lordie

A couple of days ago i've noticed pressure drops in higher revs (above 5500rpm). No matter how high i set the MBC, pressure always starts dropping around 5500rpm and falling stops at 5psi. I have checked the pipes for leaking, but they seem to be ok. I can not hear any whistle either. Can it be the actuator as It may not hold the pressure (even not with MBC) anymore?

Please, give me ideas!

BTW, I use a cheap ball/spring type MBC (taped around against leaking) and T3/T4B actuator set at 6psi (this is the maximum available, rod completely turned in) on my B16A2.

SpankedYA!

I had the same problem with mine. I changed to a bleed type MBC and put larger exhaust on so I don't know exactly what the problem was.

lordie

I tried 3 different MBCs, too. Though they all were ball/spring and not bleed type.

My exhaust is 2.5" from the turbo till last muffler, no cat. either.

turbohf

what size turbo?

lordie

T3/T4B. It worked fine for half a year, started doing this pressure drop nowadays only. First time this happened when I turned up the boost a bit on my MBC, later i set it back to 7.5psi and it droppes all time since then no matter how high i turn the MBC.

I attempted to remove the MBC to check the actuator, it seems work fine as it holds the max. available 6psi.

Also tried to remove the vacuum line from the actuator's vacuum port, the boost spike was horrible (around 11psi) and the pressure falled to 5psi (not even hold the same as with reading vacuum).

Strange...

lordie

Or do you think the MBC can cause this effect only?

And the actuator has nothing to do with it as if it holds low pressure great without MBC, it should hold higher pressure as well with good MBC?

scarecrowX

boost controller can only raise boost from the factory WG rating.

one of 3 things is happening

a. you have a boost leak. build a pressure tester and check it. do NOT rely on feeling/looking at the pipes for this. pressure test it.

b. you have an exhaust leak that's allowing exhaust around the turbine. unlikely, as you'd probably hear it.

c. the WG isn't closing all the way. pull the actuator off and check for binding, etc.

my money's on a. i don't know how many times my car has run like ---- and i looked at the pipes and thought it was something else, only to find a MASSIVE boost leak somewhere i couldn't see. pressure test the bitch and be done with it.

"how do i build a boost leak tester," you ask?
http://www.vfaq.com/mods/ICtester.html

until you've pressure tested it, assume it's leaking.

scttydb411

or your mbc is causing the boost spike...what sounds like you are describing and not holding back the boost. try a bleeder type between the boost signal port at the end of the compressor outlet and the actuator. i've only used a bleeder type and it holds boost great. the idea is it bleeds off the boost signal going to the actuator so the turbo builds more boost before it reaches the actuator...kind of like trying pump up a bicycle tire that has a leak in it.

lordie

Thanks for the ideas! I try them this order then.

ScarecrowX! So, i remove the air filter->turbo pipe and plug this tester onto the inlet of the compressor (turbo). Or can I plug this item replacing the air filter as well? (Air goes to TB from there, too, doesn't it?) Instructions says i can use a simple bicycle pump to push air through the valve. I hope it is enough.
Stupid question. I suppose i shouldn't run the car at idle and let the compressed air go in the engine (too lean A/F this case). Or shall I?

scarecrowX

do not attempt to connect the tester to the air filter. pre turbo pipes/hoses are NOT meant to hold pressure. you'll shred them if they're rubber or blow them off the comp inlet if they're metal. connect it to the compressor inlet. do NOT attempt to run your engine either. the purpose is to create pressure between the turbo and throttle plate. a little will leak through the throttle plate, as it's not a perfect seal and there are the AIC valves to deal with, but it sounds like you have a significant leak. air will escape from your leak well before it does through the throttle plate.

my MR2 had the same problem about 6 months back. i had my MBC set to 16psi but it would drop to 8psi by 5k. granted, the CT26 drops off to 10psi at 5500 no matter what due to its size, but 8 psi that early was ridiculous. my car ran like ---- too (because it's a mass flow metering system- i'm sure your car with speed density wasn't NEARLY as noticeable). tested it and there was a tear in the hose between the hotpipe and intercooler nearly halfway around the hose. i couldn't see the leak at all. the hoses were tight. it was on the underside, right by the clamp, so i couldn't feel it either. the ONLY way i found it was by testing.

i would run this test at least once every 3 months, just to make sure everything is in order.