car is running lean

[dansmith180]

Hi guys, had a spark plug explode on me after 3000 miles on Tuesday 

Looks like it didn't do any major damage though as i've replaced them all and it runs fine 

However the tips ( the 3 that remain) look at bit white and suspect the car is running lean. I have actually had the car hold back on me at the top end of 3rd a few times and I thought it was the limiter but now I'm guessing it was a fuel issue 

LOBA is 3k old and the mapper even complimented how good it was and is running well well within its limits.

Injectors were replaced at the same time but not new, think they had maybe 35k on them.

LPFP is stock and original as far as I know.

Question is how do I tell what's at fault? I'm leaning towards LPFP but of there's a way to be sure would be great.

TIA 

[Shoduchi]

Can't a VCDS log check if the LPFP is working well?

[Dan_FR]

Plugs always look white, as the car does run lean (stoich) during  day to day driving... idle, cruise, light load/acceleration.

The only way the spark plug colour would help would be to kill the engine (ignition off, car in neutral) at the absolute top of a full throttle run. Nowadays with the clever ECUs and multitude of sensors, this simply isn't needed

VCDS will tell you the LPFP pressure and duty cycle, so you can determine whether it is on its way out or not. Along with logging pressure, you can log lambda requested vs actual to see if the request is being met and whether the car is running leaner than the map is requesting

[xjay1337]

If you want help logging mate let me know and I will pop over one evening.

[Madone]

As Dan said, don't assume it's running lean, they run lean. They also run closed loop fuel injection so the afr is measured in the exhaust and adjusted to achieve the target. If it was actually running lean enough to destroy a plug I am sure it would throw an error.

If you got away with no engine damage from a plug tip breaking off you have done well, a friend is a master tech at Audi, a brand new RS6 dropped a plug tip, damaged the bore, new engine time and a £30k cost !

[dansmith180]

As Dan said, don't assume it's running lean, they run lean. They also run closed loop fuel injection so the afr is measured in the exhaust and adjusted to achieve the target. If it was actually running lean enough to destroy a plug I am sure it would throw an error.

If you got away with no engine damage from a plug tip breaking off you have done well, a friend is a master tech at Audi, a brand new RS6 dropped a plug tip, damaged the bore, new engine time and a £30k cost !

Ouch 

Yeah seems like I got lucky, I think it happened under such load that it was hopefully destroyed and just shot out as dust. What else can cause a plug to brake though? Surely something must be wrong.

[Madone]

Defective plug is the obvious one, that RS6 I mentioned def wasn't running lean and that plug was deemed as defective and just one of those things. You should put some new plugs in and keep any eye on it. If the car was running so lean that it melted the plug it would def have been knocking and pulling timing out. Can you plug in vcds and check for error codes ?  Who did the remap ?, there is a slim chance they did something wrong but still I think the ecu safety features remain unchanged, this will protect the engine from running too lean or knocking too much. My guess is the plug was bad

[pudding]

Was the white colouring crusty deposits by any chance?  That's burned oil.   If the plugs are dry and white tips with grey centre electrode and threads, sounds normal to me.   Old school plug health used to be to look for cardboard colouring but with TFSIs, they burn a bit differently.  So long as the plugs are dry and the long term trims in VCDS are tiny numbers, I'd say all is good.

[Dan_FR]

The only thing I would add to that is so long as all 4 plugs look the same, and the LTFT are small, then you should be good.

Significant differences on one can indicate issues, such as (the increasingly common) injector failure. The ECU is clever enough to compensate through the other cylinders well enough that the LTFTs can be unaffected

Just for future reference 

[dansmith180]

Thanks very much guys this is how 1,3,4 looked, all exactly the same dry with no deposits just a white/ grey colour.

This is how number 2 looked


I'm just driving it carefully ATM and am getting it fully logged and checked on the dyno.

[Dan_FR]

Can't view the images in work unfortunately.

If I were you, I would try and get one of those cheap borescopes, the ones that either connect to a laptop or android phone, and take a look inside the combustion chamber via the sparkplug hole, make sure there is nothing embedded in the piston etc.

I'd also check (via the IAT sensor hole in the inlet manifold) whether the runner flaps for that cylinder (mainly the flow divider in the head) are still present and intact.

[pudding]

1,3 & 4 look normal.  Plug 2 is black with half the ground strap blown away and half the porcelain insulator.   That usually happens when things get too hot and / or detonation.

Look like Bosch plugs.  I thought dealers fit NGKs?

[dansmith180]

1,3 & 4 look normal.  Plug 2 is black with half the ground strap blown away and half the porcelain insulator.   That usually happens when things get too hot and / or detonation.

Look like Bosch plugs.  I thought dealers fit NGKs?

I tried NGK's but it kept throwing an engine management light at high RPM's on the dyno so got binned and Bosch went in, now got 4 new Bosch's in again

[pudding]

1,3 & 4 look normal.  Plug 2 is black with half the ground strap blown away and half the porcelain insulator.   That usually happens when things get too hot and / or detonation.

Look like Bosch plugs.  I thought dealers fit NGKs?

I tried NGK's but it kept throwing an engine management light at high RPM's on the dyno so got binned and Bosch went in, now got 4 new Bosch's in again

Ah....just clicked on your build thread and seen yours is quite extensively modified!  Love all the dash upgrades you've done.  Really lifts the interior!

Anyway.... I'm thinking the Boschers may not be up to it, might need a grade colder?  I think folk tend to fit NGK Iridium 7s with your level of mods?

Any fault codes for rail pressure?  Your plug looks exactly the same as my VR6 turbo ones did when it was pinking it's tits off.

As Dan_FR suggested, I would borrow a boroscope and have a poke around in cyl 2 to make sure the bits of plug didn't embed themselves into the piston crown.   If they blew out of the exhaust valves, there's a chance they could have clipped the turbine wheel, but that won't be immediately obvious.  Is the turbo making any more noise than usual?

[Dan_FR]

Will be sure to check the images later..... Do you get any misfires (logged with VCDS) under idle/light load? If things are getting that hot (From what Pudding has described) then I would be thinking of whether that injector is doing its job properly