2G Overboost Problem

[eSpyder407]

Got my car running a few weeks ago after 2 years of it collecting dust in a garage from a blown motor. So I'm doing the third test drive trying my best to keep it under 3k rpm because of the fresh rebuild (this is tough)

Anyway, I gradually open up the throttle and the Turbo starts spooling... at 3200 it's at about 5-10 psi, 3500 jumps to 10-15, then I get to 4000 and the needle pegs out at 20psi+ and I let off the gas... At first I thought this was the MBC, so I unscrewed the bolt to where it almost separated from the MBC (lowest setting). I have the MBC connection to the turbo inlet and the other to the external wastegate.... Basically any changes to the MBC has no effect on the boost.

Is there something with the wastegate that is causing the over boost? I bought this turbo/o2 housing/wastegate from its previous owner so I don't have too many details on it. It looks like there are unplugged ports in the wastegate and the top of it looks like it's vented... Is this normal? I tried to take picks but it's a tight squeeze.

All of the vacuum lines are new and tight, I don't think there are any leaks. At idle in park the boost gauge reads -20vac; no leaks. All mods listed in profile. Still trying to learn DSMLink v3...I have logs I can post if that helps, but haven't figured out how to log my boost.

What is causing the overboost? How do I control/lower the boost?

 

[19gsx91]

I can't tell from your pictures but are you dumping externally or back into the exhaust? it's possible the spring pressure in the wastegate is set much higher then you're willing to run at the moment, Ideally you'd want to have a setup that uses only the external wastegate setup and remove the MBC from the picture

Someone more familiar with these set ups will hopefully chime in

 

[DSMPT]

That's is correct that the top port is vented with a manual boost controller.
What pressure the wastegate spring(s) have? and did you try with the manual boost controller disconnected?
Could be just the wastegate is set for 20+psi, but if the spring is set for lower psi (such as 10-11 psi or so) then could be boost creep. In that case, may need to port the wastegate hole or a bigger wastegate.

 

[eSpyder407]

Have not tried with the MBC disconnected, the wastegate has a 20psi spring... So I'm guessing that is the max it would go?

 

[GST with PSI]

Hook your wastegate line directly to the J-pipe nipple, and go do a pull. You'll likely end up with 2 outcomes:

-If the car still over-boosts, your WG is not opening/functioning and needs to be replaced.

-If you get low consistent boost (we call this wastegate pressure) your boost controller is junk, and you need a new one. This also means your WG actuator is functioning properly.

 

[eSpyder407]

Hook your wastegate line directly to the J-pipe nipple, and go do a pull. You'll likely end up with 2 outcomes:

-If the car still over-boosts, your WG is not opening/functioning and needs to be replaced.

-If you get low consistent boost (we call this wastegate pressure) your boost controller is junk, and you need a new one. This also means your WG actuator is functioning properly.

i'll give this a try and let you know what happens.

Also, i found another thread on here that said:

As with any MBC....you WILL NOT be able to lower the boost any lower that WG spring pressure.

Seems like a reputable source... is this true? My WG spring is 20 PSI. My gauge only goes up to 20 PSI, so that limits my troubleshooting ability. I am logging in ECMLink (pic attached) and it is showing just about 20 PSI from my Omni 4 Bar MDP sensor... which i think is pretty accurate until i get a 30psi mechanical gauge... I just don't want to hurt the fresh rebuild so i'm backing off the throttle when i hit 20 psi (no idea how long it would stay, or drop if i kept going.)

 

[19gsx91]

With an EWG setup and a manual boost controller you can NOT turn the boost down past wastegate spring pressure, you would need to change the springs to do that.

 

[GST with PSI]

As with any MBC....you WILL NOT be able to lower the boost any lower that WG spring pressure.

Fact.

 

[eSpyder407]

Well then that solves the boost issue i was having, thanks for the assist... prior owner had a 20psi max gauge, guess that was throwing me off.

Planning to tune it over 20 PSI eventually so the MBC will be useful then.

 

[DSMPT]

Yes, if you are planning to go higher than 20 psi, then the boost controller is usefull. Boost controllers (Manual / Electric) are only to raise the boost higher than spring pressure. They can not lower the boost than spring pressure.