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What can cause misfires on acceleration and lowered fuel mileage?


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40 replies to this topic

#11 mondy zetecs

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Posted 07 February 2020 - 11:58 AM

Test your current parts its cheaper than splashing out then finding its not 

cured the problem,i found out hard way spent over £250 guessing and the

knocking was from a £12 drop link.

Let us know your outcome as i'm looking for pointers to the problem. 


Edited by mondy zetecs, 07 February 2020 - 12:00 PM.

Fiesta 1.0 ecoboost 2014


#12 mondy zetecs

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Posted 07 February 2020 - 02:11 PM

I used NGK  PTR5D-13 (6644) laser platinum plugs,

Try motorcraft 

https://www.ebay.co....E-/372801334625


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#13 ancienttyres

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Posted 14 February 2020 - 03:02 PM

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Well I managed to get some time to swap the coil pack today on my lunch break. Haven't driven it yet so won't know if that's fixed but judging by the state of the old coil pack I'm hoping it was the problem. Number 6 plug was very loose and only realised why when I got the pack out;

 

20200214_144807.jpg

 

 


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#14 ancienttyres

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Posted 15 February 2020 - 07:46 PM

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Took it out for a 30 mile drive today, no misfires and drives quite nicely in fact. average MPG is slowly (very slowly) creeping up from 30 but I filled the tank up while I was out so I won't really know if the mileage has recovered until I've driven a few hundred miles).


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#15 ancienttyres

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Posted 23 February 2020 - 12:46 PM

So the cars running nice still, but I still have lowered MPG. I've done 380 give or take on a full tank topped off of just over 55l. Around 31.4MPG which is also what the readout says I'm getting so it's actually accurate at the moment.

 

Before this I was getting at least 450 miles on a full tank of around 55l.

 

So apparently the misfire had nothing to do with the that. Any ideas?



#16 cantfixwontfix

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Posted 25 February 2020 - 11:43 AM

So the cars running nice still, but I still have lowered MPG. I've done 380 give or take on a full tank topped off of just over 55l. Around 31.4MPG which is also what the readout says I'm getting so it's actually accurate at the moment.

 

Before this I was getting at least 450 miles on a full tank of around 55l.

 

So apparently the misfire had nothing to do with the that. Any ideas?

A long shot, but could it be E10 petrol? You say you noticed this happening a few months ago, back in september 2019 I believe (someone correct me if I'm wrong), the government made it a legal requirement that petrol pumps providing petrol with at least 10% bio ethanol in them be labelled as "E10" pumps. Prior to this they could have been providing petrol from anywhere between zero and 10% ethanol. Just depended on the petrol station and the depot they got their fuel from. But now if a pump is labelled e10 is definitely has 10% ethanol in it (or so I believe anyway).

 

My point with this is in a misguided effort to lower carbon emissions the gov require that petrol have 10% ethanol in it as ethanol produces lowered emissions, but it also lowers fuel economy! I don't know if E10 petrol could cause you to lose 50-100 miles off your MPG though, but it probably doesnt help.

 

The only other thing I can think of is similar to what happened to mine last year. A gaping hole developed in one of the vacuum lines on mine causing the EML light to come on and the DTC to read that the engine was running too lean on banks 1 & 2. Maybe you have the opposite problem! Could be you actually have a blocked line there somewhere and the engine's actually running too rich (but evidently not enough for it to cause the EML to come on and throw a DTC).


Edited by cantfixwontfix, 25 February 2020 - 11:44 AM.


#17 ancienttyres

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Posted 25 February 2020 - 11:19 PM

I don't know about fuel quality or air lines but I have today found the car misfired again in third pulling up a hill while it wasn't fully warmed up. Smelled of petrol when I started it too which I've noticed a few times lately (never used to smell like that on cold stat). I'm pretty disappointed. With the mileage still much lower than it was I'm thinking what you say about it running rich might be the problem.But with no dtc codes showing up, the coil pack replaced , and knowing the ht leads and spark plugs are ok now ive tested/checked them im at a loss.



#18 ancienttyres

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Posted 20 March 2020 - 12:20 AM

I've still not been able to diagnose this issue. The other day, I went out on a slight cold night, car seemed fine as I drove out onto the road but I put my foot down to accelerate and nothing seemed to happen for a split second then it just suddenly accelerated. Never done that before! Driving up the road it misfired like a bast**rd in fourth breifly before evening out again. FUel consumption is still higher than normal.

 

While I think replacing the coil pack has worked to cure the intermittent misfire it seems there's another problem that was there too which is unrelated to the coil pack breaking down.

 

I've searched a lot (not just with mondeos but cars in general) for things that can cause issues with increased fuel consumption and as far as I can tell, it could be any number of one of these (and perhaps any number of others but these seem to all be the ones that come up when searching):

 

- Coil pack is always the first one people seem to suggest but I know that isn't the problem obviously as mines now brand new.

 

- ht leads breaking down - mine seem fine, I have tested them and found no obvious issue with them.

 

- sparks failing - I took out the three on the front of the engine (only seeing as the ones at the back are a bitch to get at), they don't seem to be fouled beyond general wear and tear for 5 year old plugs (turns out they were ngk ptr5d-13 as suggested I replace with earlier in the thread so they should be good for 50/60k miles as far as I've read, and these have only done 30k).

 

- o2 sensors up the duff. I have no idea where any of the 02 sensors are on this engine. No doubt somewhere extremely difficult to get at judging by everything else.

 

- fuel pressure low - which could be caused by a blocked fuel filter, dodgy fuel pump, buggered fuel pressure regulator.

 

- injectors buggered

 

- vacuum leaks - can't find any

 

Any other suggestions for me to check? I'm assuming the fact no ones replied for weeks other than myself is because you've all run out of suggestions and ideas anyway. Me too. :|



#19 alpid

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Posted 20 March 2020 - 01:58 AM

Sounds like classic EGR problem to me but it depends on what year your engine is as EGR systems were only fitted to the earlier blocks to satisfy the USA market. If yours does have the EGR system you can remove it and replace it with a blanking plate. Really easy fix. Hope this helps.

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My mondy was replaced by a 2.0ltr Cougar (the mondeo with no back doors) and now partnered by a 2008 Mondeo Titanium X 2.5T estate in Blue (ambition)?


#20 ancienttyres

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Posted 20 March 2020 - 02:04 PM

That's interesting! It's a 2001 Duratec 2.5l V6. Can't really figure out if mine has one or not from looking online, even this haynes manual I bought is a bit vague ont he subject (though it does seem to give a tutorial on how to renew the egr valve on v6 models so presumably it thinks there is one). I suppose the only sure fire way is to stick my head in there with a torch and look for myself.

 

At any rate I've read about blanking this valve off and how it can actually improve MPG and engine power a bit. Sounds like it's worth doing even if it isn't the problem.


Edited by ancienttyres, 20 March 2020 - 02:05 PM.





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