4.2 Cylinder 3 misfire musings - help?

Benmac

Junior Member
Messages
59
Hi all, not been on here for a long while but I still have my QP. It has sat around a lot over the past couple of years while life got in the way. Often on a trickle charger and started up and moved occasionally. REcently I've decided to get my **** in gear, get it recommissioned, use it for a last hurrah then sell it.

So, it went off to my specialist (Lotus mainly but has worked on Maseratis and also has access to the Maserati scanner equipment via a contact at the nearby dealer). There a load of work got it back up and together generally and sorted a couple of issues such as one of the speed sensors going duff. All good.

I got it back and all was well with the world until a couple of days later it flashed the engine light at me for a few seconds then stopped and all seemed fine again. I put this down to "italian" and left it at that. It's since started doing that though a lot, basically any time you give it anything more than a tickle on the throttle. Basically there's a misfire and you can hear just that while idling. I tried my scanner on it and pulled off a pending code telling me the misfire was on Cylinder 3. Hoping and praying for the obvious to be the cause I swapped the coil on that cylinder for a new one. Same issue, bugger.

So, any ideas on where we can start to look next? It'll be going back in the new year to be scanned properly etc again but I am just wondering if anyone has any other ideas in the meantime.

The only other alarming thing it did during this sequence was that after changing the coil I had it idling outside for a while to get some temp in it and while I went and got keys and wallet etc to take it out for a short test drive. While doing that it cut out and completely and utterly died. Total electrical blackout. During the coil swap I had disconnected the battery so I first checked that in case I hadn't tightened it well enough. Seemed fine but I disconnected and reconnected it again and it came back to life. Misfire and flashing light when accelerating aside it seemed happy on the short drive but back on the drive it cut again after idling for a while. This time though while the engine cut the electrics remained on.
 

Keano

Member
Messages
287
How reliable is the battery after having it stood down for a few years. May be worth replacing as these are sensitive to battery issues
 

Geo

Member
Messages
616
You made no mention of checking the spark plug. Try swapping No.3 with No.2 and see if the misfire moves to No.2. If it does buy a new spark plug. This happened to me earlier this year.
 

CatmanV2

Member
Messages
48,546
Plugs would be what I check next. Personally I'd just buy one and swap it. For the £8 or whatever, you know you're getting a good one and it's half as much work

Fuel after that (although I'd expect a misfire on any / all cylinders, not just a single one)

C
 

Benmac

Junior Member
Messages
59
Thanks gents. OK, to answer the questions:

- Doh, yeah plugs next is obvious! Will do so.
- Yep, fuel is fresh although I am going to brim it with V power just in case
- Battery is good, was new a couple of months ago after I realised the trickle charger had tripped and the old one was a long way past best.

Right, I'll get a couple of plugs and do a swap over the weekend. Having the old plug out will allow me to check the gap etc to be certain as well. Does anyone happen to know what the gap spec should be? I have the service manual so will be able to find it otherwise.
 

Benmac

Junior Member
Messages
59
I should note that despite this annoyance I did have some success fixing the alarm which had died. Siren was duff so swapped that and then all good again so at least something has gone well. That aside, it was only after swapping the siren that I remembered that it always made me chuckle that the alarm on my 159 that I ran as a daily made the same beeps on locking and unlocking as the QP. Quick look and yep, looks like it's the same part and of course the Alfa ones are half the price! Oh well.
 

voicey

Member
Messages
660
Measure the HC and CO levels in the exhaust when it is misfiring - high HC and you have an ignition fault. High CO and you likely have a fuelling problem. You could also scope the signal from the upstream Lambda on that bank - if you have an ignition fault then the exhaust will be suddenly flooded with oxygen and the signal will spoke.
 

ttt0000

Member
Messages
113
We had a misfire on the 4200 and a loss of power. We started working through a list of possibilities. One by one we changed the fuel, swapped the spark plugs, the coils, fuel rails, fuel pipes to fuel pump. Cleaned the MAF. We bought a small camera and found the Cats were blocked. Replaced the Cats and the car runs beautifully. Not sure if any of that will help.
 

Silvercat

Member
Messages
1,166
Can only be one of 3 things; a faulty ignitor coil (but you have replaced this), a faulty spark plug or a faulty injector. I had the same problem on my 2009 QP 4.7 on the No.8 cylinder so replaced the Ignitor coil and spark plug and it's purring like a tiger again. Took me all of 30 mins to do but the plugs are deeply set so you need a long plug spanner.
 

Silvercat

Member
Messages
1,166
I've been advised that once one ignitor coil starts to fail, then they all do progressively due to the high temperatures of the engine which makes the Ignitor degrade over time. At just over £105 each to replace, then it can be costly. So what I did is invest in a new spare ignitor coil and a set of plugs just in case. So far so good,
 

voicey

Member
Messages
660
Can only be one of 3 things; a faulty ignitor coil (but you have replaced this), a faulty spark plug or a faulty injector. I had the same problem on my 2009 QP 4.7 on the No.8 cylinder so replaced the Ignitor coil and spark plug and it's purring like a tiger again. Took me all of 30 mins to do but the plugs are deeply set so you need a long plug spanner.

It's not quite a simple as that although you have listed the three most common causes for a persistent misfire on one cylinder. There could be an issue with the wiring (not on an Italian car I hear you say!). The ECU could be faulty. Valve springs have a tendency to break (more common than you might think). Very rarely, the cam lobes can move on the shaft - they are separate pieces that are shrunk in place.

As a side note, you'd be better off replacing all your plugs instead of just the one. As the gap increases the coil has to work harder to create the spark.
 

Benmac

Junior Member
Messages
59
Update to this, apologies for the lateness; I've been working abroad a lot so far this year (ironically one place was opposite a Maserati dealer, I should have popped in to ask their opinion).

Anyway, new plug in cylinder 3 alongside the new coil and hey presto it's happy, ticking over nicely and I've just been out and "exercised" it a bit and all seems good.

Annoyingly another little quirk has popped up in that it's now momentarily flashing up that the MSP and ASR have failed, then it's happy again. Can't work out a pattern to it doing it yet and it's fairly infrequent, possibly something to do with braking or changing down. With that in mind I'm wondering if the fact that when it had new front springs they managed to set the front suspension too low so it has a bit of rake is perhaps confusing the system a little. Anyway, that's for another thread!

Thank you all for the advice.
 

conaero

Forum Owner
Messages
34,593
Annoyingly another little quirk has popped up in that it's now momentarily flashing up that the MSP and ASR have failed, then it's happy again. Can't work out a pattern to it doing it yet and it's fairly infrequent, possibly something to do with braking or changing down. With that in mind I'm wondering if the fact that when it had new front springs they managed to set the front suspension too low so it has a bit of rake is perhaps confusing the system a little. Anyway, that's for another thread!

Lack of use or battery on its way out. If you have not put a new battery in it, do so. Also just check your springs have not collapsed and your tires are up to pressure. The ASR/MSP work on rotation and the car being level. It could though be a wheel bearing sensor gone which is very, very common.
 

Benmac

Junior Member
Messages
59
Ta, yes, those all make sense. Battery is only a few months old and while it's been dormant it's been sat on a trickle charger so that should be fine. A bit of use though never does any harm so I'll continue and see what happens.

Springs seem fine, they're new and pressures are reading OK on the TPMS but I will double check. It did have a new wheel speed sensor as part of the recent work as it was doing the proper total failure "go to dealer" thing with everything to do with ABS, TC, MSP etc. This is just that momentary thing; quick enough that on looking down when it beeps it flicks to whichever one of the two warnings coems second and is then gone, eyes no longer off the road than checking the speedo.