Dear Members

i hope you are well, i would like to seek your opinion and suggestions upon the following matter:

I have 1999 Honda Civic A/T with D16Y5 1.6L engine.

since beginning i have been facing with the problem of poor fuel economy and did following in this regard but no use:

1. Changed spark plugs
2. Complete engine tuning incl. throttle body service
3. Oil change (LM 10W40 MoS2)
4. LM Ceratec
5. Replaced Fuel injectors
6. Wiring check

currently it is giving around 6~7 KM/L in city and around 10~11 KM/L on highways

Please help and guide me in this regards what can be done to improve the fuel economy, is there anything that i am missing

 

That does seem low. For those of us in the US, that's about 16.5mpg city/ 23.5 mpg highways in freedom units. What did the "complete engine tuning" entail? Did you change the distributor cap and rotor as well as spark plug wires and fuel filter?

 

Post the CEL codes.

 

After pulling CEL codes, you forgot to change your fuel filter. That is part of a tune up and can have a serious impact on fuel economy as I learned with my wife's car.

Her mpg was down in the 24 MPG range, changed the filter only and now her economy is in the 33 MPG range.

Don't ask me why it has such an impact, I just saw that it does.

 

Engine tuning included valve adjustment, throttle body service, new spark plugs, engine timing check, spark timing correction

No I did not change plug wires and dist. As mech said these were fine

 

There is no CEL

 

Clean the egr passageway and egr itself?

 

There's one thing that can cause this is the primary o2 sensor. I have your engine (D16y5) and I never got a CEL ever for the bad o2 sensor. When I finally gave up on the ecu telling me anything, I broke out the multimeter and began testing the o2 directly. Yup, it was bad! I replaced it and my fuel economy numbers shot back up! So much for the CEL actually telling me something wasn't working!

The other thing that happened was the distributor was faulty. Even though the spark timing was adjusted, the sensors built into the housing were failing. That caused a lack of fuel economy as well.

One more to check is the main catalytic converter, make sure it's not plugged.

 

Thanks alot o2 and distributor is the next target !

How did you test it with multimeter? What reading should it show?

 

I was testing the ohms of the sensor I got infinity when I tested it, that right there showed it was bad. The a/t version of the d16y5 engine has a four wire primary o2 sensor where mine (m/t) has a wideband 7 wire, different.

But I did look up in the service manual for yours and on the plug side of the primary o2 sensor, the ohms should read 10-40ohms between terminal 3 and 4. These are the ones at the bottom of the plug when the connector ring is at the top.

Someone might know where to get the Civic Service manual, and probably a simple google search can find it. You'll need this. It's in pdf form now.

It will also show you how to test the sensors on your distributor. But all should be between 700-1000ohms. The service manual conveniently forgot the d16y5's distributor specs, which is the Hitachi distributor. The specs they're showing 350-700ohms is for the TEC distributor! Took me a lot of digging to find the correct info.

 

How are you checking? Does the CEL work?

 

check primary o2, timing.

 

To my amazement, there is not even one o2 sensor in my car neither in the headers nor down the exhaust.

i am blank now !!

 

Haha...this^ would throw a CEL code. Do you understand the dilemma?

 

hahah is right! (at what RonJ said).. lol.. I won't spoil the surprise, you can tell us the obvious of what you've determined now of what's wrong with your car..

 

Apparently there is no CEL what so ever

 

You would greatly benefit by responding thoughtfully to all questions posted in your thread.

 

i'm all in !!!

 

Apparently not

 

How are you verifying that the CEL works?

 

x2

I was going to ask this same question. Since it's already asked, I will expand on the question and ask..... Do you know how to verify that the CEL bulb works?

If you can answer that question, you can answer all the previous questions about the CEL.

 

https://honda-tech.com/forums/honda-...lists-1901557/

This^ is now a sticky again.

 

Whats sad is the question had to be asked twice....

 

appologies for the late reply ! i verified tha the CEL Works by removing various sensor clips like MAF, MAP, Vtec Solinoid etc and CEL comes on ! but it is quite unusual that there is no CEL where o2 is completely missing

 

What engine do you have? A stock engine won't have a MAF sensor. Post the block and head codes.

Also post pics of your engine bay. Do you have a 99 Civic HX with the CVT?

So what codes did you pull after unplugging the sensors? Post them.

There's likely an O2 sensor that you've overlooked.

Post pic of this area: