issue w/ boost spikes? i think?
 

Hey all...

First of I'm new to the site, although not new to cars I haven't done a lot (actually anything) on Supra's in general.

I have a friend here in Germany that has a MK III Supra 7MGTE..

Anyways... Yesterday I upped the boost for him... I checked out the FAQ's on the forums here, and seen that 10psi should be ok for a stock motor (as far as I could gather).

The motor is compleatly stock except for a HKS head gasket (supprise, supprise).

Anyways... I used a plain old Air Pressure Regulator (mainly used for regulating air compressors, etc) as I've used them before on other turbo cars, and they're a cheap but effective way to manual boost controllers.

Last night I upped the boost using a boost guage to around 10psi (.7 BAR), and it was a cool night, and the car ran GREAT. Pulled very nice, never went into overboost (or fuel cut) except for once while I was trying to dial it in. But after a bit of tinkering the boost stayed at a solid .7 BAR.

Anyways... I had brought the regulator inside the cabin, but then later decided (for sometimes obvious reasons) that it would be better in the engine room away from people that would have the urge to tinker.

So w/ the regulator LOCKED all I did was disconnect the hoses, pull them back out to the engine bay, cut them shorter and reconnected.

It was ok for a few passes, but soon in 3 and 4th gear the boost wasn't stable anymore for some reason. Sometimes is would boost less, sometimes way more then .7 BAR and would hit fuel cut. It was quite random, and come and go. Sometimes fully stable boost, sometimes less/or overboosting would occur.

I then turned the regulator down because I thought maybe, just maybe the hoses being shortened might have something to do w/ it. But again, at first the boost was lower, but then went to a solid .7 BAR and I thought all was well... but again, shortly after every so often it would start to overboost and hit the fuel cut.

I'm quite perplexted w/ this situation. Like I said above, I've used this regulator before w/o issues on numerous cars (including another supra from a buddy in Canada) so I find it hard to believe that it is causing this, especially since it ran great the night before (where the air was actually a lot colder/denser).

One more thing is, the connector going to the AFM is VERY loose, by that I mean the plug does clip on but the while part (connector) that is supposed to be solid on the AFM itself is loose, and u can wiggle it up and down, side to side. Now I was only made aware of this today where my buddy showed me that, and u can hear clicking when u move the connector up and down.

Sorry for the long read, but I wanted to give as much info as possible

Cheers!

I have the same problem
And it might be ur blowoff vavle too
Try bowing on it from the front if you can blow thru it , that means its broke

That's why the boost spikes cuz the line is leaking
And sumtimes it revs high and boosts high
Depending on how your driving the car

Jus try to blow on the valve, you might have the same exact problem as I do,the way you described it

Interesting...

I'll have to take a look. I actually have the OE BOV venting to atmosphere right now, so I would normally hear a boost leak... but I will check it out anyways.

It's just very strange that it changed to radically from one day to the next.

If you are both over boosting and under boosting then in my opinion its that rig of a boost controller you are using.

Where did you hook it up at?

Yea, yea I know you said you used it before, but it's not automotive quality and obviously not made for a vehicle. For instance, that regulator is meant to be subjected to just air, well now its being subjected to motor oil and blow-by gases that are very corrosive. Do yourself (or your buddy) a favor and get a real manual boost controller, they are around $100 and alot cheaper than a new head gasket (hint, hint).

You can always take it out and put it back to stock to see if it still over/under boosts. If it doesn't then you found your problem. But I'm willing to bet it didn't do this until you rigged it up.

If the connection was bad between the AFM and the harness, the car would not even run.

And come on, get a real BOV. I did the stock-vent-to-atmosphere thing but a HKS SSQV sounds SO much better.

I understand where you are coming from... The air pressure regulator is connected at the stock locations for the wastegate. So the nipple on the cold side of the turbo goes to the air press. reg. and then to the wastegate.

You are correct, it's not automotive quality, but it IS industrial quality, which is ment to see many contaminents including oil, dirt, etc, etc.

The only other issue I have with it, is that it's quite sensitive as normally compressed air systems run at a lot higher pressure (nominal is usualy 6 BAR).

I know a real MBC would be better (although not always, I've seen enough MBC's go bad or not last long at all).

And I haven't defeated any of the safety's on the car so fuel cut still happens @ the stock levels (max) boost levels.

This I might still try, although I'm thinking that maybe it's the pulsing that's causing the regulator issues now that the lines are shorter? Like I said everything is great until I shortened the lines to the regulator.

I might look into making a ball & spring type MBC myself if all else fails, they're the basics of a good MBC anyways.

This I figured as w/ most cars with an AFM the car won't run w/o it connected, but I figure since the connector is that loose, and since the problem comes and goes, I thought I'd at least mention it.

In due time the owner will be purchasing more performance goodies for his Supra, but for the time being I did that little modification for him. It doesn't bring anything performance wise, but does do a little for the enjoyment of being able to hear (although quiet) the compressed air being vented.

As for the SSQV, I'm not a big fan of it really... I don't think it sounds all that nice :P


Hopefully we'll have some more nice weather days as we've been having here so that I can tinker some more.

Next step for him will be downpipe, exhaust and ARP headstuds, as his brother who put in the HKS gasket reused the original bolts (but he didn't know better).

I have a turboxs mbc
And how do u vent the stock bov to the atmosphere?

Just take it out of the intake arm, and let it vent.

BUT! Make sure u cap off the intake arm so no unmetered air gets in or else u'r car will run lean.

Wouldn't jus cause a leak
Since the whole system is not completly sealed?

No, why would it cause a leak? Unless u'r BOV is faulty, there should be no boost leak.

i got lost for a second
there's three hoses on the stock turbo right?
which hose to you take out?
the small one?