The vacuum hose reduction: walkthrough and pics

[tachyon_ftl]

Davey07 wrote:

hey I have searched the forums and couldn't find my answers,I'm still learning. i have a 99 vr4, need to do a vacuum reduction /egr delete,,

It's difficult to do a vac reduction on '96 and up... they're OBD2. The big difference between OBD1 and OBD2 is that OBD2 incorporated a lot of sensor checking for emissions control equipment to make sure that the emissions controls are there and working. OBD1 cars incorporated emissions control stuff, but the ECU didn't check very much to make sure it was working. That's why, for example, there are 4 O2 sensors on '96 and up... two are ahead of the precats and are used for engine tune. Two are after the precats and are used only to make sure the precats are still there. (It's true that Cali cars incorporated some of this earlier than '96, but the feds didn't require it until then). The ECU also looks for things like the solenoid coils being attached, and will throw a CEL if the solenoids are missing or broken.

Anyway, EGR was one of the things that got a lot harder to fool in 1996. From '91 to '93, a thermistor was used to look for a temperature change when the EGR was in use. Well, all you need to fool that is a simple resistor, and that mod is well known. I'm not sure if the hybrids ('94 and '95) did it that way, but definitely '96 and up use a pressure sensor attached to the plenum and look for a pressure difference when the EGR is in use. Not as easy to fool; there is at least one method floating around, mostly having to do with running various of the vac lines from the plenum thru the EGR solenoid, but nothing has been shown to be 100% effective for OBD2 cars.

Bottom line is you are almost certain to get a CEL doing a vac reduction on a '99. You might want to hold off on it; it does clean up the engine bay, but it's not going to net you gobs of HP and it may be more annoyance than it's worth. Poke around, there are more threads on EGR and vac reduction; but for Gen 2's and up, it's not pretty.

[Davey07]

awesome info thanks alot, i actually found my vacuum leaks fixed them and pushed my vacuum hoses on as hard as i could, turned off my bc and then back on and it works now!!! I still here this hissing sound but i think i know what it is, thanks guys Dave

[DoctorDex]

Do a pressure test and then be done with it. If you don't have a pressure tester, you can make a ghetto tester using a garbage bag.

[92RT-TT]

So from reading this, Do I have to do a vacuum reduction in order to get my electronic boost contoller to properly control my boost levels?

[DoctorDex]

No, you don't need to do a vac. reduction to hook up an EBC.

[My92Stealth]

^correct, but it certainly does help!

[scrapiron7]

Good info! Thanks for posting this up. Looks like something I will be doing soon.

[92RT-TT]

My Electronic boost controller (Greddy profec b spec 2) was delivered to my house yesterday. I'm going to try to install it later today. I hope the directions they come with are good and are easy to understand. I've never done anything like this before Wish me luck. I'm going to need it.

[92VR4Tuner]

i am rebuilding my engine at the moment on my 92 vr4 and am planning to do the red vac mod. i was just wondering if when you unplug the boost control solenoids if it affects the way the ecu maps out the fuelk and if it will say cut back the fuel and make it run like crap. also i plan on getting rid of the egr and was wondering if that would affect the idle/performance of the car as well. also could someone post picks on the clutch and brake booster vac assist becasue i was wondering when you do the red vac mod what you do with those systems. thanks a bunch.

[tachyon_ftl]

Read the writeup that Struggly did on the first page of the thread; for a 1992, you're golden. Vac reduction refers to removing solenoids and lines for the emissions control system, the stock boost controller, and the stock FPR. Emissions because you can, the stock BC and FPR because they're usually replaced with aftermarket or plumbed differently as part of the vac reduction.

The brake booster and clutch booster- you need those, leave them alone. They're not part of the same plumbing set that the vac reduction works with, which is why they're not mentioned here.