Having serious hesitation when I put in my MBC

vrg3 · Post by **vrg3** » Tue Nov 09, 2004 12:48 am

26 inches of vacuum? Wow, that's a lot.

A leaky hose probably won't show up as low manifold vacuum, since it'll be a small leak. But it can affect the device or whatever that the hose is connected to.

syphon · Post by **syphon** » Tue Nov 09, 2004 3:44 am

Yeah, with the stock boost controller back in, the hesitation is gone (however the car doesn't pull as hard).

So far, it only got up to 5psi. I need to drive it some more to see if it'll ever go up to 9.

Do you think I should try putting the MBC inline with the BCS?

vrg3 · Post by **vrg3** » Tue Nov 09, 2004 3:45 am

Did you reset the ECU after hooking stock boost control back up? Cuz without doing that it's probably in "I can't control boost so I won't try" mode.

I wouldn't bother trying putting the MBC inline with the BCS. I don't see what'll come of it -- the ECU will give up on the BCS eventually and then it'll be more or less just like the MBC alone but with some restriction and stuff in the lines.

-K- · Post by **-K-** » Tue Nov 09, 2004 1:25 pm

Well I don't think it would hurt to bleed off the the mbc. Or at least try it. I have seen it recomended by some of the Liberty RS guys. (I don't think we realy know it the ecu knows that it's not controlling boost)

As for the data logging I'm looking hard at this
http://www.zeitronix.com/Products/zt2/zt2.htm

vrg3 · Post by **vrg3** » Tue Nov 09, 2004 3:25 pm

I'm pretty sure, -K-, that the ECU knows it's not controlling boost. And I'm pretty sure that after a short period of time the ECU will give up on boost control if you hook an MBC up with it.

Keep in mind that the Liberty RS guys have a completely different ECU from ours. As far as I can tell, the EJ22T ECU design is unique in the world.

-K- · Post by **-K-** » Tue Nov 09, 2004 7:52 pm

Well you could try my idea about using the FCD to make the ecu think it's not overboosting. And then bleed off the air to the MBC so you still get the boost you want. Another plus is that you won't get the part throttle full boost thing that some of you are worried about. Might be worth a try to keep the ecu happy.

vrg3 · Post by **vrg3** » Tue Nov 09, 2004 8:09 pm

You'd have to make the ECU's measured boost closely match its expected boost...

Also, you can't really get part throttle full boost unless a) your boost controller's not using the compressor outlet as a pressure source, or b) your throttle body is really big.

-K- · Post by **-K-** » Tue Nov 09, 2004 9:02 pm

But boost control is a open loop function, it has to vary quite a bit.

And all that crap about part throttle bla bla is crap to me.
Though it can blow up a USDM WRX, I think that's where the myth that it's bad came from.

vrg3 · Post by **vrg3** » Tue Nov 09, 2004 9:09 pm

It's not open loop. It's closed loop but the gains act slowly.

What crap is crap to you?

-K- · Post by **-K-** » Tue Nov 09, 2004 9:32 pm

Part throttle full boost being bad is crap. Unless you have a WRX.

I thought the boost control just pulsed, and changed the pulse rate by engine load and RPM. That was how I understood it.

vrg3 · Post by **vrg3** » Tue Nov 09, 2004 11:23 pm

You don't think it's bad to overspeed the turbo by making it compress against a partially closed throttle plate, pushing it up along the pressure ratio axis of the compressor effiiciency map, heat soaking the whole system before you even push the motor hard? I agree that it's possible to tune around it so it's not dangerous for the engine, but I don't see how it's good.

It does pulse, but at a fixed rate. It varies the duty cycle by throttle position and RPM, but makes adjustments to that duty cycle based on feedback from the pressure sensor.

-K- · Post by **-K-** » Wed Nov 10, 2004 7:14 am

Unless you have your wastgate line off the mainifold instead of off the turbo like it's supposed to it should be fine for normal driving.

Wow I thought my ecu was a lot dumber than it is, I still might try it though......

vrg3 · Post by **vrg3** » Wed Nov 10, 2004 3:41 pm

How do you get part throttle full boost without using the manifold as the wastegate's pressure reference?

syphon · Post by **syphon** » Wed Nov 10, 2004 8:31 pm

A little update, I hooked everything back up to stock after the new knock sensor and the hesitation seems gone. Well... it hesitated in the morning when it was cold.

As far as the "2 boost profile" issues I was having, I don't see that any more. Car boosts to 8-9 PSI consistantly now. I suspect that whatever is causing my hesitation is still there, and the knock sensor was just an additional problem.

My best guess now, is that there is a fuel pressure problem. Either the Fuel Pressure Regulator or the Fuel pump.

Either way, I will drive the car a couple more days like this to see what it does (in the past... problems didn't appear until I'd driven the car for a day or two).

-K- · Post by **-K-** » Fri Nov 12, 2004 1:58 pm

See what the fuel pressure is doing and if it's bad i'd try the parallel fuel rail mod at the same time.

syphon · Post by **syphon** » Fri Nov 12, 2004 10:35 pm

Ok, update.

The car is STILL switching between 2 boost profiles.

I haven't run the scantool, but it seems almost exactly the same as before. I suspect the ECU is retarding the timing because of detonation.

With a brand new knock sensor put in... my engine must be detonating. Any ideas why? (PS yes I'm running 92 octane at all times).

vrg3 · Post by **vrg3** » Fri Nov 12, 2004 10:36 pm

Hm.

You should verify that the ECU's seeing detonation using the scantool first...

Have you tried stuff like running Sea Foam through the intake to blow out carbon and stuff?

syphon · Post by **syphon** » Sat Nov 13, 2004 12:13 am

I've done nothing with the intake or the fuel system.

What's a good way to clean out the carbon? Dump Seafoam into the intake somewhere?

vrg3 · Post by **vrg3** » Sat Nov 13, 2004 2:25 am

People all have different methods of administering Sea Foam, so you might try some searches.

The way I like to do it is thread a nylon 1/4" MPT to 3/16" hose barb fitting in place of the PCV valve, and connect a hose to it. I run the engine at a high idle (a quarter wedged in the throttle cam), and feed maybe half a cup of Sea Foam in through that hose, feeding it in as fast as possible without stalling the engine out. Then I shut the engine off and let it sit for 5 or 10 minutes, and then start it up and let it run until it stops smoking.

CoreyMN · Post by **CoreyMN** » Tue May 09, 2006 7:28 pm

I too had a problem with my wastegate controller seeming to switch between two modes. One day when I was goofing around trying to find out if my pressure exchange solenoid was working, I found that it was actually a bad connection at the connector to the wastegate solenoid. I found this by connecting the green connectors under the dash and turning the ingition switch to the ON position. This cycles all relays and solenoids controller by the ECU. Then you can just move the connector and see if it cuts out.

oldfart · Post by **oldfart** » Fri May 19, 2006 2:47 pm

Just to let you know you're not alone, my 92 Subaru has exactly the same problems. Normally the boost runs up to nine PSI and stays there without any problems. Then inexplicably the maxim boost I can get is about five PSI exactly as your telling it.

Just about the same time that you did it, I replaced the knock sensor, no joy. And I've got a Halman MBC ready to put in, but it ain't going near the car until I get this five versus nine boost thing straightened out.

I totally agree with you, dam this is frustrating!!!!!!

dzx · Post by **dzx** » Sat May 20, 2006 6:47 am

I've heard of a few people having this problem of the computer switching between 5psi and 9psi.

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Having serious hesitation when I put in my MBC