993 Starting Problem

TMc993 · 10-18-2009, 05:16 PM

New to the forum and hoping for better luck that I've had on other forums in gaining some type of insight into a starting problem I'm having with my /97 993.

Car:
'97 NB Coupe with apprx 65K miles on the clock. All services up to date.

Problem:
Upon attempting to start the car Tuesday morning, the starter would spin the engine, but the engine would not fire/start.

Efforts so far:
Replaced DME relay with no effect on the problem.

Complications:
Upon replacing the "new" DME with the "old" DME after the "new" DME had no effect, I failed to completely close the front bonnet, leaving the light in the trunk burning (Light was "on" unnoticed for 48 hours) and completely draining the battery...No interior lights, no ignition switch chime...Nada...

I then hooked up a trickle charger (It was all I had on hand) and let it charge the battery for about 3 hours.

Out of curiosity, I tried to start the car and it started immediately and ran perfectly.

So:
Is it possible for the battery to be strong enough to spin the starter, but not "power up" all the other electronic devices necessary to start the car or I am doomed to chasing this issue for the next few months?

Thanks,
Terry

rgv67 · 10-18-2009, 05:59 PM

Recharge your battery and check DME relay (you should always have a spare DME). If engine would still turn but not start you may have a fuel pump problem. A siezed fuel pump would bust a fuse. Check it out.

Good luck!

Randy

TMc993 · 10-19-2009, 03:51 AM

Randy,

Battery was strong enough to spin the engine. DME was changed out and had no effect. Fuel pump fuse was not blown.

Old DME was put back in the car and the front boot was left ajar, running down the battery.

After the dead battery was on trickle charger for 3 hours, the car started and is running.

Here's my question: Would it be possible for a battery to be strong enough to spin the engines, but not be so strong as to activate the electronic devises (ECU, Fuel pump, DME) necessary to start the engine.

I'm trying to figure out why the battery could spin the engine, but the car wouldn't start until after the battery was charged.

Thanks for your response.

Terry

vincer77 · 10-19-2009, 10:35 AM

The amps needed to spin the starter are much more than what is needed to power the rest of the electricals - so I do not think that ws the problem. Dirty DME contacts sounds more plausible, IMHO.

TMc993 · 10-19-2009, 01:54 PM

Thanks for the ideas...

Terry

lucittm · lucittm's Garage

There are many digital devices in the late model P-cars. Think of all the semi-conductor circuits in the myriad of control units, memory storage chips, integration devices, and signal conditioners.

Many of these devices can suffer from power spikes, overload, faulty inputs, error signals, or even operator error (starting the car while rolling up the window and locking the door comes to mind), just things that the engineers never had the time, or the presence of mind, to check.

Disconnecting the battery momentarily will often reset the digital circuitry, as your dead battery did so conveniently for you. We do this in the electronics industry when all other "common sense" troubleshooting fails to produce the desired effect. It is often referred to as the "Raytheon Reset" in honor of some of the equipment that requires the technique.

Other than losing your radio station presets, it should do no damage to a modern vehicle that has properly working electricals. If it causes a fault code, then it is likely that the fault was already set, but the reset was necessary to reveal it.

Good Luck,
Mark

vincer77 · 10-20-2009, 01:52 PM

Good point as well

. One thing you need to remember is that disconnecting the battery will clear the "readiness flags" in the ECU. If you have to get the car smogged after disconnecting the battery, it will fail the test. The flags should reset after driving for a certain period, but not always. There is a BMW Drive Cycle that has been documented on Rennlist, maybe here also. The drive cycle will set the flags

TMc993 · 10-20-2009, 02:19 PM

Mark - Thanks...With input from others, I've about decided that the problem was either as you described or that the fuel pump had "locked down" temporarily (Not good I know) and my repeated bumping it got it going again. I'm hoping that it was your scenario and not some precursor to a fuel pump failure some rainly day 50 miles from home.

Vince-It was odd to me that given a total drain on the battery (The starter solenoid wouldn't even click...No key chime...No lights at all...No instrument panel lights) after a mere three hours with a 1.5 amp/hour trickle charger, the battery spun the starter at a normal speed and the car started and ran normally with no CEL (Yes, the CEL does light up as it should when the key is first twisted during starting).

At any rate, the car is currently running well...Thanks again for the suggestions.

Terry