98 Cobra battery drain

BarnStang · Oct 26, 2009

Searched around a bit. Found a few good pieces of info. After letting the car sit for 45 min, checked parasitic draw test and we are getting 80 milliamp draw. My understanding from the search is that 50 milliamps is max for all Fords.
Started pulling fuses one at a time and leaving them out. The draw drops to 10 milliamps when fuse #8 is pulled.

Oh, brand new battery put in before we started anything (third one). Charging system puts out 14.3v at idle.

Disconnnected stereo amps & modules, CD deck, radio unit, chime module, remote mirrors, dome lamp, inst cluster, anti theft mod, and even stuff not related to fuse #8

Any thoughts would be appreciated.

wmburns · Oct 26, 2009

Are you trying to find out what systems are on the fuse? I have access to 2003 and 1996 model year electrical diagrams. Will check the 1996 diagrams when I get home.

GDawg · Oct 26, 2009

I'm doing this by memory but I think fuse #8 is an IP fuse that is controlled by the engine compartment box and is controlled by fuse #25. But that is based on a '98 GT. It may be different for your car.

Burns is better at this than I am. I'm new to this and am testing for my ASE (A6) in two weeks. But Burns, if you want, I do have access to diagrams from Shop Key or All Data. Teach us.

I had .171 amp draw (171 mA) drain. I had a bad alternator with bad diodes and once fixed I dropped the draw to 90 mA. I think the rest is coming from the stereo circuit. Seems to be a common problem for some reason. 40 mA is more the accepted amount.

wmburns · Oct 26, 2009

Reviewed the 1996 model year information, Fuse #8 (10a) in the I/P fuse panel controls the courtesy lamps, radio, power mirror, remote keyless entry, clock. No surprise the amp draw went down when IP#8 pulled.

Remember there are loads powered via fuseible links. Those are hard to isolate.

To rule out the alternator has a possible source of the problem (aka GDawg), disconnect the main alternator wire and the smaller connector. If the parasitic draw is from the alternator, the amp draw will go down.

How long does it take to run the battery down? Where did you install the amp shunt? 80ma doesn’t seam like a huge draw. Especially if the target is 50ma or less.

Is the top of the battery clean? You may be surprised to know that the acid sometimes found on the tops of batteries is conductive. If the battery keeps getting covered with acid, this means the battery is over charging.

Any other aftermarket electrical accessories installed?

GDawg · Oct 27, 2009

wmburns said:
Is the top of the battery clean? You may be surprised to know that the acid sometimes found on the tops of batteries is conductive. If the battery keeps getting covered with acid, this means the battery is over charging.

Surface draw is always an issue...

wmburns said:
this means the battery is over charging.

Or over drawing on dirt or other conductive material... based on conductive material between positive and ground.

CLEAN THE TOP OF YOUR BATTERY...

BarnStang · Oct 28, 2009

Amazingly, we weren't waiting long enough. After an hour we went back out and checked again-dropped to 20 milliamps. Opened a door and back up to 80, another hour, back to 20. So all the modules are going to sleep as designed. Top of the battery is clean. After speaking with the counter rep at Carquest, they have had a few batteries returned. Luck of the draw (pun intended) we got 3 in a row, well 2 in a row, we will see how the third one holds up.

I pulled the alt main and harness conn just to check yesterday as well even though the draw pointed to the fuse.

Voltmeter set to rear DC amps in series with the neg batt cable. Interestingly, no trunk light and no under hood light on this car.

THe car gets driven 3-4 times a week over 10 miles round trip or more. May not be enough for a solid charge on an efi car. My 93 would be low if I left it sit more than 5 days.

Has Vortech supercharger added.

So, will see how it goes now. He knows it needs to be driven for longer periods. Oh, it was only sitting 1-2 days and the battery would be too low to start the car. When he drove to work yesterday it would not restart. Hense another battery...

Thanks the help. I'll post back to this thread if the problem returns, but I think it's resolved for now.

wmburns · Oct 28, 2009

Driving 10 miles 3-4 times per week should be more than enough to keep a battery charged. I sometimes do not drive my convertible for weeks at a time, and it starts right up.

I am assuming the battery connections are clean and tight. The battery terminals (the negative is the worst) are real bad about splitting when over tightened. This causes them to not make good connection. This could lead to the battery not getting a good recharge.

AutoZone makes a replacement terminal with a stud. This works very well with the short stock cables. Cut the loop off of the end. Drill out the captive screw to the same size as the stud. Clean and grease to ensure a trouble free repair.

Also a good idea to get a plug in battery charger. A few hours on the charger will ensure that the battery is starting out fully charged.

98 Cobra battery drain

BarnStang

wmburns

GDawg

wmburns

GDawg

BarnStang

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