Hello everybody. This is my first topic I've posted on here so if its in the wrong spot please forgive me. But anyways, I drive an and automatic 98 Honda Civic EX and I've been driving it for about 3 years now and the past year my MPG has been ranging from 22-26 highway and 18-20 city and I was getting around 32-34 highway and around 24-26 city the 2 previous years depending how I drove it. I haven't added any serious mods on it except for an aftermarket exhaust from headers back, a short ram intake, and lowering it 3 inches(?) and when I did all of that it still held close to the MPG but I decided to do a tune up the first time since I owned the car and that's when it got horrible. All I replaced then was the usual, NGK plugs, cap, rotor, fuel filter, air filter, oil filter, 5w30 synthetic oil, and wires and I just redid another tune up and I did the same except I replaced the pcv valve cause it was really gunked up but that hasn't helped anything but make my car idle nicely. The only thing I can think of is my transmission is messing up. Stupid I know but at the same time it makes sense. But I mainly posted this to get some insight on the problem so please only serious answers and yes I know I'm a noob. Thanks in advance to anyone that replies with help. Also if there's anything I forgot to include please ask and I'll reply back. Laters

 

Have you checked your ignition timing recently? How about your valve lash? Valve lash won't help gas mileage, but it's still an important part of a tune up. Proper ignition timing can and will affect gas mileage.

 

How do I do that?

 

Check the FAQs sticky, there are how-tos for both of those procedures. You'll need basic hand tools for both processes, and a set of feeler gauges ($15 tops at your local tools store) for the valve lash adjustment.

 

Alright thanks man.

 

Did you notice any difference in MPG;s after replacing the stock air box with the short intake? +1 on checking the ignition timing and valve lash adjustment.
Also tire wear and improper alignment will effect mileage. When was the last time you had a four wheel alignment?

 

Havent yet. And i didnt notice any difference switching to th short ram. i mainly put it in because it
makes the engine bay look better haha.

 

What else did you do to your car? It might not always be the obvious reasons, maybe your dirtied your map while messing with the intake, could be o2 sensor while you were changing our your exhaust, could also be spark plugs, just a few things to consider checking out.

 

all i did it to it is pretty that i mentioned haha

 

This may sound redundant, but did you gap your spark plugs correctly?
Don't trust that "pre-gapped" crap on the box-check it anyway! I've NEVER had one I haven't had to adjust the gap on, and if it's too small (as in someone dropped the box and mashed the electrode), it won't spark nearly as well, leading to crappy MPG and Hp.
Check them gaps!

 

I always check gaps man haha. .44 according to autozone, napa, chucks, and ngk

 

Also as an update, I checked yesterday the piping and the high flow cat is empty (no ceramics) and if I leave my silencer on I get a little bit better gas mileage.

 

Just adjusted my valves and fixed the timing. Timing was advanced and 3 valves were loose and 2(?) were tight. Noticing a small change and more power but that's really it haha.

 

Any CEL? Was this a sudden drop off of MPG or slowly over the past year?

 

No CEL man. And it seemed some what slow and then just horrible gas mileage :/

 

So recap what you did at the time it got horrible? Was it right after you did something to the car? You check tire pressure too?

 

It was like 3 months after i put in my short ram intake and exhaust system. tire pressure is at the normal to.