rough idle,no acceleration,bad mileage,misfire

The title pretty much says it all. The vehicle is a 96 jimmy 4x4, AT, 4.3V6 with about 113k miles. Bad gas milleage has been an ongoing issue since I owned it ( 3 years ), everything else has been in the past 4-5 months. It used to get around 200 miles to a tank of gas with daily use around town, but I just drove it to Georgia and got 160+ on a half tank, has always been much better on highway. It now barely breaks 140 miles on a tank of gas. There is a strong fuel smell in the cabin whenever I fill up the gas tank that goes away a couple hours later. The truck misfires intermitently according to the trouble code that was thrown, but it has only done it twice. I changed the cap, rotor, plugs, wires, and coil; the problems have improved slightly but still remain. The fuel pump and filter were replaced less than a year prior to the begining of this. I stand on the gas pedal and it chugs and stutters for about 5-10 seconds before going anywhere. Thinking it was plugged up, I had the catalytic converter checked by a reputable exhaust shop, but it is fine. The problem gets worse the longer it runs, it is decent at first in the morning. At the end of the day you can sometimes smell the unburned fuel ( I assume, it does miss extremely bad at the end of the day ). I have also cleaned the mass air flow sensor, the egr valve, and the throtle body; all had no effect.:banghead: Sorry for the long-winded post, just trying to give as much info I can think of. Someone please give me a direction to go in. Thank you for any/all advice in advance.

Air filter changed lately?

When you gas up, don't top off the tank. That's what's causing you to get the smell of gas on a fill up.

When checking gas mileage you need to keep track of the miles traveled and the amount of gas required. The speed you drive will also affect mileage, as does city driving. Driving 65 Vs 75 will make a big difference in mileage.

Actually, 160+ mile on 1/2 tank gas is about 18 MPG, which is about all one can expect on these critters at interstate speed of 75-80 MPH, especially if running the air conditioning, or driving against a head wind. You can only expect about 10 MPG around town and short trips. If you let the engine warm up in cold weather you can expect less than 10 MPG. 160 mile on a tank is about 10 MPG, which again is about the norm for city driving.

Yes, I have changed the air filter. Cleaned the pcv valve, too. Last week, also I took it to a mechanic to put it on a code scanner. All the sensors were functioning properly according to him, and air/fuel ratio was dead on. Was thinking o2 sensors were on the way out, but I guess not. Forgot those couple of things. I posted the changes in the fuel economy in relation to driving style in case it might help diagnose the problem.

Check the fuel pressure and especially check for leakdown. Leakdown may be causing your fuel odor and would also contribute to poor fuel mileage.

One thing to keep in mind with O2 sensors is that the PCM can only adjust fuel mixture as fast as the O2 sensors can react to a change. The parameters for O2 sensor reaction time is actually quite long before setting a code. O2 sensor reaction time begins to slow down as soon as the sensor is installed. Reaction time has slowed sufficiently to warrant replacement at 100,000 miles, depending on each individual sensors reaction time, maybe sooner. A scan tool that is capable of measuring reaction time is necessary to check them.

Wher would I go to get the o2 sensors checked like that? Is it a dealership thing? The fuel pressure test would be done with a test gauge hooked to the fuel rail, right? If its does leak down pressure, is there an acceptable amount? What do I look at first if it does leak? Thanks.

You'll have to ask around at the shops in your area and find one that has a scan tool capable of checking O2 sensor reaction time, or, like you said, the dealer.

The fuel pump circuits are designed to energize the fuel pump continuously any time the key is in the START position. When the key is in the RUN position the fuel pump will operate provided the engine is running. If the engine stalls, or is not running for any reason, the ECM will shut off the fuel pump after approximately 2 to 3 seconds.

Fuel pressure test:
Install fuel pressure gauge to the test port near the distributor. Turn the key to the RUN position, (do not start the engine). While the fuel pump is running, fuel pressure must be 60-66psi. After approximately 2 to 3 seconds, the fuel pump will shut off. Fuel pressure must remain between 55-60psi for several minutes. A drop in pressure below 55psi indicates a leak. Most likely the fuel pressure regulator or the lines under the upper intake manifold are leaking.

Most auto parts stores have the fuel pressure tester and usually they run anywhere from $15 up.

As far as the fuel system, have the poppet-valves been cleaned recently?

I have not had the poppet valves cleaned professionally, I was reading elsewhere that the poppet valves are problematic and this could be a symptom of dirty poppet valves. I tried a couple bottles of fuel injector cleaner over the course of a week or two, and it seemed to help as far as when it finally does go when you hit the gas it is much smoother and feels stronger. It's the misfires, poor fuel economy around town, and the bad hesitation and sputtering thats got me frustrated. From what I have read, the dealership is the best option for the injector cleaning, right? They have the actual macine that blows all the garbage out of the lines and poppets. Any idea what that service runs, I have read about swaping over to the newer style injectors, the parts run about $300-$400 depending where I get them. I really don't want to spend half the cost of the new parts servicing the old ones that are just going to crap up again, I am on a really tight budget. Thanks for all the great suggestions and help so far.

Just an update, sorry abot the long time since posting. I took it to the local dealership to ask about the poppet cleanning and o2 sensor test suggested here. The technician took a look and told me that the sparkplugs were the wrong typeand needed to be changed to platinum ones. I went home and did that and it worked, all issues I had have been resolved. The parts store didn't mention that the platinum plugs were O.E. on the truck, I had no idea either. Just posting so that if anyone else has a similar problem, they migh try it.