Fabio T

Hello - recently got an A4 2.0TDI with 49k miles on the clock

I am having issues with start time, first start of the day is very slow - 3-5 seconds -

i charged my battery full last night , same issue today so that rules out the battery (or does it) - the car will crank for 3-5 seconds and start eventually but its worrying as if i had a flat/low battery i would have no chance.

The crank is consistent and doesn't slow down to indicate battery is struggling or anything to me.

if i crank 3 seconds and then stop...(before full start) then try again it cranks fine and starts in 0.5 seconds!


Is this a fuel issue.... or a battery issue

VCDS showing no faults however there was a "starter to ground" issue once but i stupidly cleared that error and cant the exact wording, but that's only come up once

LightningTruck

Sounds like a bad connection somewhere. Start by measuring voltages and checking starter connections to find the voltage drop.
.

142 guy

It is not clear from your post. When you engage the starter motor is the motor spinning at a normal speed (since it is new to you that may be difficult to judge)? If the starter is spinning quickly then the battery state of charge is good. If the starter is slow to spin then you may have a battery issue or a bad connection between the battery and the starter. Checking the voltage at the battery terminal and the main starter terminal (not so easy) during cranking will indicate where the problem might be - if the starter is turning slowly.

I know zip about TDI engines. Is the TDI a common rail system? If so, what you describe sounds like a problem with priming the fuel rail during the start up process. You might have a problem where the fuel rail is loosing pressure when shut down which then takes longer during the start cycle for the fuel system to bring the common rail back up to the specified pressure. As long as the fuel pressure is in spec while the engine is running it may not generate any DTCs. You might need to do a pressure loss on shut down test to confirm whether you are loosing pressure. However, somebody who owns a TDI can probably give you better advice.

Fabio T

https://www.youtube.com/shorts/IdvLo0Z8Qp4

just recorded it - i may be being stupid it may be normal but having never owned a b9 its not what i am used to

i have measured fuel pressure on vcds - its at 450kpa after a start and shutdown - i will test in a few hours and see if that drops....

if the starter was the problem would it not do it every single time? it only happens after its been sat there for some time (2-4 hours + )

LightningTruck

Only clue so far...
"there was a "starter to ground" issue once "
.

142 guy

Is that the feed pump pressure that you are measuring because that is way too low for a common rail pressure? Is there a separate high pressure measurement? I don't have a service manual for a TDI.

If it restarts quickly and is only slow to start after it has been sitting for several hours that would be consistent with a slow leak someplace (check valve?) that is allowing a gradual loss of pressure. Of course, being consistent with is not necessarily the same thing as being the 'cause of'.