I have a stock ls engine with a skunk2 intake manifold, intake, and exhaust as the only modifications. My car doesn't burn oil, coolant or anything but i have been getting bad gas mileage and the exhaust smells like gas from time to time. I replaced the spark plugs, it helped a bit but is still an issue. Any ideas?

 

Possibly a clogged cat?

 

what is bad gas milage? i noticed not that long ago my gas milage dropped about 5 mpgs, im coking it up to not keeping my foot outa the gas and i slightly advanced the timing which brought the gas milage up a little but not quite what it was. advancing he timing was suggested by my automotive instructor and he helped me do it.

 

check the Coolant temp sensor for the ECU. if the ECU thinks the motor is cold it will burn more fuel.

 

I'm almost positive its this, my temp guage in my car has seemed low lately i just thought it was because it was somewhat cold out.

 

i used to get 28-31 and now the best ive gotten is 23.

 

Looks like someone needs a new Thermostat.

 

So a bad thermostat will cause the temp guage to seem like it isnt working?

 

It can but Not likely most of the time it makes the car hot but on rare ocasions it gets stuck open and the coolant flows all the time making it take longer for the Engine to heat up the coolant and showing colder temps on the guage and to the ECU.

also the guage is connected to the one wire sensor at the base of the head and the ECT is the two wire sensor.

 

This morning before school i checked the wires to the coolant temp sensor and played with them a bit and made sure the sensor was still hooked up. Got in my car and drove it about 10 miles and the temp gauge started to go back up to around normal. Thinking it may be a bad sensor or wires.

 

They are two diff. sensors...
ECT sensor sends engine temp. info to ECU/ECM.

ECT sending unit sends engine temp. info to temp. gauge in cluster.

ECT switch, controls rad fan.

The ECT sensor has no effect on the cluster gauge it effects A/F ratio.

The ECT sending unit has no effect on A/F ratio.

The ECT switch has no effect on either of the above, [unless it is not working and rad fan does not turn on]. 94

 

But if the sensor is bad, saying that my car Is always cold, my fan wouldnt come on and my car would burn more fuel correct?

 

If your fan didn't come on you would over heat and millage would be the least of your concerns. What kind of millage are you getting? How many miles are on the engine? Have you tried simple stuff like injector cleaner?

 

the ECT or Engine Coolant Temp sensor Has 2 wires and runs to the ECU as the temp of the coolant rises the Resistance of the Sensor changes and the ECU turn the Resistance into a Tempature value and adjust timing and Injector pulse. and affects your AFR.

The Engine Tempature Sending unit has 1 wire and runs to the Guage on the dash and as the coolant temp changes so does the resistance of the sending unit and the guage turns this resistance into a Sweep for Driver referance only.

the Radiator Fan switch is a 2 wire temp switch when the engine coolant reaches a set tempature range (175~210 for most newer Honda's) the switch flips and connects the 2 wires. In OBD0 cars this only want to a relay to turn the fans on. in OBDI Some systems it went to just a relay in others it went to both a relay and the ECU. And in OBDII this feeds the ECU and the ECU turns on the relay. this should be the 2 wire sensor that is on the thermostat housing.

Now if the ECT fails or is starting to fail it will fool the ECU and the engine will runn funny and can run rich or lean
If the Sending unit fails or is starting to fail the guage and only the guage will not work correctly.
If the fan Switch is to fail or is starting to fail this will affect the rad fan and only the rad fan functioning. but if the fan turn on too soon it will cool the coolant more often and the engine will run cooler and there by changing what the ECT is telling the ECU. thiss type of failure is very rare and you would hear the fan running alot.

 

If it's a sudden drop in milage of over 2 MPG its not going to be an injector 9 times out of 10.

 

it's not the ECT switch because my rad fan still works and it cant be the ECT sending unit because guage still works. So i think the ECT sensor is bad.

 

starting with the thermostat this weekend.

 

Have you ever replaced the O2 sensor? Might help a bit

 

Yeah it has been replaced. Not getting a CEL. Don't know how the o2 sensor would affect my cooling system but okay.

 

Your initial post was about how your gas mileage was going down. A bad O2 sensor will definitely do this

 

Yes thats why it was replaced a while ago. My problem now is mentioned in the coments.

 

New thermostat solved the problem, thanks for the input guys.

 

Good to hear. Thanks for the follow up.