DIY boost controller with TPS sensing ability.

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IggDawg
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DIY boost controller with TPS sensing ability.

Post by IggDawg »

I tried bleeding lines with the FBC still in place. unfortunately the MAP tells it "you're blind" and quickly adjusts the boost settings. Is there any way to fool both the MAP sensor and the FBC? perhaps a resistor in the MAP assy somewhere or something? I'm getting so sick of not being able to use partial throttle. I always look like an asshole when I'm passing people cause I'm at WOT to avoid running wicked lean and getting those nasty hesitation & EGT issues.

Also, does the MAP have to do with any other systems besides boost?
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Post by vrg3 »

What exactly do you mean by the FBC? The "factory boost controller" consists of a pressure-activated wastegate actuator, a pressure bleeding solenoid which can bleed pressure away from the actuator diaphragm (and back into the intake before the turbo, I believe), a pressure sensor which measures manifold pressure, and the ECU, reading from the sensor and controlling the solenoid.

I didn't call the pressure sensor a "MAP sensor" because it's not exactly that. The sensor measures both manifold and atmospheric pressure. The pressure exchange solenoid allows it to switch between the two.

That really trips stuff up. We can't just simply tweak the pressure sensor's signal line, since that'll throw off atmospheric measurements as well.

Which line did you place a bleeder valve in? I would think that if you took the vacuum/pressure line going off the nipple on the intake manifold to the pressure sensor, and bled off a small amount of air, you'd achieve higher boost in a pretty well-behaved way. The ECU would simply think the manifold pressure was lower than it actually was.

The ECU does use the manifold pressure information for a few things other than boost control. It retards ignition based on boost, and I believe it richens up the fuel mixture with rising boost as well. The infamous fuel cut is also triggered by a high reading from the pressure sensor.

I haven't tried raising the boost on my car yet, because I haven't yet done anything to justify it, but when I do, I'll first try a bleeder valve on the manifold pressure sensing line, with a check valve so my engine doesn't suck stuff in through it when I'm off boost.

The second option I'd try is a ball-and-spring manual boost controller plumbed from the compressor outlet. I suspect running it from the compressor outlet would do well as compared to from the manifold, which I feel is just plain wrong, since it destroys the whole purpose of the throttle.

If that doesn't work, or even if it does, I'll probably eventually replace it with a two-stage MBC setup that uses the TPS as input.
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Post by boostjunkie »

Does anyone have a a/f gauge mounted in their car?

The reason I ask is because my GT used to go into open loop mode at 1/3 throttle. I was just wondering whether the older turbo legacies have this same characteristic.

If that is true, then I don't see how the engine could run lean if the stock fuel map at open loop control is towards the rich part of the spectrum. That would lead me to believe that the problem is in the actually fueling system. If that is the case, then the partial throttle full boost problems might be aleviated by the use of an upgraded fuel pump (increasing fuel pressures) and possibly a RRFPR which would increase the amount of fuel pressures once any level of boost is obtained.

Someone correct me if I'm wrong here.
[url=http://www.angelfire.com/md3/91turbolegacy/images/On_the_Lawn.jpg]1991 Legacy Turbo (RIP)[/url]

[url=http://www.angelfire.com/md3/91turbolegacy/images/Summer_Car_Wash3.jpg]2000 Celica GT-S[/url]
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Post by boostjunkie »

EDIT: (where's the edit function on posts?)

Upgraded fuel pump: Allow for increase in fuel pressure

RRFPR: Multiply "standard" amounts of fuel going into cylinders while on boost, irrespective of throttle position.
[url=http://www.angelfire.com/md3/91turbolegacy/images/On_the_Lawn.jpg]1991 Legacy Turbo (RIP)[/url]

[url=http://www.angelfire.com/md3/91turbolegacy/images/Summer_Car_Wash3.jpg]2000 Celica GT-S[/url]
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Post by Legacy777 »

edit button is in the top right hand corner ;)
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Post by boostjunkie »

WHOOPS!! It's really hard to see when you've got a small window open at work :shock:
[url=http://www.angelfire.com/md3/91turbolegacy/images/On_the_Lawn.jpg]1991 Legacy Turbo (RIP)[/url]

[url=http://www.angelfire.com/md3/91turbolegacy/images/Summer_Car_Wash3.jpg]2000 Celica GT-S[/url]
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Post by vrg3 »

Note: What follows is just my logical thinking, not backed up by any official qualifications.

Even with proper fueling, I would maintain that full boost (at the manifold) at part throttle is a bad thing, and would cause high EGTs regardless.

If you have full boost pressure at the manifold with the throttle plate partially closed, you are very inefficiently creating that boost. The pressure before the throttle (which is in this case a huge restriction) would be very high (much more than full boost), so intake air temperatures would be very high. High intake temperatures mean high exhaust temperatures.

The throttle is normally supposed to control how much air the engine is allowed to ingest. In naturally aspirated engines, it very directly controls manifold vacuum. In a supercharged condition, then, it controls how much of the boost pressure is allowed into the manifold.

If you make your boost control system try to maintain full boost in the manifold at all times, you basically change the function of the throttle from controlling manifold pressure to controlling how efficiently the manifold pressure is maintained.

Of course, you still keep some control over manifold pressure because in certain conditions you simply can't produce the desired boost.

All said, I don't think it makes any sense to have full boost in your manifold when you're throttle's not wide open. It can make sense to have full boost upstream of the throttle body, though, so that it's all available when you open the throttle. That would probably best be accomplished with a ball-and-spring boost controller plumbed between the turbo compressor outlet and the wastegate actuator.
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Post by mile hi »

I would agree that the upgraded pump is a good idea several years ago we were running a EJ22t at the strip and found that at the top end it wasn't really pressure ( it did at first look like it) but the fuel pump just wasn't able to deliver enough fuel and with a pressure gauge attached the pressure would actually fall at high RPM. From what I have read and seen I don't think you will get much more fuel with a RRFPR but what it will do is increase pressure at the injector nozzle to overcome the increase in pressure in the chamber from boost and it will give a better pattern. I base this on if the regulator was supplying more fuel the O2 sensor would catch it and close down the injectors a bit. It is possible to trick the pressure sensor signal for boost only. I thought the factory boost control system was pretty good just set to low so I made a boost controller to work this way. Then I was told that it would never sell.
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Post by Legacy777 »

why would it never sell?


Just to throw another thing in there too.......if you have boost on part throttle.....you loose brake booster vacuum......more of an issue if you left foot brake ;)
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Post by mile hi »

I don't know why it wouldn't but people said that Blitz and the others had the market pretty much to themselves and they may be right. If you are loosing brake vacuum right away there is a check valve in the line to prevent this and they can get dirty and stick open. If it is the internal type of valve I would pitch it and get one of the older metal ones.
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Post by -K- »

Run a MBC and leave the factory BC connected just not to the wastgate. Put it back into the intake befor the turbo.
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Post by boostjunkie »

I'm curious as how this will prevent partial-throttle full boost. Can you explain, please?
[url=http://www.angelfire.com/md3/91turbolegacy/images/On_the_Lawn.jpg]1991 Legacy Turbo (RIP)[/url]

[url=http://www.angelfire.com/md3/91turbolegacy/images/Summer_Car_Wash3.jpg]2000 Celica GT-S[/url]
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Post by IggDawg »

-K- wrote:Run a MBC and leave the factory BC connected just not to the wastgate. Put it back into the intake befor the turbo.
can you explain what you mean by this? leave it connected to what? reason I ask is that if the MAP senses higher than stock boost, it'll keep telling the wastegate to close earlier and earlier.
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Post by Nate S »

if the factory boost soleniod is not connected to the wastegate it cannot tell it to close, well it could but it would not matter, your mbc would be controlling boost and the "map" sensor could do nothing about it.


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Post by -K- »

ok, the wastegate is opened by pressure, it's just a piston connected to a rod that opens a gate. Then some exhaust goes around the turbo instead of through it, so it doesn't spin any faster and make more boost. now there is a spring that holds the piston up, that spring is what your wastegate is set at. if it takes 5 psi to push that spring down that's the boost you run. now here is the fun, if you bleed off some of the air that goes to the wastegate you get more boost. If I bleed off enough air to get a 5psi pressure drop in the wastegate line I get 10 psi of boost because there is only 5 psi getting to the wastegate. The factory boost controller does this with a computer controled valve. the MBC is just a valve with a spring, you can adjust the amount of pressure it takes to open the valve. so no pressure gets to the wastegate to open it untill it opens the MBC valve first. if it takes 10 psi to open the MBC that is the boost you run.

So, I said you should cut the factory boost controller out the wastegate line but leave it connected to the engine so it knows what is going on.
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Re:

Post by CAV3MAN227 »

-K- wrote:So, I said you should cut the factory boost controller out the wastegate line but leave it connected to the engine so it knows what is going on.
-Sorry to bump such an old thread. But I was curious on this. So are you saying to place the MBC in this spot: (refer to pic)
http://hostthenpost.org/uploads/f778c13 ... 181de7.jpg
-So just "T" it into that line while leaving everything connected?

-Joe
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Re: DIY boost controller with TPS sensing ability.

Post by Legacy777 »

No,

What he was referring to is leaving the electrical connector connected, but disconnect the vacuum/boost lines.

To run the MBC, you run the line from the compressor housing into the MBC, and then run the outlet from the MBC into the wastegates solenoid diaphragm.
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Re: DIY boost controller with TPS sensing ability.

Post by CAV3MAN227 »

-Ahh, thanks for the input.

-Joe
-I'd rather loose by a mile because I built my own car, than win by an inch cause someone else built it for me. Your car, is your story, so don't let someone else write the book. ~Moog
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