i unhooked mine for about ten minites lone enough to put my chip on 140hp and play and it burried my boost guage and held it at 40psi then i hooked it back up lol

 

40 psi on stock injectors????

 

The way the wastegate system works 101:

The wastegate actuator is controlled by the wastegate solenoid valve. The valve is a normally open valve which means that all boost pressure is directed to the actuator when no current is supplied to the solenoid. The PCM regulates the current to the solenoid and when the engine is running at light load/no boost pressure, the PCM will supply a 98% duty cycle PWM current to the solenoid to close the valve.

Stock tuning begins to open the valve (reduce the duty cycle of the solenoid) at about 5 PSI of positive pressure (boost). When the boost increases, the duty cycle decreases even further letting more boost pressure act on the actuator diaphram through the red line.

The green line that runs back to the intake tube is a vent. It allows the pressure to bleed out of the actuator once the solenoid valve closes. Otherwise, the actuator would remain "pushed out" because the pressure wouldn't bleed off.

Some aftermarket tuning will change the solenoid valve duty cycle to near 100% at all times, thus rendering the wastegate control valve closed all the time. However, the actuator has a fairly weak spring in it that is easily overcome by turbine drive pressure and the wastegate opens anyway.

The thing about the wastegate on the Powerstroke is that it only vents from the passenger side bank of cylinders so the drive pressure can be fairly uneven from bank to bank.

Keep in mind that boost is not the end-all, be-all of performance as some folks would have you think. I run a maximum of 25 PSI of boost because I have a turbine housing that can breathe. Backpressure (drive pressure) is a very bad thing and stock trucks can see upward of 50 psi worth of drive pressure at 25-30 PSI of boost. By cutting the drive pressure by a third or more, power will increase and the boost pressure will remain about the same or slightly less.

 

Here is a tuning screenshot concerning wastegate control solenoid valve operation.

Black numbers are the stock program while blue numbers are a performance calibration.

There is a "desired boost pressure" map in the tuning as well that the PCM actually tries to "make happen" and it uses these wastegate values as a baseline.

 

You just reminded me of something, Cody. I noticed my backpressure sensor shows 14 psi at idle, and goes up to 45-50 at WOT. That's for 35psi of boost. Why does the boost sensor start at ~0psi, but the backpressure sensor start at atmospheric pressure? And should I be subtracting 14psi from the backpressure number to get an apples to apples comparison between boost & backpressure?? That has been bugging me since I put in my ScanGauge.

Or is it just normal for there to be 14-15psi of backpressure at idle?

 

The exhaust backpressure sensor reads "absolute" which means it is calculated by ambient air pressure PLUS the gauge pressure. So your EBP sensor is right when it shows 14-15 PSI at an idle or KOEO. You need to subtract 14 PSI from your EBP sensor reading to get an apples to apples comparison.


I don't know what you mean by "boost sensor". Is that an AE value? If so, then it is already calculated for "gauge pressure" which doesn't calculate in ambient....which the MAP sensor does.

 

Yeah, I was talking about the MAP sensor... Okay, so that makes me feel a bit better. So I'm getting 35psi of boost, and about 50psi of backpressure, that's actually 35 & 35, which is good.

 

Yep, that's good.

 

as far as i know they are stock i was not told otherwise they may not be idk the previous owner never said weather they were stock or not. but i can run 30psi like its nothing and 40psi if i really stand on it.

 

All the "boost tubes", I've seen, were a tube installed inline with a very small orifice drilled into the side of it to bleed off some of the pressure being applied to the wastegate diaphragm. I have also heard of a Ford mechanic (in one of the threads when I joined FTE) punching a small hole in the plastic red line with a pick. This does the same thing as the "boost tube".