Forum - Topic

DB9 misfire

Forum Tech corner DB9 misfire

2016-01-14 22:51:12

Hi guys,

My 2005 DB9 has developed a rough idle when hot. I have read loads about coils & plugs etc. I was thinking of only replacing the no 12 coil as that is the code that came up on my reader. I will replace all the spark plugs at the same time. Some sites say to replace all the coils while the engine is apart but is that just a waste of money if there is nothing wrong with the rest of them?

I will probably do this job myself so labour costs are irrelevant. I was also going to change the pcv valves to see if I could reduce the oil getting into the Throttle bodies or maybe just fit oil separator tanks.

What does anybody think?

2016-01-15 01:23:12

I consider myself pretty proficient at dealing with most mechanical issues on the Aston however when it came to replacing the coils this really is a lot more difficult to get right than you may think. I would highly recommend you just bite the bullet and get this done by a main dealer - they will of course recommend you replace all the coils and so would I but obviously that's your decision in the end.

Good luck with whichever way you choose to go though!


2016-01-15 09:50:43


May I ask what is the age / mileage

2016-01-15 10:15:50

alistairenser: 2005 31.5k miles

2016-01-15 10:16:45

jonnyaston: What are the main difficulties? My nearest dealer is over 100 miles away.

2016-01-15 15:54:18


I had the same issue... caused by bad petrol by the previous owner I assume. My DB9 (bought it second hand at 27000 KM) missfired on two cylinders so I replaced all coils and spark plugs in one go. Not really necessary perhaps, but I thought that if they're working on it anyway, it's better to do it all on one go instead of a couple now and a few more in six months or so. I think I paid around €2000, mainly for the work as it takes quite some time to remove the air intake. The parts themselves weren't that expensive.... I think, €110 per coil. Afterwards my car seemed like a completely different car.. .fantastic!!

Hope this helps

2016-01-15 16:00:57


That's low mileage for coils to fail ( even plugs) although not necessarily 'unknown'

Plugs should last to 70k service but are relatively inexpensive . The coils ( should be 2 pin probably) are quite costly so given the low mileage you might just want to dismantle one side and change one or all six on that bank rather than 12

Some people will say change one , others all twelve and some just the side you are working on. Ultimately it is about risk - If another fails soon ( which given the mileage is supposed to happen) then you have all the labour over again.

Additionally - You should def think about checking / changing the PCV valve whilst the inlets are off as well

2016-01-15 16:33:03

Thank you one and all for your inputs.

I will probably do the job myself, after all it really is just a collection of nuts and bolts. Cylinder 12 misfire came up on code reader and as far as anyone can tell it is nearest to the windscreen on the right hand side looking forwards.

Still not sure how many coils I will replace but probably all plugs.

I wasn't going to bother with the PCV valves as they will probably only fail again. I am considering putting a dump tank in line just before the throttle body to solve that issue.

I have just finished replacing the ball & socket joint on one exhaust bypass valve as mine had rusted through and sheared off.

2016-01-15 20:52:44

Well good luck and let us know how it goes

2016-01-26 13:45:56

Well I took the inlet manifolds off and had a look. It wasn't an easy job even after removing the small access panel between the wiper gears. I took off the temperature sender to make it easier to remove the right hand inlet manifold. I should have lowered the coolant level first.

The first spark p-lug I took out was cracked in 2 places and the porcelain was loose in the metal body. The other plugs seemed fine. I am going to replace just the 12 plugs and see what happens. I am waiting for replacement inlet gaskets and injector seals to arrive, then I'll pop it all back together and see how it behaves.

I will keep you posted even if it is a disaster, which I hope it won't be.

2016-02-09 22:59:00


I changed just the plugs because when I stood behind the car the misfire was noticeable in the right hand tailpipe. Therefore I stupidly assumed that the misfire was in the right hand cylinder bank. When I found the cracked plug in the front right hand cylinder I jumped to the wrong conclusion.

Only after I had put the car back together and found no change did I check and find that the silencer is a crossover unit meaning that the exhaust from the right hand bank exits from the left hand tailpipe and vice versa. (See A.M. workshop manual).

I am currently waiting for a new coil to arrive. This time should be a lot quicker. (Always the optimist).

2016-02-14 22:12:16

Well, the coil arrived so I installed it. The job gets quicker with practice. When putting back the access panel in the scuttle panel, I applied a little bead of non-setting gasket compound (Hylomar blue) around the edge. This should keep water from dripping onto the back of the engine.

I took the car for a run and all seems well. It is a great feeling to have it running sweetly again.

One point worth mentioning is when I went to fill up with petrol one wet day, I found a small well of water around the filler neck.

What I discovered was there was some debris around the drain pipe filter stopping the water from draining freely. I cleaned out the debris then pulled out the filter and washed it before replacing it. While a lot of our cars may not be used in the rain, there is always the possibility of getting caught out in a heavy shower, so checking on the drain tube and filter is very worthwhile and only takes 5 minutes.

2016-03-04 23:17:04

Hi all,

Well, the car ran smoothly for about a week then a misfire returned. The code reader now shows a misfire on startup and on cylinder 2. The codes are P0316 and P0302.

I have decided to change all the coils this time as it's a pain to take the inlet manifolds off each time.

I am still wondering about the pcv valves. Does anyone have a list of part numbers needed for valves and pipes as the parts diagram and list don't seem very clear.

I am also getting the "Boot Open" message. I looked at the current latch but it is riveted together so I have decided to replace rather than repair. Maybe when I have fitted the new lock I will look at repairing the old one and post a report.

2016-03-06 23:17:42

Not fun taking manifold off each time. Hoping my same age DB9 does not develop same problems. Can you tell me if they are 2 or 3 wire coils and have you bought AM or OEM as part numbers would be nice to have for when eventually have to do mine.

I had boot lock problems just same intermittent not locking. Luckily replace by dealer under extended warranty as were both door locks (drivers door twice). Seems to be common fault but dealer would not give me old ones to pull to pieces to see if could fix or find out why so again will be interested in what you find.

PCVs I have pull over of oil into manifolds. Small amount but enough to give sticking butterfly valve fault and rough idle. Just fitted two small swirl tanks to the the feed pipes that go to the down stream of butterfly and collect a few drops of oil every 100 miles. Also two in the large bore pipes nothing seen so to me it looks like the oil separators are not up to the job. Blowing down the breathers show the one way valves work and the PCVs chatter as they should. Might try fitting a pair of new PCV valves at the front where they go into manifold (i.e. just other end of the same pipe). Looking on web Jeep units look like they will be easy to fit and cheap enough but expect will make no difference. Will be interesting also to see if amount is related to number of starts rather then mileage.

2016-03-13 20:53:05

Well, I have just finished putting my DB9 back together for the third time. I have now fitted new coils (2 pin) on all 12 cylinders.

I got fed up just doing what the code reader said was faulty.

I tested all the coils on my new coil tester and none of the old ones came close to the new ones. It is a wonder that the car ran at all.

The transformation is amazing! The car runs so sweetly and is much more responsive.

The only thing on the horizon is the new boot latch.

2016-03-13 21:50:24

organeer: That is great news. Are they AM coils or from OEM supplier, Is there a part number on the coils?

My catch tanks on the inlet manifolds for the oil breathers seem to be doing their job. A few drops of oil after 100 miles or so in both which is easy to drain off and at least not getting into the inlet manifolds all over the butterflies and the air filters so idle is much smoother and general running much nicer. Not ordered any PCV valves to try in line yet. Did you replace your PCV valves when in bits or was it too hard to get to them.

Went to Geneva show last week and got to have a good look at new DB11. At least on the new engine can get to the coils and plugs without removing inlets but not sure of the additional complexity of the turbos. Styling not as nice as DB9 in my view and still family resemblance not radical enough me thinks and not sure over the new construction which is unique to the DB11. It is not configurable to a range of models as in the old platform, must be more expensive and restrict variants. Just hope the Merc based electrics are better but probably still use same OEM supplier of boot and door catches.

2016-03-13 21:58:13


The coils are genuine Aston Martin 2 pin coils. I looked for aftermarket ones but failed to find anything substantially cheaper.

A lot of the time genuine Aston parts are quite competitive on price.