Thread: electrical issue i cant figure out! PLEASE HELP

No such thing as too much grounding with these cars...

Just don't add any grounds to the intake manifold. Keep that just for the sensor ground for the ECU.

I have to question that. The ECU should be as well grounded as everything else, since that's what controls the show. If you have bad grounds anywhere, then something, somewhere won't be operating properly.

@jimbo_se-r

Sensor ground and ecu ground are different. Think of it as a reference ground. Grounds are always passing current so there is little changes in voltage at ground. Just because something is a ground, doesnt mean there isnt any voltage there. Voltage is measured by a difference in potential. This goes back to ground loops and how current travels through a circuit. Keeping all the sensors, and only the sensors grounded to the intake manifold reduces any large amount of current from changing the potential difference between the intake ground voltage and the sensor voltage. Now for 5v sensor, the output range is likely .5v to 4v +- a few mv's. This voltage range has to then be converted to a digital signal using a ADC. The digital signal is a representation of the analog signal. Once its converted to digital, you are in the clear, but even so much as a .1 of a volt change in the analog signal could change the digital representation and therefore tell the ecu the wrong information.

@ebinkerd

I understand exactly what you are saying, and I don't disagree with any of that. I've been working with electronics for a few decades. It's not unusual to see various 'grounds' at slightly different voltages from each other. My point was that this should be corrected when it is observed. Any ground point needs to be as close as possible to 0v relative to the battery negative terminal, be it the alternator, a light bulb, or a sensor. I have corrected quite a few issues on various cars by cleaning up ground wires, and when necessary running additional grounding straps to improve the circuit.

If something is marked as a ground on the circuit diagram, then it needs to be as close as possible to 0v. Otherwise it would be marked differently on the diagram, speaker + and speaker - for example.

When you have different ground points at different voltage potentials, you are going to have issues.

I just added a ground strap on my automatic daily driver P10 and I noticed a difference. Should I relocate the ground? I went from one of the grounds atop of the intake manifold to the bracket holding the air vacuum canister for the cruise control. I guess a picture would be in order if you do not understand my description of where I added a ground strap.

@Kyle Grounds are a fickle bastard. What to take away from this is that when grounding something you are either adding a ground in series or parallel. So just because something is called a ground, it does carry some sort of resistance. This resistance when passing voltage creates current. I know I don't need to go further cause you've been around the block, but when adding grounds you are either dividing voltage between ground or dividing current.

The intake grounds are used by the ECU as a reference. It will compare the sensor voltage to a "neutral" ground. I say neutral because it is fairly isolated from the rest of the engine. Changing any ground loop through the intake will affect the ground voltage/ resistance. This will, however small or large, affect the values the ECU see's. Just be observant to how the engine reacts. I'm not saying adding any is wrong, but there is concern for incorrect voltage readings.