Misfires

[Nyyyko]

2012/13 155 tsi, 145kkms. Starts fine, after about 4 sec I get intermittent misfiring in two of the cylinders. Replaced Plugs and coils. No issues while driving, only at idle. Pcv? There’s a fair bit of vacuum if I remove the oil cap, no whistling though. Good L/100. Small leak in rear main seal? Just noticed a small oil leak under the engine side. Thoughts?

[bwilkeson]

Recently replaced plugs and coils to NGK BKR7EIX and VW R8 redtop coilpacks. .27 plug gap, has developed a slight miss at idle but not under load. Only 33000 kms. Unsure where to look for answers with our issue here.....

[Nyyyko]

Recently replaced plugs and coils to NGK BKR7EIX and VW R8 redtop coilpacks. .27 plug gap, has developed a slight miss at idle but not under load. Only 33000 kms. Unsure where to look for answers with our issue here.....

I am wondering if there is an issue with the intake manifold flaps, apparently there’s an updated version in 2017, oooor carbon buildup oooor injectors. As it is only 2 of the 4 cylinders this would indicate a point specific issue rather than a global.

[tigger73]

Misfires could be a number of things.

If your spark plugs aren't gapped properly and/or bad plugs will cause it.

Also for higher mileage (>100,000km) then carbon buildup can cause this sort of thing too. Either way walnut blasting is a good preventative measure and will make your car run better and improve the fuel economy so it'll pay for itself in the longer run (well helps to justify the expense).

[Nyyyko]

Misfires could be a number of things.

If your spark plugs aren't gapped properly and/or bad plugs will cause it.

Also for higher mileage (>100,000km) then carbon buildup can cause this sort of thing too. Either way walnut blasting is a good preventative measure and will make your car run better and improve the fuel economy so it'll pay for itself in the longer run (well helps to justify the expense).

ima pull it apart soon and decarb... soak and scrape

[simon k]

I'd swap back to the old plugs and coils before I did anything else. That's the cheapest and quickest way to diagnose

[Nyyyko]

The Idle misfires in 2 and 3 dramatically improve when ac is switched on. To me this indicates carbon more so than anything electrical, mechanical, vacuum or a seal. Thoughts? There is no issue when driving. Engine is strong, smooth and responsive.

[tigger73]

Yeah I'd be getting a carbon clean anyway at 145k regardless then see how you go from there. It's something that more than likely needs to be done. If it hasn't ever been done before then it's definitely overdue.

[Nyyyko]

The quest continues. So far I have replaced the spark plugs, ignition coils, I mechanically decarbed the intake valves and manifold. Today I replaced the PCV valve which has reduced the vacuum in the engine but the misfires continue. Turning on the a/c improves but does not eliminate the random misfiring. I’m
thinking vacuum leak/air leak somewhere? Timing chain guides wear? Thoughts? Oh, and the small
Oil leak was a reused oils drain Comp washer... replaced and good to go.

[Nyyyko]

To add, I have a high fuel rail pressure code. Maybe this all leads to my injectors going bad? I cleaned them when I decarbed and put a new seal kit on them. I’m wondering if maybe the ecu needs to adjust after changing the PCV. Vacuum is way down to where is should be. I’ll drive for a while and see if it improves.

[Nyyyko]

Aaannnddd it would appear the culprit of the missing misfire cause is..... a cracked PCV breather hose. The one from the air intake into the PCV valve. Aluminium taped it up whale waiting for the replacement and it runs smooth as silk. The ecu will readjust the fuel injected and balance out. Weeee

[tigger73]

Good to hear you got it sorted. Also got a bunch of other maintenance done and learnt a bit about your car in the meantime

[Nyyyko]

It would seem this misfire situation has been trickier to pin down than thought. I finally isolated the cause of my P0088 (high fuel rail pressure) as a failed solenoid on the HPFP. Replaced the solenoid rather than the whole pump. Local dealer had a solenoid handy... very handy. Check engine light now gone! Each piece of the puzzle has improved performance yet I am still getting random misfires on 2 cylinders. Ima gonna replace the injectors. Aside from the fuel control module, which I don’t believe to be defective, the injectors are the final stop. Now. OEM vs Bosch. I’m thinking Bosch at half the cost and a reliable producer. Anyone have thoughts on these two options?

[Nyyyko]

So I received the injectors today, left work early to install. Took me ~2 hours from start to finish... not bad if I say so. Misfires are gone. Fuel rail pressure high is gone. Only current code is P2178, System too rich off idle bank 1. Changed the oil as well, reeked of petrol. I’ll pick up a HPFP tomorrow and install. Hopefully that’ll take care of my nuisance rough idle. I’ll also clean the front O2 sensor. If still persistent I’ll have to replace the N80 valve.

[Nyyyko]

To close this thread out... misfires rectified after replacing injectors. The final piece of the puzzle was the fuel rail pressure high and rich on idle. Replaced the HPFP, changed the oil. Good to go. Fuel was leaking out the back of the HPFP and into the valve cover. Sneaky sneaky. I’ll replace the haldex pump and filter and that will bring the machine to a good state.