14 mpg????

[Tobs]

Hi,

I've recently purchased a '95 Chimaera, which I have been using daily over the past week or two. I work about 12 miles away from home, so do about 24 miles a day during the week. Over the past week I've averaged 14 mpg on two tanks of fuel (with each tank giving about 130 miles) - I filled up when the gauge was between empty and 1/4 full. I know its cold at the moment - and this may make some difference, but I was expecting more like 18 mpg for 'around town' driving (which part of my commute is).

At the weekend I had a look at the plugs and they did look a bit sooty - although the end of the top electrode was whitish in colour. I also looked at the voltage from the lambdas - looked OK between 0.5V and 1V on each bank. The stepper has been cleaned. The plugs and leads are new. I've also changed the coolant temperature sensor (for the ecu), and also reset the ECU. The only thing I did notice was that the air-flow voltage was approx 1.6V at idle - this is higher that that stated in the bible (0.5-1.5V I think), although it was a cold day so that may have something to do with the higher reading.

At lunchtime today I reset my throttle pot - was reading 0.26V at idle - now at 0.35v, and adjusted the CO mixture control on the airflow meter to set it at the recommended 1.8V according to the RPI website (it was 2.13V previously). I'm not sure if this would have anything to do with the low mpg? I also tested the throttle pot on an oscilloscope to see if it was working smoothly - seemed OK. I now need to use up another tank or so to see if that has any effect.

I have noticed that with the engine warm it seems a bit hesitant on part throttles and shunty - although it didn't seem as bad tonight when I drove it home - so maybe the adjustments have helped.

I'm going to now try using a fault code reader to see if there are any codes in the ecu.

Cheers,

Toby.

[Big Al.]

HAVE YOU TRIED TAKING THE HANDBRAKE OFF?

Sorry!

Coat on and heading for the door

[HarryW]

Only thing I would add, is check the temperature sensors, coolant is favourite make sure its not telling the ECU it minus 20 all the time and fueling accordingly .
Other minor point as you've adjusted the CO trim pot on the AFM did you do a ECU reset before or after, I've always found the ECU is not the cleverist out there and any changes that feed it, it's worth resetting the ECU if only to get a warm feeling .

Harry

[Tobs]

AHHH know I forgot something .... I will try to take the handbrake off from now on....

No I haven't reset the ECU after resetting the CO adjustment on the airflow meter - I may go outside now and do that now, on the other hand groveling in the passenger foot well when its cold and dark is not the most pleasant of things! - perhaps I’ll leave it 'till morning.

As for the coolant temp sensor I replaced this as I know this is something that is quite common to give problems. Would the fuel temp sender give the same problems? The bible seems to indicate that this is fitted but not used

Toby.

[JonRB]

You haven't said which Chimaera you have.

On my 500 I get 15-18mpg tank average.

The other thing is that the fuel gauge isn't very accurate. The best way to calculate mpg is to fill the tank to full and zero the trip counter. When it is time to fill up, fill the tank to full again and note the trip counter and zero it. The fuel you have just put into the car is the amount of fuel taken to travel the number of miles on the trip counter, so it is then simple to calculate mpg as being miles/(litres/4.5459) (since petrol pumps read in litres).

Forgive me if I'm stating the obvious to you or anything.

Edit: Oh, and the other thing is that on a 12 mile trip the engine will barely be warmed up. My Corrado's trip computer shows single-figure mpg for the first minute or so after startup (especially on a cold morning) and creeps up slowly over the first few miles. I would imagine most cars would be the same, so this may also account for your poor mpg.

>> Edited by JonRB on Tuesday 22 November 19:34

[2 Smokin Barrels]

JonRB said:

You haven't said which Chimaera you have. On my 500 I get 15-18mpg tank average.

You either do a lot of stop start, or you are Mr Leadfoot of Leadfootshire!

[JonRB]

2 Smokin Barrels said:

You either do a lot of stop start, or you are Mr Leadfoot of Leadfootshire!

A mixture of driving. I've seen 26mpg tank average on a predominantly motorway miles tank, but most of my mileage in the Chimaera is for pleasure, so why bimble around like Mr. Lentil trying to save the planet, eh?

>> Edited by JonRB on Tuesday 22 November 19:37

[v8 racing]

Hi tobs to be honest i would have thought 14 mpg was about right for the distance you are traveling and time of year, it might be worth swapping the stat for one that has not got an air bleed this may help a bit! i have a standard bmw 530 v8 and only travell 4 miles to work and my mpg is down to 8!!

[2 Smokin Barrels]

JonRB said:

2 Smokin Barrels said: You either do a lot of stop start, or you are Mr Leadfoot of Leadfootshire! A mixture of driving. I've seen 26mpg tank average on a predominantly motorway miles tank, but most of my mileage in the Chimaera is for pleasure, so why bimble around like Mr. Lentil trying to save the planet, eh? >> Edited by JonRB on Tuesday 22 November 19:37

I'm not noted for my bimbling (well, not in the car anyway), & I average 22...but then who's counting

I did go through three sets of front discs in 10,000 miles in one 500

[2 Smokin Barrels]

Tobs said:

Perhaps 14mpg is OK then?

Only if you too are from Ledfootshire.

and you've not discovered fourth or fifth

[JonRB]

Tobs said:

Its a 400 Chimaera. [...] Perhaps 14mpg is OK then?

That's very much on the low side for a 400, although your short journeys and the cold weather won't be helping.

Are you married? This could be the perfect opportunity to get a Mark Adams rechip - "but, darling, there's something wrong with the car and this guy can fix it, and I'll get much better mpg so it will save money in the long run. Oh look, I seem to have gained 35 bhp too. "

[Cider Andy]

From the tests you've described you clearly know what to look for when you think something isn't right. The thermostat should open at (I believe) 82°C, but it has a wider opening than an off-the-shelf item: try a dealer or specialist; they're not that expensive. Coolant sensor, as mentioned, is a favourite. Does the car ever warm up properly?





But I'm a Yorkshireman and I'd be right peeved if it was only doin' 14mpg. Get rid of the diver's boots and buy some slippers.

[GreenV8S]

I suspect the short distance is the main factor here. It will barely be wrmed up by the end of the journey, bad for the engine and bad for fuel consumption. I suggest you see what the consumption is like on longer runs before you start looking for problems.

[Ribol]

JonRB said:

Are you married? This could be the perfect opportunity to get a Mark Adams rechip - "but, darling, there's something wrong with the car and this guy can fix it, and I'll get much better mpg so it will save money in the long run.

[Tobs]

As the engine warms up, the temp gauge initially goes upto 50c (this is when the thermostat opens as I’ve checked the top rad hose as the engine is warming up and it suddenly gets too hot to touch - this must be when the thermostat opens. However at this stage the gauge on the dash indicates about 50c.) After driving for a bit the temp gauge goes up to around the 60c mark when moving, and goes up to 80 though after a while when stopped (and I can hear the fans kick in). I know the temp gauge is very inaccurate as the sender is stuck on the end of a piece of pipe! I may try the mod using the other sender and a 150Ohm resistor to see if I can get a more accurate reading.

I'm sure the thermostat is opening at a higher temp than the 50c indicated on the dash - as the top rad hose gets very hot as soon as the 'stat opens. I've got an infrared temp gauge at work I may try at the weekend to measure the temps directly. Also may just get a new 'stat and fit it this weekend and see if it does anything.

Also -another question- when the engine is cold do people have problems with the revs dropping and the car almost stalling when you press the throttle?

As for the married bit - well i'm currently living with my GF - don't know if that counts I had enough trouble persuading her that getting a Chimaera was a good thing! (low depreciation and all that...)

[jonathant]

Tobs said:

Also -another question- when the engine is cold do people have problems with the revs dropping and the car almost stalling when you press the throttle?

TADTS. My Chim 450 seems ok from cold when the temperature is over 10C, but below that it's REALLY lumpy. If I stall, then I've got to wait for a few minutes before trying to restart. The solution is to sit and wait for 30-60secs or so idling [1] and then set off.

FWIW I'm averaging around 17-18mpg on a 6-15mile journey into work which sometimes has alot of stop-start, but that depends on the route and the time. The highest economy I've ever seen is around 24mpg on the motorway.

[1] or fast idle at 2000rpm for 20secs - I only do this if in a real hurry. In both cases, my revs drop about 200rpm when the car is ready to go.

[steve1c]

The cold weather is realy messing up MPG's at the mo. Mines gone down from 18-22 (500) to 12 - 15 over the past three wks.