I cannot figure out why it is running rich and getting poor gas mileage. I know that cylinder 3 is low on compression. We think this is due to a bad fuel injector caused that cylinder to run lean and burnt up some valves. But why would it run rich? I just replaced all fuel injectors and I am still getting bad gas mileage. Around 25-27 if I drive pretty easy. And there is no CEL on. What do I look into next without spending tons of cash? I plan on changing out the valves sometime soon but I fear that is not the only problem.

A faulty Engine Coolant Temperature (ECT) Sensor often causes poor gas mileage, by causing the engine to run rich. Easy to replace.

Hey Greasemonkey,

I replaced that and the thermostat along with some pieces in the distributor like you told me last time. DO you think my ECU could be faulty? And the PCV valve may have fixed my engine dying after a few miles but I am at a loss. What would cause the STFT to be off?

Completely go over the ignition system. Since you replaced the ICM and coil, ensure the distributor cap, rotor, and spark plug wires are in great shape. Also, be sure to only use NGK spark plugs in your Honda.

Your ECM is likely fine.

I replaced cap and rotor and I think we did the coil and ICM. I need to check that out and basically all I have left if the plug wires. What if these are all good? Any other problem solving ideas?

. Check for codes.

. A bad oxygen sensor can radically affect gas mileage, since it controls fuel injector duration.

. Check the timing with a timing light.

NO CEL showing!!

I am pretty sure the upper O2 is fine as I just replaced it but the lower I put a spark plug defouler on to pull it a little further away from the CAT. Since I am sure the CAT is probably shot with all these other problems. Would this be the problem? I hope not because a new CAT and O2 sensor would be more money than I have. I am running out of options it seems and I really do not want to take it to any other mechanics as they have ripped me a new one with this car. And I'd like to not need Honda to diagnose it either... they'd tell me to replace everything including the seats.

A failing catalytic converter would certainly affect gas mileage. How many miles, however, are on the car?

It has about 154000 on it total but I could easily spend another 1000 with all the things it needs. What should I tackle first to help alleviate tons of cost??

From afar, it's pretty hard to say, since the engine is running fine, there are no codes, and many items have been replaced already.

Thanks for the help but I guess I am stuck. I don't know what to do. I guess the CAT could be clogged and I could gut it to see what happens since it is junk anyway.

Maybe the thing to do is just drive it the way it is, until a code is thrown or it becomes apparent where the problem is. Remember, gas mileage drops in the winter anyhow.

Is it accurate to check the resistance of your spark plugs wires to tell if they are bad?

How's your Air Cleaner?
Any Brakes dragging?

Filter looked pretty good but I am trading it out anyway today. Brakes should be fine... I never use them... JK. The gas mileage was down about 10% in the summer and fall. Now it seems it will be 15 - 20% below normal. I do not have access to a OBDII scanner at all times to keep an eye on the STFT which had told me I was running at -17... which is very rich from what I know. But I am no expert

Ohms testing spark plug wires is fine.

DQ2000, yea, brakes are for sissys?
You could jack up the car and see if they all spin freely, can't hurt.
Good Luck

Do you know a basic reading that they should be at? I currently have the NGK plug wires on the car. I am a newbie to the voltmeter. If I put it on the 2000k setting from the dial and I get a 6... is that 12000K or is it the other way around? But the readings were:

#1 - 6 on 2000k
#2 - 6 on 2000k
#3 - 5 on 2000k
#4 - 4 on 2000k

Check the booklet that came with the multimeter, to be sure. I would say your readings are 4,000 ohms to 6,000 ohms, which are very good numbers.

That would have been wise. I thought they'd be able to use a multiplier. The meter instructions say it reads up to 2000k... so I assume those readings are garbage.. right??

Set the dial on 0 to 20K--then, the decimal point should be in the right place and you'll get a little more precise reading.

TXGreaseMonkey

It's been a while but still having the same problems. I did notice some cracks in welds of exhaust header when running seafoam. Would that have anything to do with it running rich? I've heard exhaust leaks can cause those problems.

It may be tricking the oxygen sensor with too much air, which may cause more fuel to be injected and wasted. Those cracks may be the source of your problem. See if you can repair it with J.B. Weld.

TXGREASEMONKEY

I changed out the header as it had some leaks in the welds. I also borrowed a wideband A/F ratio meter. It seems to run at 14-15 during normal driving. Sometimes idling at 15.5-16.2 at lights. IU also noticed as I feathered the throttle on the highway you could see it drop down to 12s and jump back up. Occasionally it would hold in the 12s which seems funny. TPS? And I noticed that trying to push up a hill as I pressed the G pedal the car went into the 12s but didn't do much in the way of performing. I did a small open throttle test at 4500 and 60-65mph... it too was in the 12s. Isn't your car supposed to stay as close to 13-14 as possible. And your computer is meant to try and keep it there. Cylinder 3 is still in need of new valves but I do not want to waste the time and money. Should I replace... will they be OK if the car is running rich?

Thanks for your time

Since you have bad valves on Cylinder 3, those readings are not out of line at all. I look at my 1993 Civic as a toy, which I enjoy playing with. I'm constantly doing things to improve it, even when it "ain't broke." I often tell people if you are not using specialized tools, you probably are not growing enough; therefore, I would tear into the car and repair the valves. You will only be happy when they are fixed, plus you will learn a lot.

So is it that the car is running rich due to the CYL 3 not being able to burn all the fuel being dumped into it? And that is why it has lag and is running rich? Running lean is what burned up the CYL but running rich will only burn up O2 sensors and the main body of the engine shld be OK... is this accurate thinking?

Yes, it's trying to compensate for the excess air. Valves frequently get burned, when they are adjusted too tight (especially exhaust valves).

TXGreasemonkey

Can you tell me the factory fuel pressure reading on the 2000 honda civic AT? We installed a gauge by tapping into the banjo bolt. It reads about 38 on the dial. Is this correct/sufficient?

Usually, it's 40 to 47 psi. 38 psi is probably not a show stopper. Make sure you have changed the fuel filter in the last 4 years or 60,000 miles.

I am sure that it has been changed in that timeframe. Does the gauge reading also tell that your fp reg is in proper condition? What other ideas would you have? I want to make sure it is functioning properly b4 i go changing the valves again. Hopefully for the last time.

FP Reg never cause problems on Hondas. No other ideas. I would focus on doing a great job of repairing and adjusting the valves.

What did you say you have for Compression on all cylinders?