The stuttering acceleration

[Simpo Two]

This was mentioned before but it got mixed up with other things. Anyway, after a trip to my friendly local mechanic today, and a chance to test it with the engine fully up to temp, it's been diagnosed as a misfire. It only happens when the engine is fully up to temp, ie after 30 mins.Unfortunately it didn't leave any codes, or at least none his scanner could see, so we don't know which cylinder it is.

The coil packs, spark plugs and fuel pumps were replaced in April (before I had the car); this was to fix a lumpy idle, the dealer told me. The invoices show they came from Aston Martin Reading, so they weren't s/h from eBay.

So we have a 2007 DB9, with 15K miles and excellent AMSH, with a misfire. As my local man can't tell what cylinder's causing the problem, is the next thing a trip to an AM dealer for a special AM code reader? Any other possibilities based on this forum's wealth of experience? All straws clutched at!

[yvr]

You won't see any codes until you've enabled the misfire monitor: https://aston1936.com/2016/03/18/relearning-the-mi...

[Tlandcruiser]

Do you know what software or scanner your mechanic was using? If you do any work on your car, you could remove the coil packs and inspect the boots for any evidence of arching. You could additionally remove the spark plugs and compare the colour, it may help narrow it down.

Were all the coil packs replaced?

Edited by Tlandcruiser on Thursday 18th November 16:32

[Simpo Two]

yvr said:

You won't see any codes until you've enabled the misfire monitor: https://aston1936.com/2016/03/18/relearning-the-mi...

Blimey, what a palaver! It seems to be saying that if you do 70 - 20mph a few times it will re-learn the settings. So is that what you do when you want it to leave codes so you can see which cylinder is the problem?

Tlandcruiser said:

Do you know what software or scanner your mechanic was using? If you do any work on your car, you could remove the coil packs and inspect the boots for any evidence of arching. You could additionally remove the spark plugs and compare the colour, it may help narrow it down.

Were all the coil packs replaced?

He used two scanners, can't recall what they were. I could find out if that helps.

The invoices lists 12 coil packs. Of course he might only have used one...!

The closest I get to tampering with cars is topping up the oil. The relevant gubbins here is under the inlet manifolds so they have to come off first, I'm told. Nope, not my department I'm afraid.

[leman600]

Engine misfires are potentially very serious if not treated swiftly so you need to take it seriously.
I think it possible that the work carried out in a April did not remedy the problem that was already there or possibly even caused the problem. New components sometimes fail.
The fact that it seems to do this when hot sounds possibly to point to the electrical side (something breaking down).
Coil packs may be the most likely culprit.
The Foxwell scanner can help identify some of the misfire issues.
Is it under load at lower revs you see the symptoms? Do you think more than one cylinder is misfiring?

[DB4DM]

Recent cautionary tale with our high mile Audi TT, developed a misfire, for safety had to keep driving a couple of miles. Turns out it was not just a misfire, it was a nonfire sending petrol down the exhaust. Killed the catalytic converter

[Jon39]

You may have already seen, but if not, might be of help.

https://www.youtube.com/watch?v=vlSUBNPpaTk

[Simpo Two]

leman600 said:

Engine misfires are potentially very serious if not treated swiftly so you need to take it seriously.
I think it possible that the work carried out in a April did not remedy the problem that was already there or possibly even caused the problem. New components sometimes fail.
The fact that it seems to do this when hot sounds possibly to point to the electrical side (something breaking down).
Coil packs may be the most likely culprit.
The Foxwell scanner can help identify some of the misfire issues.
Is it under load at lower revs you see the symptoms? Do you think more than one cylinder is misfiring?

I too suspected that the work had been an attempt to fix it; we'll never know. Because it only happens after 30 mins, the car is easy to sell or p/ex because it doesn't show up in test drives. So that's maybe why the previous owner chopped it back in after only six months. The official story is that he wanted a Range Rover instead. Again, we'll never know.

Yes, it's most noticeable at lower revs - but then I don't rev it much anyway; normal driving in D for me, with the occasional downchange for overtaking. But I'm avoiding that at present because the misfire reduces acceleration.

I have no idea how many cylinders are doing it; how would I know?

Apparently there's no way you can tell whether a coil pack is good or not without trying it. Otherwise it would be a simple case of take the inlet manifolds off, whip out all the coil packs and replace the manky ones. But life is not that easy it seems. If we could get a code we'd know where to look.

Jon39 said:

You may have already seen, but if not, might be of help. https://www.youtube.com/watch?v=vlSUBNPpaTk

It's a lesson in how not to make a watchable video. Soooo sloooow getting the info across my brain times out.

Edited by Simpo Two on Thursday 18th November 19:21

[Jon39]

Simpo Two said:

That video is a lesson on how not to make a watchable presentation! Fancy a job?

Leaving that aspect aside, do you know anything about the gentleman's engineering background ?

As others have already intimated, I certainly would not be driving your car at all.

[Simpo Two]

Jon39 said:

Leaving that aspect aside, do you know anything about the gentleman's engineering background ?

As others have already intimated, I certainly would not be driving your car at all.

I'm sure he knows his stuff inside out, but he shouldn't be presenting it because it makes the info incredibly hard to absorb (I used to produce corporate and training videos). I guess it's like asking a programmer how computers work. But I will pass it on to my mechanic so thanks very much for posting it; it may allow him to solve it.

It's the only car I have so it will have to be used, unfortunately. e-mails have been sent to the supplying dealer for his suggestions and will be followed up tomorrow. I expect he will say 'use the warranty' - which was £750 apparently.

So - regardless of who pays for it, it seems to come down to getting some codes, is that right? If we know that then the work could be done locally.

Thanks to all for the input.

Edited by Simpo Two on Thursday 18th November 20:02

[Tlandcruiser]

Simpo Two said:

it seems to come down to getting some codes, is that right?

Thanks to all for the input.

Edited by Simpo Two on Thursday 18th November 20:02

Yes and no, misfires can occur without storing a fault code because theres not been enough misfires detected within a predetermined number of cycles. However, sometimes they can be stored as pending faults until the number of cycles has been reached. Some software will be able to monitor the number of misfires that have occurred since the engine was switched on which then resets once the engine has been switched off. There’s still quite a lot of diagnostics that can be done to investigate, but it can be time consuming and costly.

The nature of the fault and with the missfire occurring around 30 mins tends to point towards a coil pack. however, considering they were all changed recently and supplied by Aston Martin, it’s unlikely to have been a faulty supplied coil pack or one that has become defective during this time. This is assuming they were all changed as per the supplied parts invoice. It could even be something like a crankshaft position sensor on its way out

If your near Chelmsford, I can plug my laptop in and see if there’s anything going on, I would not want anything in return.

Edited by Tlandcruiser on Thursday 18th November 20:48

[Simpo Two]

I can see that 'fault codes' are a degree subject in their own right. In a way it's sad that motoring has got that complex.

One small bonus is that most of my trips are <30 mins, apart from boating which won't be frequent at present. And the 'Emissions System Service Needed' warning, which came on a few days ago disappeared during today's investigations. Ah yes, and when the wheels lose a bit of traction the 'DSC Broken' light comes on and sometimes the 'Tyre Pressure' light comes on in sympathy. But they all go away the next time

Oh and YHM

[David W.]

Simpo Two said:

I'm sure he knows his stuff inside out, but he shouldn't be presenting it because it makes the info incredibly hard to absorb

Edited by Simpo Two on Thursday 18th November 20:02

Really!
Any sympathy for having a sick engine lost here.
Perhaps send him your name and address and he’ll refund what your paid for the information.

[Jon39]

David W. said:

Simpo Two said:

I'm sure he knows his stuff inside out, but he shouldn't be presenting it because it makes the info incredibly hard to absorb

Really!
Any sympathy for having a sick engine lost here.
Perhaps send him your name and address and he’ll refund what your paid for the information.

'incredibly hard to absorb'
So is Calculus and Latin, but teachers are still allowed to present it.

Even I can follow the basics of what is being described in that video and my name is not Einstein.
I also know, that when an Aston Martin clearly has an engine misfire, a V8 can still be driven, but never drive a V12.
There is a video which explains the reason why, but don't bother watching, because the presentation might not be to Hollywood standards.

[BiggaJ]

I wouldn't bother about the quality of the cinematography of one of Mike's videos but rather pay attention to what's said. In this regard it's very easy to understand and one of the closing comments was along the lines of don't ignore a misfire, don't drive it, get it checked otherwise it most likely will lead to catastrophic engine failure.

Simple really.

Edited by BiggaJ on Friday 19th November 13:40

[F1NDW]

When the engine ingests his cat and he's told it will be £25k for a new one, I think he will wish he'd paid more attention at school and not been so flippant .

[AdamV12V]

F1NDW said:

When the engine ingests his cat and he's told it will be £25k for a new one, I think he will wish he'd paid more attention at school and not been so flippant .

More like £15k for a swap out recon V12 as I understand it, but I do appreciate if you have an old car that's still a HUGE chunk of its value.

[JonnyCJ]

F1NDW said:

When the engine ingests his cat and he's told it will be £25k for a new one, I think he will wish he'd paid more attention at school and not been so flippant .

I can see it now….

“Hi is that Mike ? I’ve got a poorly DB9 and having taken the time to do some research, I’ve worked out that I need to be talking to you”

“Hello ? Mike - are you there ?”

“Hello…. ?”

[CAPP0]

Jon39 said:

I also know, that when an Aston Martin clearly has an engine misfire, a V8 can still be driven, but never drive a V12.

Out of interest, what's the difference, and why must a V12 not be driven/what is the rationale/potential outcome?

[LTP]

CAPP0 said:

Out of interest, what's the difference, and why must a V12 not be driven/what is the rationale/potential outcome?

The EGR system and primary cat location. The V8 has external EGR and the primary cats are not hard up against the headers. On the V12 the EGR is internal, achieved by large valve overlaps so the engine pulls exhaust gases in through the exhaust valve. The V12 primary cats are close by the head, right up next to the exhaust ports of (I think) cylinders 3, 4, 9 & 10. The catalysts are ceramic and, if unburnt fuel hits the hot surface (from, say, a bad misfire), they can crumble as the fuel ignites. The ceramic dust can then be sucked up into a cylinder as part of the EGR, and you can imagine what ceramic dust does to an engine. EGR = exhaust gas recirculation.

All the above information © Mike on his BR videos, despite the presentation values