Diagnose my mystery car problem

"BJ" (benjamin-bignell) 03/08/2016 at 22:43 • Filed to: Internet mechanic

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I’m going to post some details of the problem and you’re gonna do your damnedest to figure out what’s wrong with the Passat. Ok?

Not my car. Just a random pic from Google. Those wheels aren’t bad, tho...

For the record, it’s a 2008 VW Passat Wagon, 2.0T, automatic transmission. Regularly serviced, only about 135000 km on the clock.

Last week, -20 deg C and after a short drive (80 km/50 miles) the car won’t start after a short break. Fires up and immediately stalls. Gas gauge reads 1/4 tank or slightly more. Wife mentioned that it seemed to be running rougher than usual before the breakdown.

Got towed to the dealer, diagnosed with “out of gas” because of a low-pressure code in the system, they put $20 in and everything seems fine. I suspected that maybe due to low temps there was water/ice buildup in the tank preventing the gauge from working properly?

While there, we had the annual service and a warranty job done (intake manifold), as well as some replaced seals for the transmission cooler.

The car drive home just fine and was used Monday & today without trouble, total distance of about 90 km/55 miles over two days.

Today, the car died again. Outside temps about +5 deg C. Gas gauge reads slightly more than 1/4. My wife drove from work to school and, leaving the school, the car died again. Was apparently running a bit rough again beforehand.

I picked up 10 litres of gas and put it in the car - the gauge now reads 1/2 tank. After a few long, long cranks, the car fires up again. Drove it 2km to the gas station, put in another 37 litres (total 47 litres, which means it was NOT out of gas this time) and it stalled leaving the station.

I let it sit a few minutes, then after after a few hard cranks got it running again. Managed to get home and now it won’t start. Fires up, stalls immediately. Or just cranks and cranks...

Fuel pump? Fuel filter? Water/contamination in the fuel? Bad spark? I dunno...

Update: no check engine lights, no sputtering. The car either runs smooth, or doesn’t run at all.

Update 2: actaul mileage is slightly over 135000km.

Update 3: tow truck drivers sure are grunpy about towing a car that runs... it’s not like I can control when it will and won’t start.

Dr. Zoidberg - RIP Oppo > BJ 03/08/2016 at 22:48

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If that’s your Passat, it’s really nice!

Back on topic, lol i dunno eeder.

pjhusa > BJ 03/08/2016 at 22:49

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paging GE90Man

Steve in Manhattan > BJ 03/08/2016 at 22:52

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Fuel pump or clogged fuel line. But I’m probably wrong. Maybe fouled plugs?

Party-vi > Dr. Zoidberg - RIP Oppo 03/08/2016 at 22:54

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-20 degrees celcius and kms instead of miles? Probably not from Maryland lol.

BJ > Steve in Manhattan 03/08/2016 at 22:58

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Plugs maybe, but I think they were done last spring as part of the major service. I’ll double check in the service manual.

I wonder when the fuel filter was changed last...

garagemonkee > BJ 03/08/2016 at 23:04

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Coil packs.

BJ > garagemonkee 03/08/2016 at 23:06

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They’d work intermittently like this? Good for a bit until they heat up?

BJ > garagemonkee 03/08/2016 at 23:14

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Note: I’m not getting a check engine light.

A slushbox can be fun, too! > BJ 03/08/2016 at 23:15

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...being a VDub

garagemonkee > BJ 03/08/2016 at 23:16

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It’s possible. A pack going bad can do some weird things. If you have 122k km and never changed any, it’s probably good to get a set anyway, but given your report of rough running before no start, I’m betting coil packs.

AkursedX > BJ 03/08/2016 at 23:16

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When was the last time the fuel pump cam-follower was changed?

BJ > AkursedX 03/08/2016 at 23:17

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Umm, I dunno. I need to check the service manual to see what was done - is it a regular service item?

JGrabowMSt > BJ 03/08/2016 at 23:21

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Fuel tank vent. It will likely require dropping the fuel tank in order to replace the filler neck and any other associated lines with the vent system. How can you test this theory? Assuming you do not have the threat of rain, open the filler door and take off the fuel cap. If you stop experiencing problems while the cap is off, it’s 99.9% likely to be the venting issue.

2005-2006 Dodge and Chrysler LX platform cars have the exact same issue, though normally it is only an issue if the tank is filled all the way (the car will stall within seconds of being started, usually when pulling out of the station).

Other things I would take into consideration is a clogged fuel filter (though the only time I’ve seen this actually cause a problem was on Mathias Rios’ 924 that was sitting for some time before he bought it). Experienced basically the same issues you’re describing, but I wouldn’t immediately expect a car less than 10 years old to have a clogged fuel filter unless you routinely get gas while the tanker truck is refilling the station as well as run the tank down to nearly empty on a regular basis (both of those situations will cause extra sediment to enter the fuel system).

Being a VW Wagon, another thing you could try is unplugging the MAF sensor. I had to help a coworker get his unplugged because it was causing his car to stall. The connector is glued in place at the factory, so expect to really have to wrestle with it to get the connector off. It will force the ECU to go into a closed loop mode and rely on the O2 sensors for the air/fuel mix, and can lead to having lower gas mileage until it gets replaced.

AkursedX > BJ 03/08/2016 at 23:22

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I’m not even sure if it’s in the service manual from what I remember. But people will recommend it anywhere from 10k-40k. I’m on my phone and linking is too hard, but just Google “VW cam follower”

I’m thinking this might be your issue.

GE90man > BJ 03/08/2016 at 23:24

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idk, but guess I found a B6 Passat buddy! I have a 2006 and have never seen this problem yet

HammerheadFistpunch > BJ 03/08/2016 at 23:29

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Sounds like a bad sender, fill it up when it dies and find out if its really a 1/4 or if the sender is borked

BJ > JGrabowMSt 03/08/2016 at 23:31

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Great tips, thanks! The fuel cap and MAF tricks I can try, but neither will be an acceptable permanent solution for my wife’s daily driver.

BJ > AkursedX 03/08/2016 at 23:32

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I’ll look into it, thanks.

BaconSandwich is tasty. > BJ 03/08/2016 at 23:39

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As someone here on Oppo once said, it takes:
1. Fuel
2. Air
3. Spark.

I’m guessing something to do with #3. Air doesn’t seem to be a problem, unless it’s something like an O2 sensor. If that were the case, I’d expect it to still run, but run rich (or lean). #1 is a possibility, as others have said - it could be a fuel filter or pump (or something else fuel system related). My guess is something electrical.

My parents once had a Festiva that had odd problems like that. Turns out there were a number of shorts that were happening. It was identified by spraying a fine mist of water around the engine bay at night, while it was running - it was possible to see things arcing. Not saying that is the same problem here, but I do guess something electrical.

JGrabowMSt > BJ 03/08/2016 at 23:52

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If unplugging the MAF sensor gets it running again, just get a new sensor, all bueno.

If the fuel cap trick works, it’s a trip to a service shop. I wouldn’t necessarily go to the dealer unless they’ll cover it under warranty, as it’ll be a lot of labor to get the car apart.

AMGtech - now with more recalls! > BJ 03/09/2016 at 01:19

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Sounds like a fuel pump to me. Could be high-pressure or low-pressure pump. Fuel pressure will have to be tested. If you plan on doing this yourself, do not try to check the high side with a mechanical gauge unless you want things to go very wrong in potentially dangerous ways.

ciscokidinsf > BJ 03/09/2016 at 02:20

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Last but not least, may be a Crank Position Sensor, they don’t throw a code, instead is a crapshoot on when will it start when it starts failing. Extra points if the ‘running rough’ you mentioned happens when the car is driving/idling at a very low speed.

Maidee > BJ 03/09/2016 at 03:25

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Sorry, don’t have a clue. But I have to say your picture reminded me of my Passat and how much I miss it. It was a 2004 sedan in that same color. The color that sometimes looks blue and sometimes looks silver depending on the lighting. In fact I was at fuel station once when a couple asked me what color it was. The guy thought it was silver but the girl said it was blue and I had to settle the confusion. Anyways, good luck!!

BJ > ciscokidinsf 03/09/2016 at 07:04

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Good idea, thanks.

BJ > HammerheadFistpunch 03/09/2016 at 07:06

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That was my thought, but after putting only 47 litres in, it’s full. Showing 1/4 was maybe off a bit, but not that much.

Now that she’s full, she should run but no dice!

BJ > AMGtech - now with more recalls! 03/09/2016 at 07:08

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LOL, I won’t be testing any hp pumps myself but good advice.

Someone else mentioned the cam follower that drives the hp pump. This is something I could in theory replace myself but I don’t have the time or space.

BJ > Maidee 03/09/2016 at 07:10

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Not my car there, but I agree it’s a handsome colour.

I used to have a Grand Marquis in a silver green that was the same. Sometimes green, sometimes silver, and sometimes under a bright blue sky, blue.

BJ > BaconSandwich is tasty. 03/09/2016 at 07:38

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We’ve had zeeo electrical problems to date but it’s a possibility. Thanks

Steve in Manhattan > BJ 03/09/2016 at 11:28

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If they did a major service and didn’t do the plugs, something is very wrong.

torque > BJ 03/09/2016 at 11:31

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Quick google search turns up this

http://forums.vwvortex.com/showthread.php…

For this guy (also has an 08' Passat) turned out to be the “electronic column steering lock”

Others reported the same symptoms as you and found it to be the cam follower

BTW - For otto cycle VWs, VWVortex can (emphasis “Can”) be a good source of info

His Stigness > AMGtech - now with more recalls! 03/13/2016 at 03:43

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If there was a code stored for low fuel pressure then it’s the high side and most likely the fuel pump tappet which disintegrates if it and the camshaft haven’t been updated. Because it’s intermittent though it sounds like a fault with the pump, though. Generally, when it’s the tappet then the car just dies and doesn’t run again.

Fun story: I was working on my friends GTI with the BYP 2.0T engine and he wanted me to replace the tappet since they fail. I took it out and there was a hole worn in the middle. Me, my friend, and my co-worker couldn’t believe it was driving just fine. We decided to put the old one back in and just ship it to the dealer and make them do the update. They ended up replacing the pump and camshaft under warranty. They screwed up the cam seal though and he had to bring it right back. I thought that was kind of funny, but I know shit happens.

AMGtech - now with more recalls! > His Stigness 03/13/2016 at 05:49

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Sounds reasonable, but I don’t know anything about these engines. I think the OP posted again a couple days later saying it was the low side pump. I’ve seen low pressure faults set by both pumps on multiple different engines before, so I’m not inclined to just throw guesses out without some testing.