Very poor mpg all of a sudden

A

Aranshaw

Member
Hope someone can help here, have an e85 and about a month ago when I filled up a full tank rather than the computer saying I could do about 400 miles as it normally does it said 260, I checked the mpg and it read 30 which was fine, next time I filled up the same thing occurred, I reset the mpg calculation and its now calculated I get about 22 which is horrendous. Inflated tires so no issues there. Today was driving an when pulling off in first car felt like it wanted to stall due to shaking. Does anyone have any ideas as to what might be going on here?

Thanks so much.
 
Hmmm that's the N52 engine so problems like this are quite rare. Could be a lamba sensor which is screwing the mixture up. Does it drive OK otherwise? No engine warning lights? Idles OK? Power OK?

Next stage really is to get a code reader on it to see if it has any codes stored and look at live o2 sensor readings. Where are you based?
 
As above, it needs plugging in to a good scanner.

Certainly sounds like a sensor though.

Are all of your brakes good? As in wheels spin freely? Doubt it’s going to be this but maybe worth a shot.
 
ph001 said:
Hmmm that's the N52 engine so problems like this are quite rare. Could be a lamba sensor which is screwing the mixture up. Does it drive OK otherwise? No engine warning lights? Idles OK? Power OK?

Next stage really is to get a code reader on it to see if it has any codes stored and look at live o2 sensor readings. Where are you based?
Click to expand...
Silverzedtom said:
As above, it needs plugging in to a good scanner.

Certainly sounds like a sensor though.

Are all of your brakes good? As in wheels spin freely? Doubt it’s going to be this but maybe worth a shot.
Click to expand...

Hello, I'm going to buy a Bluetooth adapter so I can check o2 sensor data as I guess that's the most likely culprit. It drives fine other than the fact it was shaking when taking off in first gear today, the tires etc. are fine, no warning lights appear so my basic obd2 reader can't pull anything.

Is it more likely to be o2 sensor than sparkplugs or MAF?

Based in cambridge.
 
It's common for the upstream sensors not to cause codes when they go dodgy. My guess is that one or both of them are only swinging from about 0.1 to 0.4V instead of the 0.9V they are supposed to do. Probably also 'laggy' in their response.

MAF is a possibility but defo not a common fault on these cars. It would be last on my list. Won't be plugs with those symptoms.
 
ph001 said:
It's common for the upstream sensors not to cause codes when they go dodgy. My guess is that one or both of them are only swinging from about 0.1 to 0.4V instead of the 0.9V they are supposed to do. Probably also 'laggy' in their response.

MAF is a possibility but defo not a common fault on these cars. It would be last on my list. Won't be plugs with those symptoms.
Click to expand...

Thanks, I won't be able to understand what the results from the scan tool mean so ill post them here when I get the tool and hopefully it will be clear if its the o2 sensor or not and I can go from there.

Thank you.
 
Yeh, you need to get the car fully up to temp then post a video of the values on Youtube and link to it. First do idle then rev to 2,000rpm and hold it steady for 30 secs or so.
 
OK so I'm going to ask the low tech question - have you covered as many miles between fill ups as you would have normally done? the gauges say you are using more fuel but are you - its then gauges or poor consumption.

If its poor consumption - does it need more revs to get it moving / will it free wheel? this should point you to binding brakes or engine problem

Engine - get a reader and follow the advise above :thumbsup:
 
Jembo said:
You sure your other half hasn’t been out hooning while ur not looking?
Click to expand...

That made me smile!

Back in 2010 I was working abroad for about 6 weeks and Mrs Tidy used my car a few times just so it didn't sit idle - average MPG dropped dramatically! :headbang:
 
Mr Tidy said:
Jembo said:
You sure your other half hasn’t been out hooning while ur not looking?
Click to expand...

That made me smile!

Back in 2010 I was working abroad for about 6 weeks and Mrs Tidy used my car a few times just so it didn't sit idle - average MPG dropped dramatically! :headbang:
Click to expand...

My Mrs Jembo exceeds manufacturers claimed MPG... I’m at a total loss how she does it but Hell will have to freeze over before she gets anywhere near the Zed’s keys
 
Mrs Tidy will never get the Z keys either - we now live at different addresses! :roll:
 
I'm just surprised some of you have an other half! :poke: :rofl: :rofl: :rofl:

What fuel are you putting in the car? Unleaded, BP Ultimate, Shell V-Power, Tesco 99?
 
ph001 said:
Yeh, you need to get the car fully up to temp then post a video of the values on Youtube and link to it. First do idle then rev to 2,000rpm and hold it steady for 30 secs or so.
Click to expand...

Hello, here is a report I generated with the app.

https://1drv.ms/u/s!AiFxel1SDKFghOkPF_2x00s25AjEyg

Ill try and get the other values shortly.

No idea if anything looks amiss here.

Cheers
 
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