Absurd mileage after spark plug change.

[McWattersJ]

Howdy, first post.

I recently bought a 325iC in Chicago, IL and drove it back home to Ottawa, Ontario.

My mileage was as expected.

Importation laws required me to safety/e test.

the car failed e test due to high carbon count. Mechanic replaced spark plugs and flushed the engine with some flush machine? ( apparently they disconnect my fuel supply and hook up a special machine?)

Ever since my mileage is horrendous i drove an hour at 100km/h on the highway and it sucked back more than a quarter tank. 91 octane.

To note the mechanic replaced valve cover gasket, fan clutch and exhaust for me. I replaced the air filter (before recent drive)... fuel filter just arrived.


Ive been reading many posts, but I wanted to rule out the work recently done.

thanks

[turbo55]

Welcome!

Maybe check your O2 (oxygen) sensor? It's pretty sensitive to harsh chemicals, it's possible that the flush killed it and now your fuel mixture is super rich. Also check for vacuum leaks, maybe the flush ate away your intake manifold gaskets?

Also, 91 octane does nothing for you, unless you're running a turbo. The gas is not better, just has more octane which prevents knock. If you don't have higher-than-designed-for pressures, then you don't need 91.

[packratbimmer]

If you think the car sat for a long while before you bought it, the injectors might be clogged in the first place. Also "cleaning" the fuel system may have made the injectors worse off. The mechanic might have loosened up debris from the fuel system clogging the injector filters.

[McWattersJ]

Called the mech. Apparently the flush is done with a detergent and is not harmful. I couldn't find time to troubleshoot so the car is back at the mechanic. Thanks for the quick responses.

[E30SPDFRK]

Make sure he put copper plugs in too and not platinum

[Vivek]

If you've only driven what your gauge says is a quarter tank that doesn't mean much. Run a tank or two through it and see what your average mileage is. If your odo works.

[McWattersJ]

If you've only driven what your gauge says is a quarter tank that doesn't mean much. Run a tank or two through it and see what your average mileage is. If your odo works.

I'm comparing the consumption to when I drove 13 hours from Chicago to Ottawa.

[goldenbb]

Do the plugs indicate a rich condition? Search on here for remedies, there's tons of threads.