I just checked the spark plugs on my AU VCT (after 20,000 kms), and five of them look like you would expect - white to brown/grey insulator. But one (#5) looks silvery like aluminium, including on the centre electrode. What causes this, and should I be concerned? I have read that this could be a sign of lean detonation. But the AU has a very active knock sensor, so that would surprise me.

Below is a pic of the silvery plug on the left, compared to a normal one on the right.

Thanks for your help.

 

 

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Have seen this on cars with leaking intake manifold gaskets and with blocked injectors but the cars also ran like they had problems. How's you're car run?

Seems to be running fine, other than 10 seconds or so of hunting idle shortly after a cold start. Will check for a gasket leak with starting spray. I also have a spare set of AU injectors (to go into my EF), so will swap one of those in and see if it makes any difference to plug colour. Thanks heaps for the advice. Cheers.

Cleaning the ISC usually will fox that cold atart

after you FOX the cold start,change all the injectors or try injector cleaner on the old ones,it may fix or replace it.

Thanks for all the help. That's a lot of good ideas.

Oh come on mate, one spelling mistake and you jump on it, it's called predictive text...if you know what that is.
Rather then changing all injectors remove the one in the cylinder with the lean plug and take it to be flow tested, will tell you if you're on the right track or if you almost wasted a stack of cash on new injectors.. If it is flowing poorly get the lot of you're injectors sonic cleaned and re kitted.

it would be cheaper to just buy a new set on Ebay

Well, it was definitely a problem with the fuel injector. I swapped a reconditioned one in #5 cylinder and the spark plug colour is now normal. Also, the hunting idle on cold start is effectively gone. Thanks for all the helpful suggestions.

Until you get sold crap and have stuff all chance of a replacement at zero cost.

You can flow check them yourself.
Undo the 4 bolts holding the injector rail and raise it up as far as the hoses will let it, will give you decent access of #1 & #2 positions, which you cycle all original 6 injectors through in those positions in pairs, then your spares too.
In the E series, you can earth the top right pin of the diag connector, turn IGN on, and the pump will run, AU is probably same. Being XR, fuel pressure with no vacuum should be around 300KPa.
You can make up a power loom with a switch and an injector/EB/ED/EL coil plug, and hook it up to the car battery. Idea is then to power up the fuel pump, check injector under test for leaking, then power it and let it flow into a container for a few secs to remove air pockets, empty it into a gash container, then power the injector and let it flow for 60 secs into the container, check the spray pattern as well.
Have a measuring container sitting on a bench top, empty the fuel into it - mark the fuel level and empty it into your gash container. Do the same for injector at #2 position, then swap them over with another two, and so on.
Keep note of the levels of each injector, and you can actually measure a particular fuel level with a syringe or measuring cup, to see actually how much fluid there is.
Typically I've found AU injectors to flow 190-195ML/min @ 300Kpa. This then gives you a benchmark to work on. Without it you're clutching with straws. Return the fuel in your gash container back into the fuel tank.
I use a $50 ultrasonic cleaner to do my injectors - I soak them in straight undiluted injector cleaner(remove pintle caps and O rings) - I don't pulse them like the pros do, I might rig something up eventually, but if they're not heavily clogged, you should find the cleaner still does a good job.
Then you can flow test again if some of your injectors were low.
Key things:
-Safety specs and eyewash or water handy, fire extinguisher if handy, make sure injectors are properly clipped on the fuel rail, be aware IGN is on while the pump is running, so switch off after each flow test. The test power lead is intended to reduce spark hazard.
Leave rail for a few minutes to depressurise/and/or power up injector into container.
As usual, safety and common sense.

I've had good success with this in recent times, so I might make up a test rig with a fuel pump and injector rail for this purpose.

I have access to a sonic cleaner at work so i just use it, but you're way could give you a sorta idea of what's going on if you sorta know whats going on.

In a sorta way, yes.

Sorta