94 Civic VX - SIL and Lean burn intermittent
 

Hey guys! I have a 94 Honda Civic VX hatch with stock motor and tranny. It's my DD, and the best one I could have ever imagined. I've had it for a little over 3 years and it has always done right by me. It has just over 190k on it.

Now, one of the "small" problems I have with it is that the SIL and Lean burn are intermittent. When it works, I get over 50 mpg (in 50/50 mixed driving). When it doesn't work, I lose several MPG (stays in the low 40s or so).

Now, I'm not a super experienced car guy. I'm more like a weekend warrior type with a little bit of knowledge. With the MAJOR help of a "Honda guy" friend of mine, I've been able to do alot of repairs on it without taking it to a shop. I'm wondering where you guys think I should start in troubleshooting this weird issue.

Plugs/Wires/Cap/Rotor: about 50,000 miles ago
Timing Belt: less than 1000 miles ago
Alt Belt: 5,000 miles ago
PCV valve: around 20,000 miles ago
Intake: usually sprayed every other oil change
O2 Sensor: around 8,000 miles ago
Clutch: about 30,000 miles ago
Tranny: swapped with same model about 15,000 miles ago

There's probably more but I can't think of it right now. THANK YOU in advance for any help you can provide. :)

I just went back and read a thread I posted in a while back. It said spark plugs need to be changed every 15,000 miles. Looks like I'm way overdue for that. Could that be causing the intermittent SIL issues? I'll get on that right away regardless.

Best results are with the NGK V-power spark plugs and yes, every 15,000 miles seems like a good idea.
I use synthetic 0w 30 oil in the transmission and engine.
Something I've wondered about is my mileage and battery age, I know my starting battery is near the end of it's life and my mileage hasn't been nearly what it should be, upper 40's and that the alternator is going to always be working to try to keep the voltage up on a weak battery, thus it will put more of a load on the engine.

I've had intermittent sil problems on both my vx engines but none seem to affect my mileage. Depending what time I leave to go to work or what time I come home it will work or it won't. Seems warmer weather is when it works more often.

When it does work, it doesn't seem to kick on properly until the engine warms up.

My battery is fairly new (about 9 months old).

Lean burn won't start working until the engine warms up. The earliest I've seen it engage is when the temp needle just barely gets over te first line and that's in warmer weather (40+)

I don't have LB on my 98 DX, of course. But people say how you work the throttle affects it too. I would use the search function for other VX/HX lean burn threads (there have been a few) and maybe PM one or two really active members with your car. See what they learned. Good luck. Great car. BTW, when you swapped out your transmission, something I am in the middle of this week, did you have a transmission jack? Or did you have another good method for moving the transmissions around under the car?

LOL...no we did it the dangerous way. We had a regular floor jack, my friend under the car holding the tranny up, and me standing up holding the tranny from above while I loosed the last bolts. :) A bit scary.

There is a 180F and a 192F thermostat that fits the civic engine, if yours is old/wearing out that would explain your problems.
The thermostat from the dealer is a much nicer, heavier part but the part store one works just fine.