nisfan Posted January 18, 2017 Share Posted January 18, 2017 Ive recently acquired a mitsubishi sigma, what ive discovered is that there is a misfire under accelaration when its warmed up, the fuel was old so i stuck £20in it to no avail (the guage hardly moved hinting that the tank is MASSIVE), checked 5 of the 6 plugs, nice brown colour, 5 of 6 leads checked for resistance all fine, couldnt get to the 6th one as its hard to access in the time i had.Now could it still be stale fuel? Its fine when cold, idles fine cold and warm and when revved hot or cold in neutral its also fine.Sometimes it picks up above 4000rpm and takes off, not all the time though.Just wondering if anybody has any ideas before i drain the tank and replace the leads and plugs. Ta Link to comment Share on other sites More sharing options...
overrun Posted January 18, 2017 Share Posted January 18, 2017 Failing fuel pump relay? Second guess would be coil. Link to comment Share on other sites More sharing options...
83C Posted January 18, 2017 Share Posted January 18, 2017 Which lump is it? I've a fair bit of experience with misfiring 6G72's as found in the GTO, usually it's either coil packs, fuel pump relay (usually the relay gets bypassed - the 'hot wire' mod - to keep the pump at high speed), or the capacitors in the ECU breaking down. Link to comment Share on other sites More sharing options...
Pete-M Posted January 18, 2017 Share Posted January 18, 2017 Could be sticky lifters if it hasn't run for long. Link to comment Share on other sites More sharing options...
andy18s Posted January 18, 2017 Share Posted January 18, 2017 If plug 6 is hard to get at could it have been left unchecked/serviced by previous owners? Jifflemon and djimbob 2 Link to comment Share on other sites More sharing options...
dollywobbler Posted January 18, 2017 Share Posted January 18, 2017 If plug 6 is hard to get at could it have been left unchecked/serviced by previous owners?That was my thought. I think transverse V6s can often have this problem. If it's only when the car warms up though, that would suggest coil pack breaking up. Link to comment Share on other sites More sharing options...
nisfan Posted January 18, 2017 Author Share Posted January 18, 2017 It's the 3 litre V6 12 valve, I think it's a 6G72, I'll be able to get to the last plug with a bit more time, there isn't much out there but I'm probably better looking up the engine code.Forgot to say the check engine light came on once and when I disconnected the battery it cleared and didn't come back. Link to comment Share on other sites More sharing options...
dollywobbler Posted January 18, 2017 Share Posted January 18, 2017 From watching an episode of Mighty Car Mods the other day, it seems the coil housings break up, so the spark can leak out direct to the engine rather than the plug. Expansion from heat would probably make that worse, which is why it might not be bad all the time. Given how many cylinders there are, a misfire might not actually be that noticeable on idle. overrun 1 Link to comment Share on other sites More sharing options...
djimbob Posted January 18, 2017 Share Posted January 18, 2017 I would make sure the battery is in tip top health and bursting with charge, especially if the car has been laid up for sometime before you got your hands on it, slightly duff batteries can cause all sorts of weird issues, and doesn't hurt to be on the safe side As others have said 'tho, chances are it's the hard to access plug which has defeated previous home mechanics, and probably some unscrupulous professionals too Link to comment Share on other sites More sharing options...
DodgeRover Posted January 18, 2017 Share Posted January 18, 2017 If it's the same as the earlier Sigmas and an Aussie built one them yes the tank is big by UK standards Link to comment Share on other sites More sharing options...
406V6 Posted January 18, 2017 Share Posted January 18, 2017 If you were describing the same symptoms on my V6 I would say coil packs. As it's not a Peugeot then the spark system sounds the culprit - coil packs, leads or plugs. Link to comment Share on other sites More sharing options...
nisfan Posted January 18, 2017 Author Share Posted January 18, 2017 The battery was flat when it was picked up and required a jump start every time until I took it home and charged it as much as I could, it doesn't hold a full charge but seems enough, a nice healthy crank.It doesn't have coil packs it's just a dizzy with good old fashioned leads to the plugs Link to comment Share on other sites More sharing options...
mrbenn Posted January 18, 2017 Share Posted January 18, 2017 Does it have some sort of ignitor module in the distributor like Honda engined Rovers? Link to comment Share on other sites More sharing options...
nisfan Posted January 18, 2017 Author Share Posted January 18, 2017 No idea,As far as I'm aware there's the main coil (I think) which is between the inlet manifold and firewall Link to comment Share on other sites More sharing options...
83C Posted January 18, 2017 Share Posted January 18, 2017 It's the 3 litre V6 12 valve, I think it's a 6G72, I'll be able to get to the last plug with a bit more time, there isn't much out there but I'm probably better looking up the engine code.Forgot to say the check engine light came on once and when I disconnected the battery it cleared and didn't come back.Yes, 12v version of the 6G72. On the 24v version in a transverse application the inlet manifold covers the rear bank completely, meaning the rear three plugs (2, 4 & 6) regularly get missed on services. It'll be well worth digging out the 6th plug on yours. Link to comment Share on other sites More sharing options...
mitsisigma01 Posted February 19, 2017 Share Posted February 19, 2017 Hi Nisfan , welcome to the joys of sigma ownership ! My wagon is the 12v n/a 6g72 as well . I've only had mine about 5 years so I haven't got round to checking the spark plugs yet ! I trawled the various forums for weeks , read shit loads , done very little . Apparently you can get plug 6 out with care and patience and various sockets and swivels. Mine still has Australian Motors plug leads on it so I assume they are original , hard , cracked and chafed through but still working .It does have an intermittent idle fault but I've learnt to live with it for now.I'll keep reading with interest . Shame you're not a bit closer , only about 470 odd miles ! Link to comment Share on other sites More sharing options...
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