Very poor mpg all of a sudden

Aranshaw · Post by **Aranshaw** » Tue Oct 09, 2018 12:20 pm

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.

ph001 · Post by **ph001** » Tue Oct 09, 2018 12:26 pm

What engine?

Aranshaw · Post by **Aranshaw** » Tue Oct 09, 2018 12:32 pm

ph001 wrote: ↑Tue Oct 09, 2018 12:26 pmWhat engine?

Hi its the 2.5 SI

ph001 · Post by **ph001** » Tue Oct 09, 2018 12:38 pm

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?

Silverzedtom · Post by **Silverzedtom** » Tue Oct 09, 2018 12:43 pm

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.

Aranshaw · Post by **Aranshaw** » Tue Oct 09, 2018 12:53 pm

ph001 wrote: ↑Tue Oct 09, 2018 12:38 pm 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?

Silverzedtom wrote: ↑Tue Oct 09, 2018 12:43 pm 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.

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.

ph001 · Post by **ph001** » Tue Oct 09, 2018 1:00 pm

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.

Aranshaw · Post by **Aranshaw** » Tue Oct 09, 2018 1:08 pm

ph001 wrote: ↑Tue Oct 09, 2018 1:00 pm 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.

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.

ph001 · Post by **ph001** » Tue Oct 09, 2018 2:24 pm

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.

Crazy Harry · Post by **Crazy Harry** » Tue Oct 09, 2018 5:02 pm

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

Jembo · Post by **Jembo** » Tue Oct 09, 2018 5:36 pm

You sure your other half hasn’t been out hooning while ur not looking?

Mr Tidy · Post by **Mr Tidy** » Tue Oct 09, 2018 9:07 pm

Jembo wrote: ↑Tue Oct 09, 2018 5:36 pm You sure your other half hasn’t been out hooning while ur not looking?

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!

Jembo · Post by **Jembo** » Tue Oct 09, 2018 9:12 pm

Mr Tidy wrote: ↑Tue Oct 09, 2018 9:07 pm
Jembo wrote: ↑Tue Oct 09, 2018 5:36 pm You sure your other half hasn’t been out hooning while ur not looking?
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!

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

Mr Tidy · Post by **Mr Tidy** » Tue Oct 09, 2018 9:16 pm

Mrs Tidy will never get the Z keys either - we now live at different addresses!

skelters · Post by **skelters** » Tue Oct 09, 2018 10:19 pm

I'm just surprised some of you have an other half!

What fuel are you putting in the car? Unleaded, BP Ultimate, Shell V-Power, Tesco 99?

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