"lumpy" running + low mpg

[lyceus]

Hi All,

Just had the pleasure of replacing the battery in the Chim. However, since the operation the engine has been sounding "lumpy" - it's doesn't seem as smooth as usual, and I am getting terrible economy - around 12mpg!!! Before the battery change I was doing around 20-25mpg in exactly the same driving conditions (and no I haven't replaced my foot with a brick!)

I have a horrible feeling that I might have fried the ECU - is this the sort of symptoms one would expect? Or is there another explanation/fix?

TIA.

[That Daddy]

re/set the ECU again by disconnecting the battery for 10 mins,make sure the car is cold & start again, then drive as normal to running temp using full pedal travel every so often then see how you get on.its worth a try you may have picked up a glitch maybe when you changed battery,let us know how you get on.

[Cider Andy]

It's easier to reset the ECU by disconnecting it (rather than disconnecting the battery). Also check that the tune resistor has not been disturbed when the battery was replaced. The tune resistor is used by the ECU to select which fuelling map to use. If it's disconnected it will use a default fuel map that may well cause symptoms like you're experiencing.

[lyceus]

Thanks guys.

Reset the ECU this morning, and straight away noticed the engine was running a lot smoother. Will work out whether economy has improved after trip home tonight.

Indeed, disconnecting the ECU itself was a lot easier

[jsr]

Just out of curiosity, i have a battery cut off switch in the passenger footwell, similar to the red switches race cars have - do you guys have this?

It's very handy and makes disconnecting the electrics very easy!

[that daddy]

no i have not,good insurance though recommended.

[lyceus]

Hmmm, still getting low mpg, although not quite as bad. In the region of 16mpg now - any suggestions?

[derbygreg]

snb802 sensor

do a search - ive got the same thing... but mine has started getting worse MPG, started stalling now. Appaerently its more than likely to be this thermostat switch... that goes to the ECU and tells it that the engine is still cold and so pours fuel in (choke). This causes the stalling and the shunting under 2K rpm etc... worht a go for £15 for the sensor and 5 min job!

[lyceus]

Thanks Greg, I'll give it a go this weekend.