Raised grounds on o2 circuit?

[wpvk818]

I'm working on a 2005 Dodge Ram 1500 4.7 liter. My customer purchased a dual EFIE but before the install I consulted several mechanics and was warned about this vehicle having a "raised ground potential" on the o2 circuit. Supposedly if one was to probe the voltage between o2 ground and chassis ground you'd see somewhere around 2.3 - 2.5 volts.

Does anyone know how to properly match the EFIE to this raised ground potential?

[alpha-dog]

wpvk818 Wrote:I'm working on a 2005 Dodge Ram 1500 4.7 liter. My customer purchased a dual EFIE but before the install I consulted several mechanics and was warned about this vehicle having a "raised ground potential" on the o2 circuit. Supposedly if one was to probe the voltage between o2 ground and chassis ground you'd see somewhere around 2.3 - 2.5 volts.

Does anyone know how to properly match the EFIE to this raised ground potential?

There's a lot on this site about it. Post cat EFIE's, and any post about hemi's. Do a search for dodge, Hemi, jeep.
Russ

[mike]

wpvk818 Wrote:I'm working on a 2005 Dodge Ram 1500 4.7 liter. My customer purchased a dual EFIE but before the install I consulted several mechanics and was warned about this vehicle having a "raised ground potential" on the o2 circuit. Supposedly if one was to probe the voltage between o2 ground and chassis ground you'd see somewhere around 2.3 - 2.5 volts.

Does anyone know how to properly match the EFIE to this raised ground potential?

The only issue is that if you don't know what's going on, it can be hard to locate the signal wire. But you will find that it's the same as the instructions, but the signal wire will be raised by the same amount as the sensor's "ground". If you measure between the signal wire and the sensor ground wire, you will see the same phenomena as described in the instructions.

Once you have found the signal wire, install the EFIE normally. There is no change to the install, nor to the way you set the EFIE. It's all the same. In fact, it's the same sensor. Some manufacturers are just putting a reference voltage on the "signal low" wire, which causes the "signal high" wire to be raised by the same amount.

[wpvk818]

Wouldn't it be best to splice into the sensor's raised ground wire instead of a chassis ground for the EFIE? That way the raised ground potential goes away, right?

Or is it best to just chassis ground the EFIE and live with it? If I use chassis ground and I go to check the EFIE offset (say 300mv) would I not see 2.5v+300mv=2.8v between the offset probes?

[mike]

No, it would definitely not. The power to the EFIE would just be cut down to below it's expected input voltage, which would allow fluctuations in the engine's electrical signal to be introduced into the EFIE's operation. You want to feed the EFIE a straight 12 volts.

The output of the EFIE is completely isolated from the input voltage anyway. They have no reference to each other. The EFIE's output voltage will float on top of the sensor's voltage. As far as the EFIE is concerned, the reference voltage for the sensor could be 100 volts. The EFIE wouldn't know or care. It will just add it's voltage to the sensor's signal wire, which is what we want.

If you measure your sensor signal wire to ground it will read between 2.5V and 3.5V. If you connect your efie to that signal wire, and measure again, it will read the same amounst, plus the voltage that the EFIE is putting out. However, your computer is not seeing those voltages. Your computer is seeing the same voltages that other computers see, because it's not comparing the signal wire to ground. It's measuring the signal wire compared to the "signal low" or "ground" wire (which is 2.5V). So it sees 0 - 1 volt without the efie, or .250 to 1.25 (if the EFIE is set to .25).

[wpvk818]

Oh, one more thing. I have not seen the vehicle yet and I'm wondering if it has 4 o2 sensors or 2.

[stl_hemi]

Yes. It will have 4. 2 before and 2 after. You need a dual efie upfront and a dual efie for the rears.