Bandit2000

iTrader: (1)

So my Trans Am with its list of problems has another huge problem. Horrible gas mileage. And I mean like 80 miles to the tank! Yes thats 80 miles to the tank on average. I can drive to school which is about 16 miles there and back 4 times a week and then i have to fill up again. I drive the car normal too. I mean I have no clue what the problem is. And i have been having this problem since I put headers on the car. Im going to try and list everything I can remember that I have done since I got it.

Headers (Don't know the brand, but they are not RACE)
Exhaust
LS6 Cam
Lid
MSD Spark Plug Wires
New Spark Plugs
High Pressure Oil Pump
New Fuel Filter

I cant remember anything else I have done, but theres probably a few more things. Anyway I have read on other posts that after you install headers, there are some who are known to get terrible gas mileage. Does this have to do with the EGR, AIR? I want to do a delete but I don't even know if that will benefit me at all.

I also read something about the check valves not completely closing. But I think we replaced them installing the headers. At least thats what my motor head brother told me.

My SES light has been on for as long as I can remember. I have the PO405 EGR code that wont go away and the PO300 random cylinder misfire code that is coming on. I have about 200,000 misfires in cylinder 8 and about 5,000 in cylinder 7. Could I have not seated the Heads on right. Im probably answering alot of my own questions here, but I just need help. I don't want to race the car, I just want descent gas mileage. Anything about 10 mpg at this point would be almost twice of what I'm getting.

If anybody has any suggestions or where to start please reply soon. Thank you so much in advance.

xX-Z28-Xx

iTrader: (4)

Looks like the WOT times are in the books. Lol.

Bandit2000

iTrader: (1)

No if I go WOT I'd get maybe 2 miles to the gallon. I spend 40 dollars or more per week just driving to school, and no where else. I commute about 15 miles per day for about 4 days. And thats it. By the end of the week I'm on E or about 1/8. Explain that.

And WOT with snow on the ground, Not so smart.

David21

iTrader: (1)

So you do all that to your car and don't get it tuned and expect it to run well?

Unless I missed where you said it's tuned

Pocket

iTrader: (22)

Figure out why its only running on 6 cyls and youll have a start

parks450

iTrader: (17)

im thinking you need a good tune. that would be a good start.

xX-Z28-Xx

iTrader: (4)

Btw, it was a joke. Just FYI.

Bandit2000

iTrader: (1)

ive been trying to figure out why its only running on 6 cylinders. But if i do go WOT, it still does have the power. It gets up to speed pretty quick, but I don't like to do it because its not good for the engine.

And i dont see how a tune will fix my exhaust popping, misfires, and my ses light flashing in my face.

s25hanh

iTrader: (8)

those are probably your two main problems. 1. SES light 2. tune Alot of times somethink w/ ur SES will make ur pcm go crazy and dump alot more fuel then needed

jasonz28camaro

iTrader: (13)

change out the plugs on 7 and 8. If your going threw that much fuel than they not working correctly, it might help if the cylinders get spark and the computer doesnt just dump fuel into them.

rpturbo

iTrader: (47)

You need to work on clearing the SES light, and check your fuel pressure at the rail. Once you have the SES off, work on getting a tune on a dyno with an A/F reading. As much as your wasting in gas and maybe damaging your engine, will pay for your tune in no time.

Ollie8974

Check the spark plug wires to cyl. 7 and 8. When the wires were changed they could have gotten crossed up.

LS6427

iTrader: (2)

Make sure that those two spark plug wires, or any wire for that matter IS NOT touching AT ALL, any of the exhaust piping. You can get misfires at mid rpm's, but they will fire ok at WOT sometimes.

If you are getting misfires from wires touching the pipes, you'll use twice the gas during normal driving.

.

LCW

iTrader: (6)

No chance of this being the problem.. The GM LS engine family has 8 coil packs.. One for each cylinder. I am going to say just go get a good tune..