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Discussion Starter #1
Daughter's Passat cranks but won't start. Took a quick look today but need more ideas.

Tach moves when cranking, I think that rules out crank position sensor, right?

I smell fuel at the muffler after cranking. I also hear the fuel pump prime when I turn the key on. So I think it's getting fuel. Don't have tools to actually check pressure. Could it still be too low even if I smell gas?

When it cranks, it occasionally chugs like it's firing but still doesn't start.

Would have checked spark plugs but didn't have the socket with me.

Car sat for a week and ran fine before that.

I have VCDS. No codes. Any tests I could do?

Looking for ideas before I make another trip.
 

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Fuel, spark, compression. Sounds like you have some fuel; whether it's the right mixture can be explored later. You can pull a plug to check for spark. As to compression you need a gauge. Question: does it sound normal when it's cranking? Not faster than usual? The timing belt can break without warning, and all the spark and fuel in the world won't help you.

If you think it might be the crankshaft position/speed sensor, try an extended crank. After a while (don't remember - 30-60 seconds?) it will ignore the sensor and start without it.
 

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Check all the vacuum and breather hoses. Check the main air inlet duct to the throttle body for cracks. Make sure those clamps are tight.

Try unplugging the MAF and see if that changes anything. That should throw a code.
 

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Discussion Starter #4
Given that it ran fine a week ago (was daily-driven about 16 miles to work and then home, partly on highway, no problems reported by my daughter)...

It's not likely that all spark plugs, or all coils, or all wires, or all injectors, or compression in all cylinders would go equally bad at the same time, is it?

I would expect if any of the above were a problem, it would run, but poorly. Or at least fire and try to run even if it stalls.

So I'm leaning toward it being a problem with fuel pressure (Weak pump or plugged filter?) or a wiring problem (Bad grounds? Coil packs not getting enough power?)

I smell fuel at the exhaust after cranking, but how lean would it have to be to not fire at all? (Or just occasional sputters?)

Hmm... what about the gas (with ethanol) phase-separating after sitting a week? Is is possible that a car with some water in the tank could "run fine" if driven daily (sloshing gas around and preventing separation) but if left to sit, the ethanol/water could sink to the bottom?

I can't go back for at least a day or two so at this point I'm trying to get a list of things to check or try.

Question: does it sound normal when it's cranking? Not faster than usual? The timing belt can break without warning, and all the spark and fuel in the world won't help you.
Sounds normal to me. I replaced the timing belt/water pump/thermostat last year. Yesterday I pulled back a cover and checked. The belt is not broken, doesn't appear damaged, and has tension.

If you think it might be the crankshaft position/speed sensor, try an extended crank. After a while (don't remember - 30-60 seconds?) it will ignore the sensor and start without it.
Tach works when cranking. Does that rule out the cps? Also, wouldn't it not fire fuel injectors with no cps signal?

Although... I suppose if compression was bad, the gas smell at the exhaust could be coming from the crankcase, could't it?

I haven't found any obvious vacuum leaks yet (visually and feeling) but can check that more later. Could that cause it to not fire? Could a bad fuel pressure regulator, or vacuum connection to it, cause this?

Frustrating that the car is an hour away. I'm not an expert, but with a car in my driveway I can usually figure it out in time. Haven't destroyed a car yet. :)
 

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I haven't found any obvious vacuum leaks yet (visually and feeling) but can check that more later. Could that cause it to not fire? Could a bad fuel pressure regulator, or vacuum connection to it, cause this?
IMHO, probably not. I haven't yet seen the vacuum or PCV systems cause enough trouble to completely preclude starting.

The coil pack has (IIRC, I don't have a V6) two circuits, each covering three cylinders. Unlikely both could fail, but perhaps it only has one ground?

Nearly impossible fuel would change enough in a week to become non-flammable.

A failed fuel pressure regulator might do it, but that's pretty rare. So would a bad ECU, but that almost never happens.
 

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I don't have a V6 but my guess is that it's flooded. The V6's are susceptible to flooding fairly easy, per the internet ;) and when it happens the car won't start until you un-flood it. Search around here or PassatWorld.com for how to do that.
 

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Discussion Starter #7
Success.

I don't have a V6 but my guess is that it's flooded. The V6's are susceptible to flooding fairly easy, per the internet ;) and when it happens the car won't start until you un-flood it. Search around here or PassatWorld.com for how to do that.
I think flooding was it, caused by a weak battery that showed 12v but tested bad at an auto parts store. Flooded due to many cranking cycles where it turned over but didn't fire?

Anyway, new battery, topped it off with a charger, still took two long cranks but it started.
 
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