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Ground wires with .8 volts

jeephick85

NAXJA Forum User
Location
Montreal, Canada
Today I was fooling around checking out the power throughout the jeep and I noticed some weird stuff. When I test the ground from battery to a sensor on the truck there is a small amount of current going through them on the ground side. I general it varies from .05 to .8 volts in the ground wire. I checked the negative from battery to engine block it was 0, and battery to ground wire it was also zero and anywhere on the body it gives me "0". Can I just simply reground everything straight to the battery or is there a way to find out what is causing it to short out????????? HELP PLEASE
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jeephick85 said:
Today I was fooling around checking out the power throughout the jeep and I noticed some weird stuff. When I test the ground from battery to a sensor on the truck there is a small amount of current going through them on the ground side. I general it varies from .05 to .8 volts in the ground wire. I checked the negative from battery to engine block it was 0, and battery to ground wire it was also zero and anywhere on the body it gives me "0". Can I just simply reground everything straight to the battery or is there a way to find out what is causing it to short out????????? HELP PLEASE
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Im not sure if you wanted the message deleted or not .. but either way here you go:

Current is not measured in volts.

The voltage readings your getting is probably due too some type if interference or output since your checking it at a sensor. If your trying to check to see if you have bad grounds you need to be checking the amount of resistence from the battery to the ground spot your checking. (Measured in OHMS). If i remember correctly, anything about 1 OHM or more is too much.

Hope that helps.
 
It's not "shorting out" - if it were, you'd have zero resistance in the ground section anywhere.

Try this - disconnect the positive cables from the battery, set your meter to the low ohms (resistance) scale, and clip one lead to the battery negative post. Start tracking out along the various ground paths until you start to see significant resistance without any intervening components. Normal resistance for a solid connection runs about .005 to .01 ohms, and resistance of a wire varies by wire gage and length (I don't know the figures offhand, but you can find them all over with a little looking.)

Once you find a spot with serious resistance, you can then check each connection - yes, even putting one probe on the screw and the other on the ring can point up a dirty or faulty connection. This test can also be done on the battery connections themselves - I'd start there anyhow. Put one probe on the post and the other on the clamp.

The fact that you're seeing significant voltage on a "ground" connection tells me it isn't a "ground" per se, and that there's some resistance somewhere that you need to find and eliminate.

If you're going to check resistance, the circuit must be unpowered to get an accurate reading! The meter provides its own power when checking resistance. You can also do the test with the circuit under power and the meter set to the low DC Volts scale (usually 2VDC.) Nominal reading for a connection when checking voltage disparity is similar - .01VDC or so. Higher indicates a dirty or faulty connection - you're checking for a difference of potential, and there should be "none" (zero or close to it.)
 
So is there a problem with the way your Jeep is running ??
If not: Put the Volt meter away and walk away from the truck!
If there is: What sensor was it and what color wire were you checking.
The computer puts out a .5 volt reference to just about all of the sensors you could
have been reading this voltage.
 
jeephick85 said:
Today I was fooling around checking out the power throughout the jeep and I noticed some weird stuff. When I test the ground from battery to a sensor on the truck there is a small amount of current going through them on the ground side. I general it varies from .05 to .8 volts in the ground wire. I checked the negative from battery to engine block it was 0, and battery to ground wire it was also zero and anywhere on the body it gives me "0". Can I just simply reground everything straight to the battery or is there a way to find out what is causing it to short out????????? HELP PLEASE
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That's called a bad ground, and that's how you diagnose it.
Improve the grounds (clean the old ones or add new ones) until your voltmeter reads less than 0.1 volt at any ground point.
 
Jim Mesthene said:
That's called a bad ground, and that's how you diagnose it.
Improve the grounds (clean the old ones or add new ones) until your voltmeter reads less than 0.1 volt at any ground point.

Exactly right I would clean the grounds and see if you can get that number down alittle. But if its not killing your battery or causing it to run poorly leave it alone after cleaning ground connectors. The technical term for it is Parasitic Draw. Every vehicle has it and every vehicle has different amounts. If it gets to the point that it causes the battery to drain you can diagnose what circuit its in by removing fuses one at a time till the draw drops down into acceptable range. Once you remove a fuse and it drops you start tracing that circuit til you find the problem which could be bad/loose ground, broke wire, bad sensor or etc.
 
Well I sure will check this tomorrow, I defiantly appreciate the help. Im not too sure about how to go with the ohm thing on the meter but ill figure it out for sure tomorrow.. The jeep is running like royal shit. I'm getting 10 MPG and a rough and low idle (400), also hesitates on takeoff. I have changed my TPS, O2, Intake/ manifold seal, vaccum lines, plugs, wires, cap, rotor. It hasn't changed anything, I also cleaned the whole intake and IAC when I did the seal job about a week ago. What I dont unserstand is that for the first 10-15 mins I drive in the morning it goes great. Let me know what you guys think. Thanks Alot
 
Keep in mind, the ground on a few of the sensors is not the same as vehicle ground. Simple sensors like the TPS, the ground should be a zero volts though.

Have you checked the coolant temp sensor? Easy enough to measure the resistance with the engine hot and cold to make sure it's in the ballpark. Is this the 1985 Jeep mentioned in your profile?
 
I havent checked the CTS, its my new 87 4.0. I havenet checked any resistance yet on anything what setting do i need on the resistance it has, 100, 10000,100000 settings so which one is the one? I'll check tomorrow for sure once I know which setting. thanks
 
jeephick85 said:
Well I sure will check this tomorrow, I defiantly appreciate the help. Im not too sure about how to go with the ohm thing on the meter but ill figure it out for sure tomorrow.. The jeep is running like royal shit. I'm getting 10 MPG and a rough and low idle (400), also hesitates on takeoff. I have changed my TPS, O2, Intake/ manifold seal, vaccum lines, plugs, wires, cap, rotor. It hasn't changed anything, I also cleaned the whole intake and IAC when I did the seal job about a week ago. What I dont unserstand is that for the first 10-15 mins I drive in the morning it goes great. Let me know what you guys think. Thanks Alot

Check your EGR valve. You mentioned it running great till it warms up. Also stated you had the intake/exhaust off. Look for a small vacuum line running behind your airbox. My bet is it came undone or is leaking. One more thing, if you dont know how to find "ohms" on a multi meter, did you set your TPS right? Could also be the problem.

:patriot:
 
I set my TPS to 83% like ECOMIKE had told me to do. I did it on the square connector. One set of wires was 4.6 volts and the other I set at 3.85 which gave me 83%. When the truck idles, sometimes it sounds like its misfiring but it does have power when I floor it but it hesitates at the begining. I drive it very easy in general and the mileage still sucks. As for the ground to check the resistance do i have have to check one wire at a time or do i just go to the Ground on the engine and then put the other on the ground of the sensor to see what the resistance is? thanks
 
I checked the resistance on my grounds today and it seems to have a very high resistance. I ran a bypass wire from negative post to the TPS sensor and it had .019 Ohms. Some wires had .04 . I also checked the resistance on the CTS and got no reading it stayed on "1" as if it wasn't connected on anything. Whats the problem?
 
jeephick85 said:
I checked the resistance on my grounds today and it seems to have a very high resistance. I ran a bypass wire from negative post to the TPS sensor and it had .019 Ohms. Some wires had .04 . I also checked the resistance on the CTS and got no reading it stayed on "1" as if it wasn't connected on anything. Whats the problem?

Sounds like resistance on your grounds is acceptable.

For the CTS, were you checking resistance of the sensor using the low range? As I recall, lower temperatures are higher resistances on thermistors (which your CTS is, as well as your IAT,) and the "1" reading means that it's over the range you're in.

For instance, if you've got your ohmmeter set to the 200 ohm range (typical low range,) and you measure a value of over 200 ohms, you'll either get a "1" with nothing else, a flashing "1", or an "OL" - all mean the same thing - switch to a higher range and try again.

You'll get the same thing on a digital with voltage readings - if you're in 20VDC and trying to check a 24V system, you're going to get readings like I described above. Specifically which on you get depends on the make of your ohmmeter - and your user's manual will tell you which.
 
You want less than 1.0 ohm between the firewall and the engine, and the engine and the battery negative post, and each and every sensor ground wire and the negative battery post. CHECK THEM ALL! If that last reading was between the CTS ground wire and the battery ground post then that ground wire is bad and needs to be replaced, and would cause your problem. If it was the reading across the 2 CTS wires, then check from the CTS ground wire to the battery negative post.
 
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