M40b18 1993 Touring running rich - at a loss!

Mon Mar 02, 2015 6:55 pm

I have searched around and have had this problem a while and wondered if anyone could shed any light on the situation. I have replaced everything suggested

I do a 35 mile trip to work mainly motorway (gets a good chanced to warm up) sitting at 65-70 and get on a bad fill up 23mpg and on a really good fill up 28mpg - the exhaust smells rich and sometimes i have a dodgy idle (flicks between around 600 and 1100rpm but not all the time! - most of the time idle is good)

I have replaced the blue temp sensor and checked it at the ecu - getting 250ohms when hot, the o2 sensor has been replaced and reporting properly (car has no cat).

The temp gauge was sitting at a quarter before i changed the stat and now sits at half way (this hasn't effected the mpg in any way)

I have a spare engine so can nick bits off it, so far I have done a tank on another AFM (no difference), can't see any air leaks (sprayed easy start on all the hoses with no change to idle)

I am at a loss as to what would cause bad mpg, car has done 123k miles.. has anyone any other suggestions i can try?

Mon Mar 02, 2015 7:28 pm

Have you tried a different Ecu? I resolved similar prob on mine by switching Ecu.

Mon Mar 02, 2015 9:58 pm

bosers wrote:Have you tried a different Ecu? I resolved similar prob on mine by switching Ecu.

I can try as I have a spare..

Tue Mar 03, 2015 12:07 am

An engine that smells 'rich' can either be weak or rich. If the fuel mixture is so weak as to not ignite/burn properly, then the unburnt fuel passes straight through the engine and exhaust and can be smelt.
Take out all of the spark plugs and examine the colour of the tips, or better still, post up pics.

Tue Mar 03, 2015 6:07 am

Brianmoooore wrote:An engine that smells 'rich' can either be weak or rich. If the fuel mixture is so weak as to not ignite/burn properly, then the unburnt fuel passes straight through the engine and exhaust and can be smelt.
Take out all of the spark plugs and examine the colour of the tips, or better still, post up pics.

Ok will do

Mon Mar 16, 2015 7:44 pm

as per the suggestion of "bosers" i swapped the ECU to a spare one I had from the other engine, albeit it was a different part number it was the same engine. I have done 2 tanks worth of fuel the first averaging 33mpg and the second 32..The car no longer smells rich or of fuel (apart from from cold but goes away when warm like I was expecting) I seem to have cured the issue. I'm going to take apart my old ecu as I reckon it has a dry joint or something.. Either way a big thank you..

Mon Mar 16, 2015 10:58 pm

M40 ECUs aren't known for failing, but there's always exceptions.
Only ever had to replace one that I can remember, which was doingt a good impression of a failing crank sensor.