I had seen it on TDR, but since I'm not a member I couldn't see the whole thread. Basically some guy had wired up a switch to his MAP sensor to fool the computer to think there was full boost, when there wasn't. So he got full fuel when ever he wanted.

 

i think he was playing around with some different resistors to increase the voltage going back to the ecm on the signal wire [3 wires on the map sensor side 1=5vdc, 2=signal, 3=ground] the resistor was jumpered between the 5vdc line and the signal line.

[the sensor on our manifold has 4 wires, as it is a combined map/intake temp sensor, 1 ground, 1 5vdc, 2 signal's]

 

Here's the circuit. The zener diode prevent the voltage from exceeding the preset level in the ECM. If it goes over the ECM sets a overboost code.



MikeyB

 

I thought it was to get the TST to see full boost all the time so it would fuel off boost.

 

Will it work on an 04.5???????????????

What is it doing???

 

That schematic is of no help what so ever. What is the pinout on the stock MAP sensor? What resistor to begin with?

 

You can get the schematics and pinout for the MAP sensor here.
http://www.dodge.com/bodybuilder/200.../dr/drwdmo.pdf

The resistor isn't really needed but it's just for current and voltage limiting.
The zener is the voltage clamp to prevent the overboost code.
Most performance boxes already have a boost fooler circuit.

MikeyB

 

When I get the truck running again I'll play with it and post results

 

2003 - 8w-30-73
pin1- ground [dark green/yellow]
pin3- supply 5vdc [dark blue/yellow]
pin4- boost press signal [grey/brown]
pin2- intake temp signal [violet/white]

2004 - 8w-30-49
pin1- ground [auto=dark green/yellow, manual=brown/yellow]
pin3- supply 5vdc [auto=light green, manual=brown]
pin4- boost press signal [brown/yellow]
pin2- intake temp signal [auto=violet/white, manual=brown/white]

2005 - 8w-30-35
pin1- ground [dark green/yellow]
pin3- supply 5vdc [light green]
pin4- boost press signal [brown/yellow]
pin2- intake temp signal [violet/white]

2006 - 8w-30-27
pin1- ground [brown/yellow]
pin3- supply 5vdc [brown]
pin4- boost press signal [brown/yellow]
pin2- intake temp signal [violet/white]

the pins are the same for all years, but the colors are all different [and in the 04 manual, it is showing different colors for the same wires on different pages] use info at your own risk [the 8w-30-xx is the page number for the year factory service manual]

 

I have built something very similar to this for a gas engined vehicle. In mine, there was a potentiometer and shunt resistor to allow for a variable resistance that would result in a voltage range from just under to just over the ECM's nominal 5 volts. This is what I supplied the sensor with resulting in a lineal increase in the sensor's output voltage based on the difference I set the potentiometer at above the nominal 5 volts. as MikeyB stated, the zener diode limits the voltage passing it so at what should be, for the sake of explanation, full vacuum at 5 volts, would now be 6 volts if you had the supply set at six. So, in the case of the CTD, it would see an over-boost from the sensor- it wouldn't know any different.

By the way, a zener diode is a diode that, unlike a rectifying diode, allows full current one way, and partial the other way based on a predetermined reverse voltage. You can't use it except in electronics as it is useless for handling much in the way of wattage.

 

I found some of my original drawings. Sorry, I used a voltage regulator, a varister and a few resisters to give me a measurable and adjustable voltage with which to supply the sensor with. The range I had was about 4.5 volts to 7.8 volts. If I recall, I had it set at near 6.2 volts to supply the sensor, so the output is more or less 1.2 volts higher at any given vacuum condition. One of these days I'll have to go open up the case and see what I did. I didn't write everything down.

I didn't include a zener, but have a pre OBD multi-port injection and don't worry about codes being triggered It was used to compensate for a header and a more free flowing air filter.

Vacuum is, of course, a tad bit different to boost, but I think the same principle applies for how it is measured by the ECM. I don't have the ***** to try it with my new 05 CTD.

 

the useable voltage range of the sensor is from ~0.5vdc to ~4.5vdc. below 0.5vdc it can read as a short in the signal wire, above 4.5vdc it can read as a short to power. the actual power to the sensor can varry a bit, but the ecm knows what is going to the sensor, so it knows how to componsate for the slight variance

 

So what resistors and diodes do I hook to what wires on my 05 to make the ECU think it has boost at idle and allow more fuel at lower boost levels?

 

Buy a MP-8.

 

I have an MP8. Try lugging in OD at 40mph. Even with the MP8 all the way up there is only a slight haze with no boost because the RPM is so low.