POOR MPG-Average13 mpg

[AndyCheltenham1]

I used to average 18-20 mpg, mainly on shortish runs but over a period of time it has dropped to 13, this is mainly on short runs of 2 miles, but also on longer 10 mile runs (but still around town rather than motorway type driving).I have owned the car for 8 years, it has done 93000 miles and to me doesn't drive any different from when I first had it. It starts perfect and settles down to a normal idle fairly quickly and is as smooth and responsive as ever. It is a 1993. I took it for its MOT yesterday and it passed (again) with the only advisory being rust on front/rear springs.

The mpg is obviously getting worse over a period of time. Any ideas why it is getting worse and what I should be looking at to try and get it to improve?? I know I am getting much poorer mpg than other people are getting on here.

Andy

 

[shanra]

Might be worth checking HT leads are within specs also rotor arms could be worn and check plugs whilst you're at it. Last time air filter was changed.

[cruisermark]

andy a long run wont do it any harm just to loosen things up a bit

[Cotswold Pete]

I would also see how clean (or dirty) the throttle is.  Though if the idle settles down well I would think throttle is fairly okay.

Also agree a LS needs a good motorway run every couple of months if it does mainly town driving.

 

 

[runsgrateasanut]

If this was my situation I'd half fill the petrol tank adding half a bottle of Wynn's injector cleaner and take it for a hundred mile trip where most is duel carriageway to clean the injectors. Surprised you are not getting an emmisions failure.  Check the last results and post them on th forum for members to compare.

 

 

[mikeyv]

If you're doing more 2 mile trips than you used to, that would account for it.

2 miles from cold will give very poor economy, and will need some longer trips to balance out the average.

[Titch LS]

Andy, It's most likely to be a failing Coolant Temperature Sensor. Once it fails, so down go your mpg figures. The reason is that the engine thinks that it has not warmed up and so the ECU sets a permanently richer mixture, hence the 'drinking problem'. The sensors are quite cheap and fairly easy to replace I believe.

[Keith Bowler]

Andy - I was also experiencing what you get in MPG but mine has now improved to around 15.5 doing lots of short journeys around town after a dose of CataClean (I think that's what its called).

Mine has done around 117000 miles is serviced religiously and currently shows an overall average MPG of 16.8. When I bought the car 3 years or so ago it was showing an average of 20+ as the previous owner used it quite regularly for 40 mile+ journeys. I find on a good run mine will go up to mid 20's and the highest I have seen is 25 on a return trip to Leicester with a lot of stop starting in traffic for a 13 mile stretch on the outward journey.

I have had my ignition 'bits' checked and replaced where necessary and recently had it checked for fault codes and it did not show up any problems. I also plan to run some injector fluid through the fuel system which I try and remember to do every 6 months or so.

As others have commented, I do find that the car runs better after a good long motorway journey at a near constant speed.

I often ponder replacing my car with something a little more frugal but have yet to find something that is as reliable and gives as much driving pleasure.

 

[Spacewagon52]

I have just done a stint of town driving, approx 2-3 mile journeys. 18.2 mpg and I am VERY light on the throttle.

[alien1974]

I get around 16.8 mpg average, thats all round town doing around 3-4 mile trips 

[AndyCheltenham1]

A lot of interesting comments here. My mpg is decreasing but thinking about it I haven't been on a long trip for maybe 6 months now, my longest trip has probably been about 10 miles, so I do need to take it on a good motorway run to clear the system out. When you look on here and see people getting 25+ mpg I hadn't really thought that that is on a run and when the car is used more regularly for longer journeys. I do about 3000 miles a year but put more miles on in the summer months. Thanks alien1974 for saying you get 16.8, and spacewagon52 for 18.2 mpg-that makes my 13mpg a bit more acceptable.The emmission figures on my mot were

fast idle test-0.12 (max limit 0.2)  CO /  47ppm(max 200) HC /  1.002 (max 1.030) LAMBDA

natural idle test-0.11 (max 0.30) CO

Maybe putting in injection cleaner or cataclean would help to clean the system out when I go on a long motorway run. I've read before about  coolant temperature sensor s causing problems-can you test if they are faulty or is it best to just fit a new one if they are not too expensive?   Can I assume that my lambda sensors are not at fault and causing problems as it passed the mot ok on this?

I'll start by going on a long run over the next few weeks and see if that helps at all.

 

 

[alien1974]

those lambda readings look on the high side or i could be wrong

[Titch LS]

Andy, a lot of owners on the U.S. forums say they've seen a marked improvement to mpg figures, plus, better overall engine performance by replacing the Coolant Temp Sensor. If my mpg drops way down it's what I'm going to replace. Cheap and easy fix in my book.

[runsgrateasanut]

Thats one advantage later cars have over mine, although not knowing what the mileage per gallon is, can keep the mind happy. In the Mercs I've had they had an Econometer which is like a swingometer and you found yourself constantly watching to see if it would go into the low MPG area. In a way it did dictate sensible driving -  possibly?

If you only do a two mile run I wouldn't have thought the engine would have even warmed up and therefore you would be using coldstart fuel amounts?

The Lambda reading does look a bit high and I compared it to my last fail on CO2 emissions (.44 against .30 2nd Fast idle) but where the Lambda was 0.97

Cleaning the throttle body and maybe adjusting the Throttle sensor gave me a pass for emmisions but they never gave me the read -out. I just grabbed the Pass and ran.

[AndyCheltenham1]

I've just had new front brake pads fitted and the passenger side was hardly worn down but the drivers side was worn down much more (enough for the red brake wear warning light to come on). The mechanic said that the caliper was seized on so I've been driving with one brake seized on for a while now-so I'm sure that hasn't helped my mpg too much!!

I've had more brake dust on the drivers side front wheel than on the passenger side for a while now-so should have had that investigated before now, but too busy/lazy to find out why.

It was an easy fix with a penetrating spray so will see how my mpg changes now.

[Titch LS]

Andy, I'm surprised that your steering didn't pull to one side because of that sticking brake caliper.

[Spacewagon52]

It is a good feeling to get problems sorted without too many ££££££££££££££!

[jonthetourist]

Hi Andy

Great you are fixed. A long trip would probably still be good therapy for your car.

You inspired me to reset the computer for my 190 mile trip to York this morning. 

And I got 32.5 so I was delighted.

:)

Jon

[jonthetourist]

Sorry! Forgot to say that this was 10 mpg better than my usual figure, and my normal driving involves typically a 6 mile trip with not much traffic. So I think if you give your car a good run you may be surprised wit what you see.

 

Cheers

 

Jon