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Q&A regarding engines, turbos, and intercoolers and power upgrades
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Bad mbc?

Fri Jul 24, 2020 1:57 am

Ok so after the headgasket, a blown capacitor in the ecu and installi9ng my aem 340lph shes back to full health so i decided that it was time to crank her up to the "recommended"(lol) 17psi. but once i did it felt all wrong didnt pull as hard as at 11 psi so i closed off my mbc and that didnt help. reset the ecu and now it runs fine and pulls hard as it should. So: 17psi, not right at all
11psi, still not right
reset ecu with closed off mbc, runs great

Faulty mbc?
And also, why would reseting the ecu make things right? if i try 17 then 11 without reseting it dont feel right but once i reset its fine. Any ideas?
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Re: Bad mbc?

Fri Jul 24, 2020 3:19 am

Does it pull a bit and then cut out, or does it feel off as soon as it gets into boost? I'd test the MBC and be sure it isn't leaking. Also double check your hose routing, with the TVSV disabled it should be 6 psi in all gears, not 11.

Also which ECU are you running?

Re: Bad mbc?

Fri Jul 24, 2020 3:29 am

Car has full 3 inch exhaust/dp no cats fmic apexi filter etc etc... and my boost gauge is off by about 2 psi on the positive side(key off reads 2 psi) so i guess its at 9-10psi wich isnt unheard of with full bolt ons. it feels off as soon as the boost kicks in, kinda like its pulling timing and keeps those corrections active even if i close off the mbc, once i reset the ecu the corrections erase themselves and things get back to normal. at least thats my assumption right now. runnig a 3rd gen jdm mr2 ecu.

Re: Bad mbc?

Fri Jul 24, 2020 10:53 pm

Are you running 93 octane?

Also, 17psi is too high in my opinion. Since the 3rd gen is map based it can’t account for volume changes at the same psi. You are moving more air at 17psi then a stock 3rd gen at 17psi. This is probably leading to detonation and the ecu pulls timing. Back off the psi until you find a happy number that doesn’t pull timing.

Re: Bad mbc?

Fri Jul 24, 2020 11:37 pm

The bgb itself says working pressure is 11.9 to 16.7 psi so im sure its fine but i do see your point, it doesnt account for the people running pretty much the same setup without issue though. People in the 3s community online and the ones i know personnaly(mostly sw20 owners). Regardless i hooked everything back up like stock and its fine now. I blame the mbc anyways. I bought it in like 2004 and its been in my center console since then. It saw a bit of use back when i was still running the old 1st gen engine but since then nothing. Running 94 oct btw
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