Looking for someone to point me in the right direction

Sennema · 11-18-2009, 07:14 AM

I've got an '02 Alero 2-door with the 2.4L engine, automatic. I used to be able to clear 600km to a tank of gas (375 miles), and that's before I'm even to the fuel light. Now, from a full fill, after a little over 400km (250 miles), my fuel light comes on. I'm not really sure what would cause such a sudden change in gas mileage...

I don't have local access to an OBDII scanner at the moment... my friend has one back home but it's a 2-hour drive one-way and he doesn't head that way often as he's in school here.

I did some digging and it came up that possibly my camshaft position sensor is faulty, as occasionally the car won't start when I crank it, but if I stop, and then try again it fires up first shot. However I would think that if there were a problem with that circuit, the ECU would detect it and throw a code? Same with an O2 sensor which I know can affect gas mileage greatly if they go. Am I right in making that assumption? Previous cars I've owned would throw codes in these instances, but is it possible that if it's an intermittent problem it won't?

I've changed the oil and just recently changed out my spark plugs to try and go for the easy solution, and although they were definitely worn out (car has 148,200KM/92625miles). I know that since it's getting colder out, gasoline is winterized, but I can't see that being the problem as this is a pretty significant drop in fuel economy.

I've also heard that a bad thermostat could cause this problem as well, since it would be circulating coolant constantly through the engine? The car heats up fine, but would such a thing cause a large change like that?

Basically, it's close to Christmas and I'm headed to Cuba in about 4 weeks, so money is a concern and also I'm working a lot right now because everyone at work is getting sick, so I really don't have the time or funds to go dropping on every possible fix, so just hoping maybe some people here can toss me a few ideas, maybe start at the cheapest/most likely fixes, and work from there?

Thanks in advance.

Redog · 11-18-2009, 12:19 PM

Have you changed the air filter?

paul ron · 11-18-2009, 08:20 PM

I have a 2000 2.4, 4 dr with 45,000mi in mint condition. I take care of it as far as regular maintenance filters n oil.

A few years ago I was able to drive to Albany n back (325 miles) on one tank of gas n still have enough to do a week of local driving before the light would come on. I have noticed a cut back in MPG and the only thing I can atribute it to is 10% ethenol they are adding to gas in the past years since the prices sky rocketed.

Sennema · 11-18-2009, 10:35 PM

I've owned my car for about 3 months, so the drop is really sudden and hard to attribute to that. I did a quick check of the air filter and it seemed ok, but I guess changing it wouldn't hurt since they're only a few bucks anyway. Don't know why I never thought of that, actually. Think it's worth it to take some throttle body cleaner to it again? I did that back in August after I bought it, and it seemed to be a bit more peppy, but not sure if such a short amount of time would cause it to get that much buildup already... and if it did what would cause that to happen so quickly? Possible I'm running a bit rich and haven't noticed?

jayson_waltz · 11-18-2009, 10:42 PM

is it actually using as much gas in that amount of miles, like when you fill up do you still fput in as many gallons as before? or is your gauge just bad? if it actually taking more gas, it could be a 02 sensor since the filter is clean. But i don't see anything wrong with your miles, i get about 250 miles a tank at 80 mph cruise. but still only get 250-300 max at speed limit (65 hwy, 75 interstate).

Ethanol DOES make a difference, but only 1-2 mpg tops. not a big contribution.

Sennema · 11-18-2009, 11:02 PM

Yeah I still put in the same amount of gas... always fill it right up to the top, always use the same brands of gasoline as well (Shell and Sunoco). I don't hit the highways that often, usually in the city at around 60km/h, or 80-120km/h. I'll try the air filter tomorrow and see if that helps things any... maybe hit it with some throttle body cleaner just for the hell of it.

alero_bmxer · 11-19-2009, 12:04 AM

winter gas + dirty air filter + dirty TB + going bad o2 sensor + bad plugs = terrible gas mileage

[ion] C2 · 11-19-2009, 12:11 AM

^yep

Thermostat's fine as long as the car warms up quickly and sticks around 187-200 F (just below and just above the center line)

colonel6632 · 11-19-2009, 12:14 AM

in city driving, my car never reaches 600km a tank, i'm luck to get between 400-500 a tank. depends on my driving, and such

[ion] C2 · 11-19-2009, 12:18 AM

use km/L or MPG, "per tank" doesn't tell much and has some subjectivity lol

Cliff8928 · 11-19-2009, 01:57 AM

The standard metric fuel economy is in L / 100km. Lower is better.

Sennema · 11-19-2009, 02:28 PM

Quote:

Originally Posted by [ion] C2

use km/L or MPG, "per tank" doesn't tell much and has some subjectivity lol

I'm sitting at around 10.5-11 L/100KM (about 22MPG, which seems low as it should be around 30MPG/ 7L/100KM if I'm not mistaken)

Sennema · 11-19-2009, 02:30 PM

Quote:

Originally Posted by alero_bmxer

winter gas + dirty air filter + dirty TB + going bad o2 sensor + bad plugs = terrible gas mileage

Plugs only have about 2000-3000km on them. I'll probably replace them anyway, but if there is liquid on the plug what causes this? Fuel I assume, but how do I fix it? Replace the injector going to that cylinder?

jayson_waltz · 11-19-2009, 03:13 PM

i thought you sere talking about highway driving. 22 mpg in town is about right seeing all the stop and go stuff. highway 22 would be low, thats 90 mph cruise mileage there. bad.

Sennema · 11-19-2009, 06:17 PM

So I bought a new fuel filter and some throttle body cleaner. Turns out the filter was a lot more dirty than I had previously thought. Hopefully help my issue a bit. However I now have a more pressing concern.

At first I apparently bought the wrong filter. Must have mixed up part numbers. So I took it back but forgot to connect the sensor in the intake (MAF/MAP I presume). So about 5 min down the road my "trac off" light comes on. So I pull into Canadian tire,switch filters and leave. But when I put it into drive it does a huge clunk. Whole car shakes. Also flunks slightly when it shifts gear unless I let off the gas. As we I know have a check engine light. Is it possible that it is related to me driving about 2km with that sensor unplugged and will correct itself? Or is it just coincidence?

I assume coincidence since it seems to be an issue with the transmission. I have not checked fluid levels yet as I am now at work but I will check it on my break.

alero_bmxer · 11-19-2009, 07:56 PM

if you have plugged it back in it will correct its self after about 5 minutes of driving. same happened to me wen i did my WAI. forgot to plug it in

Sennema · 11-19-2009, 08:15 PM

Alright, well gonna try and drive it down the road a bit, and hope for the best. Drove it down the street to my buddy's house (like 1-2 min drive) and then back a couple hours later...but it sorta sounds like it might be a mechanical problem. Driveshaft maybe? FML

alero_bmxer · 11-19-2009, 08:43 PM

MAKE SURE ITS PLUGGED IN. if it still does it disconnect the neg battery cable and let it sit for like 15 minutes before driving it again.

Sennema · 11-19-2009, 09:02 PM

Quote:

Originally Posted by alero_bmxer

MAKE SURE ITS PLUGGED IN. if it still does it disconnect the neg battery cable and let it sit for like 15 minutes before driving it again.

It is definitely plugged in. Went down to the shop down the road... "Trac off" light went off right at the same intersection where it first came on... guy checked the codes (came back idle air control issue), cleared it and it is 100% fine now.

As for the gas mileage, I sprayed some throttle body cleaner into the car, and gonna run some injector cleaner when I fill up my tank and hope for the best I guess.