Poor fuel economy after service

[xain]

Hi All, I''ve recently had my 5.0 Chim serviced and now the fuel economy has dropped from a steady 22 mpg to 18mpg. The car goes very well, and feels the same as before. I usually keep a close eye on fuel economy on my cars (just out of interest) and my drive to work is pretty consistant. I don''t think that could have changed it this much. I even tried driving it very gently for a tank and that still gave me bad mpg. Anyone else had a similar experience? Any ideas? I measure the mpg by always filling the tank to the brim, driving until nearly empty and refilling to the brim, then resetting the trip meter. This should be a fairly consistant process (always was before)

[johnwilk]

I had a problem with heavy fuel consumption and it turned out that a lambda sensor had failed. MPG improved when this was replaced.

[philr]

Funnily enough, I noticed that my 500 was a bit more thirsty after its service (16 - 17 instead of the normal 19 - 20 MPG). It was only when i was checking the car over after a track day ( a few weeks later) that I noticed that the Lamda senson wasn't actually connected ! Either this connection joint had come loose (they're not the most secure conection ) in my travels/track day, or it hadn't been reconnected at when the manifold was refitted at the service. Phil

[xain]

Interesting... they do take the exhaust system off don't they. I'll check the lambda. I'm afraid it wouldn't surprise me, since they didn't bother to change the air filter as they were supposed to either.

[philr]

I don't think the service usually needs the manifold to come off, but my gaskets had gone (AGAIN !) and one of the manifolds had to have a crack welded up. Its now had 4 gaskets and both manifolds welded up in 6000 miles ! I think my air filter was changed (or at least cleaned) because they forgot to connect the air flow pipe up to it again. I wont name names because i am pretty happy with the response I have had todate and can forgive the odd minor slip (if thats what it was). Note that the air filters are not the nice clean dry type that you get on your average saloon car. Just to show my ignorance, I have only just found out that there are air filters that are intended to be oiled so as to attract and hold any dirt being breathed in. Phil

[ozzie]

how many air filters are there supposed to be?, I only have the sock filter infront of the radiator.

[xain]

I think the sock in the front is the only one, and yes, I know it's an oily one, but I checked just after collection to see what colour they are when they're new, and unless they come ready supplied with the same crud that was embedded in it before... As for the manifolds, I think they only remove from the sealing ring between the manifolds and the cats, not the manifold itself. I guess from looking at those joints that it's quite a straightforward process. They look a little like the wrist seals on astronauts' space suits.