Hi Guys, Happy Sunday. It is time I raised my hand and asked for some assistance. This is not urgent, but it's getting annoying and I'd love to clear it up on my 1998 Convertible.

Issue: Power Steering Intermittent issue

Description: When I am at idle or at very slow speeds (parking speeds) and turn the wheel and I hear a short clunk from the steering rack when I change the direction of the steering wheel (from pointed left to right; pointed right to left. Straight to either side). Then at idle or very slow speeds I hear a creek that frankly sounds like a wooden door to a haunted mansion that hasn't been opened in years as the wheel is rotated. This creaking sound continues for pretty much the entire motion of the wheel turn.

While this is occurring, power steering is a bit harder to turn, but: I can still rotate steering wheel with one finger.

Like I said this is intermittent. It has nothing to do with engine speed or power steering fluid level, or engine temperature.

History: I went through a few weeks where I was frustrated while driving at highway speeds. It felt like the steering was in a rut, you needed initial effort to change direction that wasn't normal, Then I felt like steering did not self correct to perfectly straight. Almost like what I describe here happened at highway speeds back then. So, I had an Alignment - no improvement

At that time, we had a discussion about the Variable Assist Power Steering (VAPS) in these cars and that it may be the root cause. I hoped for a simple blown fuse.

I checked the fuse all OK but pulling and re-seating the fuse seemed to clear this problem. No issues at all for a few weeks.

Now I'm back to dealing with some type of intermittent issue at low speeds as described above.

I saw the great TSB's that Motorcarman posted for power steering in the past. Not too much pertinent to this issue. Closest one described a clogged power steering fluid filter. Can I dismiss this because it is an intermittent issue?

If anyone has the time and feels like posting a primer on how power steering works in X100s I'd love to learn.

In the past folks have discussed a "VAPS relay" - Is there then a connector on the steering rack that I could check for continuity? Where should I look?

If power steering was not working at all, I couldn't turn the wheel with one finger while parking right? If yes, what in the world could be causing "partial" power steering assist?

Could it be the car is "cutting" down the assist like it should at 60mph? Where would I go to test/trouble shoot this?

Thanks for looking. I'd sure like to do an evaluation to troubleshoot this one but as you can see I don't know where to start or exactly where to look.

Any thoughts/diagrams/assistance will be appreciated.

Thanks,

John

 

The power steering "resistance" seems to be dependent on a signal from the instrument pack with vehicle speed data.
This goes to the "steering control module".

Power for this module comes from fuse #12 (10amp) in the driver's side fuse box (at the end of the fascia) but this fuse also powers various other bits of kit as well, so although it's perhaps worth checking, I suspect it's not the culprit.

Could it be a faulty connector / wire on the steering rack itself ?? I can't really visualise how this "variable power" system works as there doesn't appear to be an electric motor or any other "gubbins" on the rack so I really don't know how the resistance is controlled in the sense of converting that speed data into some sort of mechanical resistance.

Any 'proper' experts out there ?

 

Nope , but there is a connector down in the elements that could limit the command to the valve . The cleaning of the fuse as you slid it out seams to have helped . There are probably some other things the fuse to the steering ECU connect to that can be sucking the power down to power this ECU . Some models do not have this variable option so you would have to look at the steering rack and look for wires . From my understanding the voltage to the rack solenoid comes from a refereed to as amplifier as it changes the voltage value so you can short out and destroy this amplifier if your meter testing probes touch . This is testing reference from ZF , my not be the correct model number but it's the same method / operating principle . See page 35

 

Have you tried removing the fuse for the variable power steering when the intermittent fault occurs to see if there is any change?

If you look into this you will find you can disable the variable power steering and either have permanent full assistance or permanent no assistance, depending whether you cut the 12v supply or the speed pulse data. Maybe rig up a couple of switches to allow you to do this and see how the fault changes.

 

Jack the car up to get the front wheels off the ground. Then while all on jack stands turn the ignition on but do not start the engine. Rotate the steering wheel through its full travel left and right. Do you feel the clunk and the squeak that you're talking about? I'd be looking at the tie rod ends where they meet up with the power steering rack. I've seen them lose lubrication and get rusty in there and sieze.

 

I think the amplifier output voltage swings between 9 to 15 volts so if you tinker as a modification to put B + voltage ( around 13.5 ) on the servo you might get it on one side of the soft or firm range ,cant remember . As the amplifier fails it should go to firm as a engineering point of veiw to a fail safe mode . But with the information I had at the time the design was backwards but then I didn't consider complete power source interruption . If you tinker and short the named amplifier in the ECU you'll be behind the curve to restore it to what you want with a replacement ECU . Been there in the airlines on compass wiring syncro systems .

 

Lady P, good suggestions, but where is this amplifier? Anyone know?

Later today I will pull the fuse and evaluate the impact.

Yesterday she was driving fine then it all happened again. Gotta figure out what caused it to swing.

Re lifting front off ground. We, the alignment mechanic and I did this 3 weeks ago when this started. Was very hard to move suspended wheels, his diagnosis was failed power steering. At same time could see this clunk is inside steering rack.

Think still unanswered: if I can turn wheel with 1 finger while stopped - may I assume some level of power steering assist exists? Gosh that was sure true on my XJ6.

Thanks for your ideas, will update later.

John

 

[QUOTE]Was very hard to move suspended wheels, his diagnosis was failed power steering. At same time could see this clunk is inside steering rack./QUOTE]

if you already determined that it is a mechanical issue, why are you chasing electrical gremlins?

Get it back on the rack and do a systematic investigation. Disconnect the left tie rod at the wheel and exercise the steering. See if there is a change. Do the same for the right and test again. Examine the column u-joint for play and freedom of movement. If you eliminate all the above, the rack is then your problem.

 

You asked why I'm chasing gremlins. Fair question let me answer:

1) problem swings. Not typical for mechanical issue I thought.

2) seems to be related to variable power steering assist. Zero info on component location, or troubleshooting.

3) price of replacement steering rack scares me. Want to be sure of what's broken.

If I'm missing something, please wake me up. At this point any diagnosis frankly falls into the old shotgun approach.

Your 2nd paragraph mentions some logical deductions, thank you for that. Perhaps I will have to disconnect the ride. But please explain, what am I eliminating with this idea, the wheel, it's suspension. How would this help isolate the rack, IOW what has critically changed in the equation?

Don't take my question the wrong way, it is earnest.

John

Gosh I don't even understand XK8 power steering racks well enough to picture what may be intermittently happening.

 

Let's start at the beginning. If you did a test with the wheels off the ground and the engine not running, and you experienced the issues that you listed in your posting, then the electrical part that you've been chasing would not be the issue. In this case it has to be something mechanical.

The steering is not just the rack. It includes the components that transmit the steering rack motion to the uprights, which brings ball joints and tie rod ends into play, and should also include the column u- joint.

if you are able to replicate the problems that you're having with the wheels off the ground and the engine not running, then the systematic process of disconnecting components can help you isolate where the problem is.

 

First I want to thank Lady P, I just saw the great article he posted on the steering rack. THANKS!

I pulled the fuse while this was happening, could still turn wheel with 1 finger, but much tighter feel to steering. Problem still existed.

I'm beginning to think this is a bad power steering rack.

Want to read the document further, then scan the TSB that discusses clogged filter screen for power steering fluid.

Will keep you posted

Thanks John

 

If the steering rack needs a rebuild call Coventry West, one of our sponsors. I'm not sure if they do XK8 but I know they rebuild a lot of other Jag racks.

 

Your description of the symptoms strike me as mechanical, not electrical. My first thought is that the rack mounting is damaged. Next, a failure in the steering column. I have heard of columns needing replacement. I have also heard of tie rod end ball joint failures inside the rack. You will need to get a helper, put it in the air and start moving it around, listening with a stethosope.

 

Wanted to close this one out. All is now back to normal.

Replaced defective lower ball joint. This made a huge improvement. I could move the ball in out by hand, Lord knows what a few thousand pounds did to it while driving.

Changed power steering fluid- small improvement in wheel feel.

New lower bushes. Done same day as ball joint. I think ball joint made biggest improvement.

Thank you all for your help with this one. I thought i was going to have to find a new sterring rack. That would have been a big waste of money.

This issue is resolved.

Thanks John

 

Well done....