Mysterious Dying Engine when Return to Idle. Alternator? Battery? Other?

lp1holl · Post by **lp1holl** » 07 Jul 2016, 12:13

This is a strange one, at least to me.

It's a '96 850 with at least 110K (speedo and odo only work about 1/2 the time). No codes and no prior problems of significance (an incredible thing for a 20 year old car i know), but I can't keep it running.

It will jump start and drive well as long as you keep the revs above 1000. If they drop to idle, it pops off. It will idle under 1000 right after starting, but if you rev it up at all or turn on the lights or A/C, it dies.

The alternator shows a .7 V voltage drop between it's terminal and the positive of the battery, so I jury-rigged a direct cable between the two an now show only 70 mV. Reads at 13.7 V when running and a bit higher when revved up (that is, until it dies).

Since jury-rigging the cable, the problem has continued exactly the same. I left it running outside the house to charge the battery and hope that someone steals it and I can just make an insurance claim (JK).

Anyway, when it dies, it dies totally dead. No lights, no warnings, nothing. Just totally flat battery. Is this a wiring issue, the alternator, the battery, or other? I looked around, but couldn't find anyone else with the same problem...

Thanks!

FinallyGotThatVolvo · Post by **FinallyGotThatVolvo** » 07 Jul 2016, 12:44

Check for vacuum leaks.
I had similar issues but with an idle that would searching for stability.

kippster41493 · Post by **kippster41493** » 07 Jul 2016, 12:53

Most likely not a wiring issues, that will be a gradual thing and even then it would be intermittent until that wire fails completely. If you're able to get the vehicle to an auto parts store they can do a full system check for free that will test the battery, alternator, and starter. It will also tell if you if there is something draining power constantly. Does it start hard or just abnormally some how? Is there any "hissing" noises that you may hear? While the engine is running spray starter fluid around where there is vacuum.

Sommerfeldt · Post by **Sommerfeldt** » 07 Jul 2016, 15:05

kippster41493 wrote:If you're able to get the vehicle to an auto parts store they can do a full system check for free that will test the battery, alternator, and starter.

You guys don't know how good you got it - around here, a diagnostic like that runs about 200 bucks.

- S

Post by **misha** » 07 Jul 2016, 15:35

lp1holl wrote:...Anyway, when it dies, it dies totally dead. No lights, no warnings, nothing. Just totally flat battery. Is this a wiring issue, the alternator, the battery, or other? I looked around, but couldn't find anyone else with the same problem...

Thanks!

It could be b+ cable or negative cable.Voltage drop on negative side is important just like on positive side.Check the ground cables.

Could also be that battery is bad and shorting cells internally as soon as current warms it a bit.

Since you got 13.7v with engine idling....it means that alternator works.Starter have nothing to do with charging system.
So....battery,alternator or cables.
Check grounds on transmission housing and behind driver's side headlight.Search for their voltage drop.

kippster41493 · Post by **kippster41493** » 07 Jul 2016, 15:37

Sommerfeldt wrote:
kippster41493 wrote:If you're able to get the vehicle to an auto parts store they can do a full system check for free that will test the battery, alternator, and starter.
You guys don't know how good you got it - around here, a diagnostic like that runs about 200 bucks.

- S

I didn't pay attention to your location, that was my fault. With a multi-meter you can do a similar test, just takes a bit longer to do. But does it start easily with out the idle hunting around? I know you have to hold the throttle open but do the revs bounce around? It may not necessarily be an electrical issue.

Post by **misha** » 07 Jul 2016, 15:41

Oslo,Norway....among the most expensive cities in Europe to live in.

Post by **kcodyjr** » 07 Jul 2016, 16:09

This sounds like a bad battery to me (read: totally shot), but it could be cables or connections.

If it's completely flat without jumper cables, one of two things has to be true: 1) the battery is totally discharged, 2) the battery is not adequately connected to the car.

We can rule out alternator because without it, we wouldn't be running at all in this condition.

You should be able to rule out battery post corrosion or loose connection with mark-one eyeball.

You should be able to rule out wiring with a continuity tester. Verify the circuit from battery ground to chassis, and then from battery ground to engine block. Testing resistance isn't necessary; we're troubleshooting a full-dead condition. For the same reason, there's no need to test the positive cable from battery to starter, unless we get interior lights working and it still won't start.

You mentioned having an available jump source. Can you simply borrow the battery and swap it over for a test?

Post by **kcodyjr** » 07 Jul 2016, 16:13

Here's a way: disconnect your own battery at the positive terminal, and then hook the jumper cable directly to the loose clamp.

If the battery's at fault, and it's out of the circuit, you should be able to idle, if the jumper cable connections are good enough and the donor car has the gumption.

Sometimes jumping serves to pre-charge a low battery, sometimes jumping delivers enough juice to crank the starter directly. Depends on the gauge of the cable, the cleanliness and tightness of the clamps, the available spare amperage from the donor car (revving helps), and the amperage needs of the dead car.

difflock54 · Post by **difflock54** » 07 Jul 2016, 17:31

Corroded battery cable. Replace.
Get the battery tested first to ascertain that all cells are live and you are getting 12volts.