Misfire like issue.

[mark_amus]

Hi all. Recently bought a vrs with 1.8t auq. I changed the spark plugs and engine oil and then the car seemed to drive as if it had a misfire. Plugged in with autel and nothing misfire related was read. I then changed plugs back to ones fitted and still the same. I then checked all wires and seem to be OK. Next step was to try coil pack. I done this and used a new coil pack and swapped around and still the same issue when driving. Researched the issue and see oil could have had an input, I then drained the oil form a recommended 10w40 to a recommended 5w40. Has anyone got any ideas? Pic below is most recent plug In.

 

Car has apparently been mapped and has decat pipe fitted aswell as other things done in the engine bay. 

 

Thanks for reading and sorry if this has been covered before. 

[mac11irl]

Hi @mark_amus

when you say misfire, is the idle rough? fluctuating up and down and not settling? reason i ask that is the MAF fault on that list. 

if it is, try unplugging the maf and run it again. if no change it rules it out, if it settles down then the maf is done, and you need a new GENUINE one. not a pattern part, youll just end up buying an oem one anyway.  

[mark_amus]

It idles completely fine. Will rev properly with no issue. I have unplugged the maf and run the car and made no difference. Still drives but has the feeling of misfire, it backfires aswell. 

[mac11irl]

what spark plugs did you use when replacing them? and what was in it?

may need to check the gaps as i seem to recall mapped 1.8Ts needing the gap adjusted, but that may be in specific setups, may be that your map needs it and it hasnt been done..

[mark_amus]

I used bosch ones that are recommended 0242236571. These were changed back to the original ones in. Bosch super 4s are currently in it fr78 ones. 

[xman]

Is the misfire when applying power, trying to accelerate?

If so I would be tempted to have a compression check done, could be a burnt valve/seat or piston ring problem which the 1.8 is reknown for.

[mark_amus]

Yes it's when I accelerate.  I'd didn't do it before I changed plugs and oil though. Ran completely fine with no issues. Il be doing compression check over weekend. What psi should I expect to see?

[xman]

Just check all cylinders are more or less equal.

[xman]

I thought that the 1.8t requires a fine tip (platinum or iridium) spark plug? Super 4 are not really suitable

 

Edited 22 February by xman

[mark_amus]

That's what was in it before I changed them. 

[mark_amus]

Hi all. Just an update. I have done compression test and all have almost identical readings around 125psi. I have also changed the coolant sensor and crank shaft sensor. This hasn't improved the issue. I'm not sure where to look next. Any ideas? Thanks 

[mac11irl]

gap check those plugs..

 

also i am 99% sure that mapped 1.8T need ngk plugs (with a corrected gap) search that in this sub forum for the exact spec

 

and if its really really really not the plugs, get your coil packs checked.

Edited 8 March by mac11irl
After thought

[mark_amus]

OK. What plugs are recommended and what gap should they be?

[mac11irl]

i cant remember exactly, as its a long time since i recall it coming up on here last, but do a search in this sub section for NGK and Gap you should get some hits.

 

edit... search result..

this one has details

Edited 9 March by mac11irl
linked a search result

[mark_amus]

Just to update. The car seems to have improved after changing maf sensor and both lambda sensors. But The car really struggles when driving when engine is cold. I literally move the car when I finish work so I can see it when it's warning up.  Once warmed up it drives OK but will drop in power. I take my foot off the accelerator pedal and back on and seems fine again but will do the same shortly after. The pic shows fuel pump control unit. Any ideas? Thanks

Edited 10 March by mark_amus