MX73 Cressida power steering woes
Posted 06 June 2012 - 07:44 PM
Basically have just acquired an '88 Aus-spec MX73 Cressida with 5M-GE and the power steering is doing some funny things. It has the speed sensitive power steering so has a little ECU box which gets a signal from the trans speed sensor and then modulates a solenoid on the steering rack adjusting the power steering fluid flow/pressure depending on speed the car is travelling.
Well anyway something isn't right with it - it generally has super light and sensitive steering assistance at road speeds but once you slow down to a halt the power steering assistance is severely limited as if it's not quite assisted at all, but you can feel some assistance there. The limited assistance at stand-still is intermittent though, sometimes it has full assistance which is good as that's how its meant to be however the assistance doesn't tone down as the car builds up speed like it should.
Things to note:
- Spence had an oscilloscope on the system and could verify the trans was giving the steering ECU a speed signal but the ECU wasn't giving any output to the solenoid on the rack.
- I did find that the solenoid was unplugged from the wiring loom but I figure it was like that because Spence didn't plug it back in after prodding around testing with it. I plugged it back in and it made no difference anyway.
- I have replaced the steering ECU with one from an NZDM 85ish MX73 Cressida which had a different part number but looked identical and had the same plug. Again no difference whatsoever with plugging in the replacement ECU.
- The original power steering pump has a little vacuum sensor/switch on the base of it which has been removed and plugged up with a bolt. I am waiting for a replacement power steering pump with sensor/switch to arrive from NZ and will swap it over to see if it makes a difference.
- Worth mentioning is the wheel alignment is out after replacing a rack end which is probably having some effect on it wandering from side to side at road speeds and generally amplifying the affects of the over-assisted steering.
- When taken for a RWC (basically a WOF) the inspector pulled up the steering dampner as a fail as he felt it was too soft. He explained that it should be like a shock absorber and extend when compressed however I feel if that were the case then the dampner would try and push the steering rack constantly to one side. Having never felt another MX73 dampner I don't know if mine is really soft or not.
Any ideas would be most welcome, thanks!
Posted 07 June 2012 - 08:19 AM
as they start to fuck out and score the vane plates they loose pressure, but when they are in that wonderful transition zone between fucked and still just working sometimes the stars align and they produce correct pressure at idle, most of the time they dont.
it gives you that erattic "sometimes working, sometimes not" feeling.
Posted 07 June 2012 - 10:19 AM
Posted 15 June 2012 - 06:09 PM
Wrong pump fitted.
And a very distant 3rd place goes to.
Faulty solenoid on rack, this is a known problem with this model. (stuck in one mode or the other doesn't change back and forth).
One other option just jumped into my head.
At some stage someone has replaced the 2.8 rack guts with a 2.0 spec guts? Long shot/hail Mary, some of those Aussies are almost our equals when it comes to dodgy repairs.
Posted 15 June 2012 - 06:15 PM
Basically after driving it more and more I've come to the conclusion that the wandering at speed on the road is due to a fucked rack - there is no play at the tie rod ends or on the rack ends, but you can move the input shaft a few mm in each direction and the direction of the wheels don't change, there has to be a good 50mm+ of free play in the steering wheel. I think the power assistance issue is another issue altogether, whether it be a dodgy power steering ECU, faulty solenoid on the rack, or maybe even dodgy signal going to the power steering ECU. I did notice cruise control doesn't work and I assume the cruise ECU gets its signal from the gauge cluster as well.
The pump arrived from NZ but haven't had a chance to fit it. I've gone and bought a spare rack, another pump and another steering ECU so I should just about have at least two of everything to swap in and out to try sort it out.
Posted 23 June 2012 - 08:00 PM
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