Steering problem in LR4 - Strange one

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Zunni

Member
Posts
16
Location
Iceland
My 2013 LR disco 4 has a strange steering issue. When cold in the morning it's like new. But when the engine heats up the steering becomes heavy, gives out a dim squealing sound and I need to give it gas so I can turn the wheel....

Could it be: The power steering pulley is misaligned?
 
More likely the PAS pump is worn out / faulty.
What mileage has the car got?
I had to change the pump on our RR mk3 at 125,000, but obviously many last much longer.
 
I'm afraid "fine when cold" is a common faulty pump symptom.
When its cold the fluid viscosity is higher so its easier for the pump to generate higher pressure. Once the engine and pump have been operating even briefly, the oil viscosity reduces & eg if there are internal leaks within the pump, the pump output will drop.
The pump is designed to generate the required 100+ bar pressure for full assistance at engine idle & then a pressure limiting valve keeps it at that pressure as the engine speed increases so the assistance doesn't vary at different engine speeds.

If revving the engine gives you more assistance, it means the pump isn't generating the designed pressure at idle, but increases output at higher rotation speed,
Those are exactly the same symptoms I had on our RR.
I tested & changed the servotronic valve & the Body Control unit, but found no faults / change in symptoms before finally accepting I'd have to break into & test the hydraulics. I even connected the servotronic valve to a permanent 12v supply to eliminate electrical control issues & maximise the servotronic additional assistance. Steering was still really heavy at idle/ vehicle stationary.
I fitted a pressure gauge to check the pump output & I was only getting 10 bar at idle and 30 bar at 3000 rpm (It should develop 110 bar at idle and above).
I fitted a replacement second hand pump & problem was gone - 110bar from engine idle upwards.
 
I'm afraid "fine when cold" is a common faulty pump symptom.
When its cold the fluid viscosity is higher so its easier for the pump to generate higher pressure. Once the engine and pump have been operating even briefly, the oil viscosity reduces & eg if there are internal leaks within the pump, the pump output will drop.
The pump is designed to generate the required 100+ bar pressure for full assistance at engine idle & then a pressure limiting valve keeps it at that pressure as the engine speed increases so the assistance doesn't vary at different engine speeds.

If revving the engine gives you more assistance, it means the pump isn't generating the designed pressure at idle, but increases output at higher rotation speed,
Those are exactly the same symptoms I had on our RR.
I tested & changed the servotronic valve & the Body Control unit, but found no faults / change in symptoms before finally accepting I'd have to break into & test the hydraulics. I even connected the servotronic valve to a permanent 12v supply to eliminate electrical control issues & maximise the servotronic additional assistance. Steering was still really heavy at idle/ vehicle stationary.
I fitted a pressure gauge to check the pump output & I was only getting 10 bar at idle and 30 bar at 3000 rpm (It should develop 110 bar at idle and above).
I fitted a replacement second hand pump & problem was gone - 110bar from engine idle upwards.
Thank you very much for your detailed answer. Now I can take it to the garage.
 
Lack of assistance when hot can be down to the belt slipping when hot, or the fluid gone off, or the pump not sealing internally when hot. Deal with each in that order. ;)
 
Not sure what engine you have and therefore the difficulty / cost of replacing the PAS pump.
Ideally you need the pump output tested to confirm the fault diagnosis & ensure they aren't replacing a good pump - otherwise you could potentially waste £300 plus.
A good garage will have the test equipment or be able to put it together relatively cheaply.
On our 3.6 TDV8 RR installing the equipment & doing the tests probably took me a leisurely couple of hours & the test gear cost me approx. £60 - so the a garage could easily charge you £100+ to do the test.
Replacing the pump was problematic due to the pump location & took me 4 hours + & the cost of the pump was additional (typically £250 0r so for a "genuine" ZF pump.
I was lucky the second hand pump I bought for a lot less happened to be good (I'd bought it only to check the connections to allow me to put the test equipment together before taking the car apart)
 
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