I recently installed a AEM failsafe wideband gauge and I hooked up the failsafe wire with my AEM water injection failsafe which uses a normally closed relay to shut off the EBC solenoid to run off the wastegate spring pressure if there is a trigger from the failsafes. The nice AEM failsafe wideband will trigger a flashing alarm and failsafe if you go leaner or richer than you want under boost, all customizable, I really like this. I have a power fc and datalogit. But I use a 18 psi wastegate which isn't bad for a WI failsafe but still not good if for some reason my Afr go way leaner than normal to trigger the wideband failsafe, which also can be programmed for how long it grounds the failsafe wire and how it resets.

So I ordered a mac 3 port boost control solenoid off eBay for $30 I plan to hook this up to the blow off valve hose, so when the failsafe triggers the solenoid will switch from the intake manifold pressure going to the blow off valve, to a vacuum source pre turbo in my intake pipe after the air filter. The vacuum will open the blow off valve to drop the boost pressure to the engine. This is a very brief description of how it will work, I could go into more detail on how exactly it will all be installed and how it works.

So what do you guys think about this idea? Other possibilities are to use a normally closed relay to do a fuel cut or a ignition cut, but they will be cut for at least 3 seconds off the wideband failsafe or longer if the WI pump fails or the tank runs low on water.

 

I really doubt you're going to have enough vacuum in front of the turbo to open the BOV. If you do, you shouldn't.

 

I don't think he is trying to make a significant vacuum pre-turbo. Since there will be pressure in the intake pipe pushing on blow off valve, he doesn't need a true vacuum to open it...just a pressure differential large enough so that the boost can overcome the bov spring and allow pressure to escape.

With that said, I still do not think it will work exactly as you want it to. When the blowoff valve opens and it starts bleeding manifold pressure, the boost controller will try to compensate by closing the wastegates and re-increasing your boost. This would become a control nightmare.

I've never been a fan of integrating tons of systems to control everything, esp. when today you can implement an ecu that will control all of it for you. On my current build everything is integrated into the ecu and I will have boost control and water injection control with failsafes programmed in for AFR/EGT, boost, and water injection flow.

 

I wondered too how much vacuum there will be, but at full boost I was thinking there has got to be a large amount of air getting pulled into the turbo, and combine that vacuum will the fact that the boost pressure is removed from the hose going to the top of the blow off valve and the boost pressure in the greddy elbow at the bov it should open at least some. One way to find out. What do you mean "you shouldn't" ?

 

I will also have the failsafe cutting power to the ebc solenoid, so no pressure getting to the top of the wastegate trying to close it, this is how I have it setup now. And the failsafe triggers for 3 seconds and then resets, so plenty of time to let off the gas when I feel a power loss hopefully from a drop in boost pressure. Ya I'm just trying to make it work safer with the power fc. Thanks

 

Let's assume you have a Tial BOV and you have the ability to swap in different springs...

The lightest spring Tial sells for their BOV is -2 psi. First problem with that spring is that the BOV will hang open at anything less than WOT. If you use a -10 psi spring, which is pretty common with the rotary, there is NO WAY you're going to pull enough vacuum pre-turbo to trip the BOV. If you're pulling that much vacuum pre-turbo, you have a significant restriction in your air filter or plumbing. That vacuum is going to show up in poor turbo performance. I would guess, if there is enough of a restriction to create that much vacuum you'd have a hard time even getting the turbo to spool up.

If you want to do this, your best bet is to build a vacuum reservoir, just like the stock twin system uses. Use that reservoir to trip the BOV.

 

Could I tee in the stock vacuum chamber? I'm trying to get my boost control solenoid hooked up to the blow off valve tonight to test it out. Thanks.

 

You could probably use the stock vacuum chamber. It's used for the factory charge relief valve. I agree that the turbo inlet won't have enough vacuum. You should be able to get the plumbing such that you could use the 3 port solenoid to switch vacuum to the wastegate actuator and to the blowoff valve, accomplishing both at once.

 

^ Yup. Give it a try. Like the idea, Tom!

 

Thanks. Ok so how about I run a vacuum line from the uim through a check valve to the vacuum chamber, t off between the vacuum chamber and the check valve and run that hose to the nc port of the new boost control solenoid for the bv, run the old bov hose from the uim to the no solenoid port, and a hose from the com port to the bov. so the vacuum chamber should hold vacuum and help to open the bov when the solenoid switches from the failsafe. I also figure I need to make these hoses as short as possible, especially between the bov and the vacuum chamber, and if I also t off to the wastegate top port that's gonna be a lot more hose and take a lot more vacuum needed.

 

It works!! When my AEM WI or WB failsafe triggers the bov will open, when the engine is under vacuum or boost. With the vacuum chamber hooked up and the hose coming from the one UIM source for the blow off valve. See the hose diagram attached to see how everything connects. I did a good job of installing it and keeping the hose lengths to a minimum. My AEM failsafe wideband software has a test alarm button to trigger the alarm I have set for 3 seconds until it resets. When we hit the test alarm button while driving the bov opens, and then go full throttle the bov stays open and it will not really build boost, like 1 psi. Then while driving we would hit boost and hit the test alarm button and we hear the bov open relieving the boost pressure loudly and the boost quickly drops, its pretty cool! lol. We did some tests and datalogs to show it working.

I don't have my new boost control solenoid for this yet so I was using my greddy electronic boost control solenoid (same thing), and I had my wastegate top port vented to the atmosphere. When I put the boost control solenoid back for the wastegate, it will work the same way, when one of the AEM WB or WI failsafe triggers I have a normally closed relay already hooked up to cut the power to the solenoid so the solenoid vents the wastegate top port to the atmosphere. I did not try to connect a hose from the vacuum chamber to the hose going to the wastegate top port to use up vacuum from the vacuum chamber to also try to open the wastegate when a failsafe triggers.