V6 Misfires when warm.

[bigharty]

Hi Everyone,
Early days in trying to identify the fault but maybe someone can help with a tip or two. Engine starts easily and runs well from cold with full power. As soon as it begins to warm up it starts to misfire, feels like only one cylinder but difficult to tell when you have 6 of 'em. The problem developed suddenly about 1 week ago.

At first it was very noticable at tickover when you engaged drive and put a bit of gentle load on the engine but when you got moving you could rev through it, (I think, though with a V6 it is still pretty smooth). Much worse today with a cylinder, ( or maybe even 2), missing altogether i.e. running on 4 or 5. (It still misses when in Neutral or Park).

Only checked the plug gaps so far but they are all okay and a good colour which suggests to me that it might be fuel rather than ignition? I was thinking that if it was an ignition misfire I would see some wetness or soot on one of them?

Been running with a healthy dose of Redex Injector Cleaner, (try the easy remedies first), but that hasn't cured it.

Any suggestions welcome.

Chris.

[ELZE]

fault diagnosis can be expensive and this kind of fault is not easy to identify. Depending on how old the plug leads are try spraying them with WD40 and try running it again. If the insulation is breaking down on one or two, current can spark across the engine block or anywhere the lead is touching causing a short. Also a cracked dizzy can cause the same symptoms so take a look at that next. it may have a crack (impossible to visibly see) Try to eleiminate the electricals first before you look at fuel and timing issues.

whatever it is it's breaking down under load when it's hot!
Sorry I can't be more helpful. I just know that most V6 engines run brilliant but when they play up they are a pain!

[haydn callow]

First thing to check......remove the plug leads from the plugs one at a time....carefully examine them where they fit over the plugs......any cracks or damage an that could well be the problem.

[bigharty]

Thanks for the advice, a problem shared etc. That's my Saturday morning sorted then!

[ELZE]

Leads are expensive so if you identify this as the problem then having just changed mine for the sake of it (nowt wrong with the old ones) I can send you any parts you need or the whole set if need be.

Also a used Dizzy cap

[bigharty]

Thanks ELZE. I will have to get to the bottom of it so will post updates when I get them. I may just take you up on the leads.

[ELZE]

Thanks ELZE. I will have to get to the bottom of it so will post updates when I get them. I may just take you up on the leads.

No problem, I changed my leads,cap rotor and plugs because of a pending gas conversion. Having only owned a petrol version for a few months I thought that the parts mentioned may not have been changed for many years. Certainly the importer would not have bothered and unsure about the Japanes owner??

Good luck, I hope it's nothing too troublesome

[Getcarter]

I had a similar problem and it got worse once I had my gas conversion done. It was quite jerky on acceleration once warm.

Took it to 321 away and they replaced the HT leads and put in new spark plugs, runs like a dream now. The leads are expensive but they recommended the original Mazda parts

They also said one of the spark plugs was damaged and close to breaking up

Glad I got them changed!

[bigharty]

Mended!

The HT leads and suppressor caps are in good nick but the contacts inside the distributor cap were very corroded; the edge of the brass blade on the rotor arm too. It is so pitted and burnt that under a magnifying glass it looks like an Aero! I have never seen one that bad.

A bit of gentle cleaning with wet and dry and it was running again on all cylinders with no misfire. Should last until I replace them with new parts. I also put new plugs in but I don't think that was the problem, at £17.70 for the 6 they aren't worth messing with.

Fingers crossed that it is fixed but interesting that if it was ignition it was running fine one minute and not the next, rather than slowly getting worse.

Many thanks for everyone's advice, the missus is hopeless!

[mikeWalsall]

The pitted appearance on the rotor arm is the same on a brand new one and is normal ..!!!

http://www.igmaynard.co.uk/bongo/forum/ ... =3&t=63371

[Simon Jones]

As Mike says, the pitted finish is how it's supposed to look. By sanding it off, it will have increased the gap the spark has to cross which will have weakened the spark at the plugs. This is what a new one looks like:



Old and new:

[haydn callow]

If doing what you have done has fixed it I would suggest you have disturbed a poor ht connection and made it good......what you have done to the rota would not be helpful.

[bigharty]

Well that's very interesting, what's the thinking behind that then? Never seen one like that before. I didn't actually take any material off or, like you say, it wouldn't run at all; more a gesture really.

You might just be right about it being a bad HT connection. Or perhaps it was a plug after all.

[Simon Jones]

A quick google suggests its tungsten to resist the effects of arcing.

[bigharty]

A quick google suggests its tungsten to resist the effects of arcing.

That explains why the wet and dry was "reluctant" to touch it. They must last ages.