Turbocharger Boost Control System Operation

[drmayf]

I race a small car at the Bonneville Salt Flats and my car is a twin turbo unit. The control for that is really simple: boost pressure goes directly to wastegate. On my F250 PSD though there is a wastegate control solenoid in line with the wastegate actuator. I understand that there is a MAP sensor that sends the boost pressure in the manifold to the PCM which somehow regulates the pressure to the wastegate. Does anyone have a clear explanation on how this control solenoid works in conjunction with the MAP and PCM? I thought I understood how it worked but was wrong...dang, twice today.... Please send replys to both the forum and to my email addy: [email protected] I would certainly appreciate it!

many thanks,

drmayf

 

[roosterdiesel]

Welcome to SDD!

Well the MAP sensor reads boost to tell where in the fuel map the injectors need to be. 17-25 is max fuel. 25 being overboost and will cause a defuel if you don't fool it with a regulator or relief valve.

It also tells when to open the wastegate in conjunction with the exhaust back pressure sensor. At full boost the solenoid is allowing around 5psi(I put a gauge on it) through the red line to the actuator. This is helping control BP by allowing the WG to bleed some off. There's around 5lbs pre-load generally in the actuator. When I would shift gears the gauge would spike to 25 like what my engine boost gauge was reading when I lifted. That was the solenoid opening completely to open the WG completely. It would do that too when I remove my map fooler and hit defuel. This was with the Evo on level 3.

Some programming I understand applies 100% duty cycle to the solenoid to help keep the WG closed.

That's my experience with the WG.

 

[powerboatr]

Welcome to SDD!

Well the MAP sensor reads boost to tell where in the fuel map the injectors need to be. 17-25 is max fuel. 25 being overboost and will cause a defuel if you don't fool it with a regulator or relief valve.

It also tells when to open the wastegate in conjunction with the exhaust back pressure sensor. At full boost the solenoid is allowing around 5psi(I put a gauge on it) through the red line to the actuator. This is helping control BP by allowing the WG to bleed some off. There's around 5lbs pre-load generally in the actuator. When I would shift gears the gauge would spike to 25 like what my engine boost gauge was reading when I lifted. That was the solenoid opening completely to open the WG completely. It would do that too when I remove my map fooler and hit defuel. This was with the Evo on level 3.

Some programming I understand applies 100% duty cycle to the solenoid to help keep the WG closed.

That's my experience with the WG.

ditto
my predator did that with the solenoid it kept it "alive" withkey on so as not to break open at 5 psi. it would however DEFUEL and set an SEL light at 25 - 27 ish plus,( which was good becuase it really killed turbo stall or fart) some have unhooked the red line to remove the 5psi opening or cracking phase, if your getting on it it can be a bit jumpy with the red line unplugged from teh actuator. but nothing to drastic. its just not as smooth of a boost release

 

[Hoss 350]

I race a small car at the Bonneville Salt Flats and my car is a twin turbo unit. The control for that is really simple: boost pressure goes directly to wastegate.

This sounds more like a blow-off valve than a wastegate. A wastegate bleeds off enxhaust past the turbine wheel of the turbo to control turbo speed, and subsequently, boost. It also controls exhaust backpressure.

A blow-off valve directly vents boost pressure out of the intake to control the amount of boost pressure in the intake. A blow-off valve is not as efficient, because you are creating the boost, then wasting it to atmosphere, where a wastegate stops the boost from being created int eh first place. Not such a big deal, but there is a difference in the way they operate.

A blow off-valve is just a pressure poppet valve that pops open under a set pressure, and vents boost pressure.

On my F250 PSD though there is a wastegate control solenoid in line with the wastegate actuator. I understand that there is a MAP sensor that sends the boost pressure in the manifold to the PCM which somehow regulates the pressure to the wastegate. Does anyone have a clear explanation on how this control solenoid works in conjunction with the MAP and PCM?

And, as you can see here, a wastegate functions off of a sensor in the intake (and exhaust, in some cases, but not, as far as I can tell, on your truck) which monitor the pressures there and respond by opening the wastegate, which allows exhaust gasses to bypass the turbine wheel and therefore, control boost and EBP.

The MAP sensor reads a pressure signal from the intake, and sends a corresponding signal to a solenoid valve, which pushes and pulls an actuator rod that operates the wastegate. Pretty simple operation, really.

The ways that you can cheat this system to get higher boost are numerous. Banks makes an aftermarket actuator with higher return spring pressure, so it opens a little later. You can unplug the WG control solenoid pressure line from teh solenoid, and get higher boost pressures. You can crank down the adjuster nut to make the actuator arm open the WG later. Or, you can disable the whole unit, and just let exhaust backpressure blow the WG open whenever it gets high enough.

The culmination of all of these efforts will create a defuel situation over 25 psi, unless you modify your MAP sensor feed line to blow off pressure over 25 psi and lie to the sensor.

Hope this helps...

 

[roosterdiesel]

Unplugging the boost source for my WG made my turbo overspun. Cost me .2 and 4mph at the track. Didn't matter the programming, chip or programmer. With the solenoid connected it was harder to pedal of the line and had better top end. 4th gear barks. Red tube unplugged, I could tell it was overspun cleaning up all my smoke and what I call "leaning out." No chirps down track. The little .84 ex housing is the problem. I think with the 4" and ATS housing my turbo spools pretty quick and gets overspun easily! Also I got worse fuel mileage when I was running red tube unplugged trying to fix my electrical plug for the WG solenoid after squirrels nawed on it.

 

[roosterdiesel]

This sounds more like a blow-off valve than a wastegate.

Actually Hoss he has a typical hi-po WG.

Easiest mod to get more boost on a turbo Buick(if you have the fuel) is to take off the factory control and add a "Grainger" valve that's adjustable and acts like the old BOOST TUBE bleeding off the pressure going to the actuator. When a desired boost is achieved the valve lets the pressure by. If no valve, you just have a line from vacuum port and adjust the rod for more boost. Make sense?

 

[Hoss 350]

Actually Hoss he has a typical hi-po WG.

Easiest mod to get more boost on a turbo Buick(if you have the fuel) is to take off the factory control and add a "Grainger" valve that's adjustable and acts like the old BOOST TUBE bleeding off the pressure going to the actuator. When a desired boost is achieved the valve lets the pressure by. If no valve, you just have a line from vacuum port and adjust the rod for more boost. Make sense?

You learn something new every day. THe way he described it sounded like he was controlling boost via a blow-off poppett. Thanks, man!