20V Brake Booster Vacuum Problems

[ShiRi]

Hey All,

Hoping some of you can put an end to this missery i've put up with on my 20v install.

This whole setup was running previously fine in a sprinter and was just taken out and put in mine... however problems arise from my install...

excuse the shitty drawing but it's just used to give you some idea



On a 20v there are 2 points you can plug the brake booster into... the vacuum point 1 or vacuum point 2 which are at either end of the throttles... This setup used a t-joint system previously where the hose that is now blocked (on the diagram) was hooked up to vacuum point 2.

However when i run this system with the brake booster hooked up to the t-joint the engine just stops itself... At the moment the brake booster is hooked up to vacuum point 2... however this leaves this t-joint open, making a lot of vacuum noise which is rather annoying, its also leads me to believe that throttle 4 will be running on less vacuum and possible damaging the engine....

If this is indeed a ISCV problem, why was it running fine on the previous engine? the old owner doesn't remember... so please maybe you guys can?

Thanks!

Shiri

[Jonny Rochester]

Its hard to imagine your exact setup. First, block all vacuum lines and run the motor like that, using only one line to your MAP sensor, and one big line to your ISCV if you use that. The motor should run ok. Then connect the booster up to either side you want (any ports not used have to be blocked). If the engine runs different with the booster connected you either have a leak in the hose, a leak in the booster, or your one-way valve is hooked up back-to-front. A healthy booster does not leak much air, even when the brakes are used, so don't worry about that. The stock 20v setup has a balance tube anyway.

[oldcorollas]

why did you decide to run it different from the previous owner?

seems reasonable, despite the balance tubes, to take vacuum from both ends of the TB setup for the brake booster, thus minimising the effect it may have on any one TB?

Johnny, are the balance tubes large enough to accomodate the emptying of the booster? i suppose that you only have significant vacuum when decelerating, so it's neither here nor there.... so is taking it from just one end enough?

[psychofox]

I take the brake booster off the common air rail that goes between all the inlet ports that the idle air goes to. It seems works a treat. I removed and blocked off the 2 brake original booster fttings. I also run the MAP sensor off this and it works fine.

On the pic it is the hose above the Idle Air with the hose clamp (sorry it's the only pic I have at the moment). This pic was taken while I was in the middle of installing the engine, it's much prettier now!



Edited for a typo. Oops!

[ShiRi]

why did you decide to run it different from the previous owner?

seems reasonable, despite the balance tubes, to take vacuum from both ends of the TB setup for the brake booster, thus minimising the effect it may have on any one TB?

because when i tried running it like i thought the previous owner did, it didn't run... and i can't work out why it isn't working. When i hook it up to the t-joint with both both hoses connected to vacuum point 1 and 2, it just causes the engine to stop.

It's more the isuse of the sound of the vacuum than it is the running off it... It runs fine, i can't tell if its damageing the 4th TB, i just don't like the noise of a vacuum comming out of one point...

[Jonny Rochester]

You can connect it like the pic above. But it also works off the standard spot, just one cylinder. The stock standard setup (in fwd) uses the front port. The back one is the same and fits rwd better. On my 2T-G I have the brake booster only connected to the manifold at #4 with no problems, and thats the standard location also. I don't think the booster flows that much air to worry the motor, and just one throttle will give the vacuum needed. The motor only has to make vacuum every now and again, not always. The valve keeps the vacuum stored in the booster.

[Jonny Rochester]

Shiri: have you checked the valve, or that you even have one? With the brakes not operated, there should be no noise, no flow of air. Just static vacuum with no air leaks.

[ShiRi]

I don't have a valve... as i said... there is a hose running from vacuum point 1 straight to the t-joint... one end is blocked, the other open... when i block both the engine stops...

[The Witzl]

most people i've talked to (and myself) have only ever used the port at cylinder 1 to give the booster its required vacuum, and have just blocked the port at cyl 4.

further to that, if you are blocking the open hose at point 1 in your diagram and the engine is stalling, then you arent getting enough air at idle - this is why the 20V has the ISCV

i dont know if i can help more than that without actually messing around with it myself

[ShiRi]

So you think it's most likely a ISCV problem?

[Jonny Rochester]

ShiRi: You need a one way valve between the brake booster and your vacuum port on the motor. All cars have it, maybe you have misplaced yours. Otherwise the valve maybe part of the booster, but in anycase you need to have one. And it needs to be turned around in the right direction. To test, blow in one end, try blowing in the other.

Having a open hose to atmostphere to keep the idle high enough is a different problem all together. That is something the ISCV is suposted to take care of. Iff the ISCV is not working, you can just block off all hoses and get the required idle speed by adjusting the throttle stops in the same way you would do to twin sidedrafts.