Rover 75 1.8 Misfire
 

Morning,
My 1.8 Litre Non Turbo Rover 75 has developed a misfire. Would a T4 be able to diagnose the exact problem?
Regards David

It will tell you which cylinder is misfiring and a T4 expert will no doubt come along and advise - i have a 1.8t - if i get misfire and its a PO300 code -random multiple misfire my first thing would be is to swop out the coil packs and leads and possibly re-gap the spark plugs to .7mm. :shrug:

Thank you Martin.
Do you have a piece of equipment that can interrogate the onboard computer?
As regards your advice I'll check the spark plugs and look at replacing the coil packs and the leads.
Do you think it would be worthwhile trying a fuel injector cleaner?
Regards David

Injector cleaner won't do any harm, make sure its a good one, Forte? Yeah, ignore the 1mm recommended plug gap, reduce it to 0.7mm, much better on the 1.8T. See if you can borrow a known good coil pack and swap them in turn, if it cures then misfire you know what the problem is, if it doesn't it eliminates one possibility.

A lot of standard OBD readers will read your fault and give you a useful code but not all will remove the codes from the memory. On this occasion you could probably substitute the T4 with standard OBD reader to diagnose your fault (I have an Autel MaxiDiag scan tool )
If no reader available, I would first check the Plugs gaps
I would renew if the are gapped over 1 mm or the electrodes look worn

As others have said tighten the gap in your plugs to 0.7 mm although from experience on the non turbo plug gaps don't appear to be as critical
The 1.8 uses a wasted spark system meaning that 1 coil pack failing usually affects two cylinders where a the plug lead will only affect one .

Changing the lot only takes around half an hour

Don't rule out IMG leak 😎

Thank you Steve,
I have already ordered Wurth's fuel injector cleaner or I would have tried Forte.
I think I will buy a replacement coil pack and see if that resolves the problem. Any recommendations as regards manufacturer?
Regards David

I'd suggest getting it from Mat, DMGRS. https://www.dmgrs.co.uk/collections/ignition-components The 1.8 needs a pair but get one and try it in both positions.

Ronnie suggested an IMG (inlet manifold gasket) leak. With that you'll only get a misfire on initial start up. Coolant dribbles into the manifold when the engine is cold then burns off as the engine heats. You get steam from the exhaust on start up then the misfire clears.

Thank you Steve.
What sort of cost are we looking at for Autel MaxiDiag scan tool? Costs seem to vary.
As regards removing codes from the memory is that essential if you have cured the problem?
Would removing the plugs and checking them give me a good idea which was the problem cylinder(s)? What colour would the plug be if it was not working correctly?
Regards David

Hello Ronnie,
Thanks for your suggestion, however, you have got to bear in mind that I am a novice. IMG???
Having read further on "Inlet Manifold Gasket".
Thank you.
Regards David