Couldn't pop the clutch in reverse

[SP2]

Hi all,
Maybe this wasn't so smart, but I left my lights on today at work and killed the battery. I was parked sort of on a hill, but I was in the parking lot in a way that I couldn't roll the car out and point it downhill. Except I could point the rear of the car down the hill. After planning it out, I started to roll it backwards at a pretty good speed. I had the ignition on, so I put it in reverse with the clutch in, and then popped the clutch but nothing happened at all. No sounds of the engine starting at all. Good thing I called it quits when I did, because I almost crashed my rear Fuchs rim into a curb.

Fortunately we have security at work and they jump started me. But the battery was totally dead. It took a while for the battery to take enough charge to turn over the engine. I was worried I might have injured the tranny, but it seems to run fine. My guess is that reverse is too tall a gear to try this, or my other guess is that the battery can't be that dead for a pop the clutch maneuver to work.

Any thoughts?
Thanks

[snbush67]

The SC? CIS need juice to start, you could use this method if you had carbs.

[SP2]

Oh, sorry, yes the SC.

Your answer makes sense. Thanks!

[911Mac]

Had a similar experience with my SC. Left it parked all day with the lights on. I even let it sit a few more hours with everything off, but no dice. I think the fuel pump just pulls too much current. My car's been converted to EFI and normally you hear the fuel pump run a few seconds when you first turn on the ignition. On this particular day I didn't hear any noise from the fuel pump when I turned on the ignition even though I had interior lights from letting the battery rest a little.

-Mac

[911pcars]

Actually, if the battery was completely discharged, you couldn't have jump-started. An alternator needs threshold electricity to create more.

It doesn't matter if an engine has carbs, EFI or CIS. It's the battery & alternator that determines whether it's possible to jump start. However, an engine using a DC generator can usually be jump started.

Yes, reverse gear is too low of a gear to jump start. 3rd gear is more like it. You'd need a very large push to rotate the engine in 1st. BTW, the correct term is "short" rather than tall gearing for reduction gears like 1st/reverse or describing gearing differences between ratios, etc.

Be careful with running the engine with a dead/discharged battery or using the engine to recharge a dead battery. Alternators are sensitive to heat from high charging rates which can shorten its life, especially Porsche alternators. Better to charge the battery before using or minimally complete the charge with a trickle charger as soon as practical.

Sherwood

[spuggy]

+1 on either letting the battery suck up enough charge from the jump cables or charging it completely off the car. But sometimes you do what you have to... People sell combined air compressors and emergency battery packs for $40. I hate warning buzzers, but I've left the lights on myself...

You need enough juice to run the ignition (either the CDI or the Motronic, depending) and the fuel pump (and electric injectors if Motronic) or it won't run. Remember the rating on the fuel pump fuse? That's a clue as to how much current it takes... The CDI and Motronics are both heavy current ratings too. The exciter circuit on the alternator really doesn't take much in comparison - but if you don't have enough battery to get fuel into the heads and light it off when it's in there, you're wasting your time.

In my experience, reveerse is just fine for bump-starting cars, and the 930/911 was no different when my starter issues struck when I was parked on a hill. Let it build up some speed (like 8-10 MPH) and pop the clutch, works just fine.

I've also bump-started my car in 2nd on a flat 20 foot driveway, just me pushing. Not fun. Hardest thing is jumping in once you've got the speed, getting a foot on the clutch, getting a gear and popping the clutch whilst trying to get a foot on the brake too and watching the garage doors getting close... Oh, and you really don't want to fumble getting into the car, either...

Boy, was I pleased when I fixed that intermittant connector...

[TMoreken]

I've had the same problem. Like others have said, if your battery is completely depleted, no amount of pushing and popping the clutch is going to start the car. You're still turning the engine over using your gearbox, but w/o spark or possibly fuel. More likely fuel. Turning the engine over will turn the alternator and usually there is just enough DC to "excite" the alternator. As we all know, it's a circus trick to get everything rolling -- in the right gear -- not hit the neighbor's fence -- get back in the car -- not hit the neighbor's fence -- hope there's a sliver of voltage to fire everything. It can be a sinking feeling to go through all that and get to the bottom of a hill with NO STARTING, especially if you're now in the middle of traffic. Ask me how I know.