Got an MOT on my Sovereign at the second attempt. My brother is now an expert at assembling X300 half shalfts, complete with the stupid £12-a-pop shims.

Anyway it had a small misfire but we've been so pre-occupied with the suspension we kind of forgot about it. But now it's a fairly serious misfire and I'm leaving for my summer holiday on Friday and heading to the JEC 30th anniversary bash on Sunday.

It rocks like a ***** at idle when warm, making the odd chuffing sound like a stationary engine. Driving along, you'll lose power for a few seconds every so often. If you're at idle, it'll drop to 500 rpm and then pick up again. With the window down you can sometimes hear a sound like rapid firing soft peas onto a tin roof.

So, one of the three original Lucas coils or a dribbling injector?

We'll probably try both, so place your bets now!

Jonathan

 

Almost certainly a coil, and may be one of the replacements. There is a long thread on replacement coils and failures.

If you keep driving it you will destroy the catalytic converter. Get the codes read, or at least take the cover off and run in the dark and look for arcing.

 

No codes. No arcing. All coils check out at 0.8 ohms (+/- 0.1 ohm, my meter isn't that accurate).

Replacements were all Made in Japan with the correct white on black label and bought before the £25 chinese knock offs entered the market.

 

The OBD system on these cars is very reluctant to set misfire codes so no help there. And coil primary resistance being within spec doesn't prove that a coil is good, nor does lack of arcing in the dark. Experimenting with a *known good* coil seems to be the best bet. Fortunately it's very easy to swap them around.

But it sounds like all your coils have been replaced with the 'good ones'....so a new failure seems less likely than if they were cheapie replacements or 15-18 year old orignals.

Have you tried new spark plugs?

Cheers
DD

 

To clarify all the replacements were good quality, but only three have been replaced. Three are original. All plugs brand new.

Fuel injectors are now out and all look pretty crusty. An ultrasonic clean certainly won't hurt.

I'll track down some new coils Monday when places open. There's a chap on here with Diamonds but I think he's in the US. I've ranted on another thread about a major supplier's inability to provide Japanese coils despite claiming they are "two weeks away". I might have to fit cheap ones and try and use the UK's often misunderstood Sale of Goods Act legislation when they inevitability die.

 

Have you considered the coils being offered by Japthug on this forum in the long thread on cheap coils started by Doug?

 

That's the guy. Turns out he's in Japan. Four day postage would cut it *very* fine.

Actually I can probably buy three from him *and* three crap ones for the same price as my back ordered ones!

 

Well, I put the cleaned injectors back in and fired it up. No start.

Oh right, prime the fuel line. Out with the relay, in with a jumper cable. Gurgle gurgle gurgle.

Try again, and it runs. But the idle still looks lumpy. Ah, to hell with science - straight in with the new coils as well. Idle looks better. Not perfect, but I understand it never is on these damned cars. Wasn't there a TSB on changing the cam shafts to make the idle better? Anyway, on with the road run.

Up and down my favourite local stretch of road, window down listening for mysterious noises. Just a lot of wind noise really - not an ideal day for road testing. Flick the Scangauge through the options and stick it on STFT. One bank is bobbing away in the single figures as you might expect. The other bank is moving about more and sits at -25 for several seconds, several times. Ah bugger.

Bring the car home, and there's a loud crunching noise as I turn in to my road, followed by the sound of bits of metal sprinkling everywhere.

Safe to say, it isn't going on our summer holiday tomorrow, which means it isn't going to the JEC bash on Sunday. I think I just need a week off to relax and de-stress and I'll work out what the hell has happened when I get back.

The lambda sensors are only 12 months old, but I guess the misfire could have killed them. Or the cat. Or one of the injectors was beyond cleaning and needs replacing. Negative STFT means the engine is detecting richness and leaning off, right?