V12 Misfire & Cat ingestion

[Vanquish Mark]

Having recently purchased my dream car (Vanquish 2), I have done a fair bit of research into the common pitfalls. This lead me to all of the chat around the misfire, fuel burning on the primary cats, cats braking up and being ingested by the engine during scavenging that seemingly affects all V12 Astons.

I happened to be having a chat with two Ex Aston dealership mechanics the other day, both of which shrugged their shoulders and didn't know what I was talking about when I brought this up. One even said that he has seen that issue on Mercedes cars but never and Aston.

Given that between Vanqish 1&2, DB7, DB9, Rapide, V12 Vantage and Virage (sorry if I've missed any) there must be a fair number of these engines on the road with an enormous collective mileage under their belts.

All of this has me wondering just how much of an issue it really is, I would love to know if anyone on here has experienced it first hand. It seems to be reminiscent of the 911 IMS issues that were headline news but in reality on affected and small percentage of cars.

It would be good to get a measure of exactly how common this issue really is for the benefit of all V12 owners on here.

[Agent57]

Good question.

This always comes across as more of a potential, theoretical problem than an actual one.

I agree, if it were happening a lot then people would be on here posting 'Don't buy a V12'.

[AdamV12V]

This has been done to death to be honest...

The fact is it is VERY VERY VERY VERY rare! In all my years of owning AM V12s and frequenting this and other forums, I have found it to be a miniscule number of cars ever that have suffered - indeed you could count them all on one hand. That is against the thousands, nay tens of thousands of V12 AM engines built ever. I think we have seen one real actual confirmed such post on PH.

It is massively hyped and pedaled by one particular specialist, who offers to sell you a solution too. Lucky that...

Buy a secondary decat for 1/10th of the cost and the same (if not better) noise, service your car regularly and change the plugs and coils every 7yrs (or sooner) as per the recommended service interval and rest knowingly that you didn't fall into the camp of panicking that the sky was falling down.

[nickv12]

I backed away from buying a first gen Porsche 997 some years ago due to the engine issues in Porsches of that era. It was a similar reality where it was perhaps more widely reported than absolutely necessary. But I did my research on it, as I did with the V12 from Aston. I concluded it wasn’t really an issue with the Aston. If you sense the engine not running right (especially a misfire), get it inspected asap and don’t drive it until fully diagnosed. But I thought that would be common sense for any high performance car?

[Minglar]

I would agree with the responses you have already been given. There is certainly a lot of coverage available on line, mainly from one particular source, who as Adam said, offers his solution. It’s interesting to note that you mention two ex AM dealership technicians are not aware of any core issues. Bearing in mind how many of these engines have been produced over the years, one would think that if it was a common occurrence, then AM would have published something about it, ie their own solution, or a report of some kind, or a modification. Also, if it is as common as some suggest, reports of said problem would be prevalent on forums such as this corner of PH. As Adam said, it is possible it may happen, but it is rare. I too don’t recall many posters over the years on here actually saying that their engine has been affected. As Nick said, the best advice is to get any car checked over properly pre-purchase, and if your current car develops a problem, get it checked sooner rather than later.

Best Regards

Minglar

[jason61c]

As a new Aston buyer, I did loads of research. it seems there is only one garage in the world that sees this as an 'issue'.

I think its a none issue totally on the Bosch equipped cars.

[AMTony]

Happened to my mates DBS that had done abt 4,000 miles at the time.
Knew of one other that also suffered this.
Think this is a topic that has been perhaps somewhat muted?

[Simpo Two]

I'd never encountered the word 'misfire' for any of my cars until I bought an Aston V12. Every other car engine I'd had worked without having to be pulled apart every few years at a cost of thousands of pounds.

I do suspect though that as alluded to above, it is over-hyped.

[db11far]

Hi

DB11 V12 owner here. Purchased Q3 22. Misfire + debris ingestion. Happened twice.
First time in AMB dealership, around £25k spent on repairs under warranty incl. new cat, fuel pump, plugs et al.
Second time again for another misfire, same sort of thing, in AMR dealership now under warranty.
Pity as the only two times it happened (in c2500 miles), was when the lady was in the car with me... she has only been in it about 3/4 times so far.

Dealerships / AM have been fine and cannot complain (albeit would have preferred to have been given a demonstrator / loan car on both occasions rather than the first only). No complaints with AM national cover who were impressively rapid with 3 visits within an hour or so.

I am not a mechanic by any stretch of the imagination (new valve caps scare me) nor do I desire to be but my intuition tells me that there is a lot of "crud" in the system following an issue with the fuel pump and a misfire then seems to always happen. Now when I accelerate, i get a strong judder in the car. The first time AMB repaired it, it was good for 6 months or so. I did not then drive for around a week due to being busy welcoming a new little one, and then it immediately happened again within 30 mins. You tell me. I use it as a daily.

FYI I could be classed as a YUPPIE and don't want the hassle of it all (nor having to justify why its breaking down to people), but the Ferraris interior work is not good/plush enough for me, Porsche not special, too young for Bentley, McLaren does not offer a great GT. Ferrari Roma worth considering but i find it a bit sparse on the inside too. So i have to stick with this unbelievably beautiful V12 which is struggling to get rid of its misfire issue. I love her when she works and if a dealership looks after me right, will have no hesitation in upgrading to the next V12 once they get rid of these horrific cheap Mercedes infotainment buttons.

Edited by db11far on Friday 14th April 14:13

[DapperDanMan]

Steve at Aston1936 did an inspection on his DB9

https://youtu.be/niwamOI4Oos

[DB9VolanteDriver]

WRT v12 population, the DB7 should not be included since the location of the primary cat is far from the exhaust ports; very different than the later v12s with the 1 cat per 3 cylinders.

[Agent57]

DB9VolanteDriver said:

WRT v12 population, the DB7 should not be included since the location of the primary cat is far from the exhaust ports; very different than the later v12s with the 1 cat per 3 cylinders.

That's good to know.

[Simpo Two]

I get 403 forbidden when I try to reply... it will take this but not the actual text....

[Simpo Two]

DB9VolanteDriver said:

WRT v12 population, the DB7 should not be included since the location of the primary cat is far from the exhaust ports; very different than the later v12s with the 1 cat per 3 cylinders.

That bit works... strange.

And I can add this:

Are these V12s really more prone to misfires than any other engine, or is it just the proximity of the cats that can make it serious?

- but not the sentence before it...

Edited by Simpo Two on Friday 14th April 15:44

[Caslad]

The discussion on this issue often seems to become polarised between those who deny catalyst ingestion is even ‘a thing’ and those who believe it’s the sword of Damocles hanging over every V12 owner.
Of course the situation differs for every owner & every car.

If I had a car that I was planning to move on after a few years I would pay particular attention to the coils & plugs & have the misfires monitored at the yearly service & that would be it.
On the other hand if the car was to be a keeper (as is the case with mine) significant engine damage would be a disaster not just because of cost but due to the unavailability of a replacement engine & therefore a primary decat makes more sense. Going with aftermarket manifolds such as BR, Quicksilver, VAP may also add some performance improvements.

As always you pays your money & takes your choice.

[Phuketpaul]

Simpo Two said:

That bit works... strange.

And I can add this:

Are these V12s really more prone to misfires than any other engine, or is it just the proximity of the cats that can make it serious?

It's not that they are more prone to misfires, it's that a misfire is more difficult to detect when its only 1 out of 12 (8%) cylinders rather than 1 out of 4 (25%) and the proximity of the cats potentially makes an ignored misfire more serious.

[Simpo Two]

Phuketpaul said:

It's not that they are more prone to misfires, it's that a misfire is more difficult to detect when its only 1 out of 12 (8%) cylinders rather than 1 out of 4 (25%) and the proximity of the cats potentially makes an ignored misfire more serious.

Thanks. I can understand that 12 cylinders have 3x the chance of a misfire than 4, but why would they be more difficult to detect? A Foxwell with the right software can find them. (Unless you mean feel during driving of course).

Presumably the cats were put there for some other reason because they didn't realise the risks... not great design IMHO.

Is it unfeasible to retro-relocate them further away?

[M1AGM]

DapperDanMan said:

Steve at Aston1936 did an inspection on his DB9

https://youtu.be/niwamOI4Oos

Good video, explains it all very well.

[Phuketpaul]

Simpo Two said:

Thanks. I can understand that 12 cylinders have 3x the chance of a misfire than 4, but why would they be more difficult to detect? A Foxwell with the right software can find them. (Unless you mean feel during driving of course).

I meant that if 1 cylinder is misfiring it would be more difficult to detect through driving, and thus less likely to make someone break out the Diagnostic kit.

But 1 cylinder misfiring badly can destroy an engine, just read an article about an XJS belonging to Tom Walkinshaw with a 6.4 litre V12 and that dies due to 1 cylinder misfiring (or badly fueled )

[LTP]

Simpo Two said:

Thanks. I can understand that 12 cylinders have 3x the chance of a misfire than 4, but why would they be more difficult to detect? A Foxwell with the right software can find them. (Unless you mean feel during driving of course).

PhuketPaul answered this quite well - it's all about the driver noticing. There is a misfire count within the V12 ECU which, if it detects excessive misfires in one or more cylinders, will illuminate the "Engine Warning" light and disable those cylinders but, as I understand it, the calibration of this level of misfire is a legal requirement to protect against exceeding emissions regulations not for protecting the engine against cat damage. Before you ask I have no real idea why not either, but I suspect it is to prevent too many cars being returned to the dealer for an "emissions system service" if it detects misfires at too low a level.

Simpo Two said:

Presumably the cats were put there for some other reason because they didn't realise the risks... not great design IMHO.

I'm not an engines man but my understanding is you want the cats as close to the exhaust ports as possible for fast warm up, and when they are up to temperature to keep them hot and thus keep emissions down. The design problem is not so much the location of the cats but the material chosen - a metal matrix catalyst would not crumble and create ceramic dust if fuel ignited on it, so no ingestion. An alternative would have been an external EGR system as per the V8, but I don't know (apart from maybe component cost) if that's a viable solution for the V12, especially as you'd then have to re-time and re-profile the cams to eliminate the valve overlap.

Simpo Two said:

Is it unfeasible to retro-relocate them further away?

It would be possible, I guess, but see my comment about the need to get the cats hot and keep them that way (a big V12 is not an easy engine to get past emissions regs). You'd also have to package the big cats further down the exhaust system, in the tunnel area, plus I doubt you could retrofit them there as the ECU calibration for the O2 sensors would probably need updating.

Edited to fix typo

Edited by LTP on Saturday 15th April 12:28