Aston Martin Misfire and "Emission System Service Required"

[8436mike]

Hello, I'm new to the forum having purchased an Aston Martin DB9 2005 (34,860miles) earlier in the year and it has recently developed a misfire along with now I also get an "Emission System Service Required" warning. Are the two directly related? my guess is yes ! The misfire started a couple of weeks before the Emission warning.

I have checked the misfire with my OBDII tester and I get the following number of misfires over a short period of time :- Cyl 1, 7; Cyl 2, 0; Cyl 3, 651; Cyl 4, 1; Cyl 5, 6; Cyl 6, 4; Cyl 7, 9; Cyl 8, 2; Cyl 9, 105; Cyl 10, 88; Cyl 11, 14; Cyl 12, 11.

Clearly the main offender is Cyl 3 with 651 misfires the tester says "Cyl 3 misfire", but Cyl 9 and Cyl 10 also look to be starting to fail although the tester doesn't flag them up ..... yet ! Does anyone know what is the maximum number of misfires that is considered "acceptable" before action is needed.

As other DB9 DIY owners will know the work is extensive to replace the plugs and coil packs as half of the engine disappears under the passenger compartment and getting the air intake manifolds off is quite a challenge not to mention getting the plugs out of cyls 6 & 7.

I plan to change the spark plugs and coil packs on Cyls 3 and as a precaution 9 & 10. Since the other cylinder misfires are low I'm torn with the thought that I should replace them all while it's stripped down but that's not cheap !!! I have to spend £225 for the two inlet manifold gaskets but then a plug and coil pack costs £15-20 and £65 respectively so its circa £80 a pop !!! .... £960 for a full set !!! still you don't buy a DB9 expecting it to be cheap when things go wrong.

I've checked out Steve's work on Aston1936.com and it seems quite straight forward albeit access is a bit of a nightmare.

Any thoughts anyone ...... do I go with just the three cylinders or is it the full monty ???

Thanks,
Mike

Edited by 8436mike on Thursday 27th July 11:15

[8436mike]

Hi Flugplatz,
I'm hoping that once I change the three plugs and coil packs on cyls 3, 9 & 10, that I know I have to do (if not all 12 cyls), then that should stop any unburnt fuel going through the O2 sensors triggering the fault and all will then be OK !!! If I still have a problem I will then look to the O2 sensors first and hopefully not the cats.

Thanks for your reply,
Mike

[8436mike]

Hello to all who have responded and thanks,

I really appreciate the input from you all ....... I know it makes sense but the thought of dumping 9 working coils (all be it only for now) sticks in the craw a bit !!!

I've another question now and one that I've seen bantered around a bit with no real outcome that I have found [other than a bit of P1ss taking about left / right; offside / nearside; port / starboard !@*?] ... how are the cylinders numbered???

Option 1 - Logic says working along the crank shaft from front to back ...

Windscreen
11 12
9 10
7 8
5 6
3 4
1 2
Front of car looking
into engine radiator
this end !!!


Option 2 - but I've seen it like this.....

Windscreen
6 12
5 11
4 10
3 9
2 8
1 7
Front of car looking
into engine radiator
this end !!!


Option 2 - and I've seen it like this.....

Windscreen
6 7
5 8
4 9
3 10
2 11
1 12
Front of car looking
into engine radiator
this end !!!

I've got a downloaded DB9 manual and have trawled through it trying to find this answer but nothing !!!

Anyone know for sure ????

Thanks,
Mike

[8436mike]

Again thanks to all for the replies,

I've come down on the side of replacing them all ..... you know it makes sense ...... approach, besides I don't think I can be confident about which are the offending cylinders 3, 9 & 10 despite the consensus being that it is my Option 2 for the cylinder numbering and I have no idea how to test a coil once I have got it out of the engine to make sure.

Appreciate the comments about the heat being an issue affecting the coil pack life they are certainly in the heart of the engine and with a cover plate over them as well. Perhaps the cover plate should have been a mesh or even not there at all to allow better heat dissipation. I certainly see a heat haze over the bonnet (hood for you over the pond) when sat in traffic but the temp gauge sits right in the middle (normal).

Thanks to all again I'll post another comment when I've done the job ... just off to find my wife's credit card !!!

Mike

[8436mike]

Ha Ha come to think of it ..... so am I !!!!! ..... Bummer.