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What can cause misfires on acceleration and lowered fuel mileage?


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#1 ancienttyres

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Posted 06 February 2020 - 02:26 PM

Hello. My 2.5 v6 has recently started to act up a bit, it will misfire quite badly, usually when accelerating heavily. Usually I can get away in first and second without a problem but it's when I put it under load in third, fourth or fifth that it starts doing it and generally only if I'm hard accelerating, if it starts doing it for example and I ease off the throttle it'll usually stop. Accompanying this issue is that I've lost several MPG of range, I used to get (up to a few months ago) around 450 miles on a full tank give or take but I had to refill on empty around the 380 miles mark the last time.

 

I've had a look at the usual suspects, air intake looks clean enough, no air leaks. Checked for DTC's using forscan and there aren't any.



#2 twincarbs

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Posted 06 February 2020 - 02:35 PM

It could be lots of things, but have you checked the HT leads?


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#3 mike4369

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Posted 06 February 2020 - 02:53 PM

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Check coil pack as per

https://www.carsdire...aulty-coil-pack


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#4 Mondygeek

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Posted 06 February 2020 - 05:19 PM

How does the misfire feel? For example is it a sharp misfire like its missing a spark or is progressive like fuel starvation?

#5 ancienttyres

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Posted 06 February 2020 - 06:59 PM

How does the misfire feel? For example is it a sharp misfire like its missing a spark or is progressive like fuel starvation?

 

Hmm, I suppose it's sharp generally, makes the car jerk fairly noticeably.



#6 Mondygeek

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Posted 06 February 2020 - 07:07 PM

How does the misfire feel? For example is it a sharp misfire like its missing a spark or is progressive like fuel starvation?


Hmm, I suppose it's sharp generally, makes the car jerk fairly noticeably.

I'd start with a new set of spark plugs, then leads followed by coils.

#7 ancienttyres

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Posted 06 February 2020 - 08:26 PM

Ill have a look at them all then. I did change the plugs and ht leads about 6 years ago and I've done 30k miles since then, so in a perfect world I haven't done enough mileage for them to be likely the problem. I changed the coil pack at the same time but I used some cheap aftermarket replacement from euro car parts so even though that's only 6 years old it would be just my luck that because I skimped on it that'd be the thing that's gone wrong. Still, my excuse is Id already spent 150 quid on new genuine ford leads and ngk plugs and didn't fancy spending another 100 quid on the coil pack (or however much it was at the time).

 

On the off chance it isn't any of those causing the problem though, what else is a most likely culprit that I should look at? 02 sensors? maf sensor? exhaust vacuum sensor? I've read any or all combinations of them can cause misfires and lowered fuel economy if they go tits up. Although thinking about it I would have hoped if it was a sensor a code would have been thrown up.


Edited by ancienttyres, 06 February 2020 - 08:27 PM.


#8 Mondygeek

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Posted 06 February 2020 - 09:25 PM

6 years!! I'd say you've we'll with them. I replace plugs every year but then again I only have 4 to replace lol.

I'd definitely treat it to some plugs at least.

In regards to the sensors it may well be them playing up but normally you'd get a code although it does happen normally from the lambda sensors.

#9 mondy zetecs

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Posted 06 February 2020 - 10:39 PM

https://www.ebay.co....90/272379843766

I have a single jerk when accelerating hard cold start 2nd gear, after changing from

ford motorcraft plugs which were the original 16yr old plugs on 60k miles to NGK plugs

seem to get more slight jerks,looking at new HT leads and oem ford coil pack £49.

 

I would try a new genuine Ford £49 coil before anything else as its not as expensive as thought at £100


Edited by mondy zetecs, 06 February 2020 - 10:41 PM.

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#10 ancienttyres

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Posted 07 February 2020 - 10:05 AM

I suppose I should do the plugs really. Are NGK still considered top notch? Got the coil ordered too.

 

If I end up replacing the leads, I don't think I'll be getting the genuine ford ones again, they still want over 100 pounds for them even on ebay. What brand of leads are actually any good?






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