Boosting too high

[Gamble97]

My nephew came over last night and we installed a small 16g and a ported manifold onto his 2g. His other mods are bc272,intake,downpipe,exhaust,hks ssqv.
We also installed a obx mbc.
The car is spiking at 20psi and just backfiring. I adjusted the mbc from one extreme to the next and it's still boosting the same and backfiring.
What could it be?

There is also an arrow on the mbc but I have no idea whicih way it should point, I assume it should be pointed towards the wastegate which it is.

Also it doesn't feel like fuel cut it's not like your hitting a wall, just stops accelerating and backfiring.

 

[GsxEcutioner]

My nephew came over last night and we installed a small 16g and a ported manifold onto his 2g. His other mods are bc272,intake,downpipe,exhaust,hks ssqv.
We also installed a obx mbc.
The car is spiking at 20psi and just backfiring. I adjusted the mbc from one extreme to the next and it's still boosting the same and backfiring.
What could it be?

There is also an arrow on the mbc but I have no idea whicih way it should point, I assume it should be pointed towards the wastegate which it is.

Also it doesn't feel like fuel cut it's not like your hitting a wall, just stops accelerating and backfiring.

pics?Mine spiked when the MBC was set up wrong.

 

[da_reeseboy]

Is it possibly boost creep? 16g + exhaust can definitely cause that...

 

[Splitpi]

Arrow should point to the Waist Gate. It indicates the air flow through the MBC. If you didn't hook it up correctly, no amount of adjustment to the MBC make a difference..

 

[Gamble97]

Arrow should point to the Waist Gate. It indicates the air flow through the MBC. If you didn't hook it up correctly, no amount of adjustment to the MBC make a difference..

That's the funny part, I have the arrow pointing towards the wastegate and no adjustment on the mbc made a difference. It didn't come with instructions saying which way is which and I emailed them, just waiting for a response.

 

[rb25det510]

its easy to understand how it works. all you have to do is take it apart once and you understand which way to hook it up. i would recommend you just taking one apart if you had an extra(small ball and spring inside don't wanna loose em) hold it with the knob going up and on e of the nipples on it going down. the boost source/pressure goes to the bottom nipple and the line for the wastegate comes off of the nipple that is horizontal.

 

[Splitpi]

What MBC? Also take the MBC out of the loop to ensure its not a faulty MBC. Plug the air feed line to the MBC (from the Intake Manifold) directly into the Wastegate. You should only build about 9 to 11 psi of boost. Usually 9.5 psi.

 

[16gstingslikeaB]

Take the MBC off and blow in it and start turning the screw. If you can't tell any difference in the amount of air coming through then turn it around and do it again. I put mine on backwards and had the same problem. If that doesn't work take it apart and make sure the lil ball bearing is still in there.

 

[project95gsx]

What MBC? Also take the MBC out of the loop to ensure its not a faulty MBC. Plug the air feed line to the MBC (from the Intake Manifold) directly into the Wastegate. You should only build about 9 to 11 psi of boost. Usually 9.5 psi.

That's what I would suggest. Also, is the wastegate actuator moving? Try using an air compressor to open it, see what PSI it's opening.

 

[kenamond]

First, check that the two MBC vaccuum lines aren't leaking or blocked.

I agree that you'll find out if it's the MBC by just running a vaccuum line from the boost source to the WGA (preferably one without a leak ). And getting your boost source from the intake manifold isn't the best IMHO. If you have a nipple on the j-pipe, use that to get boost "straight from the horse's mouth". If you don't have a nipple, search and find out how to add one. If that test fixes your problem (get ~9psi boost), something's up with the MBC.

If that doesn't fix it (still hit 20psi), check the WGA as was suggested (do a boost leak test or use a pressure tester with a gauge). It should open at around 10-12psi and extend the actuator arm.

If the MBC and WGA check out, it might be boost creep. Disconnect the WGA arm from the lever on the turbine housing and do a test run. If you build much boost at all (more than a few psi or certainly 20psi), it's most likely creep. Read the two or three other threads posted in the past day regarding similar problems to find out more; "search" is your friend.

And it is very unwise to boost past 15psi without supporting mods and a logger. Watch the boost gauge and let off the gas to limit boost levels, or you're going to break something expensive.