Guys I Really need your help
 

I tried searching and was unsuccessful. I cant get my MBC to work. I have a 90 miata with a greddy kit with a starion FMIC and greddy downpipe with a test pipe and a catback. I cant even boost 5 psi on the stock waste gate. The most i've ever boosted is 3-4 psi. So i figured I should add a manual boost controller to boost a consistent 5 psi atleast. Anyways, I have it mounted just like this picture

http://www.geocities.com/chmwatson/F...cschematic.jpg

My question is, I have the wastegate actuators line coming to the MBC and I need to know, what happens with the spot the other end of it used to be at. by the turbo area. I tried it and my car boosts about 3 psi with the MBC tightened all the way and open all the way. Any help ?

you sure your boost gauge is reading correctly? I've never heard of the greddy kit only getting 3psi!
Did you tighten your wastegate arm?
What type of MBC is it?

What did you do with the nipple on the compressor that would normally feed the wastegate actuator?

olderguy i didnt have a nipple on the compressor, its still left open and the mbc is some no name brand that a friend gave to me. The gold looking ones. Waste gate arm is tightened all the way. Its tightened towards the wastegate actuator.

ok take a regular hose and connect it between the compressor housing and the wastegate actuator with no MBC

it was already like that before and i couldnt get more than 3 psi.

then something else is the problem, at this point you shouldn't be messing with a boost controller

make sure you have no vacuum leaks
make sure your boost/vac gauge is working properly with no kinks in the line
no exhaust leaks
wastegate closing completely, not obstructed
wastegate actuator possibly damaged(unsure how to test this)

I 2nd Mach929.

Only 3psi? Something isn't gravy?

as far as a vacuum leak goes im pretty sure there is none because my boost gauge shows about 19-20 in vacuum at idle

it is still possbile to get a boost leak when you don't have a vacuum leak.

do yourself a favor and try a new gauge, maybe borrow one from someone. you don't want to drive yourself nuts over a gauge issue

well im sure its not the gauge because if my boost gauge is open all the way it means i should be boosting well over 10 psi. And im not going over 3psi. And im sure I'd be able to tell the difference in pull between 10 psi and 3psi. And on a side note, right now i went on the freeway and in 3rd and 4th gear i was hitting 5 psi holding till redline. But i wouldnt hit 5 psi until over 5K rpms. Its like an insane LAG. I boost 1-2 psi up until 4k then after that on the freeway 3rd-5th gears boost 5 psi.

I had the same problem. When I installed the kit it was maxing at 3.5- 4 psi. I got a voodoo MBC and hooked it between the nipple on wastegate actuator and the vacume on the intake manifold. The diagram you showed will work but might cause some boost spike. Other then that i would try another gauge.

This statment confuses me. Are you saying there isn't a bung or fitting on the compressor? Or are you saying there isn't a fitting on the bung and there is a open hole?

hmm i have a hallman mbc and it doesnt say anything about teeing into the bov vacuum line. just the lines from the compressor and the wastegate.

you can tee off of any boost source.

:confused: i'm thinking it's normal not to get full boost till after 4k rpm

Sorry about the misunderstanding what I meant was that the hole is OPEN. There is a fitting its just left open now that I have the MBC. I closed it today and now my cars still the same with the difference being that it doesnt blow off any noise once i let go of the throttle in boost.

ok.

Do this.

Connect the MBC to the Compressor fitting. So the bottom leg of MBC goes towards the compressor and the side legs goes towards the wastgate.

Keep the BOV vacuum line out of the equation, make sure it's leak free and connected straight to your source.

MBC is on the lowest boost setting when turned fully counterclockwise. The tighter you tighten down the MBC the higher the boost will go.

Also verify that your wastgate actuator rod is fairly tight.


see attached:

Braineack so I did exactly what you told me to do and my car feels MUCH FASTER than the 3 psi however my boost gauge is reading 5 psi. I'm convinced that somethings wrong with my boost gauge and also one more question my MBC might be messed up or maybe my wastegate because I had it tightened down all the way and I highly doubt I was boosting 14-15 psi.

better know for sure your gauge is working, much more boost than 6-7psi without supporting mods and you'll be looking for a new motor

have access to an air compressor that you can regulate the output? just run it into your vacuum lines and verify it's giving you the correct reading. My boost gauge is exactly 1psi off. So it displays 10psi when in fact i'm only boosting 9psi. MAP sensor & the above method verified.


also make sure inners of the MBC are correct. it should be ball bearing, spring, then screw adjuster. If the ball is on top of the spring it might not work at all.

Brain is the PAINT Master!

I wish I had an air compressor. What boost gauge do you guys recommend ? I want to get a new one. I REALLY like the defi gauges, a buddy of mine has it on his evo ix and I wet my pants every time he turns the car on because of how it lights up and its all black when its off.

Stewart Warner's are really nice (visually) for the price.

No way I'm paying $150+ for a boost gauge. More like $20-50 range for me.

My guess.

A weak wastegate will still give you some boost, but will spool very slow/late in the RPM range.

So will a huge boost leak. I know you've checked all your hoses/clamps, but have you done a boost-leak test? I don't have a compressor either, so I fill a cheapie air tank to whatever psi I want to test (usually 15-20 for leaks depending on which car)

I have found a perfectly good looking coupler that was split (but not off its pipe) and leaking boost like a mofo.

go on ebay and look at the VDO boost gauges, i ordered one last week, they are electronic instead of mechanical too.