holy crappy mpg batman

[Volvit]

I went from 24mpg to 17mpg overnight pretty much.

This adds to my after carb rebuild probs.

So I rebuilt the carb, changed the plugs. Now the crappy mpg comes. Assuming it is the o2 sensor I unplugged it to see if it would help, and the mileage didn't change. Could it still be the sensor? I have a new one that I'm putting in regaurdless, but I wanted to know if I should look for something else that could be doing this. Also first thing in the morning it seems to have a dead miss until it warms up. The preheat hose is missing. Not sure what could cause this. idle adjustment? Sorry for the mass of questions, i'd figure it out on my own but I have more time in front of the computer cause of school. the idle is crap all the time too, easiest way to tweak that? The carb switch is disconnected because I can't figure out where the vaccum line goes and it doesn't seem to do much anyway.

Thanks for your time.

-Clark

[chilort]

I have no suggestions for you since I am unfamiliar with the carb'd versions. I do have sympathy. A local shop kindly unplugged my knock sensor once. The fuel mileage dropped like a rock. It took awhile to figure that one out.

[Volvit]

knock sensor....hmmmmmmmmm

[87dtna]

Carb and TBI's don't have knock sensors.

Probably is the O2 sensor
The ''miss'' is probably because it's chugging fuel being so rich. Any black smoke out the pipe?

[turbokid]

carb adjustment sounds also like a must. Make sure you have NO vacuum leaks. Anything you didn't connect cap off and see if you get an improvment.

[86 Duster]

check for vacuum leaks, but to me it really sounds like the choke isn't working properly. I'd check into the choke first, after I made sure I took care of the vacuum leaks.

[Zed]

Quote:

Originally Posted by 87dtna Carb and TBI's don't have knock sensors. Probably is the O2 sensor The ''miss'' is probably because it's chugging fuel being so rich. Any black smoke out the pipe?

carbed HO's had knock sensors. There are 3 holes on the accelerator pump, did you change the setting? Obviously the rebuild didnt take.

[Volvit]

i dont believe i changed any settings, if i did it was unknowingly. I check my haynes and there is nothing listed about knock sensors, (wish bentley made a manual.) Where is the sensor?

And I'm having trouble understand where and what the accel pump is.

the only vaccum lines uncapped right now are the one off of the carb switch and theres a T on the drivers side of the valve cover that has one part uncapped. No black smoke, but my gf says in the morning it smells bad, so im assuming its the richness.

thanks

[Volvit]

Update:

Replaced the Oxy sensor this past weekend. Also replaced all hoses that were running to/into the canister. I found a switch off sorts with 3 vacuum ports and two wires coming out of it mounted to the firewall on the passenger side. I hooked up what I thought were the correct vac lines. Anyone know what this is exactly and what lines run to it?

Now it starts and runs better when it is cold. BUT IT STILL GETS UNDER 20 MPG!!!!!

Also the air pump is not working, but i think that has to do with emmission more correct?

This leads me to ask where is the knock sensor on this beast (83 omni 2.2 carb no tbi)?

[bris09]

How does it idle was it is warmed up? May need to tweak the carb settings a little.

Just as a note I have an 83 Shelby 15k miles on the engine and I haven't get much over 20mpg since day one.

[Volvit]

idles fine when warm.

I'm still considering its the knock sensor gone bad. or could it be the switch on the passenger side firewall that i posted about earlier?, could I have hooked it up wrong after it wasn't hooked up at all?

[Zed]

Clark, stop looking for knock sensor, immediately. Thanks

[Volvit]

ok(?)

well its been a soggy day here in NEPA. I've noticed on startup after sitting it tends to miss longer until warm (or maybe dried out). Leading me to plug wires eh? But I didn't think bad wires could cause the mpg to suffer so much, wrong?

[bris09]

Wrong indeed. I had a problem a couple of years ago where the car would start bucking at light throttle. I dismissed the wires because they were fairly new. I even replaced the distributer, nothing fixed it. I finally found the problem one night when I popped the hood. There were sparks jumping from the coil wire to the valve cover. Put a new set of wires in and the problem was gone. Wanted to smack myself up along side my head for not looking sooner.

If the wires are bad and allow energy to bleed before the plug you are not getting as good a spark as you should, which could lead to the fuel not burning completely.

[85lebaront2]

Damn, that is pretty crappy fuel economy. Bad plug wires will kill fuel economy, if you drop one or more cylinders under load the rest work harder + you are pumping unburned fuel out the exhaust. My 87 Horizon used to get over 30 with a 5spd and my TII LeBaron gets around 20 in town and 26 or so highway with an automatic. Make sure all your wiring is correct, default on the feedback is full rich. I have the complete, including supplement, 83 manual set if you need specific information as to wiring, vacuum and timing procedure. Oh, my 81 Omni miser with the 1.7L got nearly 40 highway with 4spd.