Thought I would start a thread about this. Haven't seen one yet.

What are your guys' thoughts on this?
I am planning to delete mine and just run straight exhaust without cats into mufflers.
I've read that it can affect the ease of tuning the truck because the computer can't adjust to what your exhaust is showing. I'm keeping a MAF so the truck should still be able to learn itself in different climates/altitudes correct? And my truck will be dyno tuned too so my tuner should be able to nail it down pretty good right?

Let's hear what you have done and what knowledge you can share...

 

Upstreams are required to monitor the a/f. The downstreams check the cats function. A chip will delete the them or you can run a MIL eliminator.

If your running explorer manifolds you are wasting your time IMHO.

What are your specs on the engine?

 

Nothing is learned based on the MAF. It just sends a voltage level to the PCM that represents the mass flow rate into the engine and the PCM uses this and other inputs to make an initial try at an injector pulse width for the desired A/F ratio. The pulse width is then corrected to bring the mixture toward the stoichiometric ratio (chemically balanced) during idle and part throttle operation using the upsteam oxygen sensors' input.

This part throttle mixture correction (fuel trim) is continually being fine tuned during idle and part throttle operation and it is stored in a PCM table for future use under the same conditions. This is the learning process and it depends on feedback from the upsteam oxygen sensors.

The mixture offsets learned at part throttle are also used to formulate the Open Loop Fuel Multiplier used for WOT or near WOT operation. So, the sensors are helping to maintain the correct mixture even when the engine is not running at part throttle, closed loop.

Let's say that, over time, the MAF starts to get dirty which incorrectly changes the mass of incoming air that is reported to the PCM. This error would directly impact the mixture except the oxygen sensors are right there to correct the problem. There is a limit on the degree of correction of course but the sensors perform a valuable function outside of just providing a usable exhaust mix for the converters.

By comparing the activity of the downstream oxygen sensors to that of the upstream sensors, the PCM can infer the catalytic converter efficiency. Some calibations even use the downsteams to tweak the mixture slightly for greater efficiency. Without cats in the system, the downsteam sensors have no purpose.

 

So would you say that my tuner could nail down my tune pretty good allowing my truck to run good? Or should I invest in some high flow cat's and use oxygen sensors?

 

Engine Specs are pretty basic. Its just a rebuilt 302, cam retarted 4*, 1.7 roller rockers, trick flow springs. Manifolds for now since the headers are still on backorder. I'll get some headers soon though.

 

Is this an explorer trimmed 302 with explorer stock cat forward exhaust?

 

Whether or not you run cats doesn't make much difference from a tuning perspective. However, even without converters, I think you are better off keeping the upstream oxygen sensors. The downstreams are needed only to judge cat efficiency for OBDII.

Stock Ford cats are high flow. If you are going to run cats, there's no reason not to use the stockers if you already have them. The most important change to make in the 5.0 Ex exhaust system is the restrictive factory exhaust manifolds.

 

Well I do not have cat's. So i'll probably just buy one. What is the setup on the explorer? How many cats and how many o2's? I know on the engine harness I only have 1 o2 plug. So could I get away with running one cat? If so, do I need to put the cat before or after the upstream o2? And also can my tuner turn off the downstream o2, still allowing the upstream to help tune the pcm?

 

The stock 5.0 Ex has separate duals all the way to the dual inlet muffler, then the muffler has a single tail pipe out to the rear of the truck. Altogether, there are 4 oxygen sensors and 4 converters.

One sensor connector (DS upstream) is in the engine harness, the other 3 sensor connectors are in the transmission harness.

You should retain both upstream sensors for the PCM. These upstream O2s are in the exhaust pipes after the exhaust manifolds but upstream of all cats.

The downstreams are not needed unless you want to monitor the cats for OBDII. In the factory setup, each downstream sensor is mounted in the pipe in between the pair of cats for that bank. A tuner should be able to shut off the downstream sensor monitoring, no problem.

The cats are not necessary for the engine to run properly. If you want to run them, then either use two or four.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~


The top diagram is the closest to the way the factory built the Explorer. The picture only shows 2 cats. In a 5.0 Explorer, there would be one more cat after each of the downstream sensors. (O2 sensors are shown in blue, cats are grey.)


PS upstream = HO2S11
DS upstream = HO2S21

PS downstream = HO2S12
DS downstream = HO2S22

 

It makes a difference in tuning in general, you can put in more timing and run slightly closer to stoich without getting the same knock that you would with a cat. Having CATs without a wideband before the catalyst also makes it harder to measure AFR's during WOT dyno pulls. Although the CAT only really does its job when close to 14.7.

 

Interesting info. I think I am set on running up-streams right after the manifolds on each side. I now have to try and find a tranny harness though. lol All I really need is the plug and the o2 harness.

What brand do you guys suggest? I know NTK and Bosch are pretty much the main competitors. Would like to keep it under $50/sensor unless those just suck and I need to spend more money to get something quality.

 

Most OE Ford sensors of that era were made by Bosch and they will do the job.

 

Sounds good Bob. I'll go with them when the time comes.

 

Aloha, I'm having a hell of a time locating the coupling for my 2.3l upstream o2 sensor...due to the tight quarters. Any suggestions??? Are the color codes the same on the replacement??? Cause push comes to shove I can cut & splice (solder & heat shrink)...
Any better suggestions are REALLY WELCOME!!! Mahalo nui loa (Thank you very very much)!!!!!!
Chief

 

Aloha JRacer, I'm new here, got a stock 2.3l 2wd Ranger...need to replace 02 sensor. Quarters are too tight for my big arms & hands & I'm struggling to find the coupling. Ready to cut & splice, but not sure if the color codes are the same... Any Ideas??? Mahalo nui loa (Thank You very very much) for your time...
Chief