Contour Enthusiasts Group Archives Forums General Troubleshooting Poor Fuel Mileage

Just wondering why I get such horrible fuel mileage compared to other people here. For a while my cats were plugged and I was getting really bad mileage then, but now they're completely gutted (all of them), and I did the intake rebuild, but my mileage never went back up. I now get around 23 mpg with hwy driving (70mph), and 19 just city, so I guess my highway mileage isn't nearly as high as it should be. The only things I could think of are:

1) I don't know if my IAT sensor even works, I'm assuming I would get a CEL if it didn't, but once I forgot to put the sensor back in it's place (still plugged in the computer) and it drove just like it always did, no rough idle or anything. So could a faulty IAT do this?

2) How much effect does cold weather have on car's mileage, I know it does, but it seems to have more of an effect this year than last year. And why do cars suffer on fuel mileage when it gets cold outside, maybe a stupid question but I've never really known, just always took it as fact. and by cold I mean -10celcius.

Oh and the plugs are new, tires inflated properly, new fuel filter, fuel injector cleaner recently PCV valve, mobil engine and tranny fluid etc...

Wow - that is pretty bad man Hook that baby up to a scope and have it checked out!

To compare - I just went to Vancouver with my car and the following criteria:

Car loaded to the nuts with baby stroller, crib, diapers, cooler of meat, battery pack, clothes, gifts, 4 month old baby, and my wife. I also have on Blizzacks that are 4.2% oversize and drove mostly at 120km/hr. There were many semis to pass also, which made the mileage even worse than my usual 35-37 mpg that I get in the summer driving by myself. Here is one of my stops...

Fuel burnt - 52.98 L
Distance - 605km

Fuel mileage - 32.2mpg (Imperial)

P.S. - On the last leg of the trip I had the cruise set on 140km/hr and got 29.5mpg (768km and 73.9L). Overall trip average was 32.1mpg (including about 100km of city driving).

1) I don't know if my IAT sensor even works, I'm assuming I would get a CEL if it didn't, but once I forgot to put the sensor back in it's place (still plugged in the computer) and it drove just like it always did, no rough idle or anything. So could a faulty IAT do this?

Did you ever put it back in place? If not, the computer may be over compensating for the leak in the intake. The computer will throw a CEL if it senses the IAT out of range.


2) How much effect does cold weather have on car's mileage, I know it does, but it seems to have more of an effect this year than last year. And why do cars suffer on fuel mileage when it gets cold outside, maybe a stupid question but I've never really known, just always took it as fact. and by cold I mean -10celcius.


Engines run richer when it's cold out. That helps the engine warm up more quickly. That's also why they use more gas in the winter, as well as the special fuel mixtures used in certain areas to promote "cleaner air."

Alright, I'll give you my metric numbers, cause you're using imperial gallons, I was using US gallons. In summer I usually got over 500ks on a tank (47-50L)and that was city and hwy combo, i've never actually taken a long trip with the car yet, but I'm going down to minneapolis this next week, I guess I'll see then how the car truely does on the highway.

But ever since my cat problem, I haven't been getting very high mileage, like I'm at 380ks on this tank and almost empty and about 250 of that is highway driving.

Oh well at least gas is cheap right now ($.45/L)

Hmmm - well, the points that rifter brought up are valid. Have you noticed anything else is up with the car (hesitation, loss of power, etc)??? My last Mustang would not throw a CEL because the damn light was burnt out! I'm sure you have reset the computer but if you haven't, try that. But for sure either get a code reader and either check it out yourself or have them checked for you (but if you do this, do not reset the computer first, or you will lose them). Good luck!

how long does the battery cable need to be off to reset the computer? I know my CEL works, it was on until I gutted the cats. Yes the IAT is plugged back in, that was just an example to say that my car didn't seem to run any different without the IAT monitoring the incoming air. I'll check my IAT also. I just hate disconecting the battery cause then I lose all my settings on my car stereo, but oh well.

Most people say that the battery should be disconnected for at least 30 minutes to reset the PCM and clear the codes.

If you desire, I have neard that many AutoZone, or other part chain stores will read your codes for free. You could give that a shot before resetting the PCM, just for kicks and/or peace of mind.

Good Luck,
David

5 minutes should do it. If you want to be really slick, pull the two fuses in the engine fuse box for PCM power and Keep Alive Memory.

Thanks, I think I'll just pull the fuses, I also am going to check the FPR to see if it all of a sudden is going south, thanks again for your help.

I have experienced similar poor mileage. I do know that one or both of the cats have been replaced under warranty at around 45k miles, I bought it at 54k and the original owner told me so. Ever since I own the car, I have not gotten more than 240 miles out of a tank before fill up of ~13.5 gals. I have noticed that the long term trim on bank 2 is running a bit lean at around 6 to 9% (some would consider this normal) and this could be contributing to my apparent poor mileage cause the PCM will open the injectors on bank 2 for a longer period to compensate for the additional air coming into the combustion chamber. So, I could have a leak somewhere around bank 2 and based on some of the postings, it could be around the head gaskets or lower intake close to one/two of the cylinders in bank 2. Not sure cause I have not taken anything apart yet. I need to take some time off to experiment with. But, I can tell you that I am also suffering from the emergency brake problems found in the FAQ. I lifted the rear of my car, spun the tires some and you can hear a slight drag as the tires slow down quickly. I have rear disk brakes and this is one of the conditions necessary to be a victim of this problem. I have bought the kit with replacement cables which I will do next week and then I will monitor the improvement gain to see the extent of the bank 2 lean operation condition on MPG. I offer this input cause there may be some similarity in what all of us are experiencing with these vehicles. Let us know what you find if you do more investigation in your case.