Well i never lost interest in the thread I'm just a busy Dad with 9 kids.
If someone knows how I can get closer to 40 mpg on my 1999 Honda Civic EX with SOHC I am all ears.
Currently the stuff I've done to the Civic is:
1) New NGK V plugs gapped to 0.033". (I've heard smaller gap is better)
2) New NGK plug wires
3) New manual transmission gear fluid (synthetic)
4) Tires have 80% tread.
5) Fuel filter about 10,000 miles old.
6) New battery
7) Extra ground wires
8) Tires inflated to 44 psig
I haven't aired the tires up to maximum wall pressure on the 2001 Honda Accord EX so I will be interested to see how much mpg I can squeeze out. Also the tires on the Honda Accord are down to 4/32 tread depth.
I don't mind my son driving either one because he is very responsible and keeps the car immaculate. Also he earned a full ride at Univ. of Arkansas and is majoring in Electrical Engineering and currently carries a 4.0 GPA.
80% of your fuel economy gains will come from doing just that. My SE-R got its 26 mpg EPA highway estimate at 72 mph on 400 mile trips to my parents' home. When I slowed down to 62 mph, I got 33-34 mpg. When I slowed down to 55 mph, I got 38 mpg. 38 mpg in that car is 173% of its 22 mpg EPA combined estimate, and 146% of its EPA highway estimate. If I drove that car at a steady 35 mph, I got roughly 50 mpg. And the same logic applies to any other car.
The two things that make the biggest difference for me are (1) slowing down to 60 mph; and )2) drafting. Since most Hondas with manual trannys have short gearing, their mpg gets exponentially worse as highway speed increases. Going by my Scangauge, I see the mpg in my Si pick up from 28-29 mpg at a steady 70 mph to 35 or so at a steady 55 mph. Also, the Si goes from 28-29 mpg at 70 mpg to 33-38 when drafting, depending on the vehicle in front.
For the manual transmission fluid, use only Honda MTF unless your transmission is "going out" and you refuse to repair it.. If you hear a "grinding noise" coming from the transmission, especially when under load, your input shaft bearing is going out and you need to replace it asap before you destroy your transmission AND engine! (Specifically crankshaft). There is a TSB issued for the civic manual transmissions and the repair is to replace the failed/worn bearings. Just thought I should put this out there..
As for your fuel economy, the #1 thing I would do which is the cheapest as well is to replace the PCV valve and possibly any worn or old vacuum lines, especially the vacuum line running from the PCV valve. When you replace the PCV valve, be sure to replace the grommet as well. If you can get someone or yourself to do this, the next thing you should adjust is the valve lash. A clogged PCV valve could lead to ring failure and therefore burning oil and or no compression and improper valve lash could lead to burnt valves. I know at least one member gained some fuel economy by adjusting the valve lash back to spec and it's universally agreed upon that it results in a quieter engine. I know you said you added new grounds, but if you can, try checking all the existing grounds and clean them if you can. You can also test the ignition coil as per the service manual to see if it's weak or starting to fail.
General maintenance items really.. You probably don't have a bouncing idle but nonetheless I suggest cleaning the throttle body and IACV as I found that cleaning it makes the car easier to drive if your IACV is starting to stick. One test for a partially sticking IACV with a fully warmed up engine is to lightly actuate the accelerator. If you find that the idle "jumps" from idle all the way to something like 1500rpm, then you've already got a sticking IACV. Another way to see if your IACV is sticking is if you have issues maintaining speed on the highway. (Car likes to either accelerate or decelerate) I suggest the cleaning of the throttlebody and IACV because these get dirty and typically start to stick so if they don't stick now, they will in the future and I figure you mind as well do it now while you're in there.
Keeping a fuel log and posting it on here would be immensely helpful for not only you but all of us who are tracking your progress.