Misfire. Any Ideas Where To Start?

[lotusdave]

Over the last 1,000 miles or so, so a few thanks of petrol, ive had a misfire under load. Its easy to recreate and especially noticeable if in manual mode in 8th at 55mph (lowest revs itll let it go before it shifts tk 7th).

Part or full throttle and as it picks up a few more revs itll cough n splutter. It did it today off a roundabout at much higher revs which means its getting worse.

No dash light yet. Ordinary branded unleaded in it from a variety of garages. I do a decent mileage so I don't think it was a bad tank of fuel which was my original thought.

Will the ecu be logging anything I can get checked? Have fallen out with Lexus sidcup so does anyone know an independent close to Dartford? Or given the engine is so specialist should I go to Lexus anyway?

Anyone close to me who wants to hear and feel the problem lemme know. Happy to take you out and ill have my rac card incas it becomes terminal!

[rayaans]

Something as simple as a spark plug could cause the cylinder to misfire so check those to see if their dirty or damaged. Check the plug wires and distributor caps too.

You'll need to diagnose which cylinder is misfiring first. Should be able to scan for this.

Check fuel injectors, they may be clogged or dirty, there could be an air leak somewhere and you could have weak fuel pump.

Basically it could be one in a long list of things - best to go to a good mechanic.

[Arqum]

Speak to these guys. http://www.tech-one.co.uk

They are down the road from Lexus Sidcup. A mate if mine recommended me them. I will be using them soon.

[lotusdave]

And one imagines the plugs fitted by Lexus just over a year ago will be out of warranty!

I'll give tech one a call on Monday. Thanks everyone.

[Womble72]

I'd recommend "Westfield motors" in Rawreth, Rayleigh, Essex, they are "Lexus specialists" looked after my IS-250 from new, that's where I'll be taking my F to next month, would take you about 35-40 minutes to get there from dartford.

[Ace8800]

Anynews on this problem?

[lotusdave]

Hopefully be able to get it to tech one on Tuesday this week. Its getting a little worse id say and mpg has dropped off so am trying not to use it too much.

[lotusdave]

Update : bugger!

I could easily replicate the fault for the garage.

Sadly there are absolutely not fault logs, misfire counts or anything at all in the computer to indicate a problem. The car has NEVER misfired, not once, according to the logs which they say are very accurate and trustworthy.

Tech one have been brilliant and have even called in a Lexus technician and tracked the service history of the car and that Lexus did indeed change all the spark plugs last year at the 6 years service.

The lexus chap didnt believe the logs would be clear having felt the problem but checked them himself.

They've changed the coil and lead on 6 of the plugs which is not that hard to do I'm told. Two are difficult to get to and they havent checked those as it's a big job and if they do those they might as well change all 8 spark plugs again, or perhaps change four and then the other four.

They've done a smoke test on the inlet manifold and tested bits that Lexus changed under the recalls recently - the fuel rail I think they said - to be fair it was doing it before the service and recall work.

We've concluded that it doesnt seem it's about to break down and the dropping MPG is probably just me enjoying the late summer sunshine and doing more A roads and less motorways.

I'm going to drive it some more and we'll try again if it gets worse. Or if I can give them the car for a week with some notice they can change the plugs and coils, including the hard to get to ones.

SO MY QUESTION IS, for those who know the ISF better than I do, do we know of anyone else who has had this, maybe in the US?

Lastly, tech one havent charged me as they havent mended the car. Can't say fairer than that.

[Ace8800]

Hmmmm.. Weird one that is.. I guess you need to just keep driving till it happens again.

[lotusdave]

about time for an update. Its still misfiring but its not any worse nor any better. Still no MIL.  I've got used to it now. Must find time to book it in for the hard to get to plugs to be changed.

 

[Womble72]

Not sure if this helps, not the same car, but years ago I had a 24v mondeo estate, had an intermittent misfire, garage had it several times until it happened whilst on a test drive with them, it turned out one of the plugs had a hairline fracture in it, they replaced the plugs n never had an issue again, after having the 60k one on mine recently, I'd hazard a guess it's going to be one of the rear plugs, 2 to 3 hrs to replace due to location, also probably a service item that doesn't get done even though paying for it with a main dealer. Be interesting to know the outcome. Fingers crossed it's something simple 👍

[lotusdave]

the indi garage mentioned above has checked with Lexus on the qt and has no concerns about quality of care provided to date. They know the man who serviced the car at Lexus Sidcup.they have also swapped out 6 of the plugs but I need to leave the car with them for the last two. Buggers to get at it seems.

we were hoping that five thousand more miles would make it worse or give an error but not yet.

as I say, must find time to drop it off again...

 

 

 

[Peter P18]

Hi Dave,

The last two sparkplugs are the furthest back from the front, and are indeed a royal PITA to access!

I'd be inclined to get it back in for them to change those ASAP though mate. Reason being that is one area you can then tick off the checklist.

Happy to have a nose around for you at some point chap? Maybe the next Bluewater meet??

Not suggesting I will spot anything that the guys at tech-one or Lexus didn't spot, but can't hurt to look.