Boost hits 20psi.. then drops to 0

[ALL4thaN0okie]

OK.. I've been having this problem for a while now, but always attributed it to my leaking 1g BOV. Now I've replaced that with a Greddy type s.
The car will boost normally to around 18-20 psi, as soon as it hits 18-20 psi the boost will drop all the way down to almost 0. I have checked for boost leaks and there are none (checked past 25 psi). I have no idea what else could be causing my boost to drop all the way down, other than maybe my wastegate opening and staying open?
Any and all help is appreciated, as always guys.

Mod list- EVOIII16G, walbro 250, FIC 550s, greddy type s, apexi cat back 3", K&N, UICP, stock IC, Joe P MBC

 

[91gvr4]

Letting off the gas

 

[ALL4thaN0okie]

Letting off the gas

I wish it was that easy....

 

[psychlow]

What happens if you disconnect the MBC and run the boost source straight to the actuator?

Does the car still accelerate smoothly (albeit slowly) even at 0 boost? Any black smoke or backfiring? I'm just wondering if you're having ignition issues, which would cause you to not create enough exhaust to maintain boost.

Plugs/wires/coil pack may be would be suspect if you think it may be ignition related.

 

[oldman]

Where's that safc? Don't tell us you're running the 550s without safc and the 255 without an afpr.

edit: Are you venting as well?

 

[ALL4thaN0okie]

at 0 boost it accelerates fine.... pulls really hard (like it should ) when its building and at max boost for a second.... i've never had any smoke or misfiring either...

sorry i forgot to list the safc... i have the safc and logger and it's tuned as well as i can get it without steady boost...

i don't however have an afpr.... and i'm definitely not venting the bov..

 

[ALL4thaN0okie]

oh..and in response to your ignition idea.... i have had some random misfire codes in the past..

 

[oldman]

at 0 boost it accelerates fine.... pulls really hard (like it should ) when its building and at max boost for a second.... i've never had any smoke or misfiring either...

Then what happen when boost start to drop? How fast does it drop? Noises? Sputtering? Give us more.

 

[ALL4thaN0okie]

well.. when the boost drops, it drops quickly.. i dont know how to describe it other than that... the turbo stops making a spooling sound also... the only other thing is that it doesn't make any power (obviously) after the boost drops.... i can still accelerate without sputtering or any other problems just slowly

 

[dynatos]

so when the boost builds - hits 18-20, goes to 0.. does it start spooling back up imediately? If not, what happens to get it to start spooling again back up to 18-20?

 

[psychlow]

oh..and in response to your ignition idea.... i have had some random misfire codes in the past..

I'd start with plugs, wires, and coil pack then.

 

[peregrine]

and check for boost leaks

 

[truwarrior]

When does it start to spool? Is the flapper attached to the actuator? Maybe it fell off.

 

[oldman]

so when the boost builds - hits 18-20, goes to 0.. does it start spooling back up imediately? If not, what happens to get it to start spooling again back up to 18-20?

A very important question. How long does it take for the turbo to start spooling again after it drops to zero? Any more details during this period would be great. I think your random miss fire may have something to do with the lack of afpr, if ignition is the problem you should have felt some turbulence if not complete shut off, it certainly should not have driven normally like a N/A after it dropped to 0. I tend to think it's turbo related but can't figure out why without more info and testing. I have never heard of a problem like this, maybe some wiseman can enlighten us all.

 

[ALL4thaN0okie]

A very important question. How long does it take for the turbo to start spooling again after it drops to zero? Any more details during this period would be great. I think your random miss fire may have something to do with the lack of afpr, if ignition is the problem you should have felt some turbulence if not complete shut off, it certainly should not have driven normally like a N/A after it dropped to 0. I tend to think it's turbo related but can't figure out why without more info and testing. I have never heard of a problem like this, maybe some wiseman can enlighten us all.

when the boost drops to almost 0 it stays there until the end of the gear... or i could let off the gas and then step on it again it will build again... but.. by itself.. it won't start building boost again..

 

[OddyseusDSM]

If its pulling like it should even though the gauge is reading 0 have you stopped to check the gauge? I mean, you said it still pulls hard and in NA mode the turbo engine would have less power than a NT. Is your guage an electrical sending gauge?

 

[ALL4thaN0okie]

it pulls like a geo metro would pull when the boost drops.. it's still smooth though as in not sputtering... basically when it spools up.. it feels like it should... but when the boost drops.. there is a major loss of power..but it still accelerates... so i doubt it's the gauge... the gauge is mechanical (autometer ultra lite) ..

 

[ALL4thaN0okie]

another thing that i forgot to tell you guys is that it'll hold boost longer with the higher gears.... 3 holds longer than 2 ..4 longer than 3... 5 longest of all... i'm not sure if that'll help at all...

 

[oldman]

another thing that i forgot to tell you guys is that it'll hold boost longer with the higher gears.... 3 holds longer than 2 ..4 longer than 3... 5 longest of all... i'm not sure if that'll help at all...

So it's rpm related, what rpm? What happen if you go part throttle at like 15 psi?

 

[ALL4thaN0okie]

its somewhere between 4000 and 4500rpms .... part throttle or full throttle doesn't matter... boost still drops at the same rate....

 

[oldman]

I suggest doing a compression test and go from there.

 

[AllWheelPeel]

I have an 89' dodge colt turbo w/a 1.6L 4g61 (The first edition grandaddy of all these cars)
that is exibiting the exact same symptoms. Upon pulling it apart I found three things wrong.
1. The nipple on the boost solenoid was busted off allowing the boost to flash high .
after that ,I'm guessing that the ECU was pulling timing severely.
2.The exhaust manifold and turbine housing are both cracked.But the rotor spins freely.
3. My o2 sensor is dead.
I am currently changing everything over to 1g DSM stuff that came off my Talon (14b, etc.)
While I realize that I haven't answered your question directly, I can offer some ideas.
I will post again soon when its back together.

 

[truwarrior]

maybe you have a kink in your boost gauge line, mine does now and my vac reading is all messed up

 

[dynatos]

I would think a damaged nipple, teared line, cracked manifold, etc would exibit more of a a constant effect. Such as only hitting maybe 4-5lbs of boost.. or the car always running horribly, etc. Sounds like the ECU is seeing something it doesn't like, and is telling the BSC to cut boost. You shiift, or let of the gas and try again.. readings change, and the ECU tries again. Are random misfire codes all you're logging?

 

[vtracer20]

it sounds to me like something is leaking...like it spools and at a certian psi something gives and cant handle the psi but it's obviously something small....check all ur piping connects...