88red4cyl Posted February 20, 2008 Report Posted February 20, 2008 This is on the 99 LTZ (3800 Series II). The last two tank of gas I've had have only given me 6 mpg. This is all in town, but the car used to do about 25 in town.. I have already replaced the plugs, wires, and thermostat.. I have no codes being thrown.. I'm getting spark on all the plugs as well... The car runs and idles just fine too... What should be my next thing to check? Thanks! Quote
per0781 Posted February 20, 2008 Report Posted February 20, 2008 how many miles on the car? 02 sensors clean ure MAF, TB seafoam Quote
Guest GrandPrixlover1 Posted February 24, 2008 Report Posted February 24, 2008 Did you check for a leak? Check your fuel lines, gas tank, fuel filler pipe(where you put gas into and it goes into the tank), anything that might be cause for a leak. You could also put down a peice of cardboard under your car(gas tank, and surrounding fuel lines) in the driveway and turn the car on, and maybe put some gas in the tank to check the "filler" pipe for any leaks. If there's a leak you'll see it on the cardboard. Even if you smell a leak you still have to see where it's coming from. Quote
Monkton Posted February 24, 2008 Report Posted February 24, 2008 6mpg? That's like worse than a huge gas guzzling v8 my god lol Check everything suggested and if it's still terrible you may want to check your math lol Quote
Addicted To Boost Posted February 25, 2008 Report Posted February 25, 2008 Haha thats what my SE was getting when I first got it.. I put in 16 gallons and I put 100 miles on that tank before it was all gone.. it had holes in the gastank and fuel lines on the tank.. fixed now Quote
88red4cyl Posted February 25, 2008 Author Report Posted February 25, 2008 6mpg? That's like worse than a huge gas guzzling v8 my god lol Check everything suggested and if it's still terrible you may want to check your math lol lol.. I wish my math was wrong.. So far I've used a quarter tank to go 23 miles since I filled up last.. You can physically watch the needle slowly go down as you drive.. lol Did you check for a leak? Check your fuel lines, gas tank, fuel filler pipe(where you put gas into and it goes into the tank), anything that might be cause for a leak. You could also put down a peice of cardboard under your car(gas tank, and surrounding fuel lines) in the driveway and turn the car on, and maybe put some gas in the tank to check the "filler" pipe for any leaks. If there's a leak you'll see it on the cardboard. Even if you smell a leak you still have to see where it's coming from. If it's a leak, then it's one that is happening when the lines are pressurized since the fuel doesn't go down when the car is parked for a couple days.. It's rainy here today so I can't do it now, but when it dries up I will give that a try... fuel filter? I hadn't thought of that one.. Wouldn't that cause the car to run like crap if it was clogged though..? Quote
Addicted to eaton Posted February 25, 2008 Report Posted February 25, 2008 I changed my fuel filter and air filter and it made a big diffreance. When i did that at 140,000 Quote
88red4cyl Posted February 25, 2008 Author Report Posted February 25, 2008 Air filter was changed with the tune-up a couple hundred miles ago.. Hm.. Just took it for a drive and the exhaust doesn't smell like gas, but it does smell kinda like fireworks (if that makes any sense)...? Quote
Addicted To Boost Posted February 25, 2008 Report Posted February 25, 2008 Air filter was changed with the tune-up a couple hundred miles ago.. Hm.. Just took it for a drive and the exhaust doesn't smell like gas, but it does smell kinda like fireworks (if that makes any sense)...? possible bad/plugged cat Quote
88red4cyl Posted February 26, 2008 Author Report Posted February 26, 2008 Air filter was changed with the tune-up a couple hundred miles ago.. Hm.. Just took it for a drive and the exhaust doesn't smell like gas, but it does smell kinda like fireworks (if that makes any sense)...? possible bad/plugged cat Would that make my mileage suck this bad? Like I said, car runs great otherwise... Quote
1990lumina Posted February 27, 2008 Report Posted February 27, 2008 Check to see if your brakes are dragging. It's possible one of more aren't fully releasing. Quote
Dark Ride Posted February 27, 2008 Report Posted February 27, 2008 I'm going to call a gas leak, any of these other options would cause a loss in performance too Quote
pontiacmaniac94 Posted February 27, 2008 Report Posted February 27, 2008 Air filter was changed with the tune-up a couple hundred miles ago.. Hm.. Just took it for a drive and the exhaust doesn't smell like gas, but it does smell kinda like fireworks (if that makes any sense)...? possible bad/plugged cat Would that make my mileage suck this bad? Like I said, car runs great otherwise... my cat was clogged bad, on my gp, and it was gettin terrible gas mileage, and it also caused my EGR valve to go bad, and all that jazz, started throwing codes.... thought about plugging a scan tool to it and seeing if you are missing something... Quote
88red4cyl Posted February 27, 2008 Author Report Posted February 27, 2008 Check to see if your brakes are dragging. It's possible one of more aren't fully releasing. Hmm... You may be on to something.. I have noticed that sometimes at low speeds (in reverse especially), it sounds like something is rubbing.. I figured that it was ice/slop buildup... Is there a way to check without removing the wheels? Quote
hotrodolds Posted February 27, 2008 Report Posted February 27, 2008 Just get the wheels off the ground, and turn them by hand. The rears should turn easy. The fronts will turn harder by default, thanks to the transmission, but you'll still know. Quote
88red4cyl Posted February 27, 2008 Author Report Posted February 27, 2008 Alright. The rears is where the sound has been coming from, so I will probably just check those. Thanks. Quote
Guest GrandPrixlover1 Posted February 29, 2008 Report Posted February 29, 2008 MY car gets awesome gas mileage. I'm at 228 miles and still haven't used half a tank. And that's even with me layin her down a couple times to. How awesome is that? Lets see my car has a 17.1 gallon gas tank, divide that in half and you get 8.5, so 230 miles/8.5= 27.05 mpg(city and highway mixed). Not bad for a 96 GP. Having any luck finding the cause for your low mileage? What have you found so far? Quote
88red4cyl Posted February 29, 2008 Author Report Posted February 29, 2008 Nothing yet.. The weather has been too crappy here to mess with it (there's snow on the ground, again *sigh*). On Monday I will have access to a spot to have a look at it, so I should know more then.. I figured a gas leak *should* be easy to find since the car will be on concrete, so I think I would be able to find that... The rear brakes I will check too and see if they might be dragging.. I will also have access to a scantool so I will check the reading from the ecm and see if anything seems way out of line.. BTW, does anybody have listing for what readings I should be getting from the ecm while the car is running? Quote
pontiacmaniac94 Posted February 29, 2008 Report Posted February 29, 2008 after hooking up the scan tool, find out what the coolant temp sensor (not what the guage says) but what the computer says. the temp sensor should be reading close to what the gauge says, (190) or so.....with the motor hot....if the computer says it is only running 100 or so (much less) then that will affect the fuel/air ratio, which will be a killer. check mass air flow sensor. should look like a very fine spring, and if there is dirt build up, then clean with carb cleaner. if it is clean, the mass air flow sensor could still be bad, and still work, but still kill you it. i would replace that last, because it is quite a bit of money. have you been adding anti-freeze at all? maybe the intake gasket is bad. hope this helps! keep us updated! Quote
88red4cyl Posted March 1, 2008 Author Report Posted March 1, 2008 after hooking up the scan tool, find out what the coolant temp sensor (not what the guage says) but what the computer says. the temp sensor should be reading close to what the gauge says, (190) or so.....with the motor hot....if the computer says it is only running 100 or so (much less) then that will affect the fuel/air ratio, which will be a killer. check mass air flow sensor. should look like a very fine spring, and if there is dirt build up, then clean with carb cleaner. if it is clean, the mass air flow sensor could still be bad, and still work, but still kill you it. i would replace that last, because it is quite a bit of money. have you been adding anti-freeze at all? maybe the intake gasket is bad. hope this helps! keep us updated! I haven't been adding any antifreeze to it.. Last time a scan tool was hooked up to it (couple weeks ago) the coolant temp sensor was way off.. It was all corroded so it was cleaned, and then it was working right.. I thought that would fix my problem, but it didn't... Could a bad IAC cause these problems? I have noticed that it is idling a bit higher than it used to.. Quote
88red4cyl Posted March 3, 2008 Author Report Posted March 3, 2008 Going to look at the car in a little bit here.. Any suggestions about what else to check for? Quote
88red4cyl Posted March 3, 2008 Author Report Posted March 3, 2008 AAAAAAAAAHHHHHHHHH!!!! I can't find a damn thing wrong with this car!!!! All the sensor readings are fine.. There was a tiny leak on the fuel line coming into the top of the intake, and I do mean tiny.. It barely trickled out, and you had to move it back and forth for it to happen.. No other leaks.. Cat may be getting started on the road to being plugged, but it only smells if you rev on the gas real hard.. I am out of freaking ideas!!!! Quote
Guest GrandPrixlover1 Posted March 4, 2008 Report Posted March 4, 2008 That leak along with the cat could just be your problem. combustion just doesn't run on liquid gas but vapors. You might have a small gas leak but you also might have a big leak of gas vapors. Plus you could also have a bad pcm. 8-) Quote
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