horrible gas mileage cause?

[chengsta]

My '99 eclipse spyder gst has been getting horrible gas mileage withing the last 2 weeks. While the car is cruising at a coast, it would slightly shake and sputter like it was misfiring. I had a check engine light: P0136 Bank 1 Sensor 2 which would be the 2nd o2 sensor by the cat. So I replaced that o2 sensor and put new NGK BPR7ES plugs(gapped at .030) figuring it would solve the sputter/misfiring but still no luck.

I reseted and checked the ECU again for any new codes and it through this code now:

-P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control

I've done some research and found out this code might be caused by a bad FRONT o2 sensor. Would this be the cause for my bad gas mileage?

[blageo23]

It would cause bad gas mileage. If its the O2 then the computer is probably running super rich because it doesnt know what kind of air/fuel ratios you are getting.

[xveganxcowboyx]

What sort of coolant temperatures are you seeing? It sounds like you are either not getting up to temp or the soolant temp sensor is reading wrong, both of which would cause you to run rich.

[blageo23]

On a 2g that code can mean front O2 sensor too. I had a 95 talon that had the same problem. replaced the front O2 and problem fixed.

[xveganxcowboyx]

That's weird. I like my OBD1.

[chengsta]

I'm not quite sure what coolant temps it gets up to since I don't have a logger. The car doesn't overheat or anything though.

I have a new front o2 sensor on order from the local parts store, should be here sunday. I'll install it then and see if the solves the problem.

[chengsta]

installed new front o2 sensor and it solved it. No more stuttering or misfiring.

[gofastman]

That's weird. I like my OBD1.
You are high, nobody likes OBD 1 :biggrin:

[brando]

you should also change your thermostadt temp sensor as that will soon go. just a sugestion