996 won't start after dead battery, replaced new battery

As Topic states, 2003 Carrera 2, Car had deeply discharged battery, so flat not even interior lights or dash lights went on, Car is very rarely driven and battery approx 4 years old, so no big surprise it finally died, i'm surprised it made it this far. Bought a new Battery from Costco, fitted, tried to start today, starter cranks as normal but will not start. Tried jump starting with other car, in case the cranking current on the new battery they sold me was insufficient, car cranked harder and faster, but still no start. Checked fuses C1 - C4 for fuel pump etc, all OK Pulled out fuel pump relay, seems to test OK. Jumpered the fuel pump terminals on relay socket, pump is definitely trying to pull current, as jumper arcs and can hear a click from fuel pump, but no pumping whirring noises. I had replaced the fuel pump only about 18 months ago with a brand new one, I'm suspicious it has seized. I do rarely drive the car and I'm wondering if this is aggravating it, if its the pump again. It does have all the same symptoms as when the pump died last time, however I'm just suspicious as its occurred immediately after a very dead battery, as was fine prior. What should I do next, can I remove the fuel pump and run some sort of test outside the car? I'm reluctant to just order a new pump just yet as this one is seriously quite new, and done less than 1000km Is there anything you have to "reset" when you have a dead battery?

You can try e-gas calibration: turn key to the last position before crank and leave it there for 60s, then turn key to OFF and wait 10s. However, if the fuel pump does not run when jumped at the relay terminals directly, it is seized.

Thanks Ashai, I'll give that a try You were the one that stepped me through the diagnosis last time with the fuel pump, I am very grateful. From memory, I should be able to hear the fuel pump whirring where the ignition is on? Just a bit sus as the pump is quite new

You're welcome. Yeah, you should hear the pump for about 1s when you turn the key to the last position before crank. Regardless, jumping from the fuel pump relay is the most direct way so if you dont hear it, it's most likely seized. Be careful jumping a seized pump though. It may blow the fuse due to large current. If you see spark and don't hear the pump, it's definitely not running. Did you replace the whole assembly with an OE unit?

tried e-as reset, no joy Should I pull the pump out and have a look at it?

I replaced the fuel pump with a new VDO OE unit last time, didn't replace the sender assembly

When I jump the relay, with the ignition on, I do get a good spark, can hear a bit of a clunk from fuel tank when I first make contact, but no whirring pump noises

Yeah, sounds like the pump is stuck. Seems the only way is to extract it.

Actually ignition does not need to be ON because the fuel pump power at the relay terminal is always hot. You used a fat wire to jump it, right? Just want to make sure the pump gets enough current.

Yes, used 1.5 sq mm wire

Is there a safe way to test the pump once I remove it from the fuel tank?

Was the filter replace?

Quotes source post: 14262843

Test it in the tank. Disconnect the pump from the car's electrical system and then connect 12V power directly to the pump. The pump should run and run with no problems. If it runs the no start problem lies elsewhere. If it doesn't run the pump is bad.

It amazes me how many problems occur due to a dead battery...

Good idea Macster, do you know what the connections are on the electrical header without pulling the pump out There are 4 terminals 1. Thick Green/white 2.thin purple 3. Thin brown 4. Thick Brown From memory the thick brown is generally ground. Two of them will be the level sender

Filter, what filter? A 2003 doesn't have a replaceable filter than I know of?

The green/white is the +12v supply and the fat brown is the ground. Be careful with sparks on a seized motor. I would not recommend jumping the pump from there for safety reasons. There should be a teabag filter built in at the pump's intake. Not replaceable though.

Quotes source post: 14264790

Youre right, a filter is on some of the earlier 996s, such as the 1999 model.

and 2000 C4, at least.

Update, have tried direct power to the pump, dead. Removed pump from tank, measured motor, open circuit. Can't see any unusual signs of dirt or contaminants on filter, pump looks as new as the day I replaced it. Just bad luck I guess, pump was only replaced a couple of years ago and hardly done 1000kms Moral of the story, drive it more???

Glad to hear you found the culprit. You can take apart the pump and try to see what failed inside.

Also a good idea to make sure the inlet/filter is not clogged, which will strain and kill the pump.

Not familiar with Porsche fuel pumps but the experts here can/will chime in and advise if this is viable. If it is a straight DC fuel pump motor you can rock the armature and possibly break it free by reversing the pump + and - leads back and forth a half a dozen times with a separate battery if need be. Have done this on N American FI vehicles with a "frozen fuel pump" that have sat for extended periods of time with good success.