Sea foam

would it help increase miles per gallon with a 2000 GTP 106k miles

run it through once in a while it might, But dumping it in every tank, No way. You would be spending more money on a can of sea foam at every fill up than you would on gas.

The only way a fuel additive will help mileage is if you have some deposits and it frees up a partially clogged injector.

Your best bet to get better mileage is to take the lead out of your right shoe, make sure your tires are properly inflated, and keep up your maintenance.

The only way a fuel additive will help mileage is if you have some deposits and it frees up a partially clogged injector.

Your best bet to get better mileage is to take the lead out of your right shoe, make sure your tires are properly inflated, and keep up your maintenance.


i give up....ive posted million times on differnt things ive posted laptop scans of everthing...ive even had my PCM reprogrammed with tons of different programs that worked for other people, ive done tune ups, changed differnt parts. spent hundreds of dollars on sensros...ive tried everything, even on all freeway the other day crusing at 65 mph steady i only got 285 out of my tank...this car is just junk

On my GP I am getting 400 miles on a full tank. Which is almost 28 miles to a gallon, I have around 97K miles on the engine.:biggrin:

98gpking Junk the stuping bosch plugs and wires. This may be part of your problem. The best I can get from mine is 300 miles per tank highway and city combined. I'm sure it would be best at a steady 60mph. Maybe you should get a fuel pressure guage and check out fuel pressure. If its high, you could have a restriction in the return line or a faulty regulator. Another thing that comes to mind is the high speed pump. If the resistor was bypassed, the pump will be in high speed mode all the time, causing higher fuel pressure and the car will run rich. Did you check and see if your car has had the resistor bypassed? How about your O2 sensor? How many miles are on your car? These get "lazy" overtime causing poor fuel milage. Why dont you just have a mechanic hook up a tech 2 to see whats happeinig. One more question, have you check to see if your brakes are dragging? After you drive, get out and feel each wheel to see if one or more are very very warm.

98gpking Junk the stuping bosch plugs and wires. This may be part of your problem. The best I can get from mine is 300 miles per tank highway and city combined. I'm sure it would be best at a steady 60mph. Maybe you should get a fuel pressure guage and check out fuel pressure. If its high, you could have a restriction in the return line or a faulty regulator. Another thing that comes to mind is the high speed pump. If the resistor was bypassed, the pump will be in high speed mode all the time, causing higher fuel pressure and the car will run rich. Did you check and see if your car has had the resistor bypassed? How about your O2 sensor? How many miles are on your car? These get "lazy" overtime causing poor fuel milage. Why dont you just have a mechanic hook up a tech 2 to see whats happeinig. One more question, have you check to see if your brakes are dragging? After you drive, get out and feel each wheel to see if one or more are very very warm.


thanks..to answer all of your questons...the car was 100% stock when i bought it and i know i didnt replace the resistor so i know it wasnt bypassed. i just replaced my front and rear 02 sensors. that was a pretty penny and so not one bit of difference. the brakes are all brand new as of 22 days ago...calipers pads and rotors. nothing changed.

i had my car hooked up to a laptop using the same scanning system ZZP uses. probably about 15 times and nothing came up irregular. i really think the cars just junk lol

There is definitely something not right to be getting 15 mpg at 65 mph highway even in a GTP, especially stock. :grinno: I have more questions than answers but here are some possibilities to look at.

What are you using to determine your fuel economy or how? The DIC or manual calculations?

Have you tested the exhaust system for abnormal backpressure? One possibility for an unexplained mileage loss could be the CAT convertor but not enough to trigger any SES/CEL light or store a DTC code or cause any noticeable driveability probelms. Also, you can run an inexpensive engine vacuum test for an underlying cause and excessive backpressure.

How about tires? What brand? Stock wheel size? What tire inflation pressure and when was the last alignment check?

Next question is why are your running a 180 degree thermostat since you appear to be stock less the CAI? Have you tried a OEM stock 195 degree TS? The object is to get the engine to warm up as soon as possible so the PCM switches into closed loop mode. If it stays in open loop mode too long then mileage will suffer. What brand CAI?

There is definitely something not right to be getting 15 mpg at 65 mph highway even in a GTP, especially stock. :grinno: I have more questions than answers but here are some possibilities to look at.

What are you using to determine your fuel economy or how? The DIC or manual calculations?

Have you tested the exhaust system for abnormal backpressure? One possibility for an unexplained mileage loss could be the CAT convertor but not enough to trigger any SES/CEL light or store a DTC code or cause any noticeable driveability probelms. Also, you can run an inexpensive engine vacuum test for an underlying cause and excessive backpressure.

How about tires? What brand? Stock wheel size? What tire inflation pressure and when was the last alignment check?

Next question is why are your running a 180 degree thermostat since you appear to be stock less the CAI? Have you tried a OEM stock 195 degree TS? The object is to get the engine to warm up as soon as possible so the PCM switches into closed loop mode. If it stays in open loop mode too long then mileage will suffer. What brand CAI?


Bob, thanks ill try my best to answer. when i bought the car it was with 93,000 miles on it. we drove it to St louis about 530 miles one way. i did 301 to a full tank. i did nothing but put on a temporary CAI. the cheap one you buy from ebay with the lil bendy pipe and the cheap filter. i just wanted to hear the whine. i dont have many upgrades

CAI,
180 tstat
ubend and res delete
shift kit
lots of custom tunning to the PCM
reversed dog bone mounts

i noticed i didnt have the TB screen and i heard thats not good. but i also heard not all 3800's came with the screen. i dont know. i would really like to get my MPG back up

also i put 20 bucks worth of mid grade 89 fuel in and it seems to be lasting me quite a bit longer then 93. am i running to rich???

I never run across a '97 and up Grand Prix without the input screen installed in the throttle body. Since you're grasping for straws on the gas mileage best to install it. Why custom tuning to the PCM and what was modified?

thanks..to answer all of your questons...the car was 100% stock when i bought it and i know i didnt replace the resistor so i know it wasnt bypassed. i just replaced my front and rear 02 sensors. that was a pretty penny and so not one bit of difference. the brakes are all brand new as of 22 days ago...calipers pads and rotors. nothing changed.

i had my car hooked up to a laptop using the same scanning system ZZP uses. probably about 15 times and nothing came up irregular. i really think the cars just junk lol

What brand o2 sensors did you install? If you combined your junk Bosch plugs and wires with junk Bosch o2 sensors , there's a big part of your problem.
How many gallons did it take to fill your tank that you got less than 300 miles out of?
Last question, are you running premium (91-93 octane) fuel. or trying to run regular (87-89 octane)?

What brand o2 sensors did you install? If you combined your junk Bosch plugs and wires with junk Bosch o2 sensors , there's a big part of your problem.
How many gallons did it take to fill your tank that you got less than 300 miles out of?
Last question, are you running premium (91-93 octane) fuel. or trying to run regular (87-89 octane)?


i always use 93 octance per owners specs. but this last time i ran in 89 just to see. i did put in the oem sensors. whats so bad about the bosch equiptment i use to only hear good things about them.

also usualy by the time i fill up its to the point wher the display screen will no longer give a miles till empty in numbers it just says low.

So are you saying you are depending solely on the DIC to determine true or actual gas mileage? Also, you have not explained the reason for PCM custom mods which may be a factor.

also usualy by the time i fill up its to the point wher the display screen will no longer give a miles till empty in numbers it just says low.

This still doesn't answer my question.:shakehead How many gallons does it take to fill it up?! The reason I ask is that you could have a bad fuel level sensor causing the low fuel light to come on prematurely, or a bad fuel tank vent that isn't allowing you to get the tank full before the pump kicks off!