i have a 97 olds bravada and i am getting around 12-13 mpg combined highway and city, and on the highway i go about 65 to try to keep my gasmileage as good as possible, i am real easy on the pedal and try to get good mileage but i am only getttig about 200 miles to a tank maybe, i changed the spark plugs and noticed on 2 of the plugs the threads on the plugs had gas on them not the inside of the combustion chamber but on the threads of the plugs, is there anything i can do to fix this mileage issue, i kno the truck is AWD but i think it still should be getting better mileage, the idle is a little rough, nothing crazy but you can feel it running a little rough, you cant see the tach fluxuate tho. I heard about a leak in the intake or somthing with these motors, somthing with the fuel pressure regulator or fuel lines, i dunno but is there a way i can check the fuel system for fuel leaks? or is there a way i can find out what is causing me to get crappy mileage? thanks for the help - jason

 

It could be a few things such as;winter formulated gas, good 'ol MTBE, having the right oil weight in the engine, tire psi, a bad t stat <----- a cold engine will take longer to warm.

Find out what your fuel PSIw/ the engine off key on accessory, and engine idling. A Haynes or Chiltons manual will provide proper tolerances/specs

 

I would go through a full tuneup. Plugs are only half of the equation, sounds like 2 of your cylinders weren't firing properly which could be a result of worn ignition components (cap/rotor). I'd change out the cap & rotor along with the spark plug wires just to eliminate them from the equation. If that doesn't help, it may be time to install new upstream O2 sensors, but a proper OBD2 diagnosis should be done.

How many miles are on the engine and when was the last time the O2 sensors were changed? If you do want to change the O2 sensors, IMO AC Delco sensors are the only way to go.

Just for a comparison, my old 2000 Bravada would get 15-16MPG around town. The highest I ever got (the only real time it was on the interstate) was 18mpg, but that was completely loaded down with all of my tools (800lbs worth) while I was moving.

 

the car has 124k on it, the plugs looked like they were all worn equaly except for that issue on the 2 plugs with the fuel being on the threads, the car also starts a little hard when cold, it takes about 5 min to fully heat up and the temp gauge sits at about 180-190 , the needle points a little left to the middle of the gauge, how do i check the fuel pressure? do i hook up a gauge to the fuel rail with the port on it? are there 2 sides that can be tested or just one? im a college student just starting school for auto/diesel at UTI so im not rolling in the dough so id like to try and pinpoint the problem, the check engine light came on and flashed so i pulled the codes and it showed a random cyl missfire, o2 sensor, and MAP sensor, after that i cleared the codes and ran seafoam thru the brake booster vac line, after that the engine light never cam back on or the SES light if u will. i was thinking about running more seafoam thru it because it did smoke alot and maybe there is more stuff built up in the engine that can be burned out i dunno. but i heard that the injector leak or some kinda spider line in the fuel system can leak and start making the engine throwing false codes. Are O2 sensors a common thing to go bad on these cars with about 124k miles? and if i replace the 2 how much should the part cost? im just confused i had a jeep cherokee and it got way better mileage than this did, i think i should be able to average about 16 at least espically with the way i have been drving it, i try to make the trans shift before 2500rpm in all gears.

 

i got some maf sensor cleaner so im gona try that, should i remove the screen on the MAF? the 4 torx bolts that are in there, should i take them out or does the screen stay? i was also going to clean the egr and the iac valve. when i went to the auto parts store for the o2 sensor it said on the computer that there were 3 oz sensors 1 precat and 2 post cat, i thought there were four, does anyone kno what the real amt of sensors are in the exhaust?

 

Son of a... Crap.. Well I had a whole long typed up response and lost it all.

Anyway, O2 sensors, you have 4. B1S1 is located on the driver's side of the y-pipe, just below the where the exhaust manifold on the engine connects to the y-pipe. B2S1 is located on the passenger side of the y-pipe between where the exhaust manifold connects to the y-pipe and the 'Y' in the y-pipe. You will then have another sensor directly ahead of the catalytic converter and one directly behind the catalytic converter (B1S2 & B1S3 respectively). B1S1 and B2S1 are referred to as upstream sensors while B1S2 & B1S3 are downstream sensors. Only B1S1 & B2S1 have any impact on fuel mileage. The downstream sensors are for emissions monitoring only. AC Delco sensors will run you ~$75 either from RockAuto.com or if you have an AC Delco retailer near by (check ACDelco.com for a retailer near you).

For the fuel pressure, yes, you will connect a gauge into the fuel pressure test port on the supply line. It is located behind the throttlebody. You need 55-60psi with the key on, engine off. One thing that I think you should also check is the fuel pressure leak down. If you see excessive loss of pressure, you have a leak somewhere in the system.

But I am really thinking this is an ignition related problem. Something is causing incomplete combustion in atleast 2 cylinders (as you noted from the presense of wet plugs). If you can not remember ever changing the wires, cap & rotor, that would be where I would start. Cleaning the MAF sensor, throttlebody, IAC, and EGR valve are all very good preventative maintenance items. Doing those with a general tune up may cure your problems.

On a side note, please try to use the edit feature to edit your post if another member has not yet replied. That is preferred over consecutive posts.

 

ok so i cleaned out the egr valve and the MAF, i didnt have torx bits to take off the IAC but it seems to run a little smoother, i guess now i have to wait and see what kinda gas mileage i get, i have to work today delivering pizza so i should get a good idea of whats going on with my gas mileage, when i turn my car off and it sits for a while and then i start it the gas gauge reads more than when i start driving again it goes down a few notches, i think when i start up the car the position the gauge reads is prally the most accurate reading, i dont think the gauge is very accurate but reguardless of that my mileage is still pretty poor, i guess if this doesnt help then my next step will be cap and rotor then wires i guess, does anyone kno how much cap rotor and wires cost? like i said i dont have money to be throwing around, got alot of bills to pay and school stuff, and if that doesnt help either then ill replace the upstream O2 sensors, once my buddy gets back from vacation ill check the fuel pressure and see if i loose any psi and then ill kno if i have a leak. ill most likely do that before i do anything else to the car. thanks for the help- Jason



well i drove it about 75 miles and i cant say its really any better, im going to have to put on a fuel pressure tester and test for leaks. can one of those be rented or loaned out at autozone or any other parts store? turns out nobody i kno owns one.