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nelmo
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Hmm, not conclusive - another battery seemed to start it quicker but still took a couple of attempts.

Then, I went out on a run with a local club today and about 70 miles in, the misfire I had a few weeks ago re-appeared 🙄. Hacked off with the whole thing, I bit the bullet and bought a new battery, hoping the dodgy electrical issue that the testers showed up was also causing the misfire and a new battery would fix both problems.

No such luck - new battery made no difference to the misfire. I got the guy at Halfords to test the old battery (hoping their fancy looking gadget would be more accurate than my cheap multimeter) and he said it was fine - even slightly over-charged, he said.

So, back to square one and the misfire is more of a concern...😧

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I assume the emerald has the ability to datalog? Would be worth trying to capture some logs when you are next using the car so that when the misfire happens it is possible to see some data around what was happening at the time.

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Funnily enough, that's what I tried to do last time. But the data logger is a pain to get going, weirdly. The manual is rubbish and although I got it working once, I can't seem to do it again. 

Also, and this may mean something, my misfire seems to be heat-related; it only starts after a decent drive, say 50 miles. Until then, it seems OK. And also only on hard acceleration or high revs. 

I know this suggests the coil pack is the problem but I've bought a new one and it is the same - is it possible for 2 to go in the same way? Seems unlikely. 

 

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Is it somewhere where it gets very hot?! Is anything somewhere where it gets very hot, ECU maybe? ECU bolted onto something that's soaking in heat into the ECU? Coil/injector drivers are misbehaving if it gets too hot maybe?

"My misfire seems to be heat-related", ahh these little nuggets of information are soooo important!! It's why diagnosing issues like this via forum is practically impossible :)

Edited by brumster
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Did you get round to fitting a fuel filter after the HP pump? That was something left over from your previous thread, along with the custom map. You still running on a generic map?

Have been reading your blog. Good read. DB4 GT Zagato still my favourite car.

Going back to basics (but I'm still tending towards ignition), can you detail your fuel system. What pump do you have for LP/what LP filter/swirlpot/HP pump/filter/Fuel rail/pressure regulator. Can you draw up the circuits like below (which is mine and fairly typical I think).

 

fuelsystem.jpg

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4 hours ago, brumster said:

Is it somewhere where it gets very hot?! Is anything somewhere where it gets very hot, ECU maybe? ECU bolted onto something that's soaking in heat into the ECU? Coil/injector drivers are misbehaving if it gets too hot maybe?

"My misfire seems to be heat-related", ahh these little nuggets of information are soooo important!! It's why diagnosing issues like this via forum is practically impossible :)

It's like those detective shows when the witness says, 'I saw him throw something into the river but I didn't think it was important' 😁

I'm only guessing that - on short journeys, I don't seem to get a misfire - anything longer and it seems to happen. Not conclusive and I'm just desperately trying to see some pattern in it.

 

1 hour ago, Longboarder said:

Did you get round to fitting a fuel filter after the HP pump? That was something left over from your previous thread, along with the custom map. You still running on a generic map?

Have been reading your blog. Good read. DB4 GT Zagato still my favourite car.

Going back to basics (but I'm still tending towards ignition), can you detail your fuel system. What pump do you have for LP/what LP filter/swirlpot/HP pump/filter/Fuel rail/pressure regulator. Can you draw up the circuits like below (which is mine and fairly typical I think).

 

fuelsystem.jpg

Thanks on the blog - yup, that DB4 was amazing.

Yes, my setup is the same as yours BUT without the HP filter. It was on my list to add last time but then the misfire went, I didn't get round to it. Back on the list, along with new HP lines - mine seem to have very small cracks in them, on the bends. Not leaking but if they're like that on the outside, maybe similar on the inside?

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So what I'm sure longboarder is thinking is along the same lines as me - if you're getting a misfire at high revs/high throttle openings, could it be fuel delivery issues. If heat exacerbates it then it could be fuel vaporisation, but otherwise blocked injectors (no filter), incorrectly plumbed system, injector drivers on the ECU, pressure regulator, I mean - wow - it could be anything. But when it's sporadic like this, it's a nightmare! It's one thing when it's in front of me and I can see/feel how it behaves... :)

On a side-note, the Emerald logging only works to a connected PC, you have to run the software at the same time. Would be good to log injector cycle, RPM, throttle position and lambda and identify when the misfire occurs, and see if it aligns with the injector cycle - if there's a very clear relationship between one "boundary" point and going lean - so very repeatedly, as soon as the injector cycle goes beyond a certain value the misfire starts, it would suggest a blocked or faulty injector unable to sustain the necessary fuel flow (assuming your fuel pressure is all good). It's one possible cause, rare I would say but given you're not running a filter in your HP side (naughty naughty) it's one of many possibilities :(

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Well, not quite 'anything' - I think I've ruled out the horn 😉

Emerald kindly sent me a more detailed guide to using the datalogger, so hopefully I can get that working next time.

Thank you both for your continued help - really appreciated.

  • Haha 1
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Just to check you are not using a facet style square block LP pump with bullet filter are you? As shown below. These bullet filters are infamous for wierd fueling problems. Pumps are OK ish, used with a £1ebay simple plastic paper filter.

pumps.JPG

Edited by Longboarder
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No, I changed to another filter because I read those bullet ones were crud. Admittedly, mine may be no better but it is physically larger and made of glass so can you see if it has anything in it.

Pic below (ahh, it used to be so shiny):

cezVlMfOEgKsIc1Y-PMHh42bV4juK6SqvKSsrnp8WN_xtWqC-a7JA4UgSc3QtdKHG9s1jl-rlP5_nTdwmQKDsNeeoKZ4ZQae4eeuhpBea7TifNiu_3Z6E92v-kDYGRzV7jGRXah0qpMltUVKHJiNPOa8zrMr_FHEb7RMsjB0I0aAafa96uhqCnP7zjTG2-UtN6lWEdxFu41BILKhC22d0f8QqheyUX756IfRzSM4dkdqEsQswONzJ2Zj6jc71rf15qpVSq_kZJZhTGfIYzN_w5mHciUdL9tW2GvGxzG0Cpby4XgcHpupjmHSU6AcIbKKYJwqzlm5lVWRxbvQ_Z70FRB1oKbyS_KZi76bYdCYWYbRehfHo1jj19CpnRiEVnCzOXxELYvr4WU1gJ4pfjrlJejLKQBoIOhKXYmN1SOKbj47BJSHGnXt8B-qsGgRQD-rVe13qvbH6nsrs98GRepcOAGbriKC2zeq4dVqwEKMKuW92rQLXe9z7e5N-s85tzkwXFNnEVUePZZjdOeCiinVT6h8FpolC9um0XZLwGszn3UoEi2v7ZvG0qzERnmNPxCmxLOygzjDGalFidgPBAQEUMIKlUdKsay0gLnmb4O2TqFZ3_Pj7lfvnmQSjLfchrh8rqQ5iAY2F-HDuDlvoGXXTv8rI9szSEE=w1024-h576-no

Edited by nelmo
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