dizzyj

I have a lr dual port wastegate with a lr mbc. With the mbc closed (no airflow) I'm boosting to 20+ psi instead of 9 . My mtune protection is kicking in.

I verified that the mbc is not leaking and I bench tested the wastegate, I opened easily at 9psi

Only other reason for overboost I can think of is clogged lines, or that the map/klr is seeing higher boost than the wg

Anything else I could be missing?
Thanks

Scott H

Did you make any changes to the car or did this happen out of the blue?

onspeed

Did you just install this? If so, make sure your lines are routed correctly. The LR wastegate fittings are reversed from the Tial WGs, so the line going to the side port should have the MBC in line, and the top port should go straight to the hard pipe.

You have a external boost gauge to verify you're overboosting?

dizzyj

its been installed for a while by the previous owner. i've been sorting the car out for a while now. Took it to the track the last two times where I have been able to lay into it, and in 4th, im spiking past 18psi (the rogue tuning overboost limit).

I was expecting to find my wastegate stuck closed,but it seems to be working just fine. any other reasons for overboost? im going to change the lines and make sure the MBC is hooked up right.

onspeed

Possible the WG isn't opening all the way?

With the MBC completely closed in a dual-port mode, it should be boosting to spring pressure, unless there's a restriction in the line somewhere. Unless you've got the lines hooked up backwards, in which case you'll hit overboost regardless of MBC setting.

dizzyj

spring pressure should be 9#. On the bench with my air compressor the wastegate started to open at 9, and was fully open by ~15. being a diaphram, that did not seem unreasonable to me. I guess I need to check for any obstructions in the exhuastpipe that might have kept the gate from opening.

I think the mbc was hooked up correctly because when I tried turning the ****, I overboosted way easier. Guess that tells me that the gate is opening, but maybe not all the way?

User 52121

Went through something similar a few weeks ago.

The boost "system" is fairly simple. If you are overboosting, the WG is not opening. Common reasons for the WG not opening - (1) it's stuck, (2) the diaphragm failed, or (3) you're not getting boost signal to the correct side of the diaphragm.

You've verified (1) and (2) are good. So it's (3).

Either you've got the vacuum lines hooked up backwards, the line going to the top port is leaking, or your MBC is screwed up. Start by eliminating parts... I'd pull the MBC out altogether (leave the side port disconnected) and run the WG in "single port mode" but with a straight vac line to the top port. That will eliminate any influence your MBC has over the WG. If it still overboosts, then I'd say you have a leak in the vac line going to the top port. I'd run a 100% fresh line from the banjo to the WG.

dizzyj

Thanks. That was what I was going to do next. Good To know I'm thinking on the right path

MarkRobinson

I agree with Jim: usually for items such as this it leans towards installation errors: I've seen this on a lot of turbocharged cars. I also think one of the last things the past-mechanic did was install this (probably incorrectly) which took out the intercooler, resulting in patch tuning & the car's eventual sale. Lucky you!

User 52121

Keep in mind that, when on the car, you also have exhaust pressure pushing on the back side of the valve, in addition to what's coming into the diaphragm. Pretty sure the 9# spec is just to crack it off the seat.

dizzyj

Well, the mbc is installed correctly. One line from the hard pipe to the top of the wastegate. On that line is a T that goes to the mbc then to the side of the wastegate. I pressure tested the top line and it held fine. Also no obstructions in the exhaust blocking the wastegate.

I.e no reason the wg shouldn't be opening. I'm going to put it back together and hope it just works now

onspeed

The in/out of the MBC is in the correct orientation as well?

I suggest trying a single-port, WG spring pressure test, as suggested already.

dizzyj

Ya I'll put it back together and leave the side disconnected. Easy enough to do

MarkRobinson

any updates Jeff?

dizzyj

quick update. I got the wastegate back on and in doing so, noticed that the line from my mbc is cracked. Its 5/16 fuel hose. The rest of my vac system is smallish diameter silicon tubing (LR style). connecting the silicon tubing to the 5/16 hose (both lines to the wastegate) are 2 brake bleeder nipples. seems like those would be ripe for constriction. I'm going to replace them with a more proper connector, but any thoughts if that could cause the issue? is there a minimum diameter that needs to run to the wastegate to provide enough air volume to open?