Random Multiple Cylinder Misfire

[Teamllama]

Hello,

I've been having some problems with my 2.5 v6 for a couple of weeks now with a misfire. the CEL comes on and the error is "Random Multiple Cylinder Misfire". The car doesn't feel its usual smooth self. When idling the car feels lumpy and shaky and when driving it is lethargic and lumpy until it gets to just over 3000 rpm when it suddenly improves.

So far its had plugs, leads and dizzy cap replaced. reset the code and took it for a drive and all seemed fine. its done about 15 miles and then the misfire is back and CEL is back on with same error.

A new rotor arm should be hear tomorrow all being well.

If the rotor arm doesn't fix it what else can it be? I'm hoping its not the coil seeing as its one of the annoying kind built into the dizzy itself.

I'm thinking I might ask in wanted section for a second had dizzy.

I've seen mentioned when I searched that it can sometimes be caused by fault O2 sensors but I replaced the two front ones a month ago and there is no error codes coming up mentioning them. Just the random misfire one.

I'm running out of ideas (and money!) so does anyone have any suggestions on what might be the cause?

Many thanks,
Mike

[mike74]

bad earth, air leaking somewhere, leaky exhaust, fuel filter blocked to name but a few. definitely worthwhile checking all the easier & cheaper things first before shelling out your hard-earned on stuff that 'might' fix the issue.
hope you get it sorted though mate

[psbarham]

when the dizzy on mine failed it wouldn't pull below 2500 rpm, to pull away from a junction it was a max power moment, and coming off roundabouts it would spin the front wheels, think james bond smoke screen
it definitely sounds like yours has failed in the same way.

[Teamllama]

Yeah that was what i was most worried the problem would be.

Had the same thing happen in my colt.

It would be much nicer if the car used a seperate coil or coil packs.

[Teamllama]

Its official, i hate misfire problems!

After replacing the bits and clearing the code. light came on again. checked it this time and the error was "insufficient coolant temperature to enter closed loop control".

replaced the rotor arm at lunch cleared it again and light not come back on yet but car just as lumpy as before.

i decided to keep an eye on diagnostics for an hour to see what happened and after a fairly long time the front o2 on bank 2 stopped changing voltage and stuck on 3.3 volts.

its looking like one of the new universal o2s i fitted a couple of months ago was a load of crap and has died. it readings are out when cold and the longer it runs the more out they get until it jams on 3.3v

think i shall be selling a kidney to buy a new genuine mitsu one instead.

[Turbo_Steve]

Have you checked the voltage at the temperature sensor? It'll be running rich as hell if it's failed, and that will corrupt and eventually kill the lambda sensor and the cat - and it doesn't take that long, especially if it's not getting up to a decent temp.

[Teamllama]

Ive not checked the temp sensor voltage.

I kept an eye on the temperature readings from it though on the omniscan box i borrowed and it was reading around about high 80C to mid 90C.

What sort of temperature should it be reading and how do i test it?

Cheers
Mike

[Turbo_Steve]

As long as that's reporting the temperature the ECU is seeing (which it sounds like it is) then I don't see think that the temp sensor is a problem.


It sounds like the timing is out somewhere.....has it had a cambelt change recently? Might we worth checking it's not jumped a tooth.

Crank / Cam sensor signals might be worth checking, though I wouldn't imagine it would run at all if they weren't.

Could there still be a problem with the new dizzy?

[Teamllama]

I dont know when the cambelt was last changed unfortunatly. Im guessing about 25000 miles ago. The service history isnt stamped but the car does appear to have been well maintained.

I've not had a new dizzy fitted. just the new cap and rotor arm which were both badly warn. I should hopefully be getting a working second hand one soon.

The strange thing is the engine when first started is quite smooth and responsive and then after any time between a minute and ten minutes its starts running rough and lumpy.