 25. Pin 25 is a larger terminal, so you'll have to cut off the old one and solder on a new one. The larger terminals are used in lots of connectors on Toyotas, so look in your parts bin, or raid a U-Pull-It yard for some connectors from a mid 90s Camry or whaterver.




After researching the EHPS fluid issue, I choose to refill the system with Amsoil synthetic PS fluid. Working fine so far. The 1995 wiring is the same as 94. However the 93 wiring diagram does not show the MTL wire at all, so the 93 wiring diagram is in error, or the 93 is unique. If that's the case this may not apply there at all.
 

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Very interesting...I've had much the same issues with my 93 and quick steering pinion on autox courses and particularly when braking and turning. I've sort of gotten used to it but other drivers have told me it feels like the power steering is cutting out.

Where did you get this information from? How do you know it's an ECU issue detecting drop in speed? If I just replace the EHPS ECU with a 94+, will that solve the issue? Or did the motor change as well?
 

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Discussion Starter · #4 · (Edited)
hotnickels said:
Very interesting...I've had much the same issues with my 93 and quick steering pinion on autox courses and particularly when braking and turning. I've sort of gotten used to it but other drivers have told me it feels like the power steering is cutting out.

Where did you get this information from? How do you know it's an ECU issue detecting drop in speed?
I only have foggy recollections from a technical preview seminar on the updated 93 MR2 that a Toyota engineer gave at the Toyota MR2 club event at Laguna Seca in late 1992. I also seem to recall a magazine review of the MK2 in 1990 complaining about the "new" electro-hydralic power steering "falling behind" in some situations.

The 93 brochure mentions "improved computerized rack-and-pinion steering..." And since the ECU has gone through several revisions, we can conclude there were changes (presumably improvements) made over the years.

If I just replace the EHPS ECU with a 94+, will that solve the issue? Or did the motor change as well?
The newer pump is designed to be backward compatible with 91-92 cars, so I *think* you just need to update the ECU. BTW, if you just install a 94+ ECU without making the wiring changes, the EHPS will not work, and it'll throw a code 13, which isn't even in the 91 or 93 manuals.
 

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Interesting.
I never had this problem show up until this year. I know my relay is going bad because my EHPS woul cut off sometimes & not come back on & the "P/S" light would come on & I would have to raise the hood, cool off the relay & then do the on-off-on-off-on-off trick to get the EHPS to come back on.

This makes me wander if the earlier cut offs, where the EHPS did not cut completely off, was because of the issue you mention here. I do have the V-Max pinion, but again, I never felt this until this year & I have had the pinion on for 3 years (3 SCCA local AX seasons).

I will have to look into this too now. THANKS!

Daniel :thumbup
 

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Interesting. I have never really noticed this issue, but I will have to pay closer attention this this in the future. This may be something I end up wanting to do.

I imagine that a 93+ JDM ecu would be the same / have the same improvements. If so, then all of the people parting out later model JDM cars (there are several a year it seems) would have one, or you could always have one of the JDM parts suppliers find one for you. Finding a USDM 94+ ecu might be a bit tougher.
 

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Discussion Starter · #9 ·
I got my ECU & motor from someone parting out a US 94T, but yeah, that doesn't happen too often. I would expect a 93+ JDM EHPS ECU to have the same updates, but can't verify this. And most folks only get rear clips (EHPS ECU is in the frunk). Not as easy to find complete JDM cars. Perhaps in Canada.
 

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I have a 93 JDM and the P/S was first thing I observed compared to a friend's 92. It is generally heavier but gives you better steering input. It has a slight delay but it could be from my after market steering wheel adapter that's binding slightly. It never seems to cut out during quick or sharp turns in auto x but still feels heavier than the earlier model year. This made me think of swapping the 92 ecu at first but changed my mind in the end thinking that the off assist transition of the P/S is sooner from 93 up specially up speed. I might just do that for comparison. The motor does draw a lot of current even dropping my voltage to 11.2 on end to end steering at Idle RPM's which could be the case during hard braking. Higher RPM's no probs though.
 

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I finally fixed my heavy steering problems using the correct adapter for my Nardi steering wheel. My old one was for generic fitment for MR2 and may have been for spyder or aw11, nevertheless, I modified to fit but caused some unknown binding and play engaging the steering angle sensor. I can confirm on my end that 93 ps ECU should have the updates with no issues on power assist during hard braking when cornering.
 

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Well the JDM one didnt work for me. Threw a PS light and had no power steering at all. Part number was 89650 17080

Edit: I got the JDM power steering ecy to work. I cut wires 8 Y-G and 21 W and added pin 25 and soldered it to the large B-Y wire that goes to the pump. This replicates the 95 wiring schematics found in the DL section on here.
 

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Just to clarify for anyone else attempting this, the pumps ARE different, but you can make the 91 pump work with the 94+ ECU. This is what donteatbugs is talking about here:

donteatbugs said:
Edit: I got the JDM power steering ecy to work. I cut wires 8 Y-G and 21 W and added pin 25 and soldered it to the large B-Y wire that goes to the pump. This replicates the 95 wiring schematics found in the DL section on here.
Basically, if you examine the pump portion of the wiring diagram on the 91 vs 95, you will see that the 91 has one wire to one side of the pump, two wires to the other side, and then a third wire (that goes to pin 21 on the ECU) that runs through some sort of internal switch in the pump. On the 95 there are two wires to each side of the pump, and the pin 25 wire goes to the same location as the large black / yellow stripe wire. The internal switch is gone.

So what you need to do in addition to eliminating pin 8 and moving pin 21 to pin 25 is swap (at the pump end) the white wire that is now in pin 25 so that it connects to the large black / yellow striped wire. I did this by de-pinning the white wire from the small connector and the big B-Y wire from the large connector. I then soldered a short (2" or so) piece of wire to the spade connector on the B-Y wire, tinned the other end, so it formed a pin, and stuck it into the end of the white wire, and then heat shrinked the connection.

Sorry, I realize this is a repeat / summary of previously posted information, but I had a bit of trouble figuring out what exactly needed to be done and I figured it was worth re-posting with a little more detail. For reference, this was with the latest model JDM ecu, p/n 89650-17081
 

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For convenience, here are a handful of P/S ECU part numbers and info I could find on them. ECUs likely to improve steering response after heavy braking and initial turn-in (auto-x scenario) are in bold.

To-do: add confirmation on model-year and performance for each ECU model

Older style ECUs:
89652-17011 JDM/EU/UK SW20 3SGE/3SGTE 1990/1991?
89652-17021 USA/EU SW20/SW21 2SGE/3SGTE/5SFE 1991/1992?

89650-17010 JDM SW20 3SGE/3SGTE 1990?
89650-17011 JDM SW20 3SGE/3SGTE 1991?
89650-17012 JDM/EU/UK SW20 3SGE/3SGTE 1992?
89650-17020 USA SW20/SW21 3SGTE/5SFE 1991
89650-17021 USA SW20/SW21 3SGTE/5SFE 1991-1992
89650-17022 USA SW20/SW21 3SGTE/5SFE 1991-1992
89650-17030 JDM/EU/UK SW20 3gse 1991-1992?
89650-17040 USA/EU/UK SW20/SW21 3SGE/3SGTE/5SFE 1993?

Possibly improved ECUs:
89650-17050 JDM SW20/SW21 3SGTE 1993?
89650-17060 JDM SW20 3SGE 1993?

Improved ECUs:
89650-17070 USA SW20/SW21 5SFE 1994
89650-17080 JDM/EU SW20/SW21 3SGE/3SGTE 1994?
89650-17081 JDM/EU SW20 3SGE/3SGTE 1995?
89650-17090 USA/EU SW20/SW21 3SGE/3SGTE 1994
89650-17091 USA/EU SW20/SW21 3SGE/3SGTE/5SFE 1995+?
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