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Discussion Starter #1
What is the voltage threshold that the L-Jet system needs to function properly? I ask this because I've suddenly developed a cold start issue on my S3, and good cold starts have been one of the hallmarks of this car. It will crank, sputter and die, then takes cranking about 10 seconds, with the pedal to the floor like an old carbuerated car, and it will eventually sputter to life. Once warm, it fires up like new.
I'm suspecting a weak battery, and so don't want to start with TTS and CSI tests until I know that its not the battery keeping them from operating as they should. I brought the battery to NAPA to be tested today, but because it wasn't completely charged, they couldn't give me a definitive assessment, only saying it reads 'kinda on the edge', at 12.57 volts. (I only have an analog multimeter, and I know they have other testing methods they can do on it).
I'm putting it on the charger at 2 amps overnight and bringing it to NAPA for another test. What voltage should I be looking for in a fully charged, presumably healthy battery? And what is needed to get the TTS and CSI to wake up?
Thank you all!
 

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10.5 - 11 minimum cranking volts
 
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Bosch never published a threshold number for voltage. Empirical evidence suggests it is about 10.5V FWIW, our Spider measures ~ 11.6V - 11.8V during cranking. It is important to measure this at the battery during cranking. If you have one, a dash gauge is usually not wired to measure the system voltage during cranking.

A fully charged car battery should measure 12.6V. 12.3V is 1/2 - 3/4 charged. Ideally, the auto parts store will do a battery load test. This is more than just using a voltmeter but seeing how the battery reacts when it is trying to deliver a large load.

The Cold Start System (the TTS & CSI) are not under any computer control - there is no threshold for them. But if there is inadequate voltage to power up the computers it is likely all the systems will suffer. There is info in the L-jet Spider Diagnosis page for testing the TTS with an ohm meter. (the link is in my signature)

Cranking the engine with the pedal floored triggers a 'clear a flooded engine' map - basically the fuel injectors do not squirt and the wide open throttle clears out the excess gas. (I'm not sure about the CSI - remember that one is not computer controlled.)
 

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Discussion Starter #4
Thanks for the info. So the 12.57 volts they measured at NAPA for an idle battery is not so bad then. I'll ask them about the load test tomorrow, and then I'll measure voltage at home when cranking the engine. If it reads okay, I'm on to testing the TTS and CSI. I'm confident I'll find the issue.
 

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Since common things happen commonly, I'd suggest a close check for any 'false air'. Any leaks in the intake air ducts or vacuum hoses allows air to bypass the Air Flow Meter - thus unmetered or 'false' air. The accordion section of the air duct at the AFM is notorious for a split that will open/close as the engine moves on its rubber mounts.
 

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In my opinion, the symptoms you describe (starts great when warm but not when cold) point more to a fault in the cold start system than a weak battery. Real easy to test. After the car has been idle overnight, unbolt the cold start injector from the plenum, stick the tip in a clear jar or bottle, and watch it while a helper turns the ignition key to start. If no fuel sprays out, its most likely a bad cold start injector, but check the TTS terminal outputs with a multimeter to rule that out before buying a new CSI.
 

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I agree it points more to CS system, but it could also be the cranking voltage is just on the minimum threshold to awake the ECU, so that with a warm engine, the starter is under less strain so uses less power.

As suggested, get the battery charged and checked - or replaced if it won't hold charge - then check the cranking voltage is showing around 10,5-11V

& whilst you are at the battery checking cranking voltage, also check the alternator is charging (might be why the battery is low?)....with engine idling you want to see 13.8-14.4V measured across the battery terminals.

then dive in and check CSI/TTS
 

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Discussion Starter #9
Fingers crossed - I think I got it. Charged the battery overnight, put it in the car - 11 volts cranking. Took off the CSI - nice strong cone of fuel while cranking. But still sluggish to get started. Thought about vacuum leaks. Took off the oil cap while it idled, and no discernible change, when usually there was before this happened. Thought back to any hose work I did over the winter, and I had installed a new oil vapor canister-to-dipstick hose after 'reconditioning' the unit. Although I've read plenty on this forum about priming that hose with oil, I of course didn't. Put a bit of oil in it, and it fired right up. I'm hoping I've found the issue.
 

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glad it fired up!............but I very much doubt that little hose was the cause of all your trouble.
I bet if you pulled off that hose altogether it would still start fine;)

to me it was a combination of
charging the battery to finally get a decent 11V cranking
and maybe
when you pulled the CSI connector (as you have to, to actually unscrew the CSI), you probably scraped clean a contact, or re-seated a pin in the connector, so that it sprayed.
But hey, it's working...that is the main thing
 

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Discussion Starter #11
The thing is, even after the CSI showed a good spray, the car still would not start up easily. That's why I looked to a vacuum issue. And when I did add the oil, the idle behaved as it should when I took off the oil cap (dropping slightly), whereas before adding oil, no change. But I also agree about that maybe not necessarily being the cause, since the old hose was never connected, so in effect there was always a vacuum leak, although it cold started fine. Definitely confusing, and as I said, 'fingers crossed'.
 

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Discussion Starter #12
After a couple days of starting, I do believe that was the fix. Starts right up each morning. Also the idle has never been better. Since owning the car I've struggled to keep a consistent low idle. It would always revert back to about 1600 rpm, no matter what adjustments I made. Now it hums at 1000, and has in all conditions since my 'fix'. Short of it is, I do believe the OVS/dipstick hose does act as a vacuum leak if not filled with a bit of oil......
 
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