View Full Version : o2/maf

03-13-2009, 05:14 PM
ok - so this may be a "duh" to most, but just a reminder for older obd vehicles. O2's don't always through a code. I bought this t100 used of course, and one of the reasons was that the PO did just about every PM thing known to man. Since buying the truck though, my mpg just kept going down where it finally stopped at 13.5 or so combined city/highway....

I pulled codes, and nothing there.. So, I went through the documentation of what he had replaced, and low and behold, no O2 replacement. I promptly replaced them and cleaned the MAF.

They were caked, and rightly so, at 168k miles. Average life on an O2 is around 120k, so there you go.

mpg is now back up to a respectable 18.2 combined..

I was running in limp mode it turns out, at full rich.


03-13-2009, 07:11 PM
Wow, great upgrade. Were these the O2 sensors in the exhaust system? Are there others?

03-13-2009, 07:59 PM
Not to sound like a moron here, but what is an MAF? Mass Airflow Sensor?

03-16-2009, 08:55 AM
yeah - mass air flow..

o2's on the 3.4 are pre and post cat. Held in by flange bolts, and take like 10 minutes. NEVER buy generic. Either buy direct fit replacement by bosch or the oem toyota. Bosch makes most of the oem anyway.

03-16-2009, 09:44 AM
Friends do not let friends do Bosch. They can really cause issues.
OEM are ND or NGK, available at sparkplugs.com.

Hey, and thanks for the reminder, I need to replace my O2 on the '93 DD! 153K miles. Yeah, I procrastinate...

03-16-2009, 10:19 AM
bosch universals do. direct fits don't

03-16-2009, 12:47 PM
whats the difference in a universal O2 sensor and a direct fit??

03-16-2009, 01:42 PM
universals are splice in, direct fit matches oem connector.

03-16-2009, 04:56 PM
I realize that, but everybody here is saying not to go with universal.. why not? just because they are splice in?

03-16-2009, 05:09 PM
I have never been satisfied, nor had a universal o2 last on the simpler systems. Whether it's the resistance range not matching, or the durability, one or the other has bitten me.

I have never even tried to run a obd generic o2 sensor, and I wouldn't.

03-16-2009, 05:24 PM
Reason I'm asking is because I've almost always run generics (1,3, and 4 wire) and i've never really had a problem (maybe I did and I didn't know it). Even the 1 wire generic bosch sensors I used to run in the turbo cars seemed to live and work OK.

Only vehicle that has been picky is the Cruiser with the Vortec.. for some reason the 02 sensor heaters on this system run at a slightly higher voltage than the computer expects.. so it throws a code. I went through lots of 02 sensors (and sensor positions)trying to figure that one out. Spent a lot of money on OEM sensors from GM too (not toyota.. I know).

Just wondering what i can learn because i hear lots of people say not to go generic.

03-17-2009, 07:00 AM
Most of my 1 wire is from my turbo days and the days before obdII. I think with the less complex maps, and even more crude CIS systems, the voltage and resistance issues weren't as big of a problem as with the more complex injector systems.

As the injection/emission systems went to controlling more at start up as well as aiming to increase reaction times, the generics just didn't match up. I noticed back in the day as well that it depended on the systems design. Some systems went closed loop when operations went out of range/band, others went closed.

It also depends on what the operational efficiency of the combustion was nominally. Most turbo cars were designed to be "over-rich" anyway, and o2 out of range set to fail in full rich of operational range, which wouldn't be noticed by the driver, as it might actually run better, since it was set as lean as possible (still being rich) to get in the states in the first place.

I haven't turned a real wrench in years, and robbie or others are probably better at commenting on this... I think toy's in general put more into the efi mapping / computer systems vs the older german turbos (porsche) that eeked everything out of physical design parameters, now physical isn't going to cut it. With variable efi mapping, comes variable valve timing in addition to variable spark timing.. I am sooo glad my "modern car" is under warranty. I don't have a degree in ee or physics


03-17-2009, 10:17 AM
Most of my 1 wire is from my turbo days and the days before obdII. I think with the less complex maps, and even more crude CIS systems...



Would the 3FE fal into that category?

03-17-2009, 04:03 PM
CIS is constant injection system. A bosch term. Constant flow injector. Multi point, but not real fancy. http://home.hiwaay.net/~langford/CIS.html