83 308 QV: key in ignition, should there be any resistance across battery cables?

I'm not familiar with a short causing a battery drain; usually this leads to a fuse blowing. The clock is certainly close to the amp draw level of a parasitic load (though expected, as it's a running clock).

I can pull the battery panel and measure with a meter, but i'm curious as to what readings and conditions you're trying to confirm. IE, I'm not sure exactly what your concern is. Is it the dead battery?

 

Perfectly normal.

 

Can you be more specific about the measurement results:

1. When you touch the two probes of the multi-meter together it reads = ? Ohms

2. When making the measurement between the battery cable ends, and key in Pos II, it reads = ? Ohms

For #2 on your model (just going from memory), a relay or two may close, an electrovalve or two may close, the alternator light is "on", the gauges are "on", and the ignition system would be "on", so I'd be guessing could be drawing a fair bit of current (so something like 1~2~3 Ohms for #2 wouldn't surprise me). Also, what happens for #2 if you reverse the multi-meter probes? Kind of an unusual type of measurement you are making...

 

Again, perfectly normal. I'll let you guys figure out why, if it's that important to you.

 

Try this:

Disconnect the Neg batt cable at the Quick Disconnect, put your multimeter into the amps mode - you will probably have to connect the multimeter leads at a different terminal on the DMM to do amps - most DMMS have a 10 AMP max capability. Now connect one MM lead to the "fixed" QD terminal and the other lead to the disconnected "free" QD terminal (or the bolt on the chassis where that neg cable attaches).

With the key off, observe the reading - should be very low since the only thing that should be "running" is the clock - I'd think 40mA at max and would expect something considerably lower - like 20mA. BUT I don't know what it actually draws. FWIW, most modern cars with all sorts of computerized things that need full time power don't draw more than 50-60mA. Remember, if you have the door open, the light for that will be on as well (if it's working) which will draw additional current. You can turn on the ignition key if you want to see the load with the key on but do not, Do Not, DO NOT try to start the engine - DMMs and their cables cannot support the several hundred amps that will be present when the starter is engaged.

If you get a reading much beyond 30-35mA with the ignition "off", I'd start pulling fuses to see what circuits are drawing the power. Start with the fuse that feeds the clock and go from there.

Good Luck

 

In accessory mode, yes - you're going to the fuel pump + the clock and whatever else pops on.

My initial suspicion is simply that the battery died a year earlier than the average battery dies. Check the alternator output with a meter at the battery once you get the new one installed. And just confirm that your alternator is doing what it should.

 

It shouldn't with the key in Pos II and the engine not running. If your fuel pump does run in those conditions, something has been modified or the safety switch is unplugged.

 

Oh? I was under the impression that the pump runs in the "on" position, even pre-crank. Please correct me if I'm wrong, as I hate being ignorant.

 

See page 67 in the 260/83 OM for a 1983 US version 308QV (or page 65 in the 248/82 OM for a euro version 308QV):

"The pump will start running only when the ignition key is rotated in the III (Start) position."
Image Unavailable, Please Login

After the engine starts, and you release the key to Pos II, the fuel pump only stays running if air is actually being drawn into the engine (which deflects the airflow metering plate and opens the safety switch). As I said, if your fuel pump runs with the key in Pos II, but the engine is not running = safety switch unplugged or some other modification (which can be dangerous if you are involved in a serious accident and the fuel system is ruptured).

 

Sam,

You have a QV with CIS ignition. When the engine is not running, the fuel pump is not on. If it is, something is wrong, and may be draining the battery. Your tests are not indicative of what current draws should be. You should put your meter in series with the battery, and using ampere mode to detect what the current draw is.

 

Correct. The clock will draw enough current to kill the battery in a few weeks, if the car is not started

Perfectly normal, for the 3rd time.

With the key in position II, "Running Position" the ignition is on. The circuit to the coil primary is closed. If there was a battery in the car, 12V would be applied to the coil primary winding. With no battery if you measure the resistance between the + and - battery cables all you would see is DC the resistance of the coil primary winding, of which you have two in parallel, in addition to the parallel resistance of any other circuits that would normally be energized. The DC resistance of the primary is typically less than 1 ohm. So with the battery out and the ignition switch in position II you can expect a very low resistance when measure between the battery cables.

P.S. Once the car is running the impedance of the coil primary will increase as the coil charges and discharges due to the inductance of the windings

 

Actually, not. But it sounded good.

 

Ok, first I will apologize for my previous posts.

I went out and measured my car, '85 QV, as the OP requested.. With ignition switch off I got about 14k ohms. With ignition in position II I get about 2.4k ohms. I'll verify those measurements a little later.

 

Ohm's law says that if you draw 1A on a 12V circuit the resistance will be 12Ohms (V = IR), so your meter could easily look like a pretty low resistance depending on what's powered.

 

As Mitchell said above "You should put your meter in series with the battery, and using ampere mode to detect what the current draw is." I wouldn't worry about the second key position, if the battery is draining when off, that is the current drain to test. You could also have a bad alternator but suggest you get those tests done by an expert or do a bit of research on here for good instructions.

 

Checking resistance doesn't really tell you what you want to know. Do the battery amp check as per my earlier post (#6) to determine exactly how much parasitic draw you have and, if excessive, what it causing it (by pulling the fuses.)

 

Doh! I forgot how to count to 3.

Thanks Steve.

 

I have double checked my resistance measurement and also made current measurement. The car is a 100% stock 85 QV with Sony radio installed (display lights up when ignition is on).

Static resistance, no battery.

Ignition off (position 0). Rs = 14.6k ohms

Ignition in Acc position (position I) Rs = 3k ohm

Ignition in Run position (position II) Rs = 6 ohms.

Current measurements and dynamic impedance derived from R = V/I where V = 12.3 volts (battery slightly discharged as car is in storage)

Ignition off, I = 9.6 mA, Rd = 1.28k ohms

Ignition in Acc position I =0.13 A, Rd = 94 ohms

Ignition in Run position I = 2 A, Rd = 6.15 ohms.

The reason why static and dynamic resistances are different could be the result of diodes in the system which measure infinite resistance in the absence of a bias voltage.

But perfectly normal to have low resistance when the key is in position II.

 

FWIW, I just did a parasitic draw test using amp reading, not a conversion based on voltage/resistance on my '89 328. Ignition off has a reading of 14mA. If I pull the clock fuse the amp draw drops to zero. So, as is expected with these cars if stock, the clock is the only item pulling power with the ignition off. Obviously, if a car has accessories like an alarm or other component that pulls power with the ignition off, it could be pulling quite a bit.

 

Yes, the QV manual for a 308 list the 3 position you indicate. But the ignition switch has a position between 0 and II, "I", where certain accessories are energized, but not the ignition. For example, in position I, the head lights will operate but the ignition will not be energized and the alternator light on the dash with not illuminate. At least that is how it is on my US 85 QV.

In your first post you say the 3 year old battery would not hold a charge so you replaced it. But it's not clear if the new battery is also going dead. If it's only the3 year old battery that goes dead it most likely just the battery. Also, as I said, if the car sits for a few weeks without use, with the battery connected, it is not uncommon for the battery to get drained to the point where the car won't start. Best to disconnect the battery when not in use.