Bad Fuel Economy

[morganb 0]

Hi all, I know its been covered to death on here but im at a loss now. Recently put my 1.6 gti back on the road and its returning around 20 miles to a gallon at best. Ive been running the car to work which is a 24 mile round trip. No stop starting just a nice straight run and im driving very carefully no heavy foot. The car is pretty much standard apart from a stainless exhaust system.

Ive changed filters, plugs etc and bought a new ECU temp sensor and tried swapping AFMs with another used item to no avail. I am getting a strong smell from the exhaust on idle and the backbox is sooty. Although the car seems to drive pretty well and it was MOT'd only a few weeks back. On cold start it idles just under 1500rpm then dropping to around 1000rpm when warm.

Any advice much appreciated guys

[welshpug 1,657]

swapping afm's is no use these days, you need to replace them for a remanufactured item or do the old re-tracking trick, and get them set up properly following the details in the haynes manual and use a gas analyser to get it down to around 1-1.5% Co.

[Anthony 1,003]

I dunno about that - whilst fair to say that most AFM's are probably sub-prime these days, you'd be unlucky to get two that were knackered enough to give you 20mpg levels of economy. This is particularly true if the replacement was from a known good source (i.e. a running car without the same issue!)

[Tom Fenton 1,542]

The best way I found to properly diagnose what is happening is to fit a wideband lambda, you can then see what the mixture is doing whilst driving about. However I appreciate this is expensive, the other alternative is find a local rolling road and see if they will do tyou a run for say £30 and log the mixture over the working rev range to see what is happening.

[morganb 0]

Just a quick update....

 

Snapped the plug connecting to the ECU temp sensor so replaced it with a quick release junior timer plug. Noticed the wiring was filthy and brittle so cut it back ten inches or so and butt crimped some new cable to it leading to the plug. Got a length of heat shrink for the cable and got the heat shrink blower on it. Now i am not getting the strong whiff of fumes from the back, just need to clock my mpg now. Hopefully will have improved.

Many thanks