Pak_37

We're looking for advice from all the experts who have gone before us! We've read what seems like thousands of posts on the boost pump and its run times - and yet we are still looking for advice with our specific symptoms. When we start the car we get a combination of warning lights as follows: the Anti-Lock, PDAS and the ! lights all come on and we get the warning buzzer. The buzzer goes out but the lights stay on.

We have used a Motive Bleeder and bled the system. We don't have access to a Hammer so we have attempted a bleed of the drive links using the console switch.

We have no brake fluid leaks anywhere, however, we have what seems to be an excessive run time of the hydraulic boost pump. After the car has sat for 24 hours - the pump runs for 1 minute 15 seconds before it stops running. After 2 pumps of the brake pedal it runs again for about 7 seconds. The pump runs after every couple of pumps of the brake pedal.

We jumped pins 3 and 5 on Relay 51 and the pump runs, so we don't think its a problem with that relay.

We're wondering if anyone who as had the pressure switch go bad had similar experience with the pump running for a long time before the switch failed.

Any other thoughts or suggestions would be greatly appreciated!

ome911

Hi,
Having had a similar problem I can tell you that diagnostic testing is only of value to a certain degree. Your pump/relay is ok and you probably don't have air in the system. The fluid reservoir cap sensor is also worth testing but is probably ok. Generally the problem is that the pressure accumulator or/and pressure switch need replacing. My C4 was tested at a Porsche Centre and as no explanation could be found it was recommended that the accumulator be replaced- no change in the buzzer and lights. These sometimes happened at startup and sometimes while driving. Finally the pressure switch gave up the ghost and was stuck in the open or closed position (I'm not sure which- anyway the position where it says the pressure is ok when it's not). So no warning lights and no hydraulic pressure as the pump is not activated. I had a very hard brake pedal coming down a mountain road ! Replaced the switch myself after having a hex socket machined down so that it would fit over the switch. See (https://rennlist.com/forums/964-foru...placement.html) which I found useful.
Enzo

Rocket Rob

I would make sure that you have bleed your brake fluid reservoir (bomb). See

https://rennlist.com/forums/964-foru...-bomb-how.html

Pak_37

Thanks Enzo -- before your pressure switch went were your pump run times increasingly longer? Or did you get no real warnings until it just stopped working?

Also - what do you mean by a hex socket -- did you just use a regular deep socket and machine the outside so that it had a thinner wall?

Laker

+1

Pak_37

Thanks Rob -- we have bled the accumulator when we bled the system - thanks! Also - we have made sure that the fluid level is topped up.

Indycam

The bomb is what controls how many brake "pumps" before the pump runs again .
I'm going to guess that the bomb is getting weak / has lost some of it's charge .
I have a spare bomb .

http://www.tobul.com/images/scripts/...er062309v1.pdf

Pak_37

So from your experience - you think it's more likely to be the accumulator that needs to be replaced not the pressure switch?

Have you changed your accumulator, and if so - what will that job entail?

ome911

Hi Peter,
See hex socket that I had machined on the outside. The outer diameter can't be more than 45 mm. The swivel joint is need to get around the hood latch. Yes the pump was running for a long time initially (? 1 minute + after parking overnight). I suspect that the defective switch was not working to switch off the pump until the pressure was very high. it now runs < 30 seconds. As I recall the accumulator and the pressure switch are similar costs to replace. I can't advise which one is the problem. A Porsche shop with the right equipment can test the accumulator for a price.

Indycam

So lets do a test .
Let the motor run until it stops .
Unplug the motor .
Count the times you can step on the pedal until the pedal becomes hard .

Alan G.

Mine runs for about a minute, but hasn't progressed to alarms yet so I'll be flushing the bomb.

thats a cool tool;

Pak_37

Thanks for the picture Enzo. We should be able to machine a socket - it was helpful to see yours.

We only get a couple of pumps of the brake pedal after we have full pressure. Following your situation and Indycam's advice we'll probably replace both components.

Pak_37

Hi Indycam. Performed the test. Got 51 pumps of the brake pedal before it got hard.

dlpalumbo

ome911 - Could you annotate your picture? From left to right I see the swivel joint, something I'm not sure of (part of what comes next?), what could be a 36 mm black socket? (not machined?), and then what could be the machined socket (fitting inside the 36mm socket??).

Sorry for being dense. Haven't set eyes on the pressure switch yet.

Indycam

51 ?
If you really got 51 then it's not the bomb .