LordGrover Posted October 17, 2018 Report Share Posted October 17, 2018 What could cause a sudden dip in fuel economy? I've driven no differently to usual but over the last few weeks it's been dipping and down to a lowly 19 mpg the last fill. Link to comment Share on other sites More sharing options...
Menoporsche Posted October 17, 2018 Report Share Posted October 17, 2018 Overfuelling? Link to comment Share on other sites More sharing options...
JoeyH Posted October 17, 2018 Report Share Posted October 17, 2018 check your Lambda's and long term fuel trim,then Maf then the engine temp sensor, then remove and clean the throttle body and maf. vac leaks ,pre cat exhaust leaks, the list is endless sadly. codes wll help, and getting the long term fuel trims will be massive indicator as Lambda's are bank specific so will help you to narrow down which one is going bad ''if'' it is that..if for example they are ok then even without MAF codes I would start with cleaning that and going over all the jubilee clips in the induction hosing and listening /looking for any leaks...check the engine temp sensor is reading what it should, they are dual feed so what you see on the instrument cluster is not always what the DME is seeing, if the temp sensor is reading wrongly then there is potential for overfueling. This is all assuming it's had a recent air filter, fuel filter, and the plugs, coil packs and HT leads are all healthy. many things can cause poor economy but usually a sudden rather than gradual over a period of months is down to a change or degredation or of the sensors that control fueling ..I have listed them in the order of most likely culprit at the top. when you have done these checks try disconnecting the battery for 30 mins and doing a throttle re-set/adaptation. My money is on your Lambda's BTW. good luck. Link to comment Share on other sites More sharing options...
LordGrover Posted October 17, 2018 Author Report Share Posted October 17, 2018 Cripes. That's a depressingly comprehensive list. Thanks, will investigate. Link to comment Share on other sites More sharing options...
Stuart21UK Posted October 17, 2018 Report Share Posted October 17, 2018 the weather/temparature is likley to affect it no? a few short trips? not using that overpriced premium stuff for a change? Link to comment Share on other sites More sharing options...
JoeyH Posted October 17, 2018 Report Share Posted October 17, 2018 1 hour ago, Stuart21UK said: the weather/temparature is likley to affect it no? a few short trips? not using that overpriced premium stuff for a change? Not down to 19mpg it won't... Link to comment Share on other sites More sharing options...
Lennym1984 Posted October 17, 2018 Report Share Posted October 17, 2018 You could try your Lambda sensors but without a code reader you are kind of guessing. I had a duff one on Bank 1 and my MPG shot up by about 2mpg when I replaced it. Link to comment Share on other sites More sharing options...
Stuart21UK Posted October 17, 2018 Report Share Posted October 17, 2018 9 hours ago, JoeyH said: Not down to 19mpg it won't... i did an 8 mile round trip earlier tonight and managed only a bit over 19 mpg....you need to try harder Joey Link to comment Share on other sites More sharing options...
Patt Posted October 18, 2018 Report Share Posted October 18, 2018 I'm disappointed the 981 wont display under 10mpg - the 986 did - one less challenge I guess. Link to comment Share on other sites More sharing options...
JoeyH Posted October 18, 2018 Report Share Posted October 18, 2018 I think ''hoon'' MPG should be excluded from the thread due to the confusion it may cause... ? in all seriousness, I reckon I could get it really lo on a ''spirited'' drive but normal driving should return around 25 on average ..with maybe 30 on a longer run. 19 would be understandable on a barely warm engine doing lots of short trips if you are doing mixed driving and getting 19mpg then something is wrong...not very wrong but sounds to me like the car is running rich. Link to comment Share on other sites More sharing options...
Stuart21UK Posted October 18, 2018 Report Share Posted October 18, 2018 7 hours ago, JoeyH said: I think ''hoon'' MPG should be excluded from the thread due to the confusion it may cause... ? in all seriousness, I reckon I could get it really lo on a ''spirited'' drive but normal driving should return around 25 on average ..with maybe 30 on a longer run. 19 would be understandable on a barely warm engine doing lots of short trips if you are doing mixed driving and getting 19mpg then something is wrong...not very wrong but sounds to me like the car is running rich. I'd agree with this...19 mpg is short or very spirited drives, 24.5mpg is my combined and I may get 29-32 mpg on a more relaxed longer trip Link to comment Share on other sites More sharing options...
LordGrover Posted October 19, 2018 Author Report Share Posted October 19, 2018 Turns out I'm a knob. Probably. Rather forgot about the trip back from Cribbs which was an hour nose-to-tail to cover about two miles. I'll see how it pans out over next tank full. Apols. Link to comment Share on other sites More sharing options...
Patt Posted October 19, 2018 Report Share Posted October 19, 2018 LOL Relax and enjoy - the odd blip in mpg usually means a bigger smile Link to comment Share on other sites More sharing options...
Luciano casali Posted November 18, 2018 Report Share Posted November 18, 2018 Wouldn't hurt to check air filter I know about traffic from cribbs I'm from Briss if your not a local that's Bristol Link to comment Share on other sites More sharing options...
the baron Posted November 19, 2018 Report Share Posted November 19, 2018 Ive no idea why, bit I cleaned out my throttle body, idle sensor and maf, and I seem to be getting a few more mpg, so if any of those are dirty clogged that might account for the drop. Link to comment Share on other sites More sharing options...
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