I've noticed that the fuel economy of my '95 dx has been declining over the last few months and I can't figure out what's wrong. I used to get 32-35+mpg now it's closer to 20-25mpg (optimistically). It also seems to idle excessively high. I have to apply extra pressure to the brakes or put it in neutral to stop it from creeping ahead. I recently cleaned the IACV to try to correct the idle problem but it seemed to have no effect. The car has loads of power (if you can call 100hp loads) and other than the idle issue runs very well.

I'm not getting a check engine light. I'm not able to pull any codes due to the fact my car doesn't seem to have the connector that I need to jumper . My friend has the same year civic and he showed me where his is located (same spot it is in all the manuals) but on my car it's not there. We both looked very hard and couldn't find the damn thing. I'm reasonably sure it's a sensor of some sort but the lack of check engine light has me confused. A bad O2 sensor should throw a check engine light right?

Any ideas would help.

 

u cant get codes w/out a cel
yea a bad 02 sensor should throw a code

 

when you first turn your car on does the cel come on for 2-3 sec and then go off?

 

Yes the CEL comes on for a few seconds when I first turn the key on but it then goes out. This has me baffled. I replaced the plugs when I did the head gasket and I believe I changed the wires at the same time as well. The cap and rotor might be a bit older(20k kms or so) if I didn't do them at the same time(horrible memory lol). I'm gonna throw some injector cleaner in it and see if that helps. When I have a few extra bucks I might go ahead and replace the O2 sensor as it's probably due anyway(no-one around here changes them). As far as the idle problem it seems like the car gets stuck in high idle until it has reached full operating temperature, whether it's hot or cold out. I know the fast idle is impacting the fuel economy but I find it hard to believe it's hurting it that much.

 

You can activate the self check by connecting pin D4 of the ECU to ground, it's a brown wire. This wire would lead to the check connector if you had one. It is unlikely that any codes are present though because the CEL has not come on (and it does work).

Check the spark timing once you get the jumper on.

Idling too fast may be the fast idle valve mounted on the bottom of the throttle body. If you take the intake pipe off you can block the hole with your finger and see if the valve is open when it shouldn't be (should only be open below 60 F). Extra air entering the intake manifold through any leak will cause a fast idle, so check the TB to manifold gasket joint and also the manifold to head.

Make sure the engine really does warm up to proper temperature. Thermostat must be a 195 degree, lower ones are available but should not be used. Until the ECU has detected that it is warmed up, the engine runs rich in "open loop" mode, which reduces fuel economy.

 

All good things to look for thanks. Ecu ground thing will be a big help.

I did put a new thermostat in when I did the head gasket so I could have gotten the wrong one (the needle seems to be in the right spot though). I'll also check for intake leaks.

 

So you may get a laugh out of this. After pretty much giving up on the problem for the winter I stumbled upon the cause. A week or two ago I hit a bump and heard a pretty loud metallic noise but after a quick look didn't find anything wrong(I had been doing front end work and concentrated my search there :P). A few days ago I was in the McDonalds drive-thru and heard a bang, followed by a dragging sound. My gas tank straps broke :X and gas was pissing everywhere(my feed line broke too). When we replaced the straps and broken line we noticed that the line was rusted all to hell. The fuel lines are coated in plastic from front to back but that coating stops where the line runs up and over the tank. It had rusted so bad it looked like swiss cheese, the weird thing is there was no smell or noticeable leaks. I had a 1/2 tank left when we put everything back together and I put almost as many kms on it as I have been putting on a full tank.

 

wow, so very minor pinholes/evaporation casued all those problems. Glad you got it solved