Hello
I just recently had to change my auto tranny out. Not a complicated task but very time consuming. During the disassembly, I noticed my car (04 ls1 convert.) did not have front ( pre-cat) O2 sensors.

I bought the car used back in 05. I knew I had long tube headers( 1 7/8"), high flow cats and then corsa pace car exhaust. These were installed when I bought the car. With a halltech intake.

Since I bought the car, but before tranny change, I have changed out to B&B catback bullets but never saw the front 02 sensors missing because of the heat shield/ torque tube plate. I have also passed MD emissions.

My question is did this require a tune? The front O2 sensors are zip tied to other harness by the firewall with no connection point. I wrapped the harness ends with electrical tape ( they were exposed to air,water, and heat, WTF).

I wanted to tune my car to pick up a tenth or two this year with the new converter and tranny and I am now scared if I mess with the tune I may start having problems. Any help, suggestions, or knowledge is appreciated. Thanks.

 

The only way that would work is if the car is running open loop. These are the flat 4 pin connectors you're talking about, not the square 4-pin connectors?

 

I removed the torque tube cover plate to remove the torque tube and loosen from flywheel. Upon removal, 2 harness fell down on me and i noticed; after inspection, no pre-cat O2's. I Assumed ( you get the reference0 they were for the pre-cat O2's.

Open Loop? I am a plumber not a mechanic and just have basic theory of combustion cars. I also have an ESI paper and disc. No open loop is mentioned.

 

In STOCK trim the ECM MUST use the front 02's to correct the part throttle AFR to 14.68 using the fuel trims---The rear 02's do not affect how the engine runs--they are there only to report the condition of the cats--mostly for overheating
Installing LT hearders open up a whole new can of worms--Because the 02 bungs are now further back the 02's get erroneous readings (can be up tp 3' further back)---This makes your PT fuel go rich ( something like 14.2) beacause it increases the hydrocarbons they are illegal in most states
There is NO real way to correct this using the stock narrowband 02's--There are a few things that can help with tuning but not completely ever getting it back to 14.68
SO--- many tuners will go to either a "speed density" tune or an "open loop" tune
On a SD tune you DON"T use the MAF-- If your MAF is gone or not hooked up you have a SD tune--- If your MAF is there and hooked up--you may have an open loop tune-Exception is that the MAF can be turned off with a tuner and still be hooked up-- on a SD tune
Any tuner will be able to see immediately after reading your tune file what you have and re-tune using the same tune you're running (SD - or OL )
HOWEVER It's my opinion you'd be better off to hook up your 02's again and run it back on the closed loop system-regaurdless of the LT's--Typically SD and OL tunes are done on only highly modded engines--- ( cams heads etc.)
Reason being is that with a SD and OL tune the ECM is NOT ever making corrections to your PT fuel--So altitude --temperature-- air density all affect how it runs--With a closed loop tune the ECM is constantly making corrections to your fuel in any change--Greatly affects fuel mileage--driveabilty--idle quality when changes aren't being made--
I have had the best results when running LT headers in closed loop by:
1.Installing the rear 02's onto the front locations--they are much more sensitive and heat up better
2. Lowering your 02 switching points by 100-300 points
3. removing apprx 20% to your VE table from 2000 RM on down

PS: I would not use the old front 02's as when they are not hooked up and heated they foul out almost immediatley and are most likely JUNK-
You have some decisions to make --mostly depends on your car's expected use and what's most important to you (fuel mileage--driveabilty-less headaches ) or if you are planning some future mods

 

Exactly what is different about the rear O2 units? I verified that the hearer current is identical to the front O2 sensors.

What makes them more sensitive? They look identical except for the lead length and the terminal.

Not disputing, just asking.

One last point, if you go buy new GM parts, they are now different from the original ones.

Ron

 

Are you going to actually describe these harnesses or what you're looking at? Pictures would really help.

Did you look at my question about the O2 connector shape?

Does the car appear to have the rear O2 sensors?

Are there just plugs in the holes where the front O2 sensors would go?

I'm not sure what you're looking at. The connector plugs for the O2 sensors are factory attached to the frame on each side of the engine. They won't even come close to reaching the tunnel plate. Are these harnesses cut-off wires or something else? Once again, pictures would really help.

As for the open loop - http://lmgtfy.com/?q=engine+open+loop

Peter

 

Not really sure mechanically what the internal differences are between the front and rear 02's ---they just are--- differnent--I have changed the rears to the front and datalogged the 02 voltages and their oscillation before and after the change----
And can verify that the voltages oscilated more rapidly --did go from open loop to closed loop more quickly---Did not throw any 02 codes-- or go into "open loop fault" as is commom when using LT headers and the stock front 02's
As far as the 02's looking the same NOW as they did when origally installed---GM and all car companies constanly change and upgrade parts on your car when they find a design that works better or has less failure rates---

 

hello
sorry for not responding but life is a bi**ch. I don't have front O2 sensors. I looked under the car and they are 4 pin male connectors.

I had my wires and plugs changed today ( 90,000 miles). They are light brown or white. no wear.

The VetteTech at my local dealer said " Your car was tuned by a professional; 90,000 miles and your plugs show the right mix."

I still want to uprgrade my tune with the new tranny. Any suggeations for a tuner BESIDES Tony in MD? Any sugestions for program I can understand? Thanx for any help.

 

I dont even have a tap in the headers for an O2.

 

Flat or square 4-pin connectors?

Any rear O2 sensors?

I find it odd you don't even have O2 bungs since all the full-length header/midpipe kits I've seen come with spots for front O2 sensors.

 

No taps before the cats. I had the car on jacks today to make sure. The pins are flat but round on the ends. Male blue ends; 4 pin with female clip end. Sorry no pics because I am tech ignornant.

I've done a little research. The popping noise I get in my exhaust when I ride her hard then back off is " excessive backpressure" ? I'm skeptically of almost all internet "google" searches. And advice that is good and free is hard to come. Hence the reason I ask here.

Yes I have rear O2's. Wires to one had no heat fiber and looked cooked. 1 7/8" headers no tap, to 3 " cats and X pipe to 2 1/2" flange. Then 2 1/2" over axle to resonators then 3 " to quad tips.

 

If you don't have front 02 sensors than you have to be Speed Density tuned. This would also mean you don't have a Mass Air Flow Sensor. Speed Density runs off the MAP sensor and always runs at one specific AFR no matter what.

Is it possibly that your front 02 sensors are placed after the cats and you don't have rear 02 sensors? I've also seen thread where guys take their rear 02's and pin them into the flat four front 02 harness so they don't have to buy extensions.

 

I can't tell from your connector description which O2 sensors are hooked up. The front O2 connectors are a rectangular shell with the 4 pins all in a row. The rear O2 connectors are a square shell with the 4 pins in a square pattern. Does that help?

 

not the best pictures, but do they look like this?