Bad Fuel Mileage, and hesistation, O2 Sensor?

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Bad Fuel Mileage, and hesistation, O2 Sensor?

Postby Ugotgerms » Mon May 18, 2015 8:06 pm

I have just recently ordered a new cap, rotor, and plug wires. The plugs are new as of 600 miles ago. So is the fuel filter. Another thing is my aftermarket boost gauge shows 19 in. Hg at idle and the full 8 lbs of boost at full load, so I do not believe there is a terrible boost leak.

I have been noticing a fair amount of hesitation under boost. Also I just took it on a 300 mile road trip and I averaged 15 mpg, and around the city I would be lucky to see 12, and this is absolutely babying it, no hard acceleration runs. I figured I would cover my basis and do a general tune-up but I was doing some reading and see that the o2 sensor could be the cause of possibly both. Now what surprises me about that is that I get no codes thrown like I would expect.

So I tested it as per this website: http://www.gt4dc.co.uk/website/development/diagnose/diagnose.php (under poor fuel consumption)

Now on my vehicle there are two OX pins, 1 and 2. So I tested both one at a time after taking the car for a quick drive. The OX2 pin showed no voltage, and the OX1 pin showed 0.08V..... yes that's right 0.08. Now if I understand correctly perfect voltage should have been 0.5. So if the ECU is getting 0.08 from the o2 sensor it would dump fuel trying to get it up I assume? I am definitely not sure.
Now is this the proper way of testing the o2 sensor? Is there a better way? Or could my o2 sensor be reading correctly and something is causing a terribly rich condition. I would love anybodies input on this.
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1993 Toyota Celica GT**SOLD**
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2001 Honda CRV LX
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Re: Bad Fuel Mileage, and hesistation, O2 Sensor?

Postby alltracman78 » Wed May 20, 2015 11:08 pm

Ox2 is for a second O2 sensor.
You don't have one.

Also, a digital multimeter is pretty much useless for testing O2 sensor signals [and some other things too].
You need an analog meter like this
http://www.amazon.com/gp/product/B000P7 ... UTF8&psc=1

The O2 signal should "switch" just over once every second [8 - 10 times in 10 sec IIRC].
Switching is basically going from below .5 volts [lean] to above .5 [rich] volts or vice versa.

If it stays rich the engine is running rich for some reason.
If it stays lean or tends to stay lean the engine is running lean for some reason or the sensor is going bad.
Or if it doesn't switch fast enough the sensor is going bad.
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Re: Bad Fuel Mileage, and hesistation, O2 Sensor?

Postby Ugotgerms » Mon Jun 01, 2015 12:23 am

So all of the parts I ordered came in yesterday and I put them all in today. I fixed every issue I had with it including it dieing at idle and the bad acceleration horrible hesitation/ missing.

I replaced:
Spark Plugs (BKR6EGP)
Cap and rotor and wires (all Standard brand)
O2 sensor (Denso, it didn't fit the best, but nothing a little reaming didn't fix)
Coolant temp sensor (I believe I got this one in a Standard Motor Products brand as well)
TPS sensor (With one from another throttle body I had laying around)
I also found a leak in my ata intercooler as I was cleaning it. I replaced it with another I had laying around, weird because according to my boost gauge I wasn't having any vacuum or boost leaks, but no matter.

I also took the afm off and gave it a good cleaning. but it seemed ok otherwise.

I don't know if one thing or all of them helped but it revs more freely, doesn't want t die when it comes down, no more hesitation/missing at high load and rpm, and it is much more quick now. It's too soon to tell if the gas mileage went up, but hopefully it has. Hopefully this helps anybody else with similar issues
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1997 Mitsubishi 3000GT VR4 #255/510 **SOLD**
1992 Toyota Celica All-Trac
2001 Honda CRV LX
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Re: Bad Fuel Mileage, and hesistation, O2 Sensor?

Postby Rallly » Sat Aug 22, 2015 6:28 pm

Ugotgerms wrote:So all of the parts I ordered came in yesterday and I put them all in today. I fixed every issue I had with it including it dieing at idle and the bad acceleration horrible hesitation/ missing.

I replaced:
Spark Plugs (BKR6EGP)
Cap and rotor and wires (all Standard brand)
O2 sensor (Denso, it didn't fit the best, but nothing a little reaming didn't fix)
Coolant temp sensor (I believe I got this one in a Standard Motor Products brand as well)
TPS sensor (With one from another throttle body I had laying around)
I also found a leak in my ata intercooler as I was cleaning it. I replaced it with another I had laying around, weird because according to my boost gauge I wasn't having any vacuum or boost leaks, but no matter.

I also took the afm off and gave it a good cleaning. but it seemed ok otherwise.

I don't know if one thing or all of them helped but it revs more freely, doesn't want t die when it comes down, no more hesitation/missing at high load and rpm, and it is much more quick now. It's too soon to tell if the gas mileage went up, but hopefully it has. Hopefully this helps anybody else with similar issues




How did you make out? Is your All-Trac stock? How many kms are you getting in town on a full tank?
Also my car is stock 91 all-trac, when the boost gauge rises I don't feel a significant punch? Should it feel like a freight train? When my boost gauge rises it feels like 1-3psi at most. No punch, I just replaced plugs, cap, rotor, wires. I sense hesitation when I floor it at low rpms it hesitates as boost rises. Is there a way to do a boost leak test? Sorry for all the questions but I just got it and not happy with 300kms on a full tank and shot performance.
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Re: Bad Fuel Mileage, and hesistation, O2 Sensor?

Postby Ugotgerms » Mon Aug 24, 2015 4:48 am

My Alltrac is stock (engine wise where it counts) as well, my most recent tank I got 420kms, averaging about 15mpg, so definitely not what it should be. Mine actually developed a new problem where it accelerates really smoothly up until 4k ish rpms and then the power drops right off and the rpms start barely rising, I have no idea what it could be, boost gauge never drops below 9 psi, it just slows down. Really annoying that my 93 2.2l Celica has been faster than it so far just because it can't ever go past 4000 rpms.... if anyone has any ideas let me know...

Could this be a sign of a bummed fuel pump? or my turbo just not pushing any air (but holding pressure)? Is this knock response by the ecu because of bad fuel? I only ever run premium 93 octane but maybe I should try some booster just to see
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Re: Bad Fuel Mileage, and hesistation, O2 Sensor?

Postby Rallly » Mon Aug 24, 2015 4:36 pm

Ugotgerms wrote:My Alltrac is stock (engine wise where it counts) as well, my most recent tank I got 420kms, averaging about 15mpg, so definitely not what it should be. Mine actually developed a new problem where it accelerates really smoothly up until 4k ish rpms and then the power drops right off and the rpms start barely rising, I have no idea what it could be, boost gauge never drops below 9 psi, it just slows down. Really annoying that my 93 2.2l Celica has been faster than it so far just because it can't ever go past 4000 rpms.... if anyone has any ideas let me know...

Could this be a sign of a bummed fuel pump? or my turbo just not pushing any air (but holding pressure)? Is this knock response by the ecu because of bad fuel? I only ever run premium 93 octane but maybe I should try some booster just to see



I have similar problems. HeLp plz
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Re: Bad Fuel Mileage, and hesistation, O2 Sensor?

Postby ___Scott___ » Mon Aug 24, 2015 6:28 pm

Could be fuel pump dieing or fuel filter clogged.

It could also be the ignition coil dieing.

Before replacing a bunch of stuff, make sure you have good ground connections between the igniter and the engine and also between the igniter and the ECU. I was trying to fix a different problem when I added those ground connections, and while it didn't solve my problem, it did make the engine run better.
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Re: Bad Fuel Mileage, and hesistation, O2 Sensor?

Postby Rallly » Wed Aug 26, 2015 12:12 pm

Don't mean to crash the OP's post but will an O2 sensor from a USDM GEN 2 engine 91 MR2 Turbo US model fit my 91 Celica All-Trac?
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