I installed my DP Tuner yesterday and that thing is awesome! I'm getting much more boost now and have a question. I will be installing a pressure regulator in the MAP line to prevent defueling but am wondering about overboost. Right now I've got the wastegate line plugged as I have an error code indicating a faulty wastegate sensor. If I keep the line plugged am I in danger of harming my engine from overboost? Is there a way to isolate and check the wastgate actuator sensor? Or should I replace the sensor and reattach the line? I used to have to go WOT to get @18 psi boost but with the DP I can generate greater than 24 psi without any trouble.

 

Sustaining boost levels well over 25 psi on a stock turbo can have some bad effects eventually, and will most likely shorten the life of the stock turbo. So keep an eye on your boost gauge.

 

I remember reading somebody's post.
They were talking to Jody about tunes and one of the questions was about the wastegate.
Jody's response was: "Keep it connected, do no disable it."
The setup was with a stock turbo.

 

Is a stock turbo a turbo with the original housing, or is it still a stock housing with the wicked wheel??

 

Everything else being equal more fuel from the DP generates more drive HP on the turbine which turns the compressor harder and that generates more boost.

I think Ford designed the defueling feature to act as a "safety valve" to limit the boost in the event of a failure in the wastegate control feedback system which could potentially allow the spring inside the actuator canister to keep the wastegate clamped closed when the PCM is trying to open it and limit the boost. Without the defueling feature the drive pressure on the turbine will increase to a high enough value to eventually "blow" the wastegate open but not until the turbine rpm has exceeded a safe operating level. Since the defueling occurs at about a 22 psi boost this tells me that if you're interested in a reliable long lifetime for your stock GTP38 turbo you should limit your boost to this level.

First read my post #25 here ... Disconnected wastegate, WOW! ... https://www.ford-trucks.com/forums/8...ml#post7286533 ... where I explain why you should never disconnect the red line on a bone stock GTP38 turbo or even shorten the wastegate control arm! This reason is different than excessive turbine rpm and has to do with turbo surge.

I've never heard of a "wastegate sensor" but below I'll explain what I think I do know about the wastegate control feedback system and how to troubleshoot it.

The wastegate control feedback system operates as follows. The wastegate actuator canister has a red line running to it and the canister has a spring inside which normally holds the wastegate closed. The other end of the red line goes to the wastegate control solenoid on the spider. The solenoid also has a green line that runs to the large black rubber boot going to the turbo intake, and the solenoid also receives manifold pressure from the spider.

As far as I can tell the solenoid functions like a double throw switch. In one position it connects the actuator canister to the manifold pressure in the spider through the red line, and in the other position it dumps canister pressure back to the turbo intake through the green line.

The PCM continuously pulses the solenoid to switch between these two positions at a rapid rate and this constitutes a so-called "bang" feedback control system. Bang the solenoid connects the actuator canister to the manifold pressure in the spider and then bang it connects the canister to the turbo intake hose.

The PCM adjusts the degree to which the wastegate opens by varying the duty cycle of the bangs to favor either the above atmospheric pressure in the spider or the below atmospheric pressure in the turbo intake hose. The PCM varies this duty cycle until the PCM sees the MAP reading that it expects to see for the given engine load.

Under typical operating conditions the "time-averaged" pressure going to the actuator through the red line is between about 5 psi to 8 psi. When the "time-averaged" pressure in the red line exceeds 5 psi the wastegate starts to open and when the "time-averaged" pressure in the red line reaches 8 psi the wastegate is fully open. Note this "8 psi" is the "time-averaged" psi in the red line not the "steady state" boost pressure in the spider.

The easiest way to see if the wastegate control feedback system is faulty is to use a piece of hose to connect the nipple on the canister where the red line normally goes directly to the one on the spider where the solenoid receives its manifold pressure. Then as you apply the throttle the wastegate will be controlled directly by the manifold pressure and your boost gauge should rise smoothly to about 12 psi or so.

Even though the wastegate is fully open at a boost of 8 psi the boost still increases above that. At least it did on my truck and with a 70 HP chip installed the boost increased to a limiting value of about 12 psi with the wastegate fully open. If you force the wastegate to remain closed by disconnecting the red line the boost typically increases to 30 psi before the wastegate is forced open enough to limit the boost at this level.

 

That would have been me. Jody didn't even let me finish my sentence before he said "leave it connected" I think I need to open it up a bit though, right now I have it adjusted full tight and its way too easy to exceed 25 psi. I need this turbo to not blow up

 

C'mon Chase, you know your not having fun until you blow something up....

 

Defueling happens at 25psi. The overboost CEL comes on at 22ish, just for the record...

 

It's a stock wheel and housing.

 

Fun or not, blown up parts are not in the budget.

My CEL doesn't come on unless I sustain 25 psi plus for a short amount of time.

 

So, with the WW, can yu achieve more boost byt adjusting the wastegate? or plugging the line?

 

Adjusting the wastegate will help build boost some... all it does it control when the wastegate opens. Plugging the line helps to build boost faster and gives slightly more throttle response. My early 99, stock turbo and injectors, wastegate full tight but red line hooked up has no issues making 25-28 psi. I can get 30psi+ (gauge only goes to 30) if I step on it and don't watch the gauge closely.

 

According to the back-to-back dyno runs on my truck with and without a boost relief valve installed in the MAP line that I made at Brown's Valley RV after my replacement turbo was installed defueling occurred at a 22 psi boost!!!

I watched the boost gauge and I went from 279 dyno HP at 22 psi boost with the boost relief valve to 267 dyno HP at 22 psi boost without the boost relief valve!

This data indicates that the defueling is a percentage decrease that's relative to the fuel map that the chip uses to override to stock fuel map.

Also the MAP sensor output voltage versus MAP input pressure saturates at 22 psi above ambient pressure so there's no way that the PCM can possibly know if the MAP input pressure is higher than 22 psi above ambient pressure!

Please post your evidence and or explanation of how the PCM can possibly defuel at a 25 psi boost when it can't even measure a boost above 22 psi.

 

The actual pressure when the overboosting/defueling event happens depends on the PCM. Some PCM codes will trigger at 22 psi, while others at 25 psi. My own truck doesn't set an overboost code until 25 psi. My OBA is set to limit boost at the MAP to 24 psi (according to AE, it hits and holds steady at 24.7 psi, and never triggers an overboost).

Not sure about your truck, but on mine the overboost/defueling is the exact same event. If I allow the MAP to read over 25 psi, it will set the CEL and at the same instant, the truck will defuel.

 

I've wondered what "surge" was referring to in a turbo. It's basically a compressor stall, using jet engine terms.

Too slow inflow versus too high demand from the turbine-side stalls airflow through the compressor.

Now I get it.

Shortening the intake tract to shorten the "inertia" in the column of air from the filter should reduce the surge potential by allowing the air to accelerate quicker. A ram-air effect from outside air into the air box would reduce the pressure drop (negative pressure) across the air filter.

Is this summary correct?