Failed Boost Controller + Throttle Body Annoyances

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Esteban
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Re: Failed Boost Controller + Throttle Body Annoyances

Post by Esteban » Thu Oct 12, 2017 9:59 pm

There isnt much heat in that area to kill the tree if you replace it with another. But try a universal aluminum manifold from Ebay if you are worried about heat.

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Re: Failed Boost Controller + Throttle Body Annoyances

Post by thesameguy » Thu Oct 12, 2017 10:38 pm

The attraction of an aluminum manifold isn't really durability but not a bunch of unused, capped off ports. I just need to split four ways (in/booster/EGR/HVAC) leaving several ports on the tree. It's kinda ugly and a potential source of leaks.

One thing I am running into, however, is that most of these things have 6+ ports on them. I may end up using a nitrous manifold -they are small, and typically four or five ports. They're NPT threaded, so should work similarly.

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Re: Failed Boost Controller + Throttle Body Annoyances

Post by thesameguy » Fri Dec 08, 2017 11:31 am

It's now been over two months without further vacuum-related issue on this car. Admittedly, it's not a perfect test since my wastegate limits boost to about 10psi vs the 20psi I was previously running but hope springs eternal, as they say. In any case, I'm finally proceeding since the car is sidelined for wheel bearing replacement anyway.

One hangup I've been working on is the brake booster. I've been concerned for a long time that my check valve is a source of leaks. I'm able to spin the check valve around, so it's not a perfectly tight fit in the plastic pipe that connects it to the brake booster. Additionally, the performance of the check valve is awful - it takes quite a bit of vacuum for it to open, and it never fully opens - there is always a substantial amount of resistance drawing air across it. Although both my '86 and '88 are the same, I can't imagine this is by design. I suspect the check valve is old and feeble, so I'm going to replace it.

After learning yesterday that the vacuum port in the booster is the same on the '86.5+ XR4Ti and Saab 9-3/9-5 my options have been opened a bit. The little 5mm (?) fitting on the brake booster was a real stumbling block in replacing the check valve and keeping the vacuum system easy. Now that I know I can use Saab (and I'm guessing BMW) parts the world is my oyster. :)

If anyone is paying attention, I wanna discuss this:

Image

This is the vacuum supply for a Saab 9-3 '01-'03 with a manual transmission. Automatic cars actually have a discrete vacuum pump on the engine for the brake booster, but manual cars use this 3-way valve instead. The valve is a venturi and vacuum is drawn both directly from the manifold as well as inline with the PCV system. Apparently, this configuration dramatically improves vacuum in the booster. I understand BMW uses the same configuration on some of their cars, so it may be an ATE thing?

Image

In BMW-land, it's called the Sucking Jet Pump, and I can't imagine how you wouldn't want one on your car. :headbang

In any case, because I'm going to use the grommet and fitting from a 9-3, I think I'm going to try and implement this on the XR4Ti. The PCV and brake booster are quite close together... I just hope not *too* close.

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Esteban
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Re: Failed Boost Controller + Throttle Body Annoyances

Post by Esteban » Fri Dec 08, 2017 6:06 pm

Older BMWs use the same check valve. Or if you want, you can upgrade to a vacuumless unit like the boost from the Scorpio. I have one here if you want to go that route.

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Re: Failed Boost Controller + Throttle Body Annoyances

Post by thesameguy » Mon Dec 11, 2017 2:27 pm

I appreciate the offer but my whole mission with this car is replace every bit of unobtanium with commonly available parts - I definitely don't want to get involved with 30 year old Scorpio parts. :)

The grommet and plastic nipple from a Saab 9-3 works perfectly - the nipple is 3/8", so I can use a 3/8" silicone hose and a common 3/8" check Pierburg check valve right back to the intake manifold. That is sorted... though I'm definitely going to see about trying out that venturi at some point... I just need to have a bung welded onto the pre throttle body pipe for the secondary vacuum source.

Immediate next component is replacing the vacuum tree. It's proving a lot more "difficult" than I'd like... all the manifolds I've been able to find are poorly configured for use with the XR, which basically needs vacuum sent in four directions. Obviously hoses can bend and turn, but I'm holding out hope I can find one that's Just Right. :)

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Re: Failed Boost Controller + Throttle Body Annoyances

Post by thesameguy » Tue Dec 12, 2017 7:37 pm

I've temporarily abandoned the vacuum manifold project. I'm just out of energy for searching, so it's Plan B.

I can do what I need to with two vacuum fittings, the cost of which is about $1.76 combined. It'll be good enough for now, allow me to continue to troubleshoot what's actually leaking, and who knows, maybe I will stumble upon the right manifold in the future.

I found that usplastics.com carries the two fittings I need - a 3/8" x 3/16" tee and a 3/16" cross made in HDPE or Kynar. I ordered some extras to offset the $12 UPS shipping that my single-digit dollar order otherwise comprised. :D

Maybe coincidence or maybe fate, usplastics.com is located in Lima, OH. :headbang

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