Hello all,
I just bought a 2005 DB9 with 28000 miles on it. I absolutely love it, but it developed a misfire pretty much as soon as I bought it. After following Aston1936's instructions I replaced the plugs and coils, and PCV valves. I determined that the misfire was caused by one of the valve cover gaskets leaking into oil into a spark plug well, interrupting the connection between the spark plug and coil. I didn't replace the intake manifold gasket, due to it being perfectly in good shape.

After replacing the valve cover gaskets and spark plug gaskets and buttoning it up, the misfire was still there, maybe a tad better, with rough misfire at idle and hesitation when accelerating until about 3000 rpm. I also noticed a rotten egg smell while driving. After driving it for a while I plugged in my code reader and it pulled up the codes P2196, and P2198, and using another module on the code reader I found additionally P2195 and P2197 (essentially reading that the o2 sensors are stuck lean and rich at the same time.) No other codes.

I have ordered O2 sensors already for it and am hoping that'll fix it. But I was wondering if you guys have had anything similar happen or what your thoughts are. My second guess if it's not the O2 sensors is maybe a vacuum leak. Would love to hear your thoughts as I'm eager to drive it at its full potential.

 

It's been a couple of years since I replaced my coil packs, but I didn't have the same severity of misfire issues afterward. However, I DID have to do the Misfire Correction Relearn procedure (which is quite easy if you have the right road). I assume you did that? If not, Aston1936 outlines it here: https://aston1936.com/2016/03/18/rel...on-martin-db9/

 

I’ll definitely give that a shot and see how that goes, Will it still misfire if you don’t do the corrections? I never read anything about that.

 

I had all my coilpacks and plugs replaced by my dealer. Within a week I had more misfires. Turned out one of the new coils was bad & had to be replaced.

You have to do the misfire correction learn procedure to get accurate misfire readings.

 

So just got back from doing the misfire corrections, drove for about 45 minutes in mixed conditions, and it was on and off. Sometimes it would idle great, sometimes not so great. I noticed that the more I idled the more it would misfire. It would drive great with minimum throttle but anything past say 10% would cause hesitation and wouldn’t accelerate until past about 3000 rpm, it felt like a switch came on and full power suddenly came. Rotten egg smell persisted only when pushing it and driving hard.

I developed no check engine lights at all but have codes pending for P0300, P0301, P0303, and the other codes P2915-P2918 as before.

misfire counts are as follows
cyl 1: 78
cyl 2: 30
cyl 3: 63
cyl 4: 32
cyl 5: 17
cyl 6: 57
cyl 7: 33
cyl 8: 54
cyl 9: 64
cyl 10: 140
cyl 11: 75
cyl 12: 37

I also want to make it known this is the second time replacing plugs and coils (I sent the first set of coils back for replacements) and this is the second time around so I doubt it is the coils or plugs. Would appreciate any feedback on your thoughts.

 

I had a similar thing happen...A misfire on one cylinder. Turned out to be a hairline crack in a brand new plug! Aggravating but a simple fix. Good luck !

 

Well it’s all cylinders with 10 being the most prominent. After driving it again it got immediately worse with the check engine flashing and service emissions system on my dash. Same codes as before but a new one for misfire detected within the first 1000 revolutions. I’m thinking just oxygen sensors wouldn’t cause this much trouble.

 

Humm......we found the cracked (new) spark plug was in cylinder 10 that showed up on OBD. In my case I think the bad plug allowed unburned fuel to lead to the rich fuel reading.

 

When I had this issue after a coil/spark plug replacement, it turned out to be a cracked fuel evap tube in the fuel tank, allowing liquid fuel into the evap system and sending fuel into the intake. However, my misfire values only showed significant on one side of the engine, whereas yours look pretty balanced. If you have a tech looking at it (or yourself), there's a vapor management valve that's part of the evap system that can be accessed from underneath the vehicle, which can be removed and inspected to see if there's any liquid fuel in it (there shouldn't be). If there is, you know that you have a similar issue to mine. Obviously anyone can tell you that misfire issues can come from many places and the workshop manual lists a whole series of checks, should you wish to go through those piece by piece.

 

Thanks for this insight. I’ll definitely take a peek. Is vapor management valve the official name for it? Would be useful to know so I can find it in the repair manual.
Just to give more info, the fuel injectors aren’t leaking and I did reuse the intake manifold gaskets. I’ve ordered new fuel injector o rings and manifold gaskets and will be replacing everything down to the o2 sensors this weekend. I’ll also be checking the pvc hoses and valves to see if there’s a vacuum leak there. I had ordered the iridium spark plugs from ngk but I ordered the oem
ones for this time around. My worst fear is that it’s the cats, due to it misfiring for a while and possibly have clogged them. if it is I’ll have a performance manifold custom made for it. I’ll let you guys know after this weekend, I’ve been dying to drive it at its full potential. At this point I can do the plugs and coils blindfolded lol.

 

Just curious if this fixed your misfire issue?

 

Not yet, I’ve got o2 sensors coming from England. Hopefully that does it.

 

Yes that is the name of the part. You can find it in the workshop manual where it's located.

 

Sounds good, I’m gonna take a look at that now. I replaced the o2 sensors and it’s same if not worse. I was hoping it would be the o2 sensors so I wouldn’t have to get up underneath it and take the 70 bolts out from the pan. I’ll let you guys know what I find.

 

Definitely keep us updated. That's the best part of this forum, when people post the solutions to their complex problems! Saves the rest of us a LOT of time and money.