Bad mpg==bad o2 sensor?

From Tune Ups to Oil Changes, maintenance related

Moderator: toayoztan

Bad mpg==bad o2 sensor?

Postby LvX » Wed Aug 31, 2016 4:34 pm

I've finally got my celiac back on the street after a blown ecu and 10 years.
The car runs fine, the idle is quite stable but i've a little hesitation when accelerating, the rpm drops a bit and the engine quite stalls.
Also the mpg is worst than before something like 20lt/100km !!

I've checked the engine for vacuum leaks, tested for boost leaks, changed the o2 sensor, distributor cap, spark plugs,checked the fuel pressure, i've also cleaned the throttle and adjusted the tps as for bgb.
Nothing!

So i went to the test procedure for the o2 sensor, it could be a bad wiring as i had problems with the distributor's wiring too and had to use an external wire for it.
But the procedure seems really difficult, i've followed it, bridged te2 e1, let it warm up, idling for 3 min, pushed the ac button (with fan speed set to 1) and drove in 5th at 1500 rpm for 2 min... no light come on, so i've disconnected the o2 sensor and tried again, still no light...

I'm running out of idea, how can i check if i'm running in open loop or not? :bangshead: :bangshead: :bangshead:
Members don't see the above ad. Register now - it's free!
LvX
Club Member
 
Posts: 28
Joined: Tue Mar 15, 2016 3:13 pm

Re: Bad mpg==bad o2 sensor?

Postby underscore » Wed Aug 31, 2016 7:06 pm

Exhaust leaks? Sounds like over fueling.
★ 1991 GTFour RC ~ "Rebel Scum" ★
It's for sale! http://www.alltrac.net/phpBB2/viewtopic.php?f=64&t=52181
Build thread http://www.alltrac.net/phpBB2/viewtopic.php?f=44&t=44216
underscore
GTFour God
 
Posts: 3809
Images: 0
Joined: Mon Apr 09, 2007 11:29 pm
Location: Kelowna, BC

Re: Bad mpg==bad o2 sensor?

Postby LvX » Wed Aug 31, 2016 8:53 pm

Why exhaust leaks?
Do you mean between manifold and the head before the o2 sensor?
anyway the exhaust is quiet
LvX
Club Member
 
Posts: 28
Joined: Tue Mar 15, 2016 3:13 pm

Re: Bad mpg==bad o2 sensor?

Postby ___Scott___ » Wed Aug 31, 2016 10:41 pm

You can tell if the ECU is running in open or closed loop mode by monitoring the voltage on the O2 input pin to the ECU while cruising (not accelerating/decelerating.) If the voltage is changing between 0V and 1V then it's operating in closed loop mode.
Scott
Colorado Springs, CO - USA
SONY
Opera - The better browser
User avatar
___Scott___
Established Member
 
Posts: 2064
Joined: Mon Aug 09, 2004 5:30 pm
Location: - - USA - - Colorado Springs, CO

Re: Bad mpg==bad o2 sensor?

Postby celi703 » Thu Sep 01, 2016 12:07 am

I just replaced the oxygen sensor on my alltrac. I had the check engine light which will come on when the car first starts then eventually went away. Also the car would sometimes start and would have a rough idle and turn off. I also had bad mpg to the point where I would see the gas gauge needle move while I drive. Turned out to be a bad oxygen sensor and bad connection on the sensor it self.
90 ST185 3E5
14 FB6 TW
celi703
Club Member
 
Posts: 52
Images: 1
Joined: Fri Feb 10, 2012 2:48 am
Location: Fairfax, VA

Re: Bad mpg==bad o2 sensor?

Postby underscore » Thu Sep 01, 2016 4:36 am

LvX wrote:Why exhaust leaks?
Do you mean between manifold and the head before the o2 sensor?
anyway the exhaust is quiet


Because a pre-O2 leak will make it run rich. Mine had a nasty leak but wasn't noisy. Other options are bad MAF, or a problem with the old start injector circuit.
★ 1991 GTFour RC ~ "Rebel Scum" ★
It's for sale! http://www.alltrac.net/phpBB2/viewtopic.php?f=64&t=52181
Build thread http://www.alltrac.net/phpBB2/viewtopic.php?f=44&t=44216
underscore
GTFour God
 
Posts: 3809
Images: 0
Joined: Mon Apr 09, 2007 11:29 pm
Location: Kelowna, BC

Re: Bad mpg==bad o2 sensor?

Postby LvX » Thu Sep 01, 2016 6:20 am

___Scott___ wrote:You can tell if the ECU is running in open or closed loop mode by monitoring the voltage on the O2 input pin to the ECU while cruising (not accelerating/decelerating.) If the voltage is changing between 0V and 1V then it's operating in closed loop mode.


Thanks Scott, i will try
LvX
Club Member
 
Posts: 28
Joined: Tue Mar 15, 2016 3:13 pm

Re: Bad mpg==bad o2 sensor?

Postby LvX » Thu Sep 01, 2016 6:21 am

celi703 wrote:I just replaced the oxygen sensor on my alltrac. I had the check engine light which will come on when the car first starts then eventually went away. Also the car would sometimes start and would have a rough idle and turn off. I also had bad mpg to the point where I would see the gas gauge needle move while I drive. Turned out to be a bad oxygen sensor and bad connection on the sensor it self.


same as me, the needle really scares especially in italy where gas is 2$/lt :crazy:
LvX
Club Member
 
Posts: 28
Joined: Tue Mar 15, 2016 3:13 pm

Re: Bad mpg==bad o2 sensor?

Postby LvX » Fri Sep 02, 2016 8:39 am

Its seems to be the MAF, i've replaced with a friend's one and now the consumption seems good again, also the car revs better and the turbo seems to respond faster.
thanks underscore for having planted the doubt.
I still have the hesitation to be sorted out, during the weekend i will remove the egr to check if is stuck and will clean the throttle deeply
LvX
Club Member
 
Posts: 28
Joined: Tue Mar 15, 2016 3:13 pm


Return to General Maintenance and Repair

Who is online

Users browsing this forum: No registered users and 2 guests