Welcome to the North American Subaru Impreza Owners Club Tuesday September 16, 2014
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Here you can view your subscribed threads, work with private messages and edit your profile and preferences Home Registration is free! Visit the NASIOC Store NASIOC Rules Search Find other members Frequently Asked Questions Calendar Archive NASIOC Upgrade Garage Logout
Go Back   NASIOC > NASIOC Technical > Service & Maintenance

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads.
Reply
 
Thread Tools Display Modes
Old 12-30-2006, 08:34 PM   #1
amoebaman
Scooby Newbie
 
Member#: 93482
Join Date: Aug 2005
Location: Provo, UT
Vehicle:
1998 Impreza wagon
Black

Question Bad Temp Sensor=Bad Fuel Economy?

Here's the situation....my poor old '98 GF is suddenly getting terrible fuel economy. But not on long distance trips. I drove from Provo Ut to Aspen CO averaging 22 MPG which isn't great but we did have a bunch of cargo on the roof rack ruining aerodynamics. Anyway, I drive long distances and its get fine fuel economy, but my typical commute to and from work is only about 5 miles. From a cold start I have to let the engine run for about 3 minutes befreo I can drive it because I have no power whatsoever when I put it in gear, (it's an auto) the I can't move when I floor the accelerator kind of no power. but it's fine once the engine warms up. My last tank of gas was spent almost entirely on short trips like this, and I only got 13 MPG!!!!

Here's the thought generated by myself and my friends:

The Coolant Temp Sensor is bad and telling my ECU that it's much colder than it really is so at start up it's running pig rich and wasting my fule then. Makes sense to me because I only have this problem when it gets cold and I go from lots of cold starts for only short distances.

In the last six months, the spark plugs, plug wires, air filter, PCV valve, and fuel filter have been changed, so no problems there.

I'm just asking for any other thoughts and input regarding this...and also a question that makes me feel really stupid, where do I find the Temp Sensor on my EJ22? I expected to find it around the thermostat housing but it wasn't there. All help is appreciated, thanks everybody!!!

BRIAN
* Registered users of the site do not see these ads.
amoebaman is offline   Reply With Quote
Old 12-31-2006, 06:16 AM   #2
overdose
Scooby Specialist
 
Member#: 46399
Join Date: Oct 2003
Chapter/Region: MWSOC
Location: Grand Rapids, MI
Vehicle:
0000 Knows nothing,
about nothing.

Default

yes, replace.
overdose is offline   Reply With Quote
Old 12-31-2006, 08:14 AM   #3
silver2004impreza
Scooby Newbie
 
Member#: 127878
Join Date: Oct 2006
Chapter/Region: MAIC
Location: Front Royal
Vehicle:
2004 Impreza 2.5TS
2004 Outback sedan H6

Default

You might also want to replace your O2 sensors. I had my upstream sensor die on me and my fuel economy fell through the floor, as the injectors were running full rich all the time. I'm not certain where the temperature sensor is though.
silver2004impreza is offline   Reply With Quote
Old 12-31-2006, 09:47 AM   #4
Mike Wevrick
RIP 1/19/64 - 7/23/11
Scooby Guru
 
Member#: 24654
Join Date: Sep 2002
Chapter/Region: NESIC
Location: saraseager.com
Vehicle:
1957 Taggart Comet
atlasshruggedpart1.com

Default

Another possiblility is that the thermostat is stuck open. That would cause the car to warm up very slowly and not run efficiently. Doesn't explain the lack of power though ...
Mike Wevrick is offline   Reply With Quote
Old 12-31-2006, 10:11 PM   #5
amoebaman
Scooby Newbie
 
Member#: 93482
Join Date: Aug 2005
Location: Provo, UT
Vehicle:
1998 Impreza wagon
Black

Default

Yeah, thermo's fine...Engine warm up time is normal, so I don't think that it's the thermostat. I'm not the most knowledgable person when it comes to engine management, but my understanding is that if and O2 sensor were bad, I would be getting crappy mileage all the time, not just on the short trips from start up. I've also tried letting the car idle for about 10 minutes after start up to let the engine warm up and my economy was even worse...So does anybody know where that temp sensor is?

Last edited by amoebaman; 01-01-2007 at 05:29 PM.
amoebaman is offline   Reply With Quote
Old 01-03-2007, 09:27 PM   #6
Big-E
NASIOC Supporter
 
Member#: 123843
Join Date: Aug 2006
Chapter/Region: NESIC
Location: Connecticut
Vehicle:
2006 WRX Sedan SGM
Let LED's light your way!

Default

If the thermostat is fine, of course then the engine should be at operating temperature.

But with a faulty ect switch, the ecu is being told that the engine is not at operating temperature so it will keep dumping additional fuel to help the engine to "warm up".

The oxygen sensors also tell the engine how its running in terms of emissions and that's why there is an upper and a lower stream oxygen sensor to make sure that not too much or too little fuel is being used.

Also, dumping of fuel can also help to cool the engine down if the ecu is sensing a lean condition.

How many miles are on your car? Are you going to keep this car? If you're near to when the oxygen sensors should be replaced and you're going to keep the car then change-out all three items: engine coolant temperature switch and both oxygen sensors.
Big-E is offline   Reply With Quote
Old 11-03-2010, 06:22 PM   #7
subi400
Scooby Specialist
 
Member#: 216984
Join Date: Jul 2009
Chapter/Region: NWIC
Location: Hayden, ID
Vehicle:
1996 Impreza outback
Green

Default

Bumping this thread from the dead!

I have had a similar issue lately. The front fans will come on after a short time of driving and sometimes after driving for a longer period of time but they won't turn off. So I just had my car checked the other day and the local subi guy at the shop found that the temp sensor was reading slower than normal. Plus I have been getting slightly worse gas mileage as well...
So, I got a new temp sensor along with a new oem thermostat as it wasn't opening like it should. I also have to replace the plug wires so that should help some. Once I get these replaced, I'll post an update for everyone who reads this. Like the op said, if the temp sensor is being slow in reading the temperature then the ecu will dump more fuel to warm up the engine quicker therefore hurting gas mileage. So, I am thinking some of my problems are related to what the op is seeing.
subi400 is offline   Reply With Quote
Old 11-03-2010, 06:23 PM   #8
subi400
Scooby Specialist
 
Member#: 216984
Join Date: Jul 2009
Chapter/Region: NWIC
Location: Hayden, ID
Vehicle:
1996 Impreza outback
Green

Default

Bumping this so I can prescribe!
subi400 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Lamco Oil Temp Sensor Scubiesteve25RS RMIC Private Classifieds 0 06-03-2010 12:48 PM
84 gl Bad fuel economy bennn*e 'Old School' Subaru Forum 3 07-06-2007 01:06 AM
Bad O2 sensor bad for your car? kodakeos Normally Aspirated Powertrain 3 09-23-2004 08:39 AM
bad temp sensor wrxracer3 Factory 2.0L Turbo Powertrain 11 06-21-2004 07:42 PM
bad fuel economy after gettin a catback? cool555 Newbies & FAQs 3 04-21-2004 03:52 PM


All times are GMT -4. The time now is 09:15 PM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2014 Axivo Inc.
Copyright ©1999 - 2014, North American Subaru Impreza Owners Club, Inc.