Fault/misfire under load

[coreythorny]

Evening all.

I was wondering if anyone else has had the same.

Whilst out earlier, 3rd gear starting to accelerate uphill, full load, I got to ~4krpm and the car badly misfired and rev needle jumped.
Now I've had this before and istantly backed off and presumed coil pack shot. But this time I have no engine management light and no fault codes stored.

When the coil went last time I only replaced the faulty one as it gave me the full code for cyclinder 2. My car is a 57 plate with 59k miles now so I've already ordered a new set as to to be fair, I was being cheap last time and should have replaced them all out of good practice.

I'm just curious this time as to why I have no fault. Idle is 100%, starts perfect, drives perfects off full boost.
What I do find weird is, if I Rev the car in neutral (lightly) it gets to 4K rpm the misses and the Rev needle bounces from 4-2k.

Bit worrying as it sounds horrible. I'm hoping the coils will be a straight fix but was after any suggestions where to look if they don't resolve the issue.
Sparks are replaced annually also and only done in October so I doubt it's that.


Thanks.

 

[Bugeye_bob]

http://www.audi-sport.net/xf/threads/misfire-detection-on-vcds.119284/

hth, saves me typing what has been said.

 

[S3Alex]

Usual misfire cause is coil packs or plugs and neither cause warnings usually either.

Revs are limited to 4K in neutral.

 

[coreythorny]

Usual misfire cause is coil packs or plugs and neither cause warnings usually either.

Revs are limited to 4K in neutral.

Yeah I have had one gone before but it was different. It was like hitting the rev limiter.

Been doing some more questioning elsewhere and found someone had a very very similar issue with a video of it. His was the G28 engine speed sensor.

I'm hoping it's not that but it sounds more likely.

 

[coreythorny]

I don't suppose anyone knows the part number for the engine/crank speed sensor (G28).

I'm finding a few online including some Bosch ones.

 

[Bugeye_bob]

why not log the channels mentioned in the link to see if it is a coil/plug miss fire first, it doesnt always put the light on but the miss fire will show.

 

[coreythorny]

why not log the channels mentioned in the link to see if it is a coil/plug miss fire first, it doesnt always put the light on but the miss fire will show.

I don't have access to VCDS or Vagcom unfortunately.

Going on from what happened like time I had a coil going, it was rapid misfiring under load. This time it's different, it's like the engines trying to stall. Not the best way to diagnose faults I know but looking at a few videos of G28 faults its identical symptoms.

 

[Bugeye_bob]

why not find a member local that can help, has to be cheaper then randomly changing parts,
the fact you have changed just one coil pack, and I bet the rest were the same age as the old one that went faulty, would point towards another failing imo.

 

[coreythorny]

why not find a member local that can help, has to be cheaper then randomly changing parts,
the fact you have changed just one coil pack, and I bet the rest were the same age as the old one that went faulty, would point towards another failing imo.

I appreciate that but unfortunately nobody is listed around me. The coil packs are already ordered, as like you say I should have replaced them all originally. But I'm no longer confident it is that.

 

[Bugeye_bob]

where are you ?

 

[coreythorny]

where are you ?

I'm in Rutland. Nearest two are Leicester and Grantham which aren't particularly near.

 

[Bugeye_bob]

I'm in Rutland. Nearest two are Leicester and Grantham which aren't particularly near.

lol im certainly too far to help then.

 

[coreythorny]

lol im certainly too far to help then.

Lol no worries mate. Cheers.

 

[Retroman]

As it only happens under load I would tend to lean towards guessing plugs and then coils - in that order. In my experience coils tend to "play up" more when hot. A failing "timing" sensor would not tend to be restricted just when the engine is under load. An outside option would also be a fuel filter. Good luck

 

[coreythorny]

As it only happens under load I would tend to lean towards guessing plugs and then coils - in that order. In my experience coils tend to "play up" more when hot. A failing "timing" sensor would not tend to be restricted just when the engine is under load. An outside option would also be a fuel filter. Good luck

Yeah I appreciate that. But I don't think coils would cause the issue if lightly revving the engine in neutral. Coils and plugs are en route so obviously I'll do them first.