Misfiring When Cold & Damp

[AdeV]

My Mk2 (UCF10 II) is now fairly consistently misfiring on one bank when cold, especially if the weather is damp. The misfire clears up completely once the engine is fully warmed. I reckon I'm intermittently losing 2 or 3 cyls at a time.

Clearly, I need to do the coils & leads fairly soon; the best prices I've found so far are japparts (£180 for a kit of leads + 2 coils), or ePay (£210, although I may shave a few quid postage off that price). I suppose I'd better phone the local Lexus dealer tomorrow as well - I could use a laugh...

Is it possible to get the bits for less, or should I just be glad they'll do another 180,000 miles (or 0.1p/mile) between them...

[steve2006]

There were some new coils on Fleabay at £38.00 each and a set of leads at £78.00 I can't comment on quality.

You also really need to check/replace the distributor caps,rotor arms and plugs at the same time.

For now I would start the car from cold at night and have a look under the bonnet to see if you can spot the arcing/tracking main suspect is the RH coil ( passenger side) HT lead as it passes under the timing belt upper cover, there is a gromit there which may not have been refitted correctly so the lead will chafe.

Running it with a misfire could damage the cats.

[AdeV]

There were some new coils on Fleabay at £38.00 each and a set of leads at £78.00 I can't comment on quality.

Aye, the coils are still there (£39+£5 p&p each) - but the leads are now £105 + £5...

I've just looked again at the JapParts offering, the picture suggests it includes plugs for £180; there's also a picture of a dizzy cap... I'll phone them tomorrow to see what's in the pack.

UPDATE: I phoned them, and ONLY the leads are included (now for £155 inc VAT). Better deals to be had on fleabay...

You also really need to check/replace the distributor caps,rotor arms and plugs at the same time.

Damn, another £50 (£25 per side) - excluding plugs!

For now I would start the car from cold at night and have a look under the bonnet to see if you can spot the arcing/tracking main suspect is the RH coil ( passenger side) HT lead as it passes under the timing belt upper cover, there is a gromit there which may not have been refitted correctly so the lead will chafe.

Running it with a misfire could damage the cats.

That'll be tomorrow's job, then. I do know that the cats could be poisoned; and unfortunately the '94 model will probably fail emissions without the cats. I know you're supposed to have them fitted by law, unless your car is pre-'93, in which case they are optional (even if standard OE).

[AdeV]

For now I would start the car from cold at night and have a look under the bonnet to see if you can spot the arcing/tracking main suspect is the RH coil ( passenger side) HT lead as it passes under the timing belt upper cover, there is a gromit there which may not have been refitted correctly so the lead will chafe.

Hmm, no sign of any tracking at all, despite the misfire definitely being present... so. I guess the leads are OK & the problem is either the coil or plugs.

[ManicMark]

Could be a cracked distributor cap letting moisture in.

[AdeV]

Could be a cracked distributor cap letting moisture in.

Sorry, I've been away for a while (funny how work interferes).... the misfire hasn't been getting any worse, but it's absolutely definitely damp related. After a nice sunny day, she's so eager to fly around the place I've run out of tread on the rears!

I like your dizzy cap theory, as it's cheap to try out.

What's the recommended interval for changing the plugs/leads/coils/etc.?

Cheers,

Ade.

[steve2006]

Try these guys for the parts you need I seem to remember the coils were around £30.00 plus the dizzy caps and rotor arms were cheap and OEM quality.

http://www.buypartsby.co.uk/?autospares

[AdeV]

Try these guys for the parts you need I seem to remember the coils were around £30.00 plus the dizzy caps and rotor arms were cheap and OEM quality.

http://www.buypartsby.co.uk/?autospares

Thanks for the link - and wow, they _are_ cheap. Unfortunately, I already bought everything except the coils from various vendors, all of them more expensive

Ah well, lesson learned. At least if I do need coils, I can get 2 of them from that link for less than the price of a single one off fleBay. Coils are showing at £14.16 +vat + delivery presumably.

Is there a "howto" on changing the dizzy caps & rotors, before I dive in there with a screwdriver & a hammer? Ignore that, I see LexLS.com has an excellent tutorial. I shall leave the job for now, until my leads & plugs show up... may as well do it all in one fell swoop.

[lexusn1ce]

Try these guys for the parts you need I seem to remember the coils were around £30.00 plus the dizzy caps and rotor arms were cheap and OEM quality.

http://www.buypartsby.co.uk/?autospares

Thanks for the link - and wow, they _are_ cheap. Unfortunately, I already bought everything except the coils from various vendors, all of them more expensive

Ah well, lesson learned. At least if I do need coils, I can get 2 of them from that link for less than the price of a single one off fleBay. Coils are showing at £14.16 +vat + delivery presumably.

Is there a "howto" on changing the dizzy caps & rotors, before I dive in there with a screwdriver & a hammer? Ignore that, I see LexLS.com has an excellent tutorial. I shall leave the job for now, until my leads & plugs show up... may as well do it all in one fell swoop.

i had this problem on my 92ls and some injector cleaner cured it. i acted on a local garages advice, my misfire was there the whole time but less noticable when hot.

[AdeV]

i had this problem on my 92ls and some injector cleaner cured it. i acted on a local garages advice, my misfire was there the whole time but less noticable when hot.

My misfire definitely goes away; as I say, when the weather's dry, she pulls like a train. When it's been raining, the symptoms are a bit weird: 1st start, generally everything is OK. SO long as I don't ask for lots of power before the engine is fully warmed up, I don't get the misfire. If, while the engine is still cold/cool, I do use a bit too much welly, the misfire appears. If I have to stop the engine for any reason (e.g. 'cos I've popped to the garage to get milk or petrol), then the misfire appears.

You can clearly hear/feel it misfiring, and under power, the delivery is very lumpy. That's why I'm thinking it's more than 1 cyl affected. Once it's cleared up, it tends not to re-occur unless the engine is allowed to cool down significantly, and the weather is still wet...

[lexusn1ce]

those symptomes sound like a weak spark, when you glide along its good enough to ignite the mixture and when you flood the cylinder for more power its overwhelmed and gives up. I would check the spark plugs after a start up and look for one thats wet or darker than the others this indicates rich mixture due to intermitent firing on that cylinder, then change the plug and check the lead with a multimeter from end to end on k ohms and then compare the reading with another lead of similar length if its miles out then try flexing the lead along its length whilst taking a reading if it jumps around you have a break and will need a new lead if it doesnt make any difference to the reading then re-crimp the ends after cutting a small length off on the bad end ( do the plug end first) this will prob fix it as the end corrodes and breakes down the carbon. I did this on mine at an earlier date to cure a misfire when i first bought the car and it turned out to be a bad lead which i recrimped and has been fine since.

I doubt if destributers would cause this as it would be misfiring on multiple cylinders and also if it were a bad coil you would loose the whole bank on one side (had that happen as well) hope this helps.

If you can still drive it ok i would think its just one playing up its suprising how bad a little misfire can be when you demand power because you then have 7 cylinders trying to drag the 8 which isnt easy because it still has compression and also pull the car, i had 4 go down when a coil went and it was nearly impossible to start let alone drive, also it takes less off a spark to ignite the fuel once the engine is warm because the fuel mixture is reduced by the ecu so it would be a lot better when hot.

[AdeV]

Well, I finally got around to treating her to fresh plugs & leads... I didn't do the dizzy caps/rotors because they were just too inaccessible, I had a major attack of CBA.

Obviously, it's bone dry at the moment, but she seems perkier already. The real test will be what happens next time it's wet... fingers crossed...

[steve2006]

Congratulations let's hope that's sorted your problem, changing the leads and plugs is OK it's routing the leads and fixing them into all the clips and covers that takes the time, not too bad if they are the same thickness but bigger diameter leads involves some modifications to fit them,BTW did you get some dielectric grease for the plug connections so they don't stick on the plugs next time you replace them, mind you the iridium plugs are good for 100,000 so shouldn't be a problem.

[AdeV]

Congratulations let's hope that's sorted your problem, changing the leads and plugs is OK it's routing the leads and fixing them into all the clips and covers that takes the time, not too bad if they are the same thickness but bigger diameter leads involves some modifications to fit them,BTW did you get some dielectric grease for the plug connections so they don't stick on the plugs next time you replace them, mind you the iridium plugs are good for 100,000 so shouldn't be a problem.

Hi Steve,

So far, so good; it's been wet several times since, and no problems to report. I think the issue was almost certainly one of the leads (the one that snapped off when I removed it), but I feel happier having replaced the lot. I'll do the dizzy caps & rotors when I change the cambelt.

I put a bit of copper grease (Halfrauds version of Copaslip) on each plug, so that should guarantee they're all stuck in there forever (shirely you mean, guarantee they'll come out again? -ed)

I didn't have that much trouble routing the leads, mainly because I replaced them one at a time, rather than pulling them all out, then having to remember which went where. So I didn't get the clips mixed up either. Biggest problems were sheared bolts (2), and I discovered some abortion of a repair on top of the airbox, which seemed to involve blu-tac (!), some rag, and some duck tape. Nasty stuff, luckily Benfur has come through & found me replacement bits for everything I've broken/lost/damaged along the way :)

[steve2006]

Hi Ade,

Good to hear the problem has been sorted and with the cold damp weather we now have will be a sure test for any ignition related problems,Maurice is an invaluable source of good cheap parts he helped me last week with an OEM wheel nut set after I threw my originals away after a wheel change.

Did you make sure the coil lead from the distributor opposite the Battery to the dizzy cap was routed correctly and the grommit is in place as it is a pig to fit correctly?

[sir john]

Good to hear you have fixed the problem. At one time i thought the cause might have been you getting the milk and the petrol mixed up at the petrol station. (If I have to stop the engine for any reason (e.g. 'cos I've popped to the garage to get milk or petrol), then the misfire appears. )

A wee tip if you do the disis and rotas without changing the timing belt. The disi caps are held by 8mm bolt. Tie a loop of spring through the closed end of the spanner. That way, when you drop it, which you will, you wont have the heart sinking panic i had.