Poor gas mileage...

[Chkn Sanwch]

So, recently, Ive been averaging about 17-19 mpg in city...any ideas as to why? Shes a 88 Accord LX

In the last 1500 miles, the car has seen--
-Oil Change
-New spark plugs
-New spark plug wires
-New air filter
-New primary and secondary fuel filters
-Cooling system flush and overhaul
-Seafoam motor treatment(through the gas tank)
-Gumout treatment
-Lucas fuel cleaner treatment


Im stumped as what it could be thats giving me poor gas mileage. My guess is an o2 sensor? But wouldnt that give me a check engine light(which isnt on)? She idles nice and fine at around 800 RPM after shes warms up too.

There is also a slight exhaust leak that was welded shut, but just recently has been re-opened...either way, I was still getting poor gas mileage with it welded and repaired shut.

Thanks for any help,
Matt

[Chkn Sanwch]

Also, the tires are fairly new and properly inflated. And no, I dont lead foot it either. =]

And Ive also shot some carb cleaner through her recently as well.

[A18A]

where abouts is the exhaust leak? i'm gonna guess theres a flow restriction in the exhaust somewhere

[Chkn Sanwch]

The exhaust leak is in the the pipe that the muffler is also attached to(not in the muffler mind you, maybe a foot or so before it), and its a hole about the size of roughly a nickel. I want to say the pipe is called the C-pipe, but Im not entirely sure.

[greentee76]

My guesses would be o2 sensor ( which I don't believe will turn on a light on an LX) or the temp sensor for the solenoid controller(read ECM). That sensor is on the rear of the block to the right of the oil filter and is a PITA to get to.

[AC439]

I propose the EGR valve. Then check your distributor's timing and function of the vacuum advance. I have a couple of incidents with bad or stuck EGR valves which had affected mileage.

I have a 2005 caravan bought used and had been getting poor mileage. After about a year owning it, the check engine light came on and the code pointed to the EGR valve. I first took out the EGR valve and cleaned it (but was unable to do much due to the new design that is hard to take apart). I put it back, reset the ECU and the gas mileage went up from 280 to 350 miles per tank. But the check engine light came back a week after and the mileage dropped again. Finally replaced it with a brand new unit and the mileage has been normal.

Then I yanked out the EGR on my 86 LXi and completely cleaned it with throttle body cleaner and also scratched off as much deposit as possible. I made sure the valve moves freely and seated tightly when in closed position. After putting the EGR back, the mileage improved by 10-15%.

My LXi is not at its best fuel economy state because I'm also fixing the dissy which I have a broken vacuum advance. I expect my MPG further improves after I fix the vacuum advance.

Hope this helps.