Hey Guys and Gals,

Well, I purchased a used 1997 Honda Civic EX (Canadian) 1.6 SOHC non-vtec a couple weeks back to use as a daily driver, and the car has been working great; however I have been experiencing poor gas milage. On the first 3 tanks of gas I was getting approximately 22miles per us gallon (10.8L per 100km). The car has ~120k miles (193,600kms) and I have no idea about the service history of the vehicle. Basically I am going to treat it as if nothing has been done. The car was sitting in a heated garage for a year before I bought it, and it was only taken out around the block once ever couple months to keep the fluids circulating. I immediately changed the engine oil and filter after buying the vehicle. There is a CEL lit up on the dash of the car. I pulled the codes today and here are the results: I am slightly confused about one possible code..when I followed the procedure off the site for diagnosing the CEL (thanks for saving me $22 not having to get the stealership to do it), it immediatly did one short flash and a pause when I turned the key to on. I'm not sure if this is code #1 for defective circuit or unplugged/defective O2 sensor or not. There were 3 other codes: #45 fuel system running lean or rich malfunction in fuel monitoring system, #71 cylinder 1 misfire, and #72 cylinder #2 misfire. So basically that is where I am at.

I plan on changing the spark plugs and wires over the christmas break. Would bad spark plugs/wires cause the cylinder misfires? Should I also be replacing anything to do with the rotor or distributor? I'm no mechanic (I'm a science nerd actually lol), so any explanations or advice would really help!

After I change the plugs/wires etc, will my CEL shut itself off if that fixed the problem, or do I have to reset it by unplugging the battery or something like that?

What is my next step if that doesn't work? Should I replace the O2 sensor, or are there other possibilities of what might cause the system to run rich?

I am also going to do a drain/fill on the tranny fluid because I'm not sure when/if that was done.

I'm not sure if the timing belt was ever replaced. Is that something I should do right away, or would it be ok to wait until spring to do it myself?

I have also read things on the forum about a PCV valve? I have no idea what that is...but is this something I should be looking at?

Any advice you guys have would be great. I plan on using this vehicle to familiarize myself with DIY maintenance, so please assume that I am going to make a few stupid mistakes....and any comments on how to avoid them would be greatly appreciated. Thanks in advance! Cheers.

 

You should replace the timing belt right away. Always do that whenever buying a used Civic with more than 100,000 miles and you don't know for sure how old the belt is. Serious engine damage is likely if the belt breaks while driving.

Check and adjust the spark timing with a timing light. Bad spark timing will kill gas mileage. Check the distributor cap for cracks and worn electrodes, or just replace it along with the plugs and wires.

The first flash when you turn it on is not a real code. Real codes will repeat in sequence until you turn the key off. Whenever you have more than one code: make note of them then reset the ECU by disconnecting the battery, and if the CEL comes back on see which code reoccurred first.

 

Thanks! I got thinking after I posted and you are correct that the first flash didn't repeat...so I guess not a real code. I will unhook the battery and check codes again later to see which code was thrown first. And I will replace the cap and rotor also when I do the plugs and wires, because the kit is only around $30 so what the heck. I will be talking to a buddy who does work on cars with regards to the timing belt. I'm sure he could help me take care of it if I bring a case of beer or two, but I think that might be a bit ambitious for me to try on my own considering my lack of experience. But is a timing gun or light something I should invest in? I'm sure it will be needed for changing the timing belt....but after that do you need to adjust timing occasionally? One other thing I forgot is that I'm getting a bit of valve rattle on the cold startups in the morning. It goes away after a minute of warming up the car. I read that this may be caused by not having the valve clearance adjusted properly. Is the valve clearance adjustment something that can easily be done on my own? Also, I googled the PCV valve and have a vague idea of what it does now. The PCV valves are only $5 ... can you tell if it is clogged by looking at it, or should I just replace it anyway? I'm not sure about the frequency the previous owners changed the oil...so it very well could be clogged.
Thanks again for your help!

 

Hey guys,

Still having an issue with poor fuel mileage. I tuned up the civic over the break, and it is running great, but still only getting 22-24mpg with mostly highway driving. I do live in Canada, and I'm sure that the cold temps and winter tires have something to do with it, but I was still expecting better mileage than that (maybe 30mpg highway?). I have made a few full days of driving in the car, and even with 100% highway driving at 60mph at operating temp the whole time with zero stops and/or warmups, my best tank was 25mpg, and usually I'm getting 23.5mpg highway in clear weather, and 22mpg with a bit of city driving thrown in or snowy roads. I did a tune-up on the car, replaced the cap and rotor, spark plugs, wires, air filter, fuel filter, transmission fluid and of course I have been changing the oil with 5w30 dino oil and a fram oil filter. After the tuneup around Christmas, I reset the CEL by unplugging the battery, and it stayed off for about a month. I ran approximately a dozen tanks of gas with fuel injector cleaner every other tank, and the CEL never came back. Last week I stopped using the injector cleaner, and this morning my CEL came back on with the same code #45: fuel system running lean or rich malfunction in fuel monitoring system. I am on my 3rd tank of fuel without using the injector cleaner. Just wondering what you guys think my next avenue of approach should be? Do you think it is my injectors causing this code and poor gas mileage? If so, what can I do to fix it? Are there other possibilities I should be looking at? Any input would be greatly appreciated. Cheers!

 

Did you ever adjust the spark timing? You should hook up a fuel pressure gauge and make sure the pressure is OK. The vacuum hose on the back of the fuel pressure regulator needs to be hooked up. Take all 4 spark plugs out to inspect and if one looks different from the others, there may be a problem with the fuel injector for that cylinder. It's possible the primary O2 sensor is bad (the one closest to the engine).

 

Thanks for the reply. I haven't gotten around to the timing belt yet, so it very well could be the timing being off. I have a new timing belt and water pump in my trunk as we speak, but I just haven't found the time to do it myself, and can't really afford to spend a couple hundred to have a mechanic do it. But if the timing was off, would it not run poorly? And I will inspect the plugs tonight and see if they look different. They all looked really nasty last time when I changed, but the new ones should show any differences. Is there any way of checking the O2 sensor? It hasn't thrown a code or anything, but is there a way of knowing if it's "lazy"? I'll see if I can round up a fuel pressure guage and check that too. What fuel pressure should I be looking at if all is well?

 

Check the ignition timing with a timing gun. This is different than the mechanical timing determined by the timing belt.

Measure the fuel pressure -- the fuel pressure regulator may be malfunctioning causing high fuel pressure.

Another possibility is a bad O2 sensor that is not throwing a code or an exhaust leak near the primary O2 sensor.

Finally, sometimes a fuel injector gets stuck open.

 

Thanks again for the replies. Please exucse my newbishness with regards to the timing issue

I was doing some more reading and came accross a thread on club civic with similar issues to mine where the car was getting bad fuel mileage and had a hickup. I neglected to mention that my car does have a slight hickup when it is cold (if I drive before letting it warm up). It usually happens at low rpm when the motor is cold where it feels like the car hesitates a bit, and then all of a sudden springs to life. It never does this when the car is at normal operating temperature, only when the engine is cold. Anyway, other posters (including you RonJ) suggested that this could be related to the ignition timing. I will get hold of a timing gun and have that checked out. I grabbed the procedure out of the service manual and it seems really easy to do. I guess that will be my first step and I will take it from there. Thanks again!

 

First replace/inspect/test the plug wires, cap, and rotor prior to checking the ignition timing.

 

Well I have resolved my poor gas mileage issue. It was the ignition timing that was causing the problem. When I checked the timing, it was off by a few degrees, and once it was set properly, my fuel mileage went up significantly. My last tank of fuel before fixing the timing I got 21.7mpg, and then my first tank after fixing the timing I got 29mpg with a mixture of city and highway. Conditions were exactly the same for both tanks, so clearly having the timing retarded by a few degrees made the engine run really inefficiently. I should easily be able to get 30mpg on the highway, and probably better in the summer. Thanks a lot for the help guys! However, I am still experiencing that hesitation when I first drive the car after startup. It seems to only happen while going slow almost like it doesn't want to go into 1st gear. If I keep the rpm around 3k it is fine, but if I am going say 15mph and I take my foot off the gas, the rpm goes down to about 2k, then I hit the gas but nothing happens. I press the gas more and 5 seconds later it springs to life and I get thrown back in the seat lol. I'm going to try this in park today and see if it is at all related to the tranny. If the rpm bogs in park then I can eliminate that possibility. I'm thing it might be the throttle pos sensor? It seems to happen more frequently lately, but only for the first couple minutes after first starting the car. It never happens at operating temp. If any of you guys have any idea please let me know. I already have changed plugs, wires, cap, rotor, air filter, fuel filter, tranny fluid, and set the ignition timing. Thanks in advance for your help! Cheers.