db9 coils , plugs , pcv valves

[craig elam]

ive had my 2005 db9 for 8 years now and cant see myself ever selling it, its only done 33k miles & i still get the same feeling everytime i open the garage door,
one thing that bothered me from day 1 at about 16k miles was a very slight idle misfire whilst in drive say sat at traffic lights, i had the coils and plugs changed in 2016 but the miss remained. we are all aware of the possibly catastrophic engine damage caused by misfire induced cat break up and ingestion
and associated £20k bill !!.
I do my own maintenance now and started to think of ways to avoid problems in future with work i could do now ,the plan was to remove the primary catalyst blocks built into the exhaust manifolds, After a bit of research it turned out to be a fairly major job involving removing front subframe , i dont have a lift at home so after some consideration decided against it,
my plan then was to do all possible to fix the present and prevent a future misfire, along came service time and i noticed oil in the inlet manifold and air filter boxes and on the mass air flow sensors , classic pcv valve failure.
in order to replace the PCV valves and check the 3 duck bill valves in the breather pipes the manifolds have to come off giving access to the coils and spark plugs, now this is job i could tackle and nows the time to say a massive thankyou to steve, his website aston1936.com is THE source for practical advice and his in depth step by step guides to DB9 repair and service are fantastic.
So to the job, i followed steves guide and puchased the inlet manifold gaskets, injector "o" rings, and PCV valves for JCT at leeds, the coil packs were about £80ea =£960 ouch ,
As many before me i embarked on a mission to find coil packs at a more reasonable cost ,if i couldnt i would just have to pay up, it turns out i had a few choices, Beru ZS426 is a direct replacement coil listed for DB9 , i found them on autodoc for £45.00 ea , a decent saving and i suspect its the the O.E part just not branded AM , i found these Beru coils on Amazon for wait for it £7.01! but only one available, there was one only again on ebay for £14 ( which i bought ,on examination its exactly same as O.E unit, i needed a conductor spring after i stretched one thinking they just pull off , they dont , you have to twist them a bit first to loosen there grip on the spade connector theyre pushed onto)
6 speedonline aston section had a post on the subject and a chap in holland had a misfire issue on 4 cylinders and replaced those coils with Jaguar "S" type 3.0 v6 ones, the only downside was the boot and conductor spring were too short and had to be swapped from the old coil packs,it solved his problem and ran like a dream.
he used some unbranded aftermarket ones that are about a tenner , I had a look round and found that NGK 48120 coil pack for this application is widely available at about £17.00, i ordered one to have a look at it.
by now i had stripped the manifolds off so i could remove a coil for comparison, apart from the boot and spring the only real difference if the connector block is slightly higher on the coil but it does clear the cover.
I took the decision to replace all 12 coils with the NGK ones and at the same time replace the spark plugs with NGK Laser Iridium ITR6F13 which according to NGK partfinder are an upgrade for DB9, when i took my plugs out only cyl 11 had that nice grey colour that i used to look for.
with the manifolds of i discovered the source of my coolant leak, it always smelled of hot antifreeze but i could never find a leak , there it was , the 2 "o" rings on the thermostat housing had failed leaking coolant into the "V" with then boiled off when hot.
everthing went back together well but i was always aware that the coils were not for that application, but Jag was owned by ford at that time as was AM, an S type key is even the same as an early db9 key ,
It started up perfectly and ran as sweet , no warning lights , no lumpy idle nothing, so road test time and also an opportunity to do the coast down misfire corrections procedure.
after 30 miles or so i can say there is a significant improvement to engine running ,smoothness , power , idle is perfect.
next job oil and filter , replace air filters and clean oil from MAF sensors.

[R129 300SL]

Thanks for info, in particular the part numbers.

[paulrog1]

I had this problem a few years ago when changing the coils on my DB9. i used these from Eurocar parts.

https://www.eurocarparts.com/ecp/c/Jaguar_S+Type_3...

They are from a Jag S-Type 3.0 V6, the coil is identical except you need to change the rubber boot and spring and work perfectly in my DB9.

They are £41 each but they always do 50% sales so you can get them for £20 each and NGK are a very good brand.

So I would always replace the inlet manifold gaskets, injector o-rings and PCV valves.

[cressell]

Good to hear about your improvements.

I also have a misfire at idle, my independent aston specialist said not to worry about it and leave it alone, but I keep thinking I should do something about it. Has anyone found an cheaper alternative for the 3pin coils?

[Ken Figenus]

Wouldnt ignore a misfire. Cat ingest potential if its throwing petrol at those manifold cats...

These more proprietary boots and springs if you get the identical Beru Jag coil for 25% of cost - where do you get them guys? And Euro Car Parts are still making a living selling these - there's profit and profiteering

[craig elam]

some more pics, sorry not very good a this

[craig elam]

[craig elam]