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No start - oil gauge pegs to max on key turn

milkman

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Joined
24 May 2021
Messages
26
Hi folks, I've not had the 996 running for about 2 months the battery has been disconnected and in months old Bosch.

Yesterday I went move it and it would t start, on key position 2 ie crank all linghts on the dash come on and there is a click but no starter turn. The oil gauge at this point pegs max till the key is released!

I assumed the battery and charged overnight but not sure any thoughts?
 
That's the failure mode of the oil pressure sender, it's probably busted. Otherwise sounds like the battery is dead.
 
Engine to chassis earth connection.
With a poor connection the current can't flow and the engine is not being held at 0v by the chassis connection. Since the engine is not at 0v the earth for the oil pressure sender is no longer 0v which gives the dodgy oil pressure reading. Lights are on on the dashboard because battery is good but the poor earth won't allow enough current to actually start the engine.
Confirm by checking the voltage on the engine compated to chassis earth when trying to crank.

MC
 
Gentleman haha you were absolutely correct what I didn't expect to see was the engine earth disconnected- I removed it to remove the exhaust weeks ago!
How daft am I! Thanks for the help!!!
 
MisterCorn said:
Engine to chassis earth connection.
With a poor connection the current can't flow and the engine is not being held at 0v by the chassis connection. Since the engine is not at 0v the earth for the oil pressure sender is no longer 0v which gives the dodgy oil pressure reading. Lights are on on the dashboard because battery is good but the poor earth won't allow enough current to actually start the engine.
Confirm by checking the voltage on the engine compated to chassis earth when trying to crank.

MC


:bow:
 
milkman said:
Gentleman haha you were absolutely correct what I didn't expect to see was the engine earth disconnected- I removed it to remove the exhaust weeks ago!
How daft am I! Thanks for the help!!!

No problem. When I removed and refitted the engine on Pinky I had exactly the same issue, mine was due to some corrosion on the connection to the chassis. It took a bit of head scratching and thinking before I worked it out. Always easier to diagnose the second time.

MC
 
MisterCorn said:
Engine to chassis earth connection.
With a poor connection the current can't flow and the engine is not being held at 0v by the chassis connection. Since the engine is not at 0v the earth for the oil pressure sender is no longer 0v which gives the dodgy oil pressure reading. Lights are on on the dashboard because battery is good but the poor earth won't allow enough current to actually start the engine.
Confirm by checking the voltage on the engine compated to chassis earth when trying to crank.

MC


Top knowledge and description. Fantastic that. :worship:
 
Had a similar problem with my Audi but I knew teh battery was good. It was an earth issue to the engine/starter motor.

I detected it by using a jump lead from a good earth chassis point to a point on the engine and the starter engaged.

Rather than investigae the corroded earth strap to the starter somewhere underneath I bought a £5 Neg earth short battery lead off eBay and connected it from body to a generic part of the engine :grin:
 
Funnily enough, I reported a wobbly oil pressure reading from time to time before I last had my car serviced. The mechanic said he'd cleaned up the earth lead connection, as this can cause probs with the reading. Sure enough, its been much better since.
 

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