Originally Posted by BMac
I started tuning the MegaSquirt again but still have TPS problems and still don't want to burn up the engine.
too much information for you:
You can cure most TPS problems on the 5.2 by removing the sensor and cleaning the black contact patch with alcohol. Some disassembly may be required
. Check the movement of the sensor as well. Next, take the holes that attach it and use a drill or Dremel and elongate the holes. Next reattach and using a meter, adjust the home position (with the ignition on
, engine off
) so it reads .7 volts - .45 volts is the stock reading. You can go as low as .25 volts without a problem. The TPS will sometimes have a "dead" spot at idle which causes a stumble under acceleration and can cause shifting problems on the auto transmission version. I cured my original Stinkerbutt (same throttle body that you have) by adjusting the sensor slightly past the dead spot to the high voltage side.
The problem comes from three areas. First, the little plastic piece in the throttle body that moves the sensor can get worn. Second, the fitting in the sensor itself can be worn. Third is the afore mentioned dead spot. By moving the sensor so it is "preloaded" against the spring, you eliminate most problems (preload can start at about .6 volts). In other words, move the thing until you feel the resistance of the internal spring, tighten and you're good to go.
NOTE: most of these problems are caused simply by the throttle body not engaging the TPS as you come off of idle - hence preloading the spring will probably cure it by itself.
Another problems with the sensor is a poor ground. You'll have to refer to the shop manual for the exact wire colors; it is blue/yellow stripe in most models/years.
On that engine you can also adjust the ignition timing. To do this, get to the bell housing on the passenger side. The sensor is attached just above the starter motor. Remove it and note that there are two rubber grommets. Remove them, elongate the holes, use washers on the bolts that hold it in and move the sensor (if I recall; you'll have to check this with a timing light) DOWN
, which will retard the ignition timing a bit (about 2 degrees).
Another area in the Dodge Magnums (don't worry, the 5.2 was designated a Magnum) that will get you better mileage is to move the IAT (Intake Air Temp.) sensor to a hotter area. These sensors use resistance to tell the ECU what temp. the intake air is and adjust the mapping accordingly. You'll note that the higher
the resistance, the colder the computer will think the engine is so you can't just slap a resistor inline. You'll get better performance but lower gas mileage. If you add 4k to it, it will always be in the cold map and get you some extra ponies when the engine is hot.
Refer to (one of) my web site for more TB mods for that style TB (videos too):
There's also a chart of my mileage before and after the mods there too.