Resolved How to check fuel related misfire - 2012 Jetta 2.5

[CR125Honda]

Getting misfires on cyl 1 and occasionally cyl 2. Vehicle has 155K and I assumed coil pack(s). Yes, I threw money at it instead of a full diagnosis.. Changed all (Bosch), same exact issue.

Oddly enough, it hasn't thrown a code or CEL. I see the misfires happen on VCDS while doing a live test drive.

Haven't tried swapping sparkplugs to see if the misfire follows. Spark Plugs (OEM VW) are relatively new, changed at 125K.

Trying to figure out of it's fuel related, but can not find a fuel pressure measurement anywhere in VCDS.

What is the best way to determine if an injector is dirty or gone bad?

Using latest version VCDS 24.5.0 and HEX-V2

2012 VW Jetta with 2.5L

 

[Uwe]

can not find a fuel pressure measurement anywhere in VCDS.

It's old-school, port-injected and runs fixed fuel pressure, without a pressure sensor, so the ECU has no idea.

Check fuel trims.

30,000 miles on plugs? Pull & inspect. Check gaps.

-Uwe-

 

[CR125Honda]

It's old-school, port-injected and runs fixed fuel pressure, without a pressure sensor, so the ECU has no idea.

Check fuel trims.

30,000 miles on plugs? Pull & inspect. Check gaps.

-Uwe-

Thank you Uwe,
Will do on the spark plugs. Changed the original set at 125K (which were working fine) but yes it will be smart to check/inspect to rule them out.

I'll report back with the findings.

The misfires are only happening while driving and at low to mid range rpm,

 

[CR125Honda]

It's old-school, port-injected and runs fixed fuel pressure, without a pressure sensor, so the ECU has no idea.

Check fuel trims.

30,000 miles on plugs? Pull & inspect. Check gaps.

-Uwe-

And again, You pegged it Uwe.. Thank you.

Not sure why but I made a big assumption mistake. I usually use iridium plugs as most newer vehicles call for them.
Didn't remember the recommended plug for my 2.5L was a genuine VW VAG 101905601F (the large old style copper/nickel type electrode).
They were installed at 125K. They were all a nice tan color but with big gaps. I didn't even measure, looked to be .050" or more.
Replaced all plugs today and put back in the old coil packs.
30 minute test drive ...... all is well.

 

[EuroX]

And again, You pegged it Uwe.. Thank you.

Not sure why but I made a big assumption mistake. I usually use iridium plugs as most newer vehicles call for them.
Didn't remember the recommended plug for my 2.5L was a genuine VW VAG 101905601F (the large old style copper/nickel type electrode).
They were installed at 125K. They were all a nice tan color but with big gaps. I didn't even measure, looked to be .050" or more.
Replaced all plugs today and put back in the old coil packs.
30 minute test drive ...... all is well.

Glad you got it sorted out. I just want to add that if this was fuel related misfire as in shit fuel you would have misfires across the board. My next question was going to be origin and type of plug used, but we already know that so glad you got her sorted out. Always double check the basic's good rule of thumb is to move coil and plug to different cylinder this does 2 things. You can rule out if misfire follow coil or plug and you can closely inspect condition of the components used for wear or any obvious failures.

 

[CR125Honda]

Glad you got it sorted out. I just want to add that if this was fuel related misfire as in shit fuel you would have misfires across the board. My next question was going to be origin and type of plug used, but we already know that so glad you got her sorted out. Always double check the basic's good rule of thumb is to move coil and plug to different cylinder this does 2 things. You can rule out if misfire follow coil or plug and you can closely inspect condition of the components used for wear or any obvious failures.

Thanks EuroX, I became complacent. My history was with three B5 and B5.5's and 98 Jetta, all in the family at the same time. For many years.. I maintained them all. Any misfires I had over the years were due to coil packs. I probably attributed that to the duration of Platinum or Iridium plugs. A swap of the coil and my old Hex-USB VCDS would confirm. Kids are all on their own now and we're down to this one 2012 2.5L Jetta. It's been pretty much bullet proof. Happy to have this issue behind me.

Still have a question though. If, by chance an injector was causing a misfire, what steps do you take to narrow that down?

 

[EuroX]

Thanks EuroX, I became complacent. My history was with three B5 and B5.5's and 98 Jetta, all in the family at the same time. For many years.. I maintained them all. Any misfires I had over the years were due to coil packs. I probably attributed that to the duration of Platinum or Iridium plugs. A swap of the coil and my old Hex-USB VCDS would confirm. Kids are all on their own now and we're down to this one 2012 2.5L Jetta. It's been pretty much bullet proof. Happy to have this iisue behind me.

Still have a question though. If, by chance an injector was causing a misfire, what steps do you take to narrow that down?

Injector causing misfire I would scope the cylinder to see if it looks any different than the others. Being that this engine is still mpi until 2015 IIRC Moving the injector to a different cylinder would also be an option.

 

[EuroX]

All I've ever owned was vw then moved onto audi's. But I had a Mk1 rabbit, Mk2 golf gti, two Mk2 scirocco's, three corrado's, 2 mk2 jetta gli's,a b3 passat glx vr6, 2 mk3 vr6 gti's, one mk3 jetta TDI manual, a mk4 golf gti 1.8t, probably ten b5 passat's all 1.8t some wagons some sedans, after that probably 8 or 9 b5.5 passat's. I still have one now 2004 just turned 49k miles, super clean car 1.8t tiptronic which is not my forte I prefer a manual but oh well. After all that I'd say I've had at least 10 b5 a4's all 1.8t some manual some auto, after than I had a clean b5 s4 2.7T manual car early vin no esp or any of that garbage and alloy knuckles, After that the b6 a4's started I think I had about 5 sold all but two. One is a current project for an engine swap other was my personal daily beater that clocked 518k miles out of a 1.8T, 5 speed manual quattro vehicle. I cut that one in half. I still have the front clip but the rest of it I pulled everything I could from it as those parts are becoming harder and harder to come by. I have a b7 a4 that will be up for sale soon I think. I also have a 2019 audi a6 that my wife drives and a 2017 a4 that I purchased with a blown 2.0T engine that I need to repair. In my family my mother has a 2015 audi a6 and my father who works for VW has a 2015 touareg vr6 no sunroof therefore no waterleaks. Both my parents have had alot of vw's and audi's. My brother recently purchased a Lexus. I already told him he made a mistake but I'm sure he'll realize that in the winter here in NJ.