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Premium Member
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5,354 Posts
Discussion Starter #1
Hey

I got this problem with my car...

It's overboosting like crazy.. I get about 19psi in second gear (I'm automatic) and over 21psi in third gear.

Now I dont want to kill my engine so what can I do to fix this problem?

First I thought it was my MBC, but I removed it and put all the VSV-hoses like they were stock but I still overboost. :(

Before when I closed my MBC all the way I would only get 14psi, like stock boost... something is wrong with my car now but I cant figure it out.

Could it be that my wastegate actuator is sticking? How can I check it?

What else could I check?

Thanks in advance guys/gals :)

Krister
 

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Supra OG
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2,392 Posts
I have a MBC on my automatic and while it holds boost fine in first 2 gears, it does overboost in 3rd gear when under full throttle which I always attributed to the wastegate not being able to bypass enough exhaust under load to keep the boost level i.e. boost creep. Do other guys with automatics have this problem?
 

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265 Posts
ive had that prob... my waste gate is messed up rite now... i dont know if toyota sells just the waste gate itself or not... if they dont then im sure not gonna buy turbos from them i rather put that money for sp budget kit... does anyone know if they mite sell just the wastegate portion...
 

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Shawn Davis
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1,662 Posts
I have an MBC and don't have any problem. My boost is pretty around 1.05 bar in first and second and about 1.1 bar in third.
 

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Premium Member
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Discussion Starter #9
Bump

So is it the wastegate actuator shot or what? Has anyone replaced theirs and how can you test it if its broken?

Krister
 

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Spencer
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823 Posts
Do you have a Electronic Boost controller installed?? If so check all the place where you capped when installing to see if the caps fell off. One of the caps fell off on my wastegate and I was overboosting too, could not control boost with the profec B till I recapped.
 

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Premium Member
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Discussion Starter #11
Nope, I got a MBC as I said before :)

...and I have removed the MBC and put everything back to stock now..
 

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2/3 HP to the Paws
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1,519 Posts
What kind of setup are you running? If you've got an overly large downpipe (e.g. 4") and/or no MAF, you'll easily outflow the stock wastegate. A lot of the AEM guys run into this.

The only realistic fix (assuming you keep the stock twins) is to make a replacement manifold with a dump tube and use an external wastegate.
 
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I think something is wrong with my greddy profecB spec2 ebc as well. I can't even get it to the 1st bar. My buddy thinks the reason for it is because my dp isnt on yet.
 

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Premium Member
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Discussion Starter #14
Simba: I'm running just a normal RMM-clone 3" dp and stock maf..

If I dont fix this overboosting problem, could I just run racegas all the time and in time, just blow the stockers? I've planning on the SP budget kit so it wouldnt matter that much if I'd blow them.

I'm just wondering could it do some other damage to my engine if running 21psi+ all the time?

TIA!

Krister
 

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2/3 HP to the Paws
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1,519 Posts
Krister said:
Simba: I'm running just a normal RMM-clone 3" dp and stock maf..
Ah, I forgot that you have a eurospec car. I believe they have a smaller wastegate than the US cars.

Either way, the solution is the same. Rig up a dump tube and use an external WG.

OR, you could get a US-spec 1st turbo with the larger wastegate. That should hold everything you can give with the MAF and 3" DP. If you're planning on going beyond that, however, you're better to go with an external setup.

If I dont fix this overboosting problem, could I just run racegas all the time and in time, just blow the stockers? I've planning on the SP budget kit so it wouldnt matter that much if I'd blow them.
You probably won't hurt the engine if you run race gas, but you will nuke the turbos.

I'm just wondering could it do some other damage to my engine if running 21psi+ all the time?
The only issue you could potentially run into is cracking your head by running very high boost for extended periods of time. I've seen cracks between #3 and #4 exhaust port on cars that have been road raced for prolonged periods at over 18 psi. This is due to excessive heat buildup as a result of overboosting the turbos.

I'm not saying this will happen, but it can. You've got a larger margin for error with the UK hood scoop and bigass air grabber, though.
 

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Premium Member
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Discussion Starter #17
Simba said:
Ah, I forgot that you have a eurospec car. I believe they have a smaller wastegate than the US cars.
Hmm, nope we got the same one that you guys get. The jap-spec has the smaller wastegate.

Ah, screw it. I'll just run racegas all the time and upgrade to a single or a new set of stockers when these blow.

Krister
 

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i'm having the same problem. i have the profec boost controller which will maintain boost settings under normal conditions but under WOT it over boosts to about 22psi. I run 98RON fuel at all times and the only thing i notice is that it seems to bog down at very high revs in 2nd gear - not sure if i'm hitting fuel cut or something (i'm not a mechanic)

Also profec overboost alarm goes off!

i've got a 4in pipe though so that might have something to do with it.

does anyone have pics of what a dump tube and external WG looks like?
 

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Premium Member
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Discussion Starter #19
Do you have a Jap-spec car or US-spec?

If you have the Jap-spec, your car came with a 20mm wastegate instead of the Us-spec and Euro-specs 30mm. If you install a downpipe on your car without any cats your car will overboost. This shouldnt happen with the Euro and Us-spec Supras because of the bigger wastegate.

The only cure for your problem is to enlarge the wastegate, fit us-spec turbos or fit the stock downpipe.

HTH

Krister
 
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