Car won't start--unique problem or overlooking the obvious?!

[plush]

My 01.5 S4 occasionally won't start. My voltage is fine. I've narrowed it down to 3 potential issues:

1. Fuel pump
2. Starter
3. Subwoofers zapping juice from the battery?

I have the stock fuel pump (I think?), but it whines similar to a Walboro 255. I'm guessing it's NOT the fuel pump since it runs just fine with no hesitation, bucking, stalling, etc once I get it started.

Any ideas? I'm throwing no codes and it's intermittent. It has left me stranded twice over the past 3 months... Thoughts?

[ianwpb]

So you turn the key and what happens? Does it crank, or do nothing?

If it doesn't crank I'd say maybe your starter safety switch could be on it's way out. It happened to me on my old A4.

[y3ti]

More info needed. When does it happen?

Crank position sensor seems to be common. Won't allow it to start when warm/hot.

I had a similar issue with my clutch pedal safety switch. You can readjust or bypass it. I suggest starting there. Takes 10 mins.

[bradthebold]

I had a similar issue with the clutch safety switch in my Passat. Sometimes it wouldn't like to start. I finally bipassed it and never had the problem again. My S4 came with it already bypassed.

[chaos2984]

We need to know if the car cranks or not. Need all the details before we can direct you with what to do next.

[plush]

Thanks all. The car does crank--there's no sluggish sound when cranking, it just doesn't fire up. It has happened when the car is both warm and cold.

[bradthebold]

Well that's not a safety switch then.

[hibiscusS4]

check the fuel pump fuse. see if its blown
you know the fuse box on the drivers side.
my pump was shorting out and causing the fuel pump fuse to break put in a new pump and car runs great.
other then a 0442 code now.. maybe i need to tighten the top cap more tho haha.

[R1CH-5100]

Thanks all. The car does crank--there's no sluggish sound when cranking, it just doesn't fire up. It has happened when the car is both warm and cold.

Sounds like crank position sensor

[plush]

Fuse looks good.... Is there a way to check the health of the crank position sensor without using vag-com/VCDS Lite (my new cable is on the way)? When they fail is it usually visible via corrosion/cracks/chipping?

[plush]

bump for Q on crank position sensor :D

Aside from vag com is there a way to visibly determine failure of this sensor (Cracking, corrosion, etc)?

[jballou]

Cps

[Corradovolksb]

Dose it start after the first attempt or not at all? If it starts on the second try I would check the residual fuel pressure after you shut the engine off. The fuel pressure should hold around 20psi for at least 1hr and them stay around 10psi after that. If it doesn't them your fuel pump return check valve is bad causing the pressure to bleed off and a hard start condition. If it's not that then prob crank sensor. A lot of the time there won't be any faults stored when the CPS fails.


2000 Nogaro S4 stage 2 K&N intake SSAC turbo back exhaust EVOMS DV's SB stage3 daily clutch 42lb injectors V8 FSI fuel pump. 91 and E85 personally tuned.

[plush]

Thanks for the idea and input. It starts 99% of the time no problem while cold. I drove it to the grocery store to pick up milk (2 miles) over the weekend, parked it, finished in the store in around 5 minutes, came out and it wouldn't start. I went back into the grocery store to kill some time, came out, and it started on the 3rd or 4th try. Another time I drove it for about an hour, stopped for gas, and then couldn't start it up for 5 minutes after filling up. That was a few months ago. Since then it has gotten worse and the odds of having it successfully start after any amount of driving have gone down quite a bit.

I'll first try the CPS since it's only a $40 fix and most signs point to this, but I'll report back either way.

Dose it start after the first attempt or not at all? If it starts on the second try I would check the residual fuel pressure after you shut the engine off. The fuel pressure should hold around 20psi for at least 1hr and them stay around 10psi after that. If it doesn't them your fuel pump return check valve is bad causing the pressure to bleed off and a hard start condition. If it's not that then prob crank sensor. A lot of the time there won't be any faults stored when the CPS fails.


2000 Nogaro S4 stage 2 K&N intake SSAC turbo back exhaust EVOMS DV's SB stage3 daily clutch 42lb injectors V8 FSI fuel pump. 91 and E85 personally tuned.

[Jake@JHM]

Are you running extremely rich?

[s4andtls]

cps, after car cools down it starts up.

[Peter1.8t]

I vote CPS

[Corradovolksb]

Ok that could be CPS from what you have described. Does your check engine and epc light come on before you try and start it? Just asking because of they don't then you may have a bad ECM relay or a bad ECM. Kinda grabbing at straws but something to check.


2000 Nogaro S4 stage 2 K&N intake SSAC turbo back exhaust EVOMS DV's SB stage3 daily clutch 42lb injectors V8 FSI fuel pump. 91 and E85 personally tuned.

[plush]

CPS has been replaced. Once I get my control arms and new tires, I'll be able to drive it, park it, and start it to see if the problem is gone. Should know by Tuesday and will report back...