ground issue

[guitardude2007]

my 1997 ranger had the code for purge flow sensor high input. I have replaced the sensor twice to try and fix it (cheap on rockauto) code always came back. I got to futher testing and found .2 ohms at the ground on the connector. the issue I have found is that if anything is on (dome light on, key on, engine running, etc) the resistance gets high cant remember the actual reading but far above specs. I cut the ground wire off and ran it direct to battery no ground issues now at the connector but what would cause the high resistance even the ground wire off the battery to the rad support shows high resistance when anything is on. ive been cleaning up all the grounds ive found so far all where clean but being a mechanic I know that what looks clean can be a poor ground. is there any common spots I should check?

 

[RonD]

Body parts are painted and then assembled at the factory so even though they are bolted together they are not "grounded" together.

Engine and trans sit on rubber mounts so they are not "grounded"

Cab and other body parts sit on rubber grommets so they are not "grounded" to Frame

So...............
Battery's larger negative cable needs to go to engine because starter motor and alternator have the largest amp flow.
Engine needs a ground strap to the cab firewall, usually from the head, for cab electrics.

Engine needs a ground strap to the frame, for tail lights, and fuel pumps

On some battery cables there is a smaller negative the goes to rad support(head lights) and a cable from that point to inner fender, for engine electrics.
But you can add your own if needed.

You can't have too many ground connection, if in doubt add another strap


And what scale are you using to test OHMs, use lowest setting on meter.

 

[Spott]

There may be a bad ground elsewhere, and those components are having to find ground through the sensor, which is bad.

I'd recommend checking, cleaning, tightening, and repairing as needed all the grounds in the truck.

 

[adsm08]

Also, any resistance test on a circuit that has power flowing through it is invalid. Resistance is tested by applying a small amount of power and seeing how much makes it through. If you test a circuit that is powered up it messes with the resistance readings.

 

[guitardude2007]

I know not to have the circuit powered I guess I should have explained it better. but with further checking with a wiring diagram it gets its ground from g101 which is shared with many other things included the gem which from what I see controls the dome light which would explain why I was seeing the resistance. this ground appears to be the one at the rad support which would explain my reading there being high with just the door open. rookie mistake and I am only an apprentice so haven't done a whole lot of electrical diagnosing yet but with the ground wire cut from the sensor running direct to battery the signal voltage has dropped within specs now when before it was high which set the code. so I know with .2 ohms the ground should have been good to the sensor so could it be something connected to that ground that has a bad wire or connection somewhere causing the sensor to get a bad ground as soon as that is powered up?