Matt,
Your comment about the p1188 is well timed. I spent a few hours with the service manual today, and another hour trying to put what my theory of the p1188 error is caused by into words.
Here Goes:
Looking through the Service Manual, A few things begin to make more sense. The p1188 error Code that refers to the Throttle Inlet Pressure (TIP) apparently shows up for a specific reason.
The Solenoid and Vacuum Harness schematic shows the Wastegate Solenoid (#2) being fed by the pressure from the Turbo. However, Downstream (closer to the Throttle Body), The TIP solenoid (#1) gets its pressure readings.
Both get the pressure input at the top fitting of the solenoid, and both vent to atmosphere at the bottom fitting of the solenoid. The Middle fitting feeds the Wastegate on #2 and the TIP sensor on #1.
#3 gets it's signal at the intake manifold, where it feeds the brake booster; the point that most of us have used for combo Vac/Boost gauge source. This goes to the top fitting of solenoid #3. It's center connector goes to the Surge Valve Actuator (imitation BOV?), and it's lower fitting gets vacuum below the throttle body.
With the 2 vacuum circuits measuring above and below the throttle body (shown in the schematic as a throttle plate), we see 2 sources of vacuum; below the "plate" is higher vacuum when throttle plate closer to being wide open (acceleration), and above the plate is higher vaccum when the plate is closer to being closed (Mid cruise, idle)
#2 is at the turbo, and sees pressure when it is spooled up; assuming 2300 RPM and above.
#1 sees pressure downstream from the turbo when it is spooled up; assuming around 2300 RPM. It also sees vacuum when the turbo isn't spooled, or while it is being vented. There are no
check valves or vacuum ejector valves in this circuit
They both should see the same pressure, but #1 should see vacuum below 2300 and when the turbo is venting through the Wastegate and Surge Valve. Also, if #2 were to see vacuum, it would be a safe bet that #1 saw it first, due to proximity to the throttle body control mechanism.
The TIP is a variable resistance that changes with the pressure read downstream from the turbo, in the throttle body. It is mounted to the firewall on the passenger side, right about where the speed control cable exits the speed control servo.
I haven't measured resistances, and the service manual doesn't go into resistance checks on this sensor.
Now, if the sensor says the turbo is making 15 pounds of boost, and tells the PCM, then the PCM sends a special delivery to the Wastegate Solenoid to vent. It tells it to keep venting until it says when. When comes as the TIP sensor detects boost pressure within the limits set by the PCM.
My guess is that it has to do with the start of pressure build up as it starts to spool around 2300. Between 2300 and 3500 the motor undergoes an identity crisis. It thinks it is a powerful Turbo Charged Animal, and it asks for 12.9 pounds of boost to be able to prove it. However, at 3500, the motor starts to hit it's natural powerband, which extends effectively to around 5500 RPM before starting to flatline. The RPM build up is faster here; an inherit design characteristic of the 2.4L motor. At 3500, the PCM tells the Wastegate Solenoid to start venting pressure; anticipating a shift coming as the RPMS reach around 5500, or the driver lets off the gas, and the Wastegate Solenoid goes into full vent, as does the Surge Valve. The vent starting as the RPMs hit the powerband is where we see the boost pressure dropping to 5 to 7 pounds. This all assumes that the pedal is to the floor from the time it hits 2300 until either a shift, rev limiter kicks in or driver gets out of the pedal.
This is going somewhere, I promise.
When we install a manual boost controller (MBC), the amount of pressure that the TIP sees and the Wastegate Solenoid sees is "conditioned" by the MBC. When this happens, a point is reached when the Power Control Module (PCM - Brain) tells the Wastegate Solenoi
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