Constant battery drain

[Highway Q45]

I haven't been here for awhile but another Q bug has reared it's ugly head. For the last week the Q's been starting hard after sitting. I thought the battery was giving out. Tested it this morning and discovered that the "dark current" is 4.25 A. I know this is way too high. I figure maybe a high resistance short somewhere. I've pulled every fuse and relay individually and still the drain is there. I can't seem to get the 2-100 fusible links out to see if it's going through those circuits though. Other than hard starting, there are no unusual readouts on the dash. Only thing I've done electrically was a new stereo but that was 10 months ago.

1. What unfused circuits are always hot that I should check?2. Would a Consult be able to track it down any closer?3. Any suggestions or "non-consult" testing procedures.4. What is normal "dark current" for this year?

Again any help would be greatly appreciated, a trip to the dealer is not in my current budget.

Thanks,Steve:help

[Q451990]

How are you checking the "dark current" (new term to me but I like it!)

Let me know and I'll check my 90 - should be about the same.

Heath

[VenCountyQ]

Try checking the charging line that runs from the battery to the alternator. "dark current" shouldn't be more than .25A

Having a DC current clampmeter (Hall-Effect) is a big help. Hard to find, but Sears recently starting carrying a nice one (auto-ranging, True RMS) for $99.

[MinnyQ]

Hmmmm ... my '95Q has gone through for batteries in the last three years. I haven't asked the dealer to do an aggressive search for this, since i can tell when the next one is going ... about every eight months ... and just get a new one. Not very ecologically friendly, obviously. i think its an over-charge problem. Anyone have any thoughts?

[Highway Q45]

Q451990-I've always called it dark current but I test it by two methods. The simplest which adds the resistance of a good ohmmeter is just to disconnect the battery neg. and hook it up directly in series on 10 A. scale. The other way is I have a calibrated shunt I clip in with a very low resistance and read the voltage drop (IR) across the ears. They were nearly the same. The shunt works well for low current applications but can't be used for starting currents, etc. If you want to check your 90 remember you'll lose all your radio settings but the info would be good to know.

VenCountyQ-After looking at the wiring diagrams, the starter and alternator are wired hot from the battery. I'm wondering if the starter is slightly shorted or that the alternatnor is shorting out although it seems to be charging fine. Yes, I've used the clamp-on ammeters but never thought the lowest ranges were all that accurate but they sure are convenient.

The 25 ma sounds about right. My Miata is 22ma, the 944 is 18ma...all the Q has to provide is 12V memory to the ECU, Clock, radio, who knows what else but 4+ amps is way too high.

I guess I'll have to root through the manual and try to figure it out from resistance values. I don't have a means for load testing either the starter or alternator except at the local auto parts store.

If anyone has experienced a similar drain problem and solution, the beer's on me!

Thanks,Steve

[VenCountyQ]

If the drain is steady you should be able to rule out the alternator by disconnecting the charging wire. On my 94Q there is a harness on the positive terminal cable with 2 connectors carrying middle-size lines. One goes to the alternator which you should be able to unplug. I've had similar symptoms to yours but haven't been able to catch the current drain as it is intermittant. I've got the ammeter ready when it surfaces again.

I agree your comment regarding the accuracy of clamp-on ammeters. Although in this case you are more interested in locating the current drain vs. measuring it. Finding a DC clamp ammeter at a reasonable price is hard enough vs. the AC variety which are a dime a dozen. I have recently seen a DC clamp ammeter pickup with a diameter of a pencil meant to measure small current at greater accuracy. It is meant to be hooked into any standard multimeter. I will let you know if I run into it again.

[VenCountyQ]

Highway Q45 - I found a site that sells the mA DC/AC Current Clamp - http://www.alfaelectronics.com/CA60.HTM

[Highway Q45]

VenCountyQ-Thanks for the link to the nice clamp-on. I have to use both a low range and high range unit for my Fluke Scopemeter but the jaw size presents a problem in tight spaces. You are right though, I'm not looking at the problem from "how much" but "where". My 91, from the battery +, has a single large gauge to the starter and paired connector type 2-wires feeding the 100A and 120A fusible links. From there the 120A link shares a buss, one to the alternator I assume, and the other to the adjacent fuse/relay box. The 100A link also feeds the same box. Seeing how I'm too dense to figure out how to remove those links, I guess I'll do them one at a time by unscrewing the lugs or pulling the connectors at the positive battery terminal. It would sure help if someone knew the trick to pulling those links, there doesn't seem to be a latch and I'm afraid I'll break them if I keep pulling straight up.

Are the alternators or starters on the Gen1 Q's prone to failure? if they are it's new to me. It's still a lo-mileage car at 120K. I'm going to try a bootleg alternator test tonight. Problem is, a high-resistance short would still show decent charging if the short current was lower than the operational load on the alternator. In real world terms, a 4.25A draw is negligible for a high current alternator like the Q.

Now if I can find the open circuit resistance of the starter and alternator I might make some progress. It seems most of the testing in the manual is set up for a Consult and not the garage monkey like me.

The search goes on...thankfully there's 4 other cars here that WORK!

Steve

[Q45tech]

That clamp on unit is what I use with an oscilloscope to look at the fuel pump, ignition coils, and injector currents to see the waveforms!