Multimeter Weirdness

Imatk

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This isn't necessarily specific to a GT500, more of a general question about multimeters.

I'm trying to figure out why my car won't start after it sits for a few days.

I have a video here


I'm not sure if this current draw is enough to kill the battery... not sure why it starts high and then slowly goes down (it would go down to zero if I waited long enough).

The second part is another car I have. It has the same behavior... except it starts very high and then quickly goes down to zero.

I've tried this on two different multimeters and it's the same behavior on both.

So what causes this?

Is this normal?

Is that enough amp draw in the first video to make a battery die after a few days?

If not could it be something else... solenoid?

Thanks for any help.
 

DSG2003Mach1

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I don’t have it on my phone but there’s a guide to properly checking current draw. Part of it involves making sure all the systems have had time to go to sleep mode. If it’s over the normal amount gotta start pulling fuses to isolate the offending circuit.

My Mach has been where it’ll be dead in a week or so for eons, I just put it on a trickle charger now
 

fullboogie

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Can't help with the multimeter readings, but: define "a few days." I ask because a mysteriously draining battery has plagued the S197 forever. You can find threads going back to 2007 with owners complaining of dead batteries after the car sits for a few weeks. Some suggested the factory Shaker was causing it, but lots of others said no.

My car suffers the same issue. Battery drains after sitting for a few weeks. Testing shows a small milliamp draw but I've never been able to find it by pulling fuses and relays. I even have an aftermarket head unit so the Shaker theory is out.
 

RBB

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I have the same problem. Always put it on a trickle charger if it'll be sitting for more than a week.
 

Imatk

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I don’t have it on my phone but there’s a guide to properly checking current draw. Part of it involves making sure all the systems have had time to go to sleep mode. If it’s over the normal amount gotta start pulling fuses to isolate the offending circuit.

My Mach has been where it’ll be dead in a week or so for eons, I just put it on a trickle charger now

Yeah this car has been unhooked from the battery for a week so no chance it's drawing current from a computer. It's a '91 as well so not a whole lot of computer going on there :)
 

fullboogie

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Oh man, I miss my '92 and '93. I saw my Procharged '93 at the track two years ago and felt like offering to buy it back. Can we get a pic?
 

Race Red Boss

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I just replaced the Motorcraft battery in mine. It's date code was Feb.2018, so not very old. It *appears* that its just a bad battery, BUT....I'm not totally convinced yet. I have a battery tester and the new battery is showing much better cranking amps/cold cranking amps so far....it's also maintaining a good voltage level.

According to the YouTube's I've seen on checking for parasitic draws, the car shouldn't drawn any more than 25 to 30 milli amps when turned off. Your's looks like it's within spec....

When you disconnect the battery, and then put your multimeter probes on the battery cable lead and the battery terminal (should always do negative side to be safe), it will "wake up" the ECM and you'll see a higher draw initially (make sure you have your meter measuring high enough amps....or you'll blow the fuse and/or damage it). The amperage should lower fairly quickly ...down to the 25-30 milli amp level.....not to zero (from what I've seen). There is always some draw on the battery from the car systems, i.e. security. Reading the meter I found can be confusing. You also have to be careful how long you keep the meter attached when measuring amperage....many of the cheaper meters will say no longer than 15 secs. at a time and to wait some period in between before re-measuring.

Also, rather then pulling fuses to see if your amperage reading drops (to determine which circuit is the culprit), you can use your multimeter to measure voltage drop (using milli volts setting), by putting the meter leads on the contact points on top of each fuse. If it reads voltage.....there is amperage being drawn on that fuse. Check your owners manual for what's on that circuit.

I'm considering buying an "Amp Clamp" type meter so I don't have to disconnect the battery (which is a hassle besides also resetting your radio, etc.) to see if there is a parasitic draw....or not.

How old is the battery? Also, do you have any aftermarket stuff on the car that requires wiring, i.e. stereo, security system, sequential tail lights, etc.? Improper wiring often is the source of trouble....
 

Imatk

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Found out that it isn't likely parasitic draw. Looks like it's a bad solenoid so going to replace that and hopefully fix my issue.

Fortunately the car wouldn't start when I went to test it again... but this time the battery was fully charged and checked with over 600 cca so I knew it wasn't the battery at that point.

My next thought was the clutch safety switch, OR the solenoid.

Tested the solenoid because it's easy on a fox car and it wouldn't turn over. Just clicked a few times. Kept testing it and it finally turned over. So I think the solenoid is just failing. It's the original part so it's 28 years old... time I guess :)
 

RedVenom48

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This isn't necessarily specific to a GT500, more of a general question about multimeters.

I'm trying to figure out why my car won't start after it sits for a few days.

I have a video here


I'm not sure if this current draw is enough to kill the battery... not sure why it starts high and then slowly goes down (it would go down to zero if I waited long enough).

The second part is another car I have. It has the same behavior... except it starts very high and then quickly goes down to zero.

I've tried this on two different multimeters and it's the same behavior on both.

So what causes this?

Is this normal?

Is that enough amp draw in the first video to make a battery die after a few days?

If not could it be something else... solenoid?

Thanks for any help.
On newer cars with modules controlling different aspects of the car, it should be considered normal for what you are displaying. Thats the ECUs staying awake when the key is turned off. Some need time to save settings, data etc. Some are kept on to make restarting easier if its done in a certain amount of time.

As the internal timer starts counting to predetermined points after last ignition cycle, the ecu's will start going into sleep mode to preserve the battery. On Lexus vehicles with all the computers we are running, a normal off and sleeping current draw is typically 50mA.

If Im reading the settings on your meter correctly (.15 in the mA setting) you're less than 1 mA draw once the ecu is shutting down to sleep mode.
 

Imatk

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Yeah it turned out to be the starter :/

Bought a new one about a year ago so it lasted just long enough to go out of Autozone warranty.

That's the problem with older cars. You just can't find decent parts for them a lot of times unless you get lucky on Ebay and even then the prices are outrageous.
 

RedVenom48

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Yeah it turned out to be the starter :/

Bought a new one about a year ago so it lasted just long enough to go out of Autozone warranty.

That's the problem with older cars. You just can't find decent parts for them a lot of times unless you get lucky on Ebay and even then the prices are outrageous.
Im starting to think about some of those things for my 2011. Hard to fathom my 2011 being built 9 years ago this month... but Father time marches on.
 

Imatk

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Oh yeah. My '07... just bought a clockspring for it. Why? My clockspring went out on my '91 and you can't find them anywhere.

If you're planning on keeping your car then yeah all those little things you don't think about become harder and harder to find.
 

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