My 96 850 is at it again. The battery died about a week ago. Normal thing. Well, I waited too long and ended up not being able to start it one day. No biggie, the battery was actually still under warranty so I got a free replacement.

For the past year I've had a check engine light triggered by a bad O2 sensor. I believe it has three doesn't it? One down isn't going to hurt it, so I let it stew with the light.

When I got the new battery in (and blew my ears apart when the alarm went off) the light had reset itself.

It started right up but was running very rough. It never did stall, but it was most definitely the epitome of "running rough".

I made sure it wasn't going to stall by driving it around so I'd know if I could take it places. It was running rough no matter what the engine temp.

Last night I came home, parked it, and was just kind of sitting there watching it run rough. I decided to move it from park to reverse to see if it would get worse (it doesn't BTW), and when I pressed in the brake pedal the engine revs would suddenly drop. I never got it to stall but I think I came close. I sat there doing it for about ten minutes.

I tried again today but I couldn't replicate the drop in RMPs.

The engine also surges to about 2000 about once every fives times whenever I'm backing up and move the shifter to neutral from R to let the car slow down before I put it into D.

Well, today I drove it to my parent's house. It was still running rough, but not trying to stall or anything. Like I said, I tried to replicate the brake pedal thing but couldn't. Well when I got in it to come home all the interior lights came on normally. I put the key in, turned it enough to get the normal dash lights to come on, and when I went to crank the engine all power cut off. There were no lights at all. No interior lights, no dash lights, no headlights, and no clock. No nothing.

I thought I might have not tightened the battery connections good enough (even though the lights were working when I got into the car). I checked and everything was tight.

It's still in their garage. The only thing that worked when my wife picked me up was the little red light on the dash that comes on when the alarm is on, and it was only popping on intermittently. Heck, I even tried to set the alarm off. Nothing.

Any suggestions? I expect I'll have to have the stupid thing towed, but I'd like to check if you all have any ideas as to what caused it first.

It can't be just battery, or it wouldn't have been running rough. And it couldn't have just been the engine, or else the power wouldn't have cut out completely. Keep in mind it's a brand new battery.

Thanks for any help.

 

Could be a bad battery cable or engine ground. They get old, they corroded, a broken one could cause your car to not start.

 

If it was fine and now its bad after just replacing the battery I would disconnect the battery, Postive side then touch the cable to the negative post. This will discharge the voltage. Then connect it back up and start the car....let it idle for about 5 min. What your doing is resetting the ECU then letting it learn again.

 

Do what Boxpin said, and if it still won't run, check the positive battery cable. On that, you will see a stud with a bundle of wires attached. Remove the nut holding that down, clean off any corrosion or burn marks (from arcing) that the ring terminal has, as well as on the battery with a wire brush, then coat it with vaseline or dielectric grease, and reinstall. That little tiny terminal is basically what sends power to the entire car, and they frequently get loose/ corroded, which causes resistance, which makes it get hot and corrode even more, which increases the resistance, and so on until the nut often loosens up, and current arcs across, causing all sorts of odd behavior. The thick positive cable ONLY supplies the starter and carries current from the alternator.

 

Thanks for the replies everyone!

It turns out that it was a coincidence of breakdowns. The electrical problem was independent of the mechanical abnormalities.

It turns out that I suck at installing batteries. I just redid the connections and it started right up.

The rough idle was the fault of a vacuum line that was slowly rotting through. I must have split it when I was digging around for a screw I dropped. My FIL discovered it when it snapped off completely when he jiggled it.

Now it runs smoother than it ever has. Kind of refreshing.

Thanks again for the replies!

 

good to hear. Now, go through and change all the vacuum hoses... they're probably all cracked and deteriorated- it's not hard to do, get a spool of hose and get crackin'. It'll save you trouble down the road.