2005 grand am 3.4 very poor fuel mileage

Chevy,

What's goin on man how are you? In terms of usin excessive fuel and gettin poor fuel economy your trim numbers could mean a few different things. Gotta know the following guy.

Were any O2 sensors ever replaced and were universal O2 sensors installed instead of OE Sensors?

Was the catalytic converter ever replaced and was a universal converter installed instead of an OE converter?

Have you made sure there are any vacuum leaks?

Have you made sure there isn't a partial (or small) obstruction in the exhaust system? Most common form of an obstruction would be a problem with the catalytic converter.

Trim numbers like yours are most likely gonna set error codes. If there are codes we gotta see them, so post them.

This more, but I don't wanna hit you with everything all at once. Just answer the above for now.

ok. As far as I know o2 sensors and converter have never been changed. I bought the car shortly after it was off warranty, so if they were changed on waranty then I was assume it would be OE parts. There are no vacuum leaks that I can find, and would a vacuum leak also cause rough idle? How would I determine if the exhaust is obstructed? It hasnt set any codes which is strange because the trim numbers are all over the place.

Chevy,

You gotta be 100% sure about the O2 sensors and catalytic converter. If necessary contact the previous owner, or if the car was bought from a dealer check back with the dealer. Yes a vacuum leak can cause a rough idle. You said there are no vacuum leaks, well how are you checking for them? The most accurate way is with an engine vacuum pressure tester. I have 65 tool Snap-On tool boxes, and several million dollars worth of tools. The tool I use the most is an "Engine Vacuum Pressure Tester". It doesn't matter what engine problem you're tryin to fix. If you take the time to become proficient with this tool you can fix any engine problem. Yes you can even check for the mentioned exhaust obstruction/excessive back-pressure problems you could be having with an engine vacuum pressure tester. Here's a link that will help you learn how to use this valuable tool.

http://www.secondchancegarage.com/public/186.cfm

Have the items below been replaced recently?

Spark plugs (Must be A/C Delco)
Ignition cables (Must be A/C Delco)
Air filter
Fuel filter
PCV valve

Plugs tell the story of what's goin on inside an engine. With that being said are there signs that the engine is running rich? Best way to tell a rich issue is to pull the plugs and check the electrode burn for dry black soot (carbon in other words).

Make sure the EGR valve is functioning normally, and the related EGR passageways are clear and free of carbon.

look for a vacuum leak on that side of intake, ect...

it is a leak at the EGR valve as far as I can tell.

Chevy,

A leak at the EGR would do it. Confirm, check everything else out, and get back to us.

Replaced the egr gasket. It didnt totally fix the problem. No more leak there, but fuel trim number for that side went down from 93% to 62% now, but it still stays there. I cant seem to find another leak, although there could be another leak somewhere, or maybe another problem?

Chevy,

Well atleast that's an improvement.

What method are you using to check for vacuum leaks?

Are you still looking at LTFT? If so, have you cleared the computer? It can take a while for LTFT to come around.

What are your STFT readings?

Big Block,

Obviously you remember Chevy but do you recall telling him he needed to pay for a round of drinks when he got his last lean missfire problem fixed by replacing an injector? Just curious. Did I miss drink night? YOU HEAR ME CHEVY? :-)

Chevy,

(You said) but fuel trim number for that side went down from 93% to 62% now, but it still stays there. I cant seem to find another leak.

Your above statement speaks for itself man. You're missin the vacuum leak because you're not lookin for it correctly. It's like I told you buddy.

TAKE SOME TIME TO LEARN HOW TO USE AN ENGINE VACUUM PRESSURE GAUGE

That side?

Chevy, your reference to "that side" means the "Intake Manifold" is leakin on "That Side".

Drive,

Chevy never got back to me about drink night. I'm still open if he is. If it happens I'm bringin Pete and ASE to help in the destruction of the bar :-).

I dont know if drink night is possible, where are you guys from?

Chevy,

(You said) I dont know if drink night is possible, where are you guys from?

DRIVABILITY lives in a sewer system somewhere on planet earth.

OLD PETE is homeless and lives out of a cardboard refrigerator box under the Throgs Neck bridge in Queens New York.

ASE MASTER also lives in Queens New York but he is not homeless. He's gotta be kept in a cage and can only be let out at the start of happy hour and quickly returned to his cage at the end of happy hour. Problem for ASE is that (for him) happy hour starts everyday at 5:00 AM and doesn't end till the next day at 5:00 AM.

That leaves me. I'm the only normal one :-). I live on the "Old Side" of Howard Beach Queens New York with all the gumba's. You just gotta love them for all their contributions :-) :-).

Still think that drink night is not possible? If you do then you don't know too many MARINES.

You set it up.
Just let us know when and where?

Guarantee you that me, ASE, and at least a hundred more MARINES will show. Can't guarantee Drivability and Pete. Those guy's aren't MARINES :-(.

well, thats a long way to go, i'm up in brandon, manitoba Canada, so thats a bit of a drive. Sorry guys!

Chevy,

(You said) well, thats a long way to go, i'm up in brandon, manitoba Canada,

Sorry you missed it the first time guy, so here it is again for your convenience.

You REALLY don't know too many MARINES do you?

Just set it up.
Let us know when and where?

Guarantee you that me, ASE, and at least a hundred more MARINES will show. Can't guarantee Drivability and Pete. Those guy's aren't MARINES :-(

I'll be there but as long as my wife gives me note saying I'm allowed to out at night. Then there's the problem of what time I'll be getting back home and in how many pieces?