Improving gas mileage

Hi I have a 98 GPGT. I relaced the fuel filter and run a fuel system cleaner. Also a friend told me to help Gas Mileage I could replace the chip set?? Which Chip set? And replace the O2 OS sensor?? What and where can I find these parts. And what else can I do?

Hi I have a 98 GPGT. I relaced the fuel filter and run a fuel system cleaner. Also a friend told me to help Gas Mileage I could replace the chip set?? Which Chip set? And replace the O2 OS sensor?? What and where can I find these parts. And what else can I do?

Putting in a re-programmed PCM such as DHP may not give you any better gas mileage. The 02 sensors may help so that is a good route. Front is AC Delco AFS-109, Rear AFS 123. Use AC Delco only and not any Bosch brand.

The AC Delcos show up on EBay periodically or you can get them through the dealer or someone who sells AC Delco parts.

Also the basics like proper tire pressure and tune up - spark plugs and driving conservatively.

Putting in a re-programmed PCM such as DHP may not give you any better gas mileage. The 02 sensors may help so that is a good route. Front is AC Delco AFS-109, Rear AFS 123. Use AC Delco only and not any Bosch brand.

The AC Delcos show up on EBay periodically or you can get them through the dealer or someone who sells AC Delco parts.

Also the basics like proper tire pressure and tune up - spark plugs and driving conservatively.

Hey Bob,

I thought the rear was AFS-141?

Coorect me if I'm wrong, but that is what I just got in the mail and I'm a little concern now :screwy:

Hey Bob,

I thought the rear was AFS-141?

Coorect me if I'm wrong, but that is what I just got in the mail and I'm a little concern now :screwy:

It depends on your year model. 99 and up uses the AFS-141. What year, model and engine?

BTW - I see you have a '99 so you are good to go.

Good to go then.

Thanks again :thumbsup: !!!

Good to go then.

Thanks again :thumbsup: !!!

Whew!!!! You had me worried. :bigthumb:

Also, weather and the fuel blends have some effect. In colder weather your car runs on an open loop until it warms up and then rely more on the emmission control system. That's why people, especially me in Nebraska notice a 2-3 MPG drop from late October until April.

I just filled up and got 22.7MPG - mostly city, rush hour interstate driving. Don't drive it like you stole it either :) Stop and go traffic I have to deal with to and from school are my killers.

Hi I have a 98 GPGT. I relaced the fuel filter and run a fuel system cleaner. Also a friend told me to help Gas Mileage I could replace the chip set?? Which Chip set? And replace the O2 OS sensor?? What and where can I find these parts. And what else can I do?

how many miles on your car?

when i put in my DHP pcm i actually lost gas mileage. it has since gotten better with colder plugs, bigger throttle body and my 3" downpipe

okay i guess ill do the list
replace fuel filter, pcv, air filter, do a tranny pan drop &* filter exchange, run synthetic oil, replace 02 sensor if high miles (www.sparkplugs.com (http://www.sparkplugs.com), get a denso), replace plugs and wires (again if high miles), clean throttle body, tire pressure always up to snuff, get the lead out of your foot (keep rpms under 3k), get rid of the u-bend, ...drawing blank hehe

you guys can add what i missed

when i put in my DHP pcm i actually lost gas mileage. it has since gotten better with colder plugs, bigger throttle body and my 3" downpipe

So are you recommending that he mod with a DHP PCM, take a hit with gas mileage and then go with "colder plugs, bigger throttle body and my 3" downpipe" to get back to where he started? :screwy:

And if you are really serious about mods that actually do something fuel economy is a moot issue. Just my two cents. :2cents:

So are you recommending that he mod with a DHP PCM, take a hit with gas mileage and then go with "colder plugs, bigger throttle body and my 3" downpipe" to get back to where he started? :screwy:

And if you are really serious about mods that actually do something fuel economy is a moot issue. Just my two cents. :2cents:

much to the contrary, i wasnt suggesting he do anything...you had mentioned that with a new pcm you can lose gas mileage..i was merely verifying this! And also giving some insight on what might counter this.. from what ive seen and read some people experience no gas mileage loss whatsoever, while some do. however.. what i should have said..is that i dont think it will improve your gas mileage any.

to the modifying and being concerned about gas mileage..yes very true..but when you're N/A the intake and exhaust mods usually improve gas mileage. the mods ive done have gotten me well above where i started! i was seeing around 23 max on the highway before any mods.. now i see 25.5 consistent doing 80 mph =) i think 2-3 mpg increase is consistent for doing some intake and exhaust mods on a GT. please dont give me the loopey symbol it hurts my feelings lol

much to the contrary, i wasnt suggesting he do anything...you had mentioned that with a new pcm you can lose gas mileage..i was merely verifying this! And also giving some insight on what might counter this.. from what ive seen and read some people experience no gas mileage loss whatsoever, while some do. however.. what i should have said..is that i dont think it will improve your gas mileage any.

to the modifying and being concerned about gas mileage..yes very true..but when you're N/A the intake and exhaust mods usually improve gas mileage. the mods ive done have gotten me well above where i started! i was seeing around 23 max on the highway before any mods.. now i see 25.5 consistent doing 80 mph =) i think 2-3 mpg increase is consistent for doing some intake and exhaust mods on a GT. please dont give me the loopey symbol it hurts my feelings lol

Keeping the issue on track, the original poster appears to be looking for fuel economy. That is why I question the info he received. Based on my experiences with supercharged and normally aspirated Series II 3800 engines which is extensive a re-programmed PCM is definitely not the way to go if you are seeking fuel economy. Everyone that I know gets the opposite effect. Also the biggest complaint I get is no noticeable increase in performance when just a DHP PCM is used compared to the stock PCM. Thats why a lot of GT/SE owners perform other mods such as intake and exhaust.

BTW - If you were only getting 23 mpg on the highway before mods you probably had other issues. Most GT/SE with a 3800 get much better than that at 70 - 80 mph and that is without any mods. My Regals LS (3800 NA) gets 29 mpg at 75 mph. On my GTP fuel economy is moot and I could care less about it.

Here is a nice smiley for you on your mods progression. :bigthumb:

And I forgot to mention DHP specifies premium fuel over regular when using their PCM. So much for saving money.

The kind of gas you get is also important. If it is reformulated fuel (10% ethonol) then you will get worse gas mileage than non-reformulated fuel. Thank the tree huggers for that one.

Reformulated gas is usually around major cities. You have to go outside of the cities to get the good gas.

My 99 GT only gets about 24/25mpg going 80mph, about 26/27mpg if you keep it at 75mph & 28/29mpg 65mph. If you live in a windy state like I do that can make a difference too