Misfire Rough Running Condundrum

[Andy JB]

So my RV8 500 96 vintage has developed what appears to be a slight misfire/ rough running which is also intermittent, ie shunting at low revs & unhappy at anything other than heavy throttle.

Having replaced most of the ignition system this year as preventative maintenence i'm struggling to identify the fault. Engine air & mixture tuned last month & has since run well. New coil, plugs, leads, dizzy, rotor, & temp sensors, ignition amplifier. The only missing link is plug extenders last changed 2006 for which supply has dried up so i can't replace these at present.

With Le Mans looming I'm struggling to identify why suddenly its started doing this.

Petrol refreshed & newish pump & filter & lamdas this year. I did change 4 relays (loose ones in footwell 12v 30 amp) before day it occurred but i can't see this having any correlation.

Anything i've missed?

[venusdimilo]

Hi Andy.

I had the same fault and changed all as you have. Turned out to be the extenders. If you remove them and go for a drive you can at least be sure if it is them or not. I also could not get any new extenders and so have used these.

http://www.ebay.co.uk/itm/BLACK-1200-SPARK-PLUG-WI...

They seem to be working at the moment and at a price that when the extenders come back into stock a short term solution.

Good luck
Steve

[Steve_D]

Andy JB said:

.....I did change 4 relays (loose ones in footwell 12v 30 amp) before day it occurred but i can't see this having any correlation.......

Are you sure you replaced them with the correct type? They are not your normal run of the mill relay.

Steve

[Andy JB]

Yes all Bosch relays - i have change dthem back again to no avail so removed them from the list.

Plug extenders looking the most likely but you can't get these currently - Beru are making some for all resellers

[TaimarTurbo]

Here's the Bosch alternative for the spark plug extender, and is also 5kOhm.
http://www.besteonderdelen.nl/bosch-1155185.html
http://www.onderdelenshop24.com/1155185-bosch

Can't find any for sale in the UK though.