'95 Ls400 Steering Over Sensitivity

[dougs 400]

A couple of months ago, I had a new power steering pump installed in my LS400. Also had to replace the high pressure hose. While it was being done, I requested that the system be flushed and the various filters be cleaned. I am not leaking any more and the PS pump is not whining, but I have a problem. The steering is very sensitive now. Extremely so. What controls the variable ratio power steering on these cars. No gearing changes were made when the repairs wer made. But it is actually much more difficult to drive now. You can sneeze and run off the road, because the power assist is so sensitive. What can I do. The mechanics say there is nothing that could have changed---that I'm imagining it. I say bull sh--.

Any suggestions? Thanks in advance for any answers you can give.

[jpourcy]

A couple of months ago, I had a new power steering pump installed in my LS400. Also had to replace the high pressure hose. While it was being done, I requested that the system be flushed and the various filters be cleaned. I am not leaking any more and the PS pump is not whining, but I have a problem. The steering is very sensitive now. Extremely so. What controls the variable ratio power steering on these cars. No gearing changes were made when the repairs wer made. But it is actually much more difficult to drive now. You can sneeze and run off the road, because the power assist is so sensitive. What can I do. The mechanics say there is nothing that could have changed---that I'm imagining it. I say bull sh--.

Any suggestions? Thanks in advance for any answers you can give.

Hi Dougs,

Was it a brand new factory steering pump or a rebuilt one?

If it was a rebuilt one it seems like they didn't get the flow control valve correct. This valve can cause pressure that is too low or pressure that is too high if it is not done right.

Sounds like your pressure is too high.

Inside the flow control valve is a relief valve. It could have a faulty relief valve. The service manual says to change the whole control valve.

Jerry

[dougs 400]

A couple of months ago, I had a new power steering pump installed in my LS400. Also had to replace the high pressure hose. While it was being done, I requested that the system be flushed and the various filters be cleaned. I am not leaking any more and the PS pump is not whining, but I have a problem. The steering is very sensitive now. Extremely so. What controls the variable ratio power steering on these cars. No gearing changes were made when the repairs wer made. But it is actually much more difficult to drive now. You can sneeze and run off the road, because the power assist is so sensitive. What can I do. The mechanics say there is nothing that could have changed---that I'm imagining it. I say bull sh--.

Any suggestions? Thanks in advance for any answers you can give.

Hi Dougs,

Was it a brand new factory steering pump or a rebuilt one?

If it was a rebuilt one it seems like they didn't get the flow control valve correct. This valve can cause pressure that is too low or pressure that is too high if it is not done right.

Sounds like your pressure is too high.

Inside the flow control valve is a relief valve. It could have a faulty relief valve. The service manual says to change the whole control valve.

Jerry

Is the relief valve servicible or adjustable? Thank you for your help and reply.

[jpourcy]

Hi dougs,

Is the relief valve servicible or adjustable? Thank you for your help and reply.

No. According to the service manual it says to not disassemble or adjust the relief valve but rather to replace the flow control valve as an assembly.

Here is a quote from the manual:

"The clearance between the flow control valve and the pump body installation hole is very important. After manufacture, the factory measures the size of the installation hole and outer circumference of the flow control valve, and punches a mark accordingly. Therefore when replacing the flow control valve, be sure to do so with one having the same mark in order to insure the proper clearance."

It sounds to me that the hole in the pump and the diameter of the flow control valve have to be very precise. The illustration they give shows an "A" marked on the pump and an "A" marked on the flow control valve. Obviously you have to make sure that the pump has the exact size flow control valve. The inscribed marks should be A,B,C,D,E or F. If your pump has an "A" on it and your flow control valve has a "D" on it, then it is not right.

If the one you have is rebuilt, they could have messed it up. If this valve is not correct, it will cause your pressure to be too low or too high. Of course, the marks could be the same but the relief valve could be faulty.

According the the manual, the line pressure should be a minimum of 1067 psi at idle. It does not give a maximum, but obviously if it is too high, then your steering will feel a little squirrelly.

If this problem came up right after they changed your pump, it would seem to me that the flow control valve could be your problem.

Jerry

[forsash]

Here is a quote from the manual:

Jerry

My steering is too hard.

Could you mail me a service manual or tell where to download it? I can't solve my ps pump problem for a few month already. Tryed everything. alfor-4@yandex.ru.

[jpourcy]

Here is a quote from the manual:

Jerry

My steering is too hard.

Could you mail me a service manual or tell where to download it? I can't solve my ps pump problem for a few month already. Tryed everything. alfor-4@yandex.ru.

Hi Forsash,

I do not know where an online manual is but here is a parts breakdown of the pump:

http://www.toyodiy.com/parts/p_E_1994_LEXU...EPGKW_4502.html

Jerry

[forsash]

Here is a quote from the manual:

Jerry

My steering is too hard.

Could you mail me a service manual or tell where to download it? I can't solve my ps pump problem for a few month already. Tryed everything. alfor-4@yandex.ru.

Hi Forsash,

I do not know where an online manual is but here is a parts breakdown of the pump:

http://www.toyodiy.com/parts/p_E_1994_LEXU...EPGKW_4502.html

Jerry

Yeah? thanks Jerry. I have this picture. and more - i disassemble and assemble back my pump thanks to lexls. but I can't see where is the problem. I thought you have the manual...

[jpourcy]

Yeah? thanks Jerry. I have this picture. and more - i disassemble and assemble back my pump thanks to lexls. but I can't see where is the problem. I thought you have the manual...

I do, but it is not online, it is in book form so I will not be mailing it to you. If you are planning on keeping your vehicle and doing a lot of work yourself I highly recommend purchasing the correct service manuals for your vehicle. You can get them from:

Toyota Publications

1-800-622-2033

The price for a 1991 Lexus LS 400 manuals are (American dollars):

Engine $91.44

Chassis $94.75

Electrical $26.99

Your 1994 should be about the same. Power steering is in the chassis manual. The manuals will pay for themselves after the very first time you use them. I highly recommend getting them. It cost me $250.00 for the manuals and that is nothing compared to paying for mechanic labor on a Lexus. $250.00 amounts to just one small service fee at a Lexus dealership. Get the same manuals they have and do it yourself.

These manuals are huge. When you stack them up together they are about 6.5 inches thick. Tons of information. Definitely worth the money if you plan on doing a lot of work on your vehicle yourself. It will save you tons of money.

The tutorial on the LEXLS website is pretty good and follows the manual very close.

The flow control valve controls the pressure. If it is not working properly, Lexus recommends changing the valve. There is no rebuild procedure on the valve, you have to buy a new one. Rebuilding the pump does not rebuild the valve, it has to be replaced if it is bad.

This is what the manual gives on checking and replacing the control valve:

"If the flow control spring is not at least 36mm long, it needs to be replaced. They can compress over time.

To inspect the valve for proper working order:

(A the valve must be able to move in the valve hole of the pump under its own weight.

(B To check it for leaks, close one of the holes in the side of the valve and apply compressed air (57-71 psi, 392-490 kPa) into the other side, and confirm that air does not come out from the end holes.

If necessary, replace the valve with one having the same letter as inscribed on the front housing.

The inscribed mark will be: A,B,C,D,E or F.

In the flow control valve, there is a relief valve which controls the maximum pressure of the pump. The amount of this maximum pressure is very important; if it is too low, there will be insufficient power steering assist and if too high, it will have an adverse affect on the pressure hoses, oil seals, etc. If the maximum pressure is either too high or too low due to a faulty relief valve, do not disassemble or adjust the relief valve, but replace the flow control valve as an assembly."

If you have already rebuilt your pump, and everything seems to be OK, then your low pressure problem might be coming from a faulty relief valve inside of the control valve. This calls for changing the whole control valve.

This is all the manual tells us about the flow control valve. If it is bad, all you can do is replace it.

I hope this helps.

Jerry