huh.. I would think that it would throw a code for faulty o2 sensor. But also why would it make it have low horse power as well

 

you will need a custom tune to get around having no CATs....

You should go read this:

http://www.12v.org/engine/index.php?section=hw&sm=o2


That will give you a basic understanding of how the O2 sensors and CATs work together...

Basically what is happening is this:

On a cold start-up the PCM runs on a set of tables that have nothing to do with Oxygen Sensors because they are not warmed up yet, so they would give out false readings to the PCM. So depending on the Car the PCM will run on the Intake Air Temperature (IAT) sensor and the Mass Air Flow (MAF) sensor [Note: some vehicles run on a Manifold Absolute Pressure (MAP) sensor instead of a MAF or in conjunction with it]. So they bypass the Air-to-Fuel Ratio (A/F) sensors (AKA Oxygen Sensors), so when your truck is all warmed up it switches to the normal tables, and the following is likely happening:

There is an unexpected similarity from the Pre-CAT (Upstream) O2 sensor and the Post-Cat (Downstream) O2 Sensor that the computer was not expecting which are also likely LEAN (above 14.7) so the PCM will think there isn't enough fuel, then when it dumps fuel in it still isn't seeing a change in the Upstream O2 sensor readings so it will max out the fuel injectors & fuel pump. [Note: The Upstream O2 Sensor is what detects the instantaneous Air Fuel Mixture before it is changed by the Cat. The Downstream O2 Sensor acts as check-point to make sure the CAT is operating correctly.]

Once that happens the computer will say "okay what I've done has had no affect" and then switch to "Limp-Home-Mode" (Limp Mode for short) which is a type of "Open-Loop System". Limp Mode will pull drastic timing, as well as reduce your rev limiter to around 4000-4500 RPM regardless of gear and likely max out your speed limiter as well.

Then it will disregard the upstream O2 sensor readings intermittently (performing re-check of it during the closed-loop) and it will run on a super safe fuel & timing tables and read from the MAF/MAP and IAT sensors, until it likes what it sees from the O2 sensors.

I see you also have a Cold Air Intake, which may be a larger size than the OEM intake diameter, which also throws off your MAF sensor readings (reading more air than usual), so it will increase fuel to compensate and nearly completely negate the Horse Power and Torque Gains you are suppose to see (another reason to get a tune/reprogramming to see proper gain).

So in short, you screwed up by taking the CATs off without having the PCM reprogrammed correctly to accept the resultant sensor readings.

If you have a tuner that you bought with an off-the-shelf program then it is overriding some of the OEM programming so your truck might not exhibit the normal Limp Mode characteristics and it might not even throw the proper DTCs.

Go put a set of High-Flow CATS on your truck and watch the problem go away almost entirely (you will likely still need to have a custom tune programmed). You might also need to replace your Oxygen Sensors as they are likely going to fried b/c of the super rich fuel mixture they have been exposed to.

I would also invest in a proper Wideband Oxygen Sensor and Gauge (AEM UEGO is nice and not too expensive) and have the sensor installed 18-24" back from the headers but before the CAT, that will show you EXACTLY what Air Fuel Ratio you are running, and let you know if something is wrong with the engine's Emission Control System and also let you know that the truck is operating just as intended or not.

 

Thank god i was close... lol nice write up IZero glad to know i was some what right.

 

Yeah you were on the right track... I just wanted to clarify... I'm planning on making a detailed write-up because I see a lot of threads like this on here.... might come in handy for sure....

 

The question I have and all that you said makes sense. But would that cause a gradual decrease in horse power like it is now

 

I don't know how much more simply we can put this.... YES!

 

I'm not trying to be a dumb *** here just simply asking a question cause it doesnt seem to me that it would cause a gradual decrease in horsepower. sudden change in horsepower yes

 

You are overwhelming your computer with false fuel trims... so the problem would gradually get worse. I've explained it all above.

You need to either get a custom tune on there (possibly with a piggy-back ECU) or put some high-flow CATs on it and then see where you're at.

 

Dodge put high flow Cats on the truck stock.

But what IZero is saying is that no matter if you have had the same setup for four years it can still make it go bad one day. look into getting some cats, also since you have ran it this long with out cats id be safe and buy post cat o2 sensors just to be sure. ROCKAUTO.com is the place to go just put the stock o2 brand back on your truck.

 

He'll likely need to replace both upstream and downstream.

Also I just did some more reading on Dodge Rams in particular, and they actually use a MAP sensor instead of a MAF sensor, similar principal to the MAF sensor but it actually calculates the Mass Air Flow (aka Air Density) by using the Intake Air Temperature & the Engine RPM, using the Speed Density Method of calculation.

You should also give the MAP/IAT a check as well and make sure they are reporting correct values.

If you want to read more on MAP vs MAF sensors I suggest this article as well:

http://www.pcmforless.com/index.php?...ning&Itemid=56

Hope that all helps....