Bad Gas Mileage

[sanjay]

My new to me 2001 Grand Am GT seem to be getting very poor gas mileage. Actually there are a few problems but the mileage is the one that concerns me the most at the moment. So let's start from the top.

First I have a few dash warning lights that don't turn on when I start the car, SES, SVS, Trac Off, ABS, Parking Brake.

Second, My ABS and traction control don't work. This actually doesn't bother me at all. I was going to disable them anyway.

Third I have a Ghetto WAI that I installed the day I go the car. It's basically a cone right on the MAF and the MAF is not supported. I was going to make a bracket for it this weekend.

So the day I got the car I filled the tank to the top. I've done 150KM (93 miles) so far and burnt 2/3 of a tank of gas according to the gauge. Now the car get's warmed up for a few mins before I drive it and yeas i did have a little fun with it when i put the cone on but I've been driving it like a sane person for the past 4 days. The mileage has been mostly city. After I'm done this tank I'm going to fill the tank again and put the stock aibox back in and see if that makes a difference.

I also have my buddy who works at GM bringing me a Tech 2 this weekend for some more testing.

Any other ideas??

[Superdave]

I'd change the front o2 out with a GM unit first thing.

I have a cone on my MAF just like that, never had any problems. (2004 GAGT).

[no_doz]

go to autozone & have them scan it-see what all is throwin codes-swap 02 sensors and check the plugs & make sure each is good-gapped properly-and throwing hot spark every time-only things i figure that -could- be --

-plugged exhaust-
-bad o2 sensors/maf or map-
-bad ecm-
-incorrect cam timing (like the chain stretched or skipped)-
-leaking intake or exhaust valves-
-leaking or plugged vac lines-
-bad/plugged injectors-
-coilpacks-
-plugs-
-plug wires-
-whiped cam-
-faulty pushrods-
-faulty rockers/valves/valve springs-

thats pretty well it

are there any strange noises or does it lack power-what year-make-model-trans-etc... is it? how many miles?

[sanjay]

go to autozone & have them scan it-see what all is throwin codes-swap 02 sensors and check the plugs & make sure each is good-gapped properly-and throwing hot spark every time-only things i figure that -could- be --

-plugged exhaust-
-bad o2 sensors/maf or map-
-bad ecm-
-incorrect cam timing (like the chain stretched or skipped)-
-leaking intake or exhaust valves-
-leaking or plugged vac lines-
-bad/plugged injectors-
-coilpacks-
-plugs-
-plug wires-
-whiped cam-
-faulty pushrods-
-faulty rockers/valves/valve springs-

thats pretty well it

are there any strange noises or does it lack power-what year-make-model-trans-etc... is it? how many miles?

Alright..I'm in Canada so no Autozone for me. My buddy just called, says he's bringing the Tech 2 home tonight.

The car was scanned last nigth with a generic scanner and I only had a code for the thermostat openign too early. I changed the thermostat a few days ago and never reset the code. I reset it last night and checked again and ther eare no more codes.

The car is an 01 Grand AM GT Coupe Auto Tranny (They All Were Grrrr!!) with 140 000KMS so 87000 Miles. The car is in quite good shape. There are no wierd noises so I'm staying away form mechanical issues. I don't think it's lacking on power. I just got it so I have no comparison but it pulls pretty damn hard for a stock car. Plugs and wires were changed just before I picked it up. I really don't think it's coilpacks either. Usually I'd get a misfire and I have no misfire codes nor am I feeling any.

This is what I'll be checking over the coming week in this order.
Spark Plug Gap (GM Mechanics are tellign me if the gap is too wide fuel economy goes out the window)
Upstream O2 Sensor
MAF & MAP
Clogged Cat

The Tech 2 is appearently goign to allow me to do a number of tests I can't do with a generic scanner so I should have some news as to what's going on with my car tonight.

[55trucker]

Toronto here.....don't forget it's the middle of winter, and it's been colder up here more than usual, the car isn't going to give you the same mileage as it's capable of in the summer. If you're concerned about the high fuel consumption and if possibly the gauge is inaccurate, try keeping a full 2 gal. gas can in the trunk, next fill up reset the trip odometer, run the car until the tank is empty and note how many kms you've gone. At least then you'll have some sort of an accurate measurement as to how far you can go on a full tank (at this time of year). Returning the OEM intake parts may indeed help. Brrrrr -19c here right now.

[sanjay]

Toronto here.....don't forget it's the middle of winter, and it's been colder up here more than usual, the car isn't going to give you the same mileage as it's capable of in the summer. If you're concerned about the high fuel consumption and if possibly the gauge is inaccurate, try keeping a full 2 gal. gas can in the trunk, next fill up reset the trip odometer, run the car until the tank is empty and note how many kms you've gone. At least then you'll have some sort of an accurate measurement as to how far you can go on a full tank (at this time of year). Returning the OEM intake parts may indeed help. Brrrrr -19c here right now.

Even taking the weather taken into account the car still seems to be burning wayyy to much gas. I filled up last night cause I didn't want an low tank with cold weather. I reset the odometer too. Before I reset it I had 170KM (105 miles) and according to the guage I used just over 3/4 of a tank. After filling straight home and put my stick intake back on. I also checked plug gap which was at 0.060. I drove 30 KM (18 miles) today and the guage went form over full to 1/8th under full. So the cone wasn't the problem. Aciiring to GM infonet (what GM mechanics use) my spark plug gap is fine.

Stepping back and viewing my problems for a min as a whole instead of a bunch of little problems I'm starting to suspect a bad BCM. Today my DRL were going nuts and my radio kept going on and off. I'm thinking now that my mileage is fine and the BCM is sending a faulty signal to my fuel gauge. I need to find a wiring diagram to confirm if this is actually possible but my parts guy thinks it is. I've done the calculations and with Tank size Vs price of gas vs gauge the numbers are off. Not by a huge margin but still a lot. Also when I pulled the spark plugs there wasn't an excess amount of black soot so according to the plugs I'm not running rich. Hopefully I get that tech 2 soon so I can do some more tests.

I still haven't ruled out Bad O2, MAP or MAF...

[55trucker]

Hmmmmm.......let's assume for discussion sake that the gauge is giving you incorrect readings. What is the size of the fuel tank in an '01 Grand Am? (I don't personally know)...get the size (in litres ...for metric sake), next time you fill it up (completely full)...drive until say the gauge reaches 1/2 full.(reeeeely close to 1/2 full on the gauge). Once again top off the tank completely....now note how much you've put back in.....is it truly half a tankful?...or more or less than.

[no_doz]

thats a good point-if you have a 10-12 gallon tank & you drove 18 in town in the winter you very well could have used a gallon depending on how you drive it-that could easily explain why you used an 1/8 a tank. how many gallons/liters/etc... does your tank hold?

[sanjay]

Hmmmmm.......let's assume for discussion sake that the gauge is giving you incorrect readings. What is the size of the fuel tank in an '01 Grand Am? (I don't personally know)...get the size (in litres ...for metric sake), next time you fill it up (completely full)...drive until say the gauge reaches 1/2 full.(reeeeely close to 1/2 full on the gauge). Once again top off the tank completely....now note how much you've put back in.....is it truly half a tankful?...or more or less than.

To do that test accurately you have to do it from full to empty. Due to the shape of most tanks the float level vs volume of fuel used usually doesn't linearly relate (unless it's a rectangular fuel cell).

I see specs for 32MPG City & 21MPG City. Let's assume that due to winter and maybe a bit of rough driving that I'm getting 17MPG (I rarely go on the highway). With a 14.3 gallon tank I should have a range of 243 Miles or 391 KM. I'm seeing 200KM to 3/4 of a tank (according to the guage) which works out to 266Km a full tank. I'm getting 11.6 MPG according to my Trip Odometer and Gas Guage which in Canadian measurement is 20L/100KM. My GTP 3.8 SuperCharged was getting 18.9L/100KM. That's the reasonI got rid of it. I can't believe a 3400 in a car would be sucking that much gas unless my tranny was slipping like crazy. Hell My minivan with a 3.3L V6 and a slipping tranny got me better mileage that I'm seeing.

I have no black smoke ever. I have no buildup on the plugs. I don't smell gas in the exhaust. It never floods. There is no evidence of an abnormally rich condition under any circumstance.

If the engine was burning twice the amount of fuel I'd see it in the exhaust and it would foul the plugs real quick. I'd certainly smell it. That's why I think now that the problem is instrumentation not an actual fuel control issue. I was probably between a third and a half of a tank when my gauge read under a quarter. A quarter tank difference in reading would certainly make it look like I was getting 100Km less in range which is what I'm expecting i lost. But did I really lose it or is it just an illusion caused by a bad BCM?? We'll find out soon!!