hesitation, low boost

[boro]

Well my first post has to be a rough one.
91 SS, just have an mbc, some very minimal Power Commander tuning and some suspension work. I run around 11-12 psi, no boost gauge so Im not terribly sure of my highs and lows.

Had a pretty tough run down the highway the other day, playing with a Toyota, a bit warm outside...maybe 80-85 or so.

Prior to this the car was into boost at around 2k rpm, even if I was light on the throttle. Pulled decently firm up to about 5500.

After this run down the highway, got home, cooled it, shut it down for the night. It sat for a couple days, till I drove it again.
Easy on the throttle I get very low boost if any at all. Just enough to hear the bov. Doesnt really change the power. Heavy on the throttle it is definately boosting, but not very much. Pretty much uses the motor to accelerate even in normal driving, when before Id just spool it up a little tiny bit and be way ahead of traffic.

Air filter is pretty clean, could be better. Took off al my hoses and cleaned some soot out of them. Noithing was clogged that I could see. Wastegate opens and closes fine. Its pretty hard to open (that was the firast tie I have ever opened a wastegate by hand) but it made it, freely.

Any ideas?
The car runs fine. It hesitates slightly at around 3k rpm then goes into boost, but to be honest, I think it always did that. It was just covered up by obviously higher boost.

I'm a little scared...

[vrg3]

If you're worried about your engine, the first thing to do is stop pushing it past its safe limits. Messing with the boost level on a stock engine, especially without the means for measuring boost, is reckless!

What are you basing your judgements about how much boost you're getting on? It seems to me that you could just be making less power, with boost levels unchanged.

Do you have the means to run my scantool? You can get some idea what the ECU is seeing.

The wastegate actuator is pretty stiff, so it does take a lot of effort to move the rod.

[boro]

Scan tool - the guy who did it called it Power Commander or something to that effect- is what was used to view the ecu operations and is how the boost level was monitored/set. 13 psi is fuel cut so it was set at 11.
I dont push past any limits friend, I am operating well with in the limit.
The EJ22 is stable to well over 300 hp.

[Splinter]

The EJ22T is stable to 300hp and well beyond, however, the stock legacy air intake, fuel system, ecu and pistons are not. Running 11PSI boost without an intercooler or even a boost gauge is nothing short of reckless.

[boro]

Is your only suggestion ease off the boost? I'm sure there are plenty of people here who have had or still have a similar setup.
*edit*
I forgot to mention the intake is not stock either.

[Splinter]

No.

1. Ease off the boost
2. Borrow a laptop if you dont have one, build VRG3's or the other scantool (check the electronics forum), go for a drive with a friend and get your friend to record the readings at different throttle and RPM ranges
3. Check for oil consumption
4. Check for vacuum leaks, you could have broken or popped off a hose
5. Use a bigass screwdriver as a stethescope to listen to the engine
6. Check your diff fluid
7. Do a compression test
8. Get a boost gauge
9. Spend some time searching and reading the forums. There is more information on here than any one person could ever absorb. Exploit it. These cars CAN be modded for cheap, but you cant just throw power at it willy nilly and expect it to take it. You need a plan. I myself have fubared my car pretty good a couple times, Ive been lucky enough to make a few recoveries.

If you want my uneducated a guess, you've either blown a piston ring, or a headgasket. Combusting 11PSI unintercooled air makes for some really hot hot pops.

[boro]

all pretty basic stuff to check, I guess I was looking/hoping for a differnt answer.
Thanks!

[vrg3]

A modified intake doesn't make your chosen boost level safe. You are overboosting, pushing past the limits determined by the engineers who designed your car.

I am suggesting more than just going back to stock boost levels. For example, I am suggesting you explain how you know the things you say you've observed, so we might be more successful in trying to help. And I'm suggesting you use my scan tool to aid in diagnosing this.

Want more suggestions? Sure:

Do a compression test.
Check the exhaust (especially the catalytic converter).
See if the blowoff valve is leaking.
Look for intake tract leaks.

[boro]

I unfortunetely purchased the car already modified as it is.
The bov, it would appear, at one time had a vaccum nipple on the under side. That has been broken off and the only free vaccum line I can see (a rather large one, at least 2mm) has been plugged.
All the piping is intact with no visable cracks or leaks. I guess soapy water is the next step.

I'll break out the comp tester this weekend.

As far as explaining what I have obeserved...I can feel it.
One day the car was moderately quick with strong boost, the next day it felt like stock. Maybe its just having a bad day. Cars tend to do that here in Missouri.

[Splinter]

That would be the actuator for the BOV

So what it sounds like to me, is that the turbo has been repeatedly backspun.

You've probably got a damaged turbo.

[boro]

backspun, eh?

explain please, or is it as simple as it sounds

[Splinter]

Its pretty much as simple as it sounds.


The idea behind a blow-off valve isnt just to sound cool, but to allow compressed air to escape when the throttle plate closes.

Without a BOV, the compressed air has no where to go, and with the throttle being shut and exhaust gas at low pressure, it goes BACK through the turbo, spinning it in the opposite direction.

This is bad for your turbo, and its also bad for the engine, because now you've got everything working backwards. Your turbo exhaust housing is now acting as a compressor, trying to force the exhaust fumes back through the valves.

Bad times.

[boro]

Im sure the bov functions just fine, as it is the loudest thing on the car. unless it is not cycling properly.
BTW, I am not a nub, I may be new here, but I have a few cars under my belt, I was just wondering if there was something I missed. this is my first Subie, its all new to me even though it seems a pretty straight forward setup. I'm not a complete idiot, I do know the purpose of a bov. Again, just making sure there is nothing I missed.
Thanks though for the ideas guys! keep em rollin and man Im impressed by the speed at which there was a response!
Thanks again. I thin I am going to build the scan tool, see what I can see. That and a comp test shuld tell me all I need to know. If [the problem] doesn't show there the possibility of it being completely serious should be lessened. I may need to be filled in on the proper parameters.

[boro]

come to think of it...the bov is noticably more quiet since the problem arose. it is usually suprisingly loud!

it makes me smile

[vrg3]

You can remove the MBC though, and I think you should. In the worst case you may have to buy a few OEM pieces.

http://www.graphics.cornell.edu/~v/vacuum/

If your blowoff valve's 5.5mm hose is not connected, then you have some funniness going on. For one thing, the valve is not opening when you shift. That "hearing the BOV" thing you're talking about is more likely actually the sound of the compressor surging (this is the "backspin" Splinter is referring to -- the combination of high pressure ratio and low flow makes the compressor wheel turn erratically and puts great load on the bearings).

For another, though, the blowoff valve is opening whenever you're above a few psi of boost. That means that the compressor has to spin extra hard to create whatever boost levels you're seeing, since it has this huge bypass leak.

If I were you, the first thing I would do is bypass the boost control. Get your boost down to wastegate level to minimize further damage to the turbo. You can do this with a few inches of 1/4" vacuum hose; just connect the nipple on the compressor outlet directly to the nipple on the wastegate actuator.

The next thing to do is replace the blowoff valve.

Then, see how things run qualitatively (by observing while driving) and quantitatively (using my scantool).

Then, if things are okay, set up the stock boost control system.

[boro]

thanks for the info.

anyone have a bov for sale?

[boro]

Ok, os I left the car alone after all your guys' advise and drove to work. HAd the same problems, obviously. Pretty much had to faroce it into boost...well any ammount of boos tthat made a difference anyways...
During lunch I went outside and did the onlything I could realy do at lunch; I bypassed the MBC and ran the vaccum hose directly from the nipple on the compressor housing to the wastegate actuator.

Leaving work, I let it warm to opp temp, then I drove noramally. Seemed much like it did before the problems started. Got onto a bigger stretch of road and dipped into boost a tad and it was much more responsive, spooled quicker with more grunt at less throttle.
Still not quite as potent as before but damn close!

Drove home with a good mix of stop n go and highway driving, everything seems back to normal.

I noticed every once in a while (this has always happened)
that it idles at around 750 - 800 or so then drops to about 500 rpm and the entire car vibrates. Doesnt feel like its going to die or anything, just idles low and causes a vibration.

[vrg3]

I'm guessing you're just judging the boost behavior by listening to the sound of the turbo or something? I wouldn't rely on that.

That's odd that it felt more responsive with boost control bypassed. This is actually the minimum boost possible. It's possible you were detonating before, though, and that the ECU was retarding ignition because of it.

You still won't get proper boost behavior until you replace the blowoff valve, though.

It's not that unusual for our cars to have very slight idle problems. In most cases they're due to a slightly sticky IAC valve or to a slight vacuum leak.

[boro]

yeah there is o real accurate way for me to monitor boost till I splurge on a decent gauge. Just need to get paid first.

But it is honestly more responsive w/o the mbc...I was suprised it boosted at all. I figured the bypass would hold the wastegate mostly open bleeding off the majority of the pressure.
I just hope it is safe to drive daily till I can dive deeper into it.
Thanks for the help.

[vrg3]

The wastegate actuator has a springloaded diaphragm in it. The spring is preloaded, so some amount of air pressure has to be supplied to make the wastegate open. It's set up so it will regulate boost to about 6 psi.

[boro]

thats what I was wondering