I get horrible MPG about 8-10 MPG on road, and 12-15 highway, i've changed the plugs, plug wires, dist cap, rotor, got a new exaust system ( not the cat, from the cat and back ), new IAC valve, new TPS adjusted to .54, new transmission filter and transmission fluid, got the oil and oil filter but haven't changed it just yet previous owner stripped the bolt in the damn pan (gonna be a days work cant figure anyway around than just drop the pan unless u got something else?), new gas cap(got a strong fuel odor, the gas cap got rid of 80% of it, there is still some odor near the backend of the car the cargo area but no fuel leaks!!! wtf... any suggestions?), did a lube job on the entire car grease fittings and all, also i have a broken switch which is on the left upper hand side of the passenger cylinder head i believe it's the fan overdrive switch? think that will affect MPG?, other than that any suggestions? im going to hook Win ALDL up this weekend and see if i can decifer the information...but wondering if anyone had any input?

 

brakes maybe? maybe your brake shoes are up against the drums to much. thats what mine did. then they got locked up and i think the brake cylinder is broken now.

 

lol, sad part is my brakes suck ***, they have good vacuum and my power booster is good i just guess them front pads aint cutting it, not sure why i can't stop on a dime, plus i adjusted my back brakes last week, and also reverse, stopped, reversed, severall times to self adjust them.

 

You've got gas fumes inside the car? in the cargo area? Pull up the carpet in the package tray area and see if someone did a hill-billy fuel pump access door. Also check the fuel tank where the fill neck meets the tank, look for holes in the weld.

 

Bringin this back, cause youre still having problems. I would say that if you can smell gas anywhere around/in your car there is a leak or hole of some kind. I would make sure that your fuel system is leak free...I would check from the gas cap all the way to the injectors.

 

does the exhaust have a strong gas smell? if you just turn the key on only...not start will you smell gas? you may have a rich condition, or maybe a small leak somewhere. small gas leaks can be hard to find sometimes, since gasoline evaporates kind of quickly and theres many possibilities for leaks.

 

so far this is what i've checked, i've took the upper plantium off checked for fuel rail leaks of any sorts, i had a tiny leak in one of my gas lines hooking up to the fuel rail i fixed that it was just the o-ring seal, all my injectors are all leak free, and i also started the car and took looks at all the injectors and placed a screwdriver on the injectors to check for proper working condition there all clicking at the same rate, i changed my fuel cap with a brand new stant gas cap (got rid of any outer gas smell i did have) but as i drive the car get out if i smell right under the left side rear fender you can smell the gas, i've also checked all my fuel lines for leaks and checked the vapor valve under the gas tank, i changed the charcoal canister filter and check the valve on top, and the valve that leads to the canister, there are no vacuum leaks (re-did all the old lines with the lines it calls for), the only problem i found so far are the donut leaks where the exaust manifolds meet the pipes, and the exaust manifold broken bolt i spotted that is leaking some exaust.

and after driving i do NOT smell gas out the tail pipes, just near the rear fender but no leaks..

 

Im not trying to sound like a jerk...but if you have no leaks, where is the smell coming from? Sounds to me like there might be a leak in a place you cant see, like on top of the fuel tank near the fuel pump, or on the filler nozzel.

 

there is 0 leaks, could be a vapor leak! not a gas leak, but vapor leaks are pretty impossible to find don't ya think, and would a vapor leak cause horrible gas milage? eh?

 

91-92 camaros had a recall...the fuel filler neck was cracking or developing holes where its soldered. you may have a similar problem, but i dont know if gm would cover it like they did for the camaro

 

Well first of all, I never said anything about gas(the fluid) leaking out of the car. And yes I do believe that a hole, that would let the fumes escape the system, would make it seem like you have bad MPG. Gas(fliud) evaporates to fumes pretty quickly. So if there is a leak somewhere you could be losing your fuel, in fluid or fume form.
But I havent seen your car, and if you say there is no leak than there is no leak. Just trying to throw out ideas.

But you should never be able to smell gas outside/inside your car.

 

I'll second that, smelling gas at any time in an EFI car is a bad sign. It's leaking somewhere you just haven't found it yet. Pull the carpet up in the back and make sure someone didn't mount an amplifier with some nice 4" long sheet metal screws. The gas tank is right under the sheet metal in the package tray, where people like to mount stereo equipment. Keep your eyes open for a potential hillbilly fuel pump access door too, since if it's been done the hillbilly in question probably hacked and spliced the fuel lines on top of the tank back together. You'll never seen them leaking from under the car.

 

for the sake of it, im going to replace all the rubber fuel lines near the gas tank, and i know it's bad to smell gas inside/outside of the car, see at first it was a strong smell on the whole left side of the car, but now it's not that strong and is more under the rear left fender since i changed the gas cap.

im going to check the charcoal canister again as we'll, is the big black spaceship looking thing hook on the left fender near the battery have something to do with vacuum? it's not a cruise control thing but im not sure what it is newho.

 

i removed the ventilator valve under the gas tank, is it not suppose to be blowable with my mouth? or is it a certain psi?

 

I had that same problem with my 88 firebird. I never found any leaks or holes in the lines or tank. I did however notice that the ring seal for the fuel pump on top of the tank was dry rotted and needed replaced. Another problem that I noticed that caused the smell was the gas cap not fitting in the filler neck like it should. It was almost like the threads were off just enough to allow the fumes and vapor to escape from around the gas cap and the cap itself not actually be bad or damaged in anyway. Hopefully this has been helpful.

 

Does your fuel gauge wave with impunity, and will say 4 Galons at a stop, and then get up to ~8 when driving, and then go down to "zero" when goign to a stop? Mine gets MORE FULL when its in motion, then settles down at a stop. I havea carb'd car, though.

As to bad gas mileage, what grade of Oil? 10W-40? I used to put that in EVERY CAR I HAD.. now im realizing new 5W-30 is different than it used to be, oil has changed, its all you need except in some cars!!!

I also have to agree my bad MPG (i dont even know howe much i do or dont get, it depends on what the gauge reads, which changes..) .. may be due to Brakes. i head a squeal/squeak while the car is driving.. but wow, what good performance

Also the V6 doesnt get that good MPG anyway, particularly carb'd.. what is the best one can hope for?

My car:

- New Oil (5W-30) and Filter, a nice slippery oil too (there are small differences, i have researched.)
- New Air Filter
- New Water Pump
- New Fuel Pump
- New Spark Plugs and Spark Plug Wires.. took two out the other day, they looked fine
- Seafoam treatment, twice
- I -CANT- find my -TINY- Fuel Filter, nor do i know how to change it...
.. - Air pipe and CHeck Valve blocked off, thinking of putting new both of those back on, or leaving it, idk. Thoughts?

And i cant say what my MPG is, as i dont exactly know. What is the best way to check it?

Hope this helps - 84.

 

Yeah my gauge fluxuates alot when driving and stopping. That mostly has to do with the placement of the pump and sending unit. The pump and sending unit are located in the very back of the tank, which is weird considering the fact that the lines and relays go in through the top center of the tank. Oh FYI if you didnt already know about it, because I didnt know it, but the vacuum selonoid that controls the EGR valve also controls the fuel gauge. If thats bad, it may also cause the gauge to flux.

 

EUREKA!! I did some nice "blocking off" of that with some Permatex Ultra Copper. Its on top of the air tube on the passenger side of the 2.8, right? I have been tempted to replace my "Blocked off" (plugged with dimes and RTV to avoid a vacuum leak) part i mentioned with a new, as-intended functioning part. I didnt know that!!!

.. That IS the EGR on the carb'd 84 2.8, yes?

And im surprised nobody has asked.. what is the gas mileage SUPPOSED to be? On the carb'd 2.8, and FI engines? If the only way i can figure out my actual mileage is with a calculator and pen to write down mileage, so be it......

 

Yeah thats the one. The EGR valve is located on the passenger side of the block on top of the exhaust manifold. There is a vacuum line that runs from it back into a splitter line that comes off of the intake manifold. The selonoid is the base for the splitter. The selonoid and exhaust manifold both work in conjunction to operate the EGR valve. If the EGR valve is good and the selonoid is not, your valve will either be stuck open or closed causing a major loss in MPG and visa-versa, selonoid bad and EGR valve good, valve will either be stuck open or closed. Carb'd or FI the EGR valve should be in the same place on the 2.8. As far as mileage itsself goes, they should be around the same, 20 in city, 24 to 26 highway, and about 22 to 23 mixed. Hope this helped.

 

Haha, no... EGR parts have NOTHING to do with the fuel gauge (can prove this with the FSM AND wiring diagrams). Problem is the shape of the tank. If you've never seen it, it's rectangular at the top and a triangle at the bottom, where the fuel sender is. Driving causes the fuel to shift to the back of the tank, and stopping forces it to become level again, which is why the gauge drops. It will also sink like a rock on cornering due to the shape of the tank in the center that forms over the rear differential.

Again, 84Camaro, the fuel filter is in the carb's fuel inlet line connection (pretty sure on this)... All you have to do is follow the line coming to the carb from the fuel pump and it will be in a large extended fitting... And fix that carb base gasket or whatever it is that's causing your vacuum leak (which makes your mileage and money disappear down the toilet).

 

That is true. Te EGR valve and parts have nothing to do with the gauge. They only control the fuel itself. But, if you disconnect the vacuum selonoid, your gauge will stop working. I know this because thats what happened to mine when the selonoid went bad. Now Im not sure if the gauge is on a relay connected to the selonoid or not, but once I replaced it, the gauge started working. Is there anyway you can find out?

 

Wrong, Ace. My car had a bad EGR solenoid for a year or so, and it was disconnected for a while anyways, and I haven't had any problems with the fuel gauge except for wiring problems under the dash (that started well after the EGR solenoid was replaced and code 32 disappeared and I have the dirty tube gaskets and IAC to prove my EGR works just fine).

 

Thanks, guys. i changed my Thermostat gasket out today (?) just to celebrate the half-hour drive myc ar will now have daily on the highway.. and for nothing else to do. (I also suspected a super-small leak, allowing the coolant to boil slightly. Not fully, just slightly.. but still.) I also still hear the air/whistle sound, but i can NOT pin-point it. Seems to be by the front of the engine, idk.

btw.. may i inquire what STOCK Fuel Economy was supposed to be ? 2.8, 3.1, carb'd, FId.. what were the numbers? This will help me judge if i have a problem.

 

Thanks maverick, I don't know why it started working on mine when I replaced it. As long as it's working I'm good.

 

i would just replace that vent under the left rear arch.
does your gas cap 'vent' when you undo it ? it should do, if it dosnt there is def a vapour leak.