[] I am in desperate need of help, I have a 1988 3.5efi classsic that has a chronic missfire at around 2500-3000 rpm, I have fitted new plugs, leads, rotor, cap and coil with no success, anybopdy got any ideas where to look next, all answers gratefiully appreciated.

 

If you have a multimeter you can do quite a lot of tests yourself

Download the article 'Testing the RR classic Lucas 14cux efi setup' from
http://www.users.zetnet.co.uk/barnes_firsnorton/lr_efi/

The prime culprits for this behaviour are the temperature sensor you should measure the resistance of this when hot it should be around 280ohms, then check the lambda sensors are switching voltage correctly again when hot. If you go to the following site www.lambdasensor.com it explains how. If that hasn't fixed it then you might have to get a dealer to run the diagnostics on it to give you an idea.

If you take the connector off the ecu then it will reset the ecu and you may find it runs better for a bit which would allow you to do the above tests and if it initially runs better it also shows a sensor input is faulty.

Let us know how you get on if you live near Aberdeen Scotland I have the ROVACOM diagnostics package.

One final thing on a dark night open the bonnet and check there is no rogue sparking anywhere especially with the engine @2500-3000revs, let your eyes get adjusted first.

Good Luck
JJ