Too much boost. >:\

[gray fox]

ok guys maybe yall can point me in the right direction here.

Been tinkering with my 7mgte past few weeks replacing HG and stuff. before i had BHG tho, i noticed that the car produces too much boost and hit fuel cut.

got it back together and still same result.

anyways, heres what i have going on

*hks 1.2mm MLS headgasket
*ARP headstuds
*3in. turbo back exhaust

no sort of boost controller. appeared to be the stock turbo, and it had no shaft play.

timing, base and ignition are spot on.

Just think its interesting that its pushing more than 8psi considering lack of boost controller or WG shims.


any help is greatly appreciated.

Thanks,
Brad

 

[mk3-4-me]

Do you have a aftermarket boost guage on it? How do you know it's boostin more than 8?

 

[Dan_Gyoba]

First things first.

Verify that you're actually over 8 and not hitting FCO due to charge pipe leaking.

Then...

Check wastegate operation. Apply a pressure pump to the wastegate actuator and verify that you get movement at an appropriate pressure level. (Visual confirmation of movement of the actuator rod.

Check that the line from turbo outlet to wastegate actuator is not plugged.

Check that the turbo outlet fitting is clear. These are all fairly simple things to do.

If that all checks out good, remove the turbo elbow and repeat the wastegate check, but this time ensure that the flapper on the wastegate actually moves to the open position.

 

[kotu100]

Whats the boost at? Check for boost leaks, that can cause fuel cut early.

 

[gray fox]

i do not have an aftermarket gauge, working on that at the moment.

I have noticed that the stock gauge does not read vacc at all. ( i did a vacc test on the engine, 20hg @ idle ) so I am curious as to how true the actual boost reading is.

the line from the WG to the turbo checked out okay.

ill try looking for boost leaks, and try pressure testing the actuator. I really do appreciate the help guys, i searched around and really havent seen a thread with this particular situation so i figured a new one was good to go lol.

thanks thanks! will check in with results probably by tomorrow morning (going to work now )

 

[kotu100]

Also it hasn't been mentioned but make sure theres no washers between the wastegate mounting flange and the turbo. This is done sometimes to raise boost slightly.

 

[gray fox]

no shims or washers on the wastegate.

 

[Poodles]

You say you have a 3" turbo back exhaust. What downpipe/elbow are you using? Make sure that the wastegate can open, as I've seen it where the arm hits the elbow part of the downpipe so it doesn't open fully.

 

[gray fox]

its a divorced downpipe, no sign of manufacturer on the DP or the exhaust. the bend of the DP didnt look severe enough to cause issues, but seeing as a possibility ill look into it as well.

 

[shutupnshift04]

I have been having over boost problems with my 7m as well with a divorced dp. car was leakdown tested boost leak tested smoke tested timing tripple checked and i even hooked up vacume hand pump to wastegate. Nothing is fixing it. It hits boost cut everytime. Im almost positive it the divorced downpipe

 

[gray fox]

interesting. well cant say i hate the divorced DP too much, aint nothing like coming home, smelling like boost ehh? ehhh???

picking up a boost gauge tomorrow morning and ill check in with results on that.

 

[tomsupra8683]

i too installed a divorced downpipe and the boost went from 8lbs too 14lbs.And i have verified that the wastegate is working properly.

 

[gray fox]

alright. got me a boost gauge today, $20 @ harbour freight FTW!!!!

indicated 12psi when fuel cut hit. soooooo, im guessing boost leak is out of question ehh???

Seeing these other claims of higher boost with the DDP, Im guessing the WG just cant keep up with the exhaust flow???

 

[radiod]

My car was hitting fuel cut when you put load on it above 3.5krpm with a full 3" turbo back w/ divorced downpipe. I swapped exhausts with a buddy that had a bone stock '90 turbo to get through emissions and he experienced the exact same thing. Having a free flowing exhaust and being so close to sea level makes it easy to hit fuel cut.

 

[Dan_Gyoba]

And here I thought that the idea of a divorced downpipe was to give the wastegate exhaust more flow so as to prevent overboost. There should be no reason at all for boost pressure to increase with a correctly functioning divorced downpipe.

Okay, you've verified boost pressure. 12PSI is about right for FCO for anyone between about 1800 and 3200 ft altitude.

So... Verify that the wastegate is opening. Get a hand pump and put pressure to the wastegate actuator. It should open at about 8-10 PSI, and you should be able to see the actuator rod move. While it's out, check that the hose between the turbo outlet and the wastegate actuator is clear of obstruction by blowing through it. It should offer about the same restriction to blowing through as a soft drink straw. No more.

Once you've done that, ensure that you can get air through the turbo outlet nipple.

If all of these things are working, check the downpipe for a restriction in the wastegate section.

 

[radiod]

The divorced downpipe relieves the exhaust side of the turbo of the nasty turbulence that is caused by an internal wastegate dumping in to the exhaust. Less turbulence = less restriction = exhaust wheel spins easier = more boost. Most people without the divorced downpipe and just a good 3" replacement are coming in JUST under fuel cut or even hitting it when the weather is cold and they're really loading up the engine. That extra little bit of flow that the divorced downpipe gives will usually tip push it in to the fuel cut zone earlier.

Still not a bad idea to make sure your wastegate is opening all the way and not getting stuck on the tab or the pipe of the downpipe. On some of the cheaper ones they didn't give the wastegate flap enough clearance and it's actually hitting something.