Random Non Starting C5 RS6

[shamierc]

I have this really odd problem with my C5 RS6....

Sometimes after a long or spirited drive (or in hot weather) she refuses to start for about 20min to an hour after switching off. Doesn't even crank and you cannot even hear the fuel pump priming. She will however start if jumped from another car. I have replaced the battery and it has helped as it now happens less frequently...but it hasn't resolved the problem.

I was thinking heat soak on the starter solenoid maybe? But would that account for the car being able to start when jumped?

Any advice...

Oh, No codes...

[bmlee007]

Alternator possibly failing. It might be charging just enough to keep you running, but not to maintain a full battery charge. When you turn the car off, turn the key back to accessory. What voltage do you show then?

[shamierc]

Alternator possibly failing. It might be charging just enough to keep you running, but not to maintain a full battery charge. When you turn the car off, turn the key back to accessory. What voltage do you show then?

Always shows a steady 12 volts and more than 13.5 when running...I'll have the alternator tested anyway...

[Bigglezworth]

Alternators provide AC current to charge batteries and provide electricity for accessories when the engine is running. They have NOTHING to do with starting a car. Battery's sole purpose is to provide DC current to the starter to start the motor. Starter obviously just starts the car. Your descriptions are that of heat soak and it's likely affecting the solenoid in your starter...OR, a bad wire running from your battery to the starter. First place I would check is the connections on your battery and where the positive connects to the starter. Ensure they are clean and tight. Further, ensure the cable hasn't melted on something (shouldn't as it wrap down the side of the passenger frame and back up under the header). Bitch to R&R a starter on this car.

[lswing]

Always shows a steady 12 volts and more than 13.5 when running...I'll have the alternator tested anyway...

Shouldn't this always be at 14v when running? (maybe 13-13.5v when running with AC) So the battery is not charging enough?

If the battery is dead/low you should get a clicking/banging as the starter is trying to work but doesn't have enough juice to turn over. Sounds like a woodpecker is in your engine, but no turnover at all.

You do any stereo wiring or something else parasitic?

[shamierc]

Alternators provide AC current to charge batteries and provide electricity for accessories when the engine is running. They have NOTHING to do with starting a car. Battery's sole purpose is to provide DC current to the starter to start the motor. Starter obviously just starts the car. Your descriptions are that of heat soak and it's likely affecting the solenoid in your starter...OR, a bad wire running from your battery to the starter. First place I would check is the connections on your battery and where the positive connects to the starter. Ensure they are clean and tight. Further, ensure the cable hasn't melted on something (shouldn't as it wrap down the side of the passenger frame and back up under the header). Bitch to R&R a starter on this car.

Gracias, I will check the wiring to the starter. I had issues recently with the fuse box under the coolant bottle. Space had become flooded and all the connectors/cables corroded. Rebuilt/replaced all but the problem occured before and after the repair so don't think the problems were related. Hoping the starter doesn't have to come out...

Shouldn't this always be at 14v when running? (maybe 13-13.5v when running with AC) So the battery is not charging enough?

If the battery is dead/low you should get a clicking/banging as the starter is trying to work but doesn't have enough juice to turn over. Sounds like a woodpecker is in your engine, but no turnover at all.

You do any stereo wiring or something else parasitic?

It is 14V, I was quoting from memory but just checked now. No clicking at all...nothing...totally dead...not even the buzzing/humming sound (That I assume is fuel pump priming) that normally happens when toy turn the key to power accessories...Accessories do get power however. Parasitic drain is a possibility. I have an unused motorola hands free kit installed that may be the culprit as its main buttons remain lit always...

[lswing]

Parasitic drain I guess, but I would think it would at least "tick" over. Fix or get rid of the BT unit for now. I had a wireless bluetooth OBD2 reader plugged in that was supposed to shutoff and not drain the battery. Aha, come to think of it, when it died completely a few months back there was an attempted turnover on starting, then nothing, not the clicking, just plain dead, but still with interior and gauge lights. The starter clicking must happen if there is just enough juice to try and engage the starter; ie battery dying on it's own from old age. My car had the same symptoms, but was in my garage luckily where I have a trickle charger.

PS; update your location if you can, and welcome to the board.

[nene]

I ran through the same list of possible root causes, even end up buying a new battery without need (know that now).
In the end it was the silly G28 speed sensor in my case.

My original post.