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What can cause misfires on acceleration and lowered fuel mileage?


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40 replies to this topic

#21 mondy zetecs

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Posted 20 March 2020 - 04:21 PM

Sure our 2.5 v6 don't have egr's, o2 sensors one on exhaust after cat other further up towards manifold if duff EML should alight or code reader. Did you put a oem Ford coil on some aftermarkets coil gives problems. 387c49aad2b608e0600c410b46512a0f.jpg

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Edited by mondy zetecs, 20 March 2020 - 04:31 PM.

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#22 ancienttyres

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Posted 20 March 2020 - 08:01 PM

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I haven't checked for dtc codes for a week, but last time I did there still weren't any so hopefully then an indicator the 02 sensors are ok at least in that case. And yes I replaced the coil with a genuine brand new ford motorcraft one this time, the one that failed was a cheap aftermarket pack however.


Edited by ancienttyres, 20 March 2020 - 08:01 PM.

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#23 ancienttyres

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Posted 22 June 2020 - 09:26 AM

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Me again, the misfire is gone, I decided to just do the plugs and the leads during this lockdown. The old ones all seemed OK except one plug at the back looked a bit fouled up more than the others so I suspect that was the same plug and lead that was on the gunked up point on the old coil pack (see picture I posted ages ago). Must be why I still had a misfire under certain conditions.

 

my fuel econemy has supposedly gone up a bit according to the readout, to 33mpg which is +3mpg on what I was getting with just the coil pack done. Not great if true, as thats still around 360 miles on a tank and I was definitely getting over 400 before. I'm not sure now if I used to get 450 on a full tank like I first suggested before; that may have been with motorway driving and I had a false memory of it being that way all the time.


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#24 mondy zetecs

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Posted 22 June 2020 - 10:04 AM

Checked my 3 front plugs only and HT leads for a misfire, found one lead has a small clip missing

put it all back and misfire in 2nd gear gone but accelerating in 3rd/4th has returned,need to get at

rear 3 plugs and coil then try new HT leads first. 


Edited by mondy zetecs, 22 June 2020 - 10:05 AM.

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#25 ancienttyres

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Posted 22 June 2020 - 01:07 PM

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My old leads seemed ok tbh, tested the resistance etc didn't seem a problem but i replaced them anyway with some fancy red performance ones when i did the plugs which didn't cost too much in the end. I'm fairly sure now i've replaced the coil, the plugs and the leads i've eliminated the misfiring. Only thing that was a bit weird was I took it out earlier, after I last posted, car started fine, engine revved up then slowed down as it usually does then it started to run closer to idle and it felt like something happened almost as if it was about to stall then the revs surged up to about 1200 again and it settled down after that.

 

Honestly the car's been giving me so many mixed signals lately I feel like I'm in a relationship with a teenaged girl.


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#26 mondy zetecs

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Posted 22 June 2020 - 02:21 PM

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Changed ICV valve using a Ford part cos of moosing,it does the rev jump and down

then settles to idle now and then,probably the electronics adjusting to certain conditions.    


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#27 ancienttyres

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Posted 29 June 2020 - 02:05 PM

I changed my ICV too. Might explain the reving I had then, probably just normal or it might be to do with the extra fuel use I'm seeing.

 

Today however... A possible bad turn of events. I checked the oil, haven't checked it in a few months (justified because I've barely been using it in this lockdown). While I was playing with me dip stick, I caught a whiff of the oil. It almost smelt a bit like petrol. Now this might just be me mistaking general crap and dirty buildup in the oil for a petrol leak but given I've lost a few MPG somewhere I'm inclined to think it might actually be because the fuels going into the poxy oil pan somehow.

 

It doesn't normally use oil I must say - engine condition was always very good and I have always driven it gentle (mostly) so it can generally go for upwards of six months without needing topping up. But during this time I've actually had to top it up twice, once a few months ago and today. It had got a bit low last time and today it was showing halfway between min and max on the dipstick (but I like to keep it close to the max so I put some in anyway).

 

I know that when petrol gets into the oil first thing suggested is the piston rings but before I go worrying about that can fuel leak into the oil in other ways? Through the vacuum lines maybe? Only reason I'm asking is because I found this video:

 

 

Around the 17:40 mark the guy has unplugged the fuel pressure regulator while trying to diagnose running rich engine among other things and found it's been pissing fuel into the vacuum line. Would that line maybe be connected to the oil seperator assembly? Because if it is tha'd both explain why my engine runs rich and also how petrols getting into the oil. Only problem is I'm going to have a problem getting at the regulator to check it it seems. It's hidden under the inlet manifold according to a post I found that was only posted a few weeks ago.

 

I really don't want to take the manifold off. What an absolute bast**rd especially seeing as I just did the plugs and actually avoided removing it then.



#28 ancienttyres

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Posted 27 August 2020 - 03:45 PM

Welp. I finally got around to having a look at the fuel pressure regulator (wait for it), by not quite but sort of taking the manifold off, and I still couldn't find it. Took the manifold off enough to look under it but there's no regulator there, just the fuel injection rail. I was expecting it to be fairly obvious, attached to the rail on the end where the air intake is on the manifold but there wasn't anything there that looked like a regulator. I'm glad I didn't faff around taking the whole manifold off like haynes wanted me to do.

 

But I'm left at square one again with regard to the fuel consumption. It's still misfiring when I put my foot down in fourth/fifth (that's when it's noticeable at any rate, I suppose it probably does it a bit in any gear if I accelerate hard enough, I just don't tend to do that in 1st/2nd so I don't notice it). I say misfire, I dunno, feels like the entire engine cuts out for a split second and I know for a fact now that it isn't the coil the plugs or the leads as I've now done them ALL.

 

Unless any of you clever clogs can come up with an idea I think I'll just admit defeat and take it to a garage and hope it doesn't wind up costing me an arm and a leg.


Edited by ancienttyres, 27 August 2020 - 03:46 PM.


#29 ancienttyres

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Posted 01 September 2020 - 10:38 AM

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Appears I have got a buggered downstream 02 sensor. Sensor 2 bank 2 is reading constant 1.27v regardless of how long engine runs for when driving. The other three sensors all work OK it seems. Looks like your were right mondy zetecs.

 

I even think the picture of the sensor you posted is the one I have to look at. That's going to be fun.


Edited by ancienttyres, 01 September 2020 - 10:39 AM.

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#30 mondy zetecs

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Posted 01 September 2020 - 04:34 PM

The pic of sensor i posted is for after cat. rear sensor, not sure if its same as sensor 2 bank 2 


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