tonkaforce

Hi i have a 2004 545i, and atm im getting around 12 mpg, so far ive cleaned my air filter (have a k&n on the way) , ran some seafoam though my oil and then changed it, new oil filter, new spark plugs, put some seafoam in the gas to clean the fuel injectors, and ran some seafoam though the vacum line. helped a little, before i was at around 8-10 mpg.i use 92 gas, i drive very easy , barely ever push it, i live in a very flat land area, no hills.my father did say he notice an unusual smell of gasoline coming from the exhaust. also the car does smoke from the exhaust a bit, its gotten better, but last time my friend reved it , a cloud of smoke shot out of the exhaust. the car idles fine an sounds good, there is a little clicking sound at the engine, but im pretty sure thats because i just changed the oil. also i did notice a weird sound come from under the car ( under the car on the driver side near the exhaust) its sounds like a high pitch buzzing sound jus like when u turn on HID lights. also, i just remembered, about 4 days ago, the check engine light went on, i scanned it an it said P1890 . cleared the code and it never came back.im starting to think that it may be the catalytic converter, would make sense because of the smell from the exhaust, also once a rev it a huge build up of smoke just shoots out as if its clogged or something, an also, when i turn on the heat, its not very strong, (experience from another car, the car was not shooting out any heat when i would turn on the heat, as soon as i changed the catalytic converter, the heat an air was much stronger in the car) . an lastly, when im driving, an i let go of the gas so the car can roll, its feels as if the car is being forcefully being slowed down as if im down shifting in a manual car, but my car is auto, my guess is the car is being restricted from breathing from the cat, but im a newbie, so if anyone has a better suggestion, please do say. i did a little more research an found out that a bad thermostat may cause unburned fuel and obviously a lack of heat for the heater

sorry for the long post, i had a thread going on before, but it kinda died out

E60I

Maybe it's normal? I bought and own my 2006 530i since it had 4 miles on it. From day one, I have often averaged 18.9 miles per gallon. It's a V6, automatic.

Sorry if I am not giving you the answer you want to hear.

JWMich

I don't have this vehicle, but I have an X5 4.4i that's consistently around 17, half city. Given that, with a big, heavy AWD, I wouldn't think 12 sounds normal, I always thought that was more like M5 consumption. Not sure what to look at to diagnose, though.

Wolrab

That isn't normal. I get about 19 in mixed driving with the same engine. It will probably save you some money to get it diagnosed properly by an indy shop, rather than throwing parts at it, although my first guess would be it's not warming up properly due to a bad thermostat.

After it's fixed, you might want to take it for a little scream down a long straight road to blow some of that carbon away. Have some fun, and red-line it a few times! That's what it was built for.

paul-g

agreed with above, i have an 07 550i and i get (normal driving ) 18 in city and doing 70-80mph 24-26 highway so you have somthign going on. first what's milage and i tend to agree with thermostat issue. if car doesn't see the right temp level will keep car running rich

advancedlogic

I'm in SoCal and commute home in some of the worst traffic in the country (101/405 freeways). I average around 17 in my 545i. Again, as stated on the prior thread have your exhaust system checked for restrictions. The thermostat can also be checked with any scan tool that has PID maps.

If you're smelling exhaust, you are dealing with

1) Unburned fuel. Coil packs/spark plugs should be checked for faults/replaced. Especially plugs.
2) Failing catalyst - clogged catalytic converters will sap mileage quickly
3) Faulty O2 sensors - will lead to 1 and 2
4) Faulty fuel sending unit
5) Vacuum leak
6) Failure of fuel vapor recovery system. Allowing fuel vapors to escape.
7) Fuel system leak

"Sticky" brakes, etc. could also be causal. Best thing to do is to put it in the shop for diagnosis.

tonkaforce

well i just took it to the mechanic shop, he did an emissions test and it passed an came out really clean. so the catalytic converter is scratched off the list, i also doubt its an o2 sensor just because there is no check engine light on and it passed the emissions test, i dont think its a vaccum leak also because i think i would notice the car running a little rough at least or hear a whistle, but theres none of that, idles fine, and i dont think its a fuel system leak just because i think i would notice some sort of dripping. he also said that the thermostat is not really a big deal if it is or is not working, but from the looks of it, he said it was fine also.

he suggested i manually calculate the mpg im getting, he also said that i should buy a fuel injector cleaner and pour a quarter of it when the tank is near empty, and do this 4 times after every time the tank is near low. he did notice a smell from the exhaust though while donig the emissions test.

but im going to calculate it manually and put some more fuel injector cleaner.

if anyone has anymore suggestions as to what might be causing this poor gas mileage, please go ahead, thanks for the replies guys

luigi524td

You mentioned a heater warm-up issue. It's possible your car isn't reaching the proper operating temperatures - running cold will greatly reduce your fuel economy.

tonkaforce

well according to the temperature gauge it seems as if its functioning, like in the morning i can see it move down as the car warms up.

info@trinityautosport

+1 for calculating the mpg manually. I am curious to see if it will come out to be the same as idrive tells you.