Ok, I'm getting about 11mpg on my new car and it's bone stock except for a flowmaster muffler and the cats removed. It leaks a little oil ( I read on here that's common so I went for it cause it's good for the price I paid), and you can smell where the oil is being burnt when you drive, but usually only after you come to a flat space after going uphill. I thought i had a fuel leak, but when they put it up today at the muffler shop we walked under it and you can't see any leaks. I still smell the gas smell though. I don't think it's from someone putting in a fuel pump the wrong way because I had that on my last car and I know it. Any ideas on what to check cause I'll be sitting at home a lot until I can fix this and I don't have the money to fix everything until it works better.

 

A lot of things can cause it to run rich. Leading problems are exhaust leaks before the O2 sensors and misfires. Both those cause the PCM to add extra fuel the engine doesn't need. May also be faulty O2 sensors, leaking injectors, excessive fuel pressure...... you need to systematically rule out each possible cause.

Have you had it scanned for codes? Any possibility you could run a scan using DataMaster or Freescan? That would show any [possible problems with the long term fuel corrections... typically elevated by one of the problems above.

 

The SES light isn't coming on so I figured having it scanned wouldn't do anything. I don't have a cord to hook up my car to a laptop right now either.

I did have the exhaust fixed because it was leaking yesterday, but that was before I did the mileage check. I have a little red light that comes on when it wants to inside the tach area. I think it is the coolant light, but I checked and the coolant is full and it never goes above the first quarter mark on the temp guage.

 

The warning light near the "6" in the tach area is the low coolant light. That is related to the level switch on the radiator only. Has nothing to do with the computer, how the engine runs, etc. Its just telling you to check the coolant level. Common for the switch to gum up and stop working, turning the light on.

Since you had the exhaust fixed, it may take a bit of driving for the computer to change the long term fuel corrections. Where was the leak in the exhaust system? If it wasn't between the engine and the O2 sensors, it won't affect fuel mileage.

 

All right, here's some more information. The leak was above the rear axle. Anyway, my dad said it might be a bad spark plug because the engine doesn't seem to have an even idle. He said it might be missing and checked the first three plugs going back on the driver side and they were all good and clean, looking pretty new. He didn't want to try on the rest cause he thought he might lose them. You can still smell the fuel, maybe its coming out the exhaust.

I found a loose hose right beside the oil filler on the engine and reconnected it but that didn't help either.

If this was on my old car I could tell if it was missing cause I knew how it felt, but I just got this one so I'm kinda lost. I'm going to try to save up and buy a cable and use one of my friend's laptops to check it.

Any advice after this information?

 

Come on guys, you know this engine better than me.

 

What about the list of possible causes I gave you above? Did you check for leaking injectors (lift the fuel rails, injectors intact and turn the key to on - do not start - to pressurize the fuel system, look for drips)? Did you check the fuel pressure? How old are the O2 sensors? Rough idle may be misfires... that's one of the possible causes of poor fuel mileage.

Other possibilities would include a leaky EGR valve.

What is you driving like.... mostly freeway, mostly city? Are your tires inflated correctly, no dragging brakes? Does it go into O/D and can you feel the converter lock up?

 

Ok, I'm not as mechanically inclined as I would like to be, so I'm probably going to have it tuned up on Friday.

My driving is about 50 percent highway, 10 percent city, and 40 percent WV backroads. The tires aren't bad, and I've got a compressor so I'll fix that later tonight if it's messed up. I'm not sure if it goes into overdrive or not. I'm about retarded with this setup, I'm use to my 3.4L. I knew it pretty well.

 

Ok, I took it to the dealership today and had them hook it up to their computers. They took about an hour and looked everything over. Anyway, it came back with having 0 volts in the MAP sensor. So they told me that was the problem. They said it was either a wire messed up (the mechanic said it's probably not that since he moved the wires around a lot and that should have given it a kick or somethign even for a second) or the sensor was messed up. So it would costs me two hours of electrical work from them (100+ dollars) or I could replace the sensor and see how that goes.

So I went the sensor route. I bought one for 32 dollars at advance and replaced it. The old one had some rubber seal or something around the sensor, but the new one didn't come with one so I just put it in the engine. So the car has a lot better throttle response (it use to go to 2500 rpm before it would really pick up, now it picks up as soon as you touch the gas), but it's still sucking gas. So is there some way I can just check the wires coming to the MAP sensor and check their voltage?

They told me the air temp sensor was in the same situation, but it probably wasn't working because the MAP sensor wasn't working. Any ideas on that?

 

The new sensor didn't have a grommit, do I need to buy one or does it matter?

 

Well noone has thought of this yet so ill say it. You went from a v6 to a v8 and you just got the car so if your getting on it alot expect 11 mpg to be good lol. Theres so many little things that can cause bad fuel mileage. Fuel filter, air filter plugs wires etc try those kind of things first depending on mileage and etc . I know in my daily driver i changed the stock old filter and gained 4 mpg just with a 8 dollar air filter.

 

I had the dealership go all over the car looking for stuff to bring the gas mileage down and they told me it's the MAP sensor. Either its wires are messed up (unlikely by what they say) or it's the sensor.

 

Was the SES light on? If the MAP sensor volts were "0", the SES light should have been on, and it should have set a code.

Again, was the SES light on? A faulty air temp sensor (at least the one in the water pump housing for the PCM) would turn on the SES light and set a code. Saying that the IAT sensor problem was because of the MAP sensor problem makes no sense at all.
You have to use the grommet/seal on the MAP sensor. Otherwise, air can leak in around the nipple on the MAP sensor, and that's basically a vacuum leak.

 

Maybe the bulb is blown or something in my SES light. I'm 100% sure it has never come in since I've owned the car. I guess I'll have to find some way to check that. Doesn't it come on just to let you see it when you start up the car?

Anyway I had to go to the dealership to get the seal for the MAP sensor and even though apparently every GM car from the early to mid 90's used the same seal they don't have it. They had to order it and it won't be in till Tuesday. That costs me just a little under 5 dollars, which is ridiculuous since it should come with the sensor and Advance doesn't even carry it.

I put in the sensor without the seal just to see if it would make a difference and at first the car ran a whole lot better. The throttle responses was insane compared to what it was before. Then I guess the air started to leak so it ran pretty crappy so I put the old one back in for now until I get the seal.

 

If i have a hole in my y-pipe about 6" from the end of the LT headers will that throw off my O2s and give me bad gas mileage?
Also, does the dealership do those checks for free?