[alan_b]

I fitted the correct specification NGK plugs about 3k miles ago and gapped them to 1.1mm. However, a severe misfire developed yesterday and the car became virtually undriveable. This all happened after a weekend of heavy-footed driving I cleaned the plugs and checked the gaps, but the problem remained. However, I changed the plugs and the misfiring disappeared.

I'm surprised by the short time that the plugs lasted and I'm wondering whether the high boost that I'm running (I peak at about 24psi and sustain about 20 psi) might be responsible. I checked the plugs and there is no sign of damage and the electrodes look a healthy colour. The DI unit is five months old

Any suggestions?

Alanb

 

[Julian]

I have come across the odd dodgy NGK plug in the past, on a mate's old 900i 8v. New plugs were fitted, the idle became lumpy and a slight misfire developed. He replaced all plugs with more new ones and the problem disappeared in an instant. I guess the occasional duff plug must slip through their quality control.

 

[ms08]

I would tend to agree with Julian that you may have been unlucky with a dodgy plug - it is not unknown to happen.
Mike

 

[mark e]

Alan,

I don't know what "state of tune" you're in at the mo, but if you're still running a bit lean on max boost, this will be increasing combustion temperatures and thus accelerating plug wear...

 

[billj]

I've had no problems at all with plugs, running about 1.6 bar for nearly a year. I tend to agree with Mark, though. If you find another set goes the same way (i.e. it's not just a bad plug), then it could be down to the dangerously lean mixture you were (are?) running.

 

[alan_b]

Yes Bill, to be honest I have a feeling that this could be the cause. The warmer weather combined with a tussle with an Elise may have been too much.

I'm taking this as a very kind warning that I may have gone too far with the current set-up. Once I get the water injection fitted I think I'll try to get the exhaust temp measured. Does anyone know who does this or how it can be done myself? Do Power Engineering have the equipment to do this?

Alanb

 

[murphwiz]

you can buy various gauges and probes to measure EGT's...

http://www.red-ibex.com/EGTgauge.htm

http://www.scoobymania.co.uk/interior_info.asp?c=2

Hmm the aircraft ones seem very cheap!
http://www.airworlduk.com/falcon4.htm