96' Replaced Oxygen Sensors

Hi all!!

This is more of an experiment to see what results I can get, but I wanted to post here so I could share with the outcome.

First here is what I have.

1996 S-10 Blazer w/ 4.3l Vortec, newly rebuilt engine. The engine has about 10,000 miles on it, so I guess not so "newly rebuilt". Before you ask, yes, all new AC Declo tune up parts were installed. New cold air induction kit. New Fuel pump pusing 65 psi at start up and just above 60 psi during cruise. New Fuel filter....you get the picture I hope.

Total miles on the truck by the way just hit 143,500.

Since my engine was installed I have noticed my fuel mileage go from about 18.5 MPG down to what is now averaging 15 MPG.

I have no codes on my ECM, so nothing out of the ordinary there.

Today I replaced my 143,500 old Oxygen Sensors, three to be exact. Two ahead of the Cat Converter, and one behind it.

Every Sunday I go through the pre-work week routing to make sure the truck is good to go. So tires aired up and a full tank.

I am curious to see how much, if any, improvement comes from installing these new sensors. I will track and over the next few weeks/months report back.

I am not sure it will get me the 3.5 MPGs I have lost, but it should show some improvement.

Lastly, I only use it for work which is 52 miles round trip. Stop and go combination of highway and street....majority stop and go Arizona I-10 traffic.

Wish me luck and I am always willing to hear any insight or pointers.

:popcorn:

Did the fuel mileage drop with the cold air kit?
Did the rebuilt engine get good mileage when first installed?
MT

I track my truck's maintenance and fuel mileage in Autowolf (great program). Looking back at when I installed the cold air kit I show a slight decrease in MPG over a two week period, but then it came back up to the average level. I am not sure what exactly cause that (bad gas, high outside temps??). This kit was installed post new engine install.

After the engine was installed I did notice a 3 - 3.5 drop in the MPG, the shop that installed it told me it was because the engine had not seated all the rings and seals yet. Told me it would get better over time. That is when I started using the MX program to track all the maintenance and fuel mileage.

When I removed the three old O2 Sensors they were really rusted and discolored, even had some of the slits rusted over. I know that could not have been good so I am glad I did the R&R.

This week is my first full tank of gas since the MX was done on the truck. Now I don't want to get to excited, but normally I am at about 80 miles on the trip at a 3/4 of a tank. I am now sitting at 102 miles at 3/4 tank.

MT is there any truth to losing MPG with a newly O/H engine installed or is my chain being yanked?

I track my truck's maintenance and fuel mileage in Autowolf (great program). Looking back at when I installed the cold air kit I show a slight decrease in MPG over a two week period, but then it came back up to the average level. I am not sure what exactly cause that (bad gas, high outside temps??). This kit was installed post new engine install.

After the engine was installed I did notice a 3 - 3.5 drop in the MPG, the shop that installed it told me it was because the engine had not seated all the rings and seals yet. Told me it would get better over time. That is when I started using the MX program to track all the maintenance and fuel mileage.

When I removed the three old O2 Sensors they were really rusted and discolored, even had some of the slits rusted over. I know that could not have been good so I am glad I did the R&R.

This week is my first full tank of gas since the MX was done on the truck. Now I don't want to get to excited, but normally I am at about 80 miles on the trip at a 3/4 of a tank. I am now sitting at 102 miles at 3/4 tank.

MT is there any truth to losing MPG with a newly O/H engine installed or is my chain being yanked?

I am afraid they are feeding you a big line hook and sinker on that one.
A new engine should actually do a little better or just as good as you were getting.

But depending on the engine that was put in it could have a little different pistons or camshaft that could affect gas mileage.

Also the computer system and sensors could affect mileage.
Mass air flow sensor and tempt sensors and 02 sensors or even fuel pump pressure can affect fuel mileage to.

What kind of cold air and air filter do you have.
Does it draw cold air from grille or fender area?
If the oil type filter go easy on the oil and keep the maf sensor clean.

Or clean it anyway with some electrical or Maf sensor cleaner.
And make sure the engine is running at full tempt 195-200 degrees.

I am afraid they are feeding you a big line hook and sinker on that one.
A new engine should actually do a little better or just as good as you were getting.

But depending on the engine that was put in it could have a little different pistons or camshaft that could affect gas mileage.

Also the computer system and sensors could affect mileage.
Mass air flow sensor and tempt sensors and 02 sensors or even fuel pump pressure can affect fuel mileage to.

What kind of cold air and air filter do you have.
Does it draw cold air from grille or fender area?
If the oil type filter go easy on the oil and keep the maf sensor clean.

Or clean it anyway with some electrical or Maf sensor cleaner.
And make sure the engine is running at full tempt 195-200 degrees.



I had my suspicions when they told me that. Even it were true, what they told me was after the engione broke in the MPG would improve. LOL!!:runaround:

The cold air system is the one I found on Ebay after reading about them in the forums here. It is an oil type and I do go very lightly on the oil as I also read (here of course) that it could cause issues with the MAF Sensor. It draws from just rear of the left headlight, next to the window washer fluid container. Of course, cool air in Phoenix, AZ is hard to come by no matter where it draws from:uhoh:

The engine temp varies from two clicks left of 210 to one click over 210 during idle. Of course this is idle in 115+ degree heat...more I would imagine coming of the blacktop of the street itself.

I will examing the MAF Sensor this weekend and clean it just for good measure with electrical cleaner.

I am not sure how to test my engine temp sensor, but I am sure someome on here has done it and posted. That is unless you dont' mind giving me a quick and dirty version.

BTW - My fuel pump is newly installed and is currently getting 65psi at turn of the key and a little under durnig idle.

The only way to test the engine computer tempt sensor or the air tempt sensor is to read them out with a engine scanner.
Good luck and let us know how it does.
MT

Just an update.

3 tanks of gas and I am averaging 16.8 MPG. While this not back to my original spec when i bought it, it is good to see some improvement.