# Mystery Misfire, 2012 Passat 2.5



## 1slow3.0h (Dec 27, 2018)

Just a quick background on myself and the car. I am a mechanic, and I normally don't have to leech post like this on forums.. so I apologize in advance for that. However this car has racked my brain a bit and I'd let to get some opinions. I'm a BMW guy (yea.. yea... I know), but we found a DEAL on this 12' model Passat earlier this year. Guy pretty much said it has a misfire every now so he parked it and bought a new one. When we got there, we cold started the vehicle, plenty of coolant, oil looked great, ran and drove PERFECT. I brought my trailer just in case, but it was fine. Threw insurance on it, drove it all night that night, and for almost a month with no issues. I thought I had struck GOLD (Gave $2k for the car). 

Anyhow, one morning my girlfriend was heading to work and when she fired up the car it misfired. CYL 1. I did the immediate and easy thing, swapped the coil out (I had a spare from another VW I rebuilt a while back).. and the car was fine for that day. I went ahead and ordered a set of R8 coils through ECS and picked up a set of plugs as well. I figured at the mileage, the car was due a fresh set anyhow. With them installed, the car went another few days with no issues (Keep in mind, at the point the only time we've seen it misfire was the one morning I previously mentioned). 

We thought it was fixed, but again, it misfired one morning. I decided to attempt to Diag it, CYL 1 again, pulled the injector plug with it running for whatever reason, and it idled up ever so slightly, idled smooth for just a second, and then settled back to a misfire.. but then when I plugged the CYL 1 injector back in, it idled normally! At this point, I assumed the injector was leaking over night, loading up the cylinder, and by unplugging the injector I was giving the engine a chance to clear it out. I replaced the injector, and the problem went away.. for about another week. Warrantied the injector like an asshat, same problem.. about a week later- again. 

Now at this point I can replicate the "unplug/replug the injector" procedure and get the misfire to go away much quicker than if I just let the car idle or give it a "small rev", and it will only do it if the car sets for 8+hours. 

The last thing I've tried is temporairly bypassing the N80 solenoid/valve because I've read a thing or two about those giving issues by allow too much evap fumes into the intake choking Cyl1.. this hasn't changed anything for my situation. 

Short summary: 

New injector
New coils/plugs 
Misfire isolated to CYL1 regardless of swapping Injectors/coils
Not consuming any oil/coolant
Only misfires when engine has been setting 8+hours. 
Once it quits misfiring (after 10-30 seconds), the car is perfectly drivable.. and we've taken it on several 2+ hour trips like this.


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## Ichabod0525 (Feb 11, 2018)

Sounds like you replaced possibly bad parts so that leaves checking for intermittent signal. Probably a good place to start would be ground signal to the #1 injector from the PCM, under load, when cold at the injector plug.


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## 1slow3.0h (Dec 27, 2018)

Checked the harness side of the injector, all checked out.. 

Also wouldn't make sense for a bad ground to cause a single cylinder to "flood itself" overnight.


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## Ichabod0525 (Feb 11, 2018)

1slow3.0h said:


> Checked the harness side of the injector, all checked out..
> 
> Also wouldn't make sense for a bad ground to cause a single cylinder to "flood itself" overnight.


Thinking was; #1 is not getting a signal when cold. Injectors have a constant common 12V and are signaled to fire by a ground signal from the PCM. A poor connection to the PCM for that particular injector might only show up when it's cold, like you describe " _it will only do it if the car sets for 8+hours_." Flooding? A check of residual fuel pressure after standing for 15min should isolate that I'm thinking. Are you sure it's flooding? Then it can only be the injector but you've already swapped that.


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## Ronny Bensys (Apr 17, 2014)

Cylinder 1 misfire do not always mean bad coil, plug or injector at cylinder #1. Sometimes a malfunction in the fuel system causes only Cylinder 1 to appear as a fault code. Check compression at cylinder #1. Next, change fuel filter if service records do not show any recent fuel system service. What is the total milage of the car?


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## Luckranout (Oct 16, 2020)

Same issue same car... cylinder 5 any luck?


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## Ronny Bensys (Apr 17, 2014)

Luckranout said:


> Same issue same car... cylinder 5 any luck?


Did you resolve the issue?


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## Luckranout (Oct 16, 2020)

Have not


Ronny Bensys said:


> Did you resolve the issue?


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## nutsofast1.8T (Feb 4, 2004)

Possibly an intake leak? Those seals dont last forever. Spray some starting fluid around the intake-to-head area and see if that affects your idle. Each Intake has its own individual o-ring seal. If one is bad, I would replace all 5.


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## halbwissen (Jul 20, 2001)

I, too, was going to suggest checking the intake manifold gaskets and to also check that the intake manifold bolts are tightened to spec. I’ve heard of several users here and elsewhere having cold start misfires on the outward cylinder(s) because of loose bolts.


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## Luckranout (Oct 16, 2020)

Not the case thank you, it seems to be internal.


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## Ronny Bensys (Apr 17, 2014)

Luckranout said:


> Not the case thank you, it seems to be internal.


Do you have CEL? Have you scanned the car for codes?


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