MX73 Cressida power steering woes

phillip.weston, Jun 6, 8:01am
Hey guys thought I would chuck this up here to see if anyone could be of any help.

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:

- The previous owner 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 the PO 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!

phillip.weston, Jun 7, 4:56am
Well obviously all the advice I give on here is totally reciprocated.

bellky, Jun 7, 4:57am
But you're an expert!

craig04, Jun 7, 5:00am
It's a pity you haven't gotten any advice as you are one of the most helpful unbiased posters on here. I sorry I can't help though.

saffa2, Jun 7, 5:02am
Wish I could help, I have an '88 grande mk11 diesel which I believe is the same platform at 400,000km but apart from one steering belt it's never had a steering problem.

gmphil, Jun 7, 5:03am
had a prelude do that when i was a young fella after clutch change the fella that did the clutch broke of a little vacum hose from bottom of gearbox

bellky, Jun 7, 5:04am
Maybe it's out of petrol, I mean fuel.

gmphil, Jun 7, 5:05am
when it turn purple its because ur hands to tight

bellky, Jun 7, 5:06am
You're the expert.

thejazzpianoma, Jun 7, 5:24am
I have zero experience with these PW. However since you are head scratching, one thing I would do that it looks like you havn't yet is change the power steering fluid. (Siphon out and refill, turning the steering with the engine running to get it to pump out the last of it).

Variable assistance aside, when power steering assistance comes and goes like that a change of fluid often seems to solve the issue. I would assume it helps free up sticky valves etc in the system. I have come unstuck in past looking for the complicated answer with sophisticated systems only to have occams razor prick me in the bum.
BTW, what colour is the fluid and is it foaming or doing anything weird!

I assume you havn't changed the fluid because of the replacement box coming and were going to do it then.

My only other thought is to be suspicious of the blocked off valve.

Other than that, if it were me I would have my scope out and be logging whats happening through the course of the drive and tracing things that way.

Sorry, probably not anything you havn't thought of but since you have had no other responses from someone with actual experience with these thats my 2C.

Happy troubleshooting!

mm12345, Jun 7, 6:02am
I agree about the steering damper - there's no way it should "spring back" when compressed, and IMO unless the inspector removed it, he's working on nothing more than a guess as he's got no way of assessing how much resistance it's offering, nor probably any real idea of what it should be.
I'd wait to refit the sensor on the PS pump. then see what happens.

fordcrzy, Jun 7, 7:08am
are they the same racks as the early supras! maybe the supra forums may help!

panicky, Jun 7, 7:29am
Hook up power straight to the solenoid, you should hear it click.You should also get battery voltage between B+ on the ECU and earth with the ignition switched on.Also check that the earth is actually connected.

phillip.weston, Jun 24, 12:16am
to those who cared, I got it sorted with a replacement rack. The rack which had come out had actually been reconditioned in the past but it still had a good 50mm of free play in the steering wheel and was leaking fluid out the input shaft seal. Seems with the new rack with the original power steering pump and suspected dodgy power steering ECU it's all functioning fine - so strange to see a faulty rack exhibit many issues all at once.

jason18, Jun 24, 2:54am
Hey Phil, wish I saw this thread earlier I would have suggested that ;) Or shoulda kept the camry or bought a mitsi as those toyotas are unreliable

phillip.weston, Jun 24, 3:27am
hahah! nice one jase.

keeping the camry was a no-go, rego was due on it and I couldn't justify spending $400 on something I absolutely detested driving.

speaking of Mitsis I've found a couple VR-4s I'm considering buying. Damn expensive here in Australia though!

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