gas milage drop

[cordovaass]

the last time i filled up my gas tank i calculated a 3 mile per gallon drop! i was at 10 now at about 7!.... i didnt do anything to my truck latley... i have a 350 2wd with the tbi.... any help would be nice.

[thecackster]

Have you been driving with a lead foot latly? makes a big difference. or possibly bad gas...try a higher octane. It has been warmer lately as well...if you have A/C that could be sucking the gas as well

[cordovaass]

i think my driving style has stayed the same. and i dont run the a/c and i always used high octane gas

[jveik]

one tank like that is not indicative of a problem, if you have been averaging ten for a long time and it does seven for a few more tanks, then theres most likely a problem.

this may sound stupid but check to make sure the e-brake is not on lol that would be a big problem. maybe some sensor went bad somewhere too i dunno i dont know much about newer trucks, mines a 73 with a holley four barrel lol

[Cadillakin'98]

Fuel filter?????

[cordovaass]

Originally Posted by Cadillakin'98

Fuel filter?????

brand new

[67malibu]

Check for trouble codes in the computer. Just because the check engine light isn't on doesn't mean there are no codes in the ECM. First thing to blame for sudden gas mileage drops: pollution control systems. While certainly not always at fault, that crap is quite often the culprit. A problem here is usually accompanied by a loss of power and/or driveability though. As said before, see if the bad mileage repeats itself first and pay attention to your driving/towing habits.
BTW, a 2x4, 350 getting only 10 mpg? My 1988 350 4x4 with 160K miles gets 14/20 (with exhaust, fuel & electronic upgrades.)

[cordovaass]

Originally Posted by 67malibu

Check for trouble codes in the computer. Just because the check engine light isn't on doesn't mean there are no codes in the ECM. First thing to blame for sudden gas mileage drops: pollution control systems. While certainly not always at fault, that crap is quite often the culprit. A problem here is usually accompanied by a loss of power and/or driveability though. As said before, see if the bad mileage repeats itself first and pay attention to your driving/towing habits.
BTW, a 2x4, 350 getting only 10 mpg? My 1988 350 4x4 with 160K miles gets 14/20 (with exhaust, fuel & electronic upgrades.)

how do i check the ecm???

[67malibu]

Originally Posted by cordovaass

how do i check the ecm???

Sorry, I was away for a week and didn't check the posts. My truck is an '88 so it has OBD I (on board diagnositc 1st generation) which is as easy to check as sticking a wire into the correct two spots in the computer terminal underneath the dash below the steering column. Once the jumper is in place, turning on the ignition starts the diagnostic mode where the check engine light will flash in a two number sequence to give trouble codes. A Haynes manual as well as others will give a complete list of trouble codes as well as what they mean.
Starting in 1996, all vehicles have OBD II (some earlier than that.) My wife's '99 malibu luckily hasn't had a serious screw up yet so I haven't had to deal with any OBD II computers (I don't think you can just put a jumper in them like OBD I) but I know that you can get a code reader for it that plugs into the aforementioned diagnostic socket. In their simplest form they can be had for ~$25. The decent ones run $150 to $250 but the basic one will give the codes and reset the computer. I can't vouch for any of them. Being a 350 with TBI I'm assumming yours is pre-'94 but at least an '87 so the best thing I could recommend is getting a Haynes manual if you don't have one. While there are a few inaccuracies and omissions in them, a Haynes manual has alot of good info including all trouble codes and how to get them. Reseting an OBD I computer is as easy as unhooking your battery for 60 seconds so don't do this in case there is a trouble code lurking in your computer. You can also find a diagram showing which pins to jump and a list of error codes out on the web. (Sorry, I don't remember the site but there are several out there.) I once got a little booklet with the error codes and a key that had two prongs in the right spacing to stick into the port to check OBD I computers at Autozone for free ( I asked) but that was a fair number of years ago.
As for me, only the one truck and car have computers. Everything else I own was built while a single computer still took up an entire room. Things are so much easier to work on without all that crap.