986 Forum - The Community for Porsche Boxster & Cayman Owners - View Single Post - Alarm cause no-start?

Porsche-Eh · 10-16-2018, 09:10 PM

OP: that is a strange one. If it starts with a boost ignore all electronics and concentrate on looking for a bad ground that is causing the voltage to drop when just off a battery. I could be wrong but I would guess a running car (boost vehicle) wlll deliver more than 13v because the alternator should be delivering 13-14. So if it starts with more volts then something, when just off the battery, is dropping a few volts and maybe not energizing the key pill. With a boost vehicle you will have more than 12v so you can afford to lose 1-2. With no boost vehicle you are getting less than 12v for some reason. Maybe to test this theory you can get some volts back on startup by pulling various fuses - radio - daytime running lights, interior lights, etc. And see if it starts.

Found this on the Interwebby: Fully charged automotive batteries should measure at 12.6 volts or above. When the engine is running, this measurement should be 13.7 to 14.7 volts.

10-16-2018, 09:10 PM	#15
Porsche-Eh Registered User Join Date: Dec 2017 Location: Canada Posts: 73	OP: that is a strange one. If it starts with a boost ignore all electronics and concentrate on looking for a bad ground that is causing the voltage to drop when just off a battery. I could be wrong but I would guess a running car (boost vehicle) wlll deliver more than 13v because the alternator should be delivering 13-14. So if it starts with more volts then something, when just off the battery, is dropping a few volts and maybe not energizing the key pill. With a boost vehicle you will have more than 12v so you can afford to lose 1-2. With no boost vehicle you are getting less than 12v for some reason. Maybe to test this theory you can get some volts back on startup by pulling various fuses - radio - daytime running lights, interior lights, etc. And see if it starts. Found this on the Interwebby: Fully charged automotive batteries should measure at 12.6 volts or above. When the engine is running, this measurement should be 13.7 to 14.7 volts. Last edited by Porsche-Eh; 10-16-2018 at 09:37 PM.