93 940 weird ignition electrical

bonzaijoe · Post by **bonzaijoe** » 25 Dec 2009, 17:45

About 80% of the time when I turn the key to start the car the only instrument panel indicator lights to come on are the SRS and seatbelt lights. When I start the car the seatbelt light will go out and the SRS stays on. All the electrical systems are under stress like they are running directly off of the battery (which is what's happening)

If I give a quick push to the gas pedal to bring the engine RPM up everything returns to normal and the charging system works fine.

If you don't kick the accelerator the car will only operate until the battery is completely drained. The car has left me stranded a number of times and I just replaced another battery and alternator. Mystery problem that has been going on for 5+ years. These incidents occur less in the summer.

New battery is fine and the new alternator is putting out 14.2 volts when it is in it's normal charge mode.

Hopefully someone has seen this before.

thx,
jw

Post by **JDS60R** » 25 Dec 2009, 22:48

The electrical system needs to be tested under load. Take it to your local Advance or autozone and recheck the battery and alternator output under load.

If you have done that then something in the car may be draining the battery while the car is off. Can you tell us what the voltage is prior to start up after the car has sat overnight.

I am assuming the grounds and main leads to the battery have alredy been inspected and cleaned where corrosion existed.

bonzaijoe · Post by **bonzaijoe** » 26 Dec 2009, 20:20

I will read those voltages tomorrow but I don't expect any surprises. Will follow up.

thx,
j

bonzaijoe · Post by **bonzaijoe** » 27 Dec 2009, 16:52

After 36 hours in a temperature range of -4F to 27F and without starting the car, the battery voltage was holding in the low 12 volt range. Starting the car in the condition stated previously, the battery started it's slow drain. When I kicked the throttle up, the alternator was putting out a steady 14.35 volts and the battery was taking the charge with the battery back up to 14.16 volts within 10 seconds or so.

This has been the symptom for almost 5 years. It doesn't happen nearly as much in the summer time. Things switch on as they should with the turn of the ignition key.

Post by **billofdurham** » 28 Dec 2009, 12:47

How low in the 12 volt range?

A car battery is considered fully charged at 12.6 volts. When a battery drops voltage, even by a small amount, it makes a big difference.

At 12.45 volts, a car battery is only 75% charged. At 12.24 volts, it's 50% charged. At 12.06 volts it's 25% charged.

A car battery is considered charged at 12.4 volts or higher. It is considered discharged when it's at 12.39 volts or less. The current is heavily dependent on the type of battery and the resistance of the 'load'.

Bill.

bonzaijoe · Post by **bonzaijoe** » 28 Dec 2009, 19:42

Under the conditions explained earlier the battery was reading 12.12 volts and holding. I saw no trickling of the charge as I monitored it. The battery was deep cycled after the alternator was replace. It certainly is possible that the wind was taken out of it's sails. However if I replace the battery with a new one (again) the symptoms will stay.

The symptom when starting the car this morning was the same as stated. Oddly, every other start today (4 of them) showed normal indicator lights across the dash without having to kick the accelerator. It may or may not do the same thing tomorrow.

All of the "charging circuit" analysis has been done in the shop and with the exception of this intermittent nightmare the circuit operates as designed.

thanks

Post by **billofdurham** » 29 Dec 2009, 11:59

12.12 volts is very low for a new, fully charged battery. I don't think you will see a "trickling of the charge" over a very short period of time. A voltage drop will take longer. Have you taken a voltage reading when you have finished with the car for the day and another reading before starting it the next day? It would be interesting to see if it is draining down overnight and by how much.

Have you had the alternator tested? It is not unknown for a new alternator to have a faulty diode. If it has been tested was it tested for the usual voltage output test and current load test? The second one is often missed.

You may have a parisitic drain. It may be a light left on that isn't easily seen, eg glove box, luggage compartment, engine compartment, or some other piece of equipment drawing current when it should be closed down.

You can check for a parasitic drain quite easily.

Make sure that your vehicle is turned off with the key out of the ignition. Also ensure sure you have all doors closed otherwise the lights that come on will create a false reading.

You’ll need an ammeter or multimeter.

Disconnect the negative battery cable from the terminal and connect the ammeter between the cable and the negative battery post.

Once the car has been off for a few minutes, check the ammeter. You want to find a reading that is between 25-50 milliamps. If it is higher, then you definitely have a parasitic drain somewhere.

To find the drain you’ll need to start pulling fuses, starting with the lowest amp fuses first. As you pull each one, watch the ammeter. When it drops down to an acceptable level, you’ve found the drain, and you’ll want to check each electric device on that fuse to see what you’ll need to disconnect. This should ultimately take care of the problem.

Parasitic drain can sometimes be caused by the battery itself. If there is water or corrosion between the battery terminals, it could cause a current to drain between them. Battery terminals can, and should, be cleaned regularly with a solution of baking soda and water.

Bill.

bonzaijoe · Post by **bonzaijoe** » 30 Dec 2009, 11:14

Thank you. I will give the current reading a try later today. That suggestion is a good one.

Oddly, the normal configuration of dash indicator lights (when the ignition key has been turned to the ready position) has been 80% or so over the 3 days.

It has been suggested to me to change out the secondary voltage regulator??

lummert · Post by **lummert** » 30 Dec 2009, 18:15

If your car has an aftermarket stereo installed. Check to make sure that the radio is off with the ignition. My 88 765 had a Kenwood stereo wired incorrectly and the battery would be discharged enough by morning that the car would barely start. for a long time I just removed the fuse for the radio when not using the car. Then I rewired the stereo and the problem was solved. The stereo had a yellow and a red wire that were wired to the constant 12 volt wire from the fuse panel. I noticed one day that the stereo was displaying off after turning off the ignition.