37ish MPG/Civic VX
 

Recently, I'd found a thread that was written by jlk16188, where he was only getting around 41mpg on his Civic VX:

I'm finding myself in a similar spot as you were, whereas I've been averaging around 37mpg on my 94 Civic Vx, with over 233,000 miles on the engine. My goal is to also achieve the ever coveted 50mpg.

So far, I have done the following:

-Installed & indexed new OEM NKG spark plugs.
-Installed a new OEM wire set from Majestic Honda.
-Installed a new OEM fuel filter/Majestic Honda.
-installed a new OEM cap & rotor/Majestic Honda
-Installed a new air filter.
-Cleaned out the idle control valve (i.e. but the hunting idle came back after a week)
-Cleaned out the throttle body.
-Did an oil change with Amsoil 5w30 with Amsoil filter.

Soon enough, I plan on installing a new PCV valve & a new exhaust in addition the the new 5-wire OEM O2 sensor.

In addition to all of this I've also considered:

-Replacing the fuel injectors.
-Replacing the screen on the fuel pump.
-Adjusting the timing.

Is there anything that I should add?

Clean the egr valve and passageways.

regards
Mech

Is it lean burning, and if so, how wide is the lean burn "window"?

Hunting idle is electrical load (general or a short triggering the ELD), or a vacuum leak. The later will kill the lean burn window.

That's another issue. I really don't if or when it's in lean burn mode. In fact, I don't know how to recognize that mode. What I can tell you is that when traveling at 65mph, the needle on the tachometer hovers around 2000 rpm.

You'd need a wideband to know for sure. Since you can't tell, assume its not going into it. That mpg is about right or that. Start easy, check the clutch and brake pedal stops, and vacuum leaks (unlit propane, or incense/cigarette). Report back, and we'll go from there.

I will do that once I replace the exhaust. As I understand it, a bad exhaust can ruin a good 5 wire O2 sensor. To that end, do I need to buy an OEM muffler, or can I simply use an aftermarket equivalent?

The lack of heat kills the O2 (its heated, so it overworks that system). A good restrictive exhaust should prevent this.

The cost of the oem is not that much more. It will last, fits right, and works right. You might get lucky with craigslist or a dismantler. If not, order from majestic honda.

Fyi, a vacuum leak would cause both problems.

Hmm, maybe I should replace the vacuum lines. I had considered that; but I'm not sure how many I should replace.

Rather than just shotgun troubleshoot, consider using propane or carb cleaner and check for leaks around the vacuum connections. With the car running, spray it in suspect areas and listen for a change in idle to find a leak.

What's your driving like? Under 40 mpg in a VX indicates a serious problem if you stay under 70 mph. Sounds like a vacuum leak to me.

My driving is approximately 90% of in town driving with the occasional run on the expressway. I shift at around 1500rpm, and coast whenever I can. In spite of all the low mpg, I'm happy to say that I'm not getting a check engine light, oil leaks or trouble with the cooling system. I think I will follow up with that advice.