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post #1 of 24 (permalink) Old 01-16-2010, 04:38 PM Thread Starter
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EGT Sim Basics

2007-2009 Dodge Ram 2500/3500/4500/5500 Exhaust Temperature Sim Basics

There is a lot of confusion about exhaust sims for the Dodge Ram with the 6.7L Cummins engine.

Some of the questions you may have are:

What is regeneration(regen)?
What are exhaust sims?
What do they do?
How they work?
When do I need them?
Will I get a Check engine light(CEL) with them?
Why does the sim setup my friend installed on his truck not work for my truck?
Why is my truck in “limp mode”?
Why does my overhead console say “catalyst full”?
Why is my check engine light(CEL) on?
Is it street-legal to remove my DPF or EGR and use sims?

I will attempt to answer these questions in the simplest way I can. By the end you will know what sims are, the differences between 330 OHM sims and 100 OHM sims, and be able to make an educated decision on if you need them, and which will work best for you.

Technical information has been condensed or scaled down for ease of reading! This is meant to be the BASICS, so many in-depth details have been left out. I am in no way claiming to be the world’s foremost expert on this topic, but I have spent thousands of hours researching it, and don’t mind passing along what I have learned. Thanks for taking the time to read!

The regen process.

Regen is the way that the factory exhaust system cleans itself out. Soot and other exhaust contaminants are constantly being trapped by the DPF(Diesel Particulate Filter). Using a complex system of backpressure and temperature sensors, the vehicles ECM will determine when the DPF is getting full, and command a regen. The flash calibration (tune) currently installed on the ECM will control how often this needs to occur, and which sensor readings it will use to determine a “full” state. As regen starts, the fuel system will start to inject fuel into the exhaust via the injectors, and will attempt to heat the exhaust system to high enough temperatures to clean the DPF out. During this process, the ECM will run from a completely different set of operating parameters(timing, fuel pressure, turbo vane position, etc.), and you may even notice a loss of power. The turbo will spool up while idling, as the Variable Geometry Turbo will try to aid in obtaining optimal burn conditions in the exhaust. Once the sensor readings confirm that the DPF has been sufficiently cleaned, the regen will end, and running parameters will return to normal. On occasion, the system may not be able to bring the DPF to a clean enough state to satisfy the ECM. The ECM will then cause a Check Engine Light(CEL), as well as cause your overhead monitor or dash readout to say “Catalyst Full, Service Required". The message may also be accompanied by a percentage of how full the ECM estimates the DPF to be.

What are sims?

Sims are merely a factory style plug with an internal resistor, and are primarily used for 2 reasons:
1.To turn off the regeneration(regen) process when using an aftermarket exhaust kit.
2.To keep the CEL from coming on due to aftermarket exhaust kit.

How sims work

The way a sim works is by telling the ECM that the exhaust temp probes located in the exhaust stream are a certain value, or temperature. If a high enough temperature is maintained, or perceived with the use of sims, the ECM will not command a regen, as it assumes the DPF is staying hot enough to clean itself. There is a timer in the ECM that either counts up when the temps are low, or counts down when the temps are hot. If the temps are low for a long enough period of time, the counter will reach the pre-determined limit and start a regen. The temperature threshold and time limit in the ECM will be different depending on the year of the vehicle and the calibration currently installed on the ECM.

Do I need sims?

I cannot stress enough that a tuner specifically designed to eliminate the DPF/EGR is BY FAR the best method if you plan on installing aftermarket exhaust. Sims are more of a “Band-Aid” fix for those that don’t have the money for a tuner, or have a 2009-on vehicle that a tuner may not work on.

If you do plan on running aftermarket exhaust and DO NOT plan on purchasing a tuner SPECIFICALLY DESIGNED TO ELIMINATE REGEN, you will need some form of an exhaust temperature sim. If you do not use a tuner that is designed to eliminate regen, and do not install sims, your vehicle will unsuccessfully try to regen and will cause a “limp mode” state. ‘Limp mode” is where the vehicle is placed in a de-rated state and cannot achieve full power potential, as the ECM has sensed a situation that may potentially damage the drivetrain. The CEL will also illuminate, and your overhead monitor or dash readout will say, “Catalyst Full, Service Required”.

100 ohm VS. 330 ohm

330 ohm

On every calibration we have monitored, installing 330 ohm sims will not stop the regen counter, only slow it down considerably. Depending on the calibration, it is estimated that the counter will activate a regen between 2,000 miles and 40,000 miles. Obviously, that is a wide range, and many factors come into play such as load on engine, other sensor readings, and idle time, etc. The timer will generally speed up when the vehicle is at idle, thus reducing the amount of miles before the regen. The good thing about 330 ohm sims is that they themselves do not cause an immediate CEL. If used in conjunction with a device that clears CELs on startup, this setup can provide a code free way to run aftermarket exhaust. (Note: Some products on the market will clear the regen counter, and some will not). The reason that this works, is that almost all DPF codes are 2 key cycle codes. This means that the ECM must see a problem for 2 consecutive start-ups to set the CEL on the dash. By clearing the codes before every single start-up, the ECM never has a chance to set the light.
To me, this method is somewhat dangerous, as many other vehicle systems also use 2 key cycle codes. You may be continually clearing a code that is trying to warn you of a potential problem the vehicle is experiencing, but you will never know it until it becomes more serious.

Keep in mind that when using 330 ohm sims, but NOT using a product that clears the counters, eventually you WILL go into a regen. You will know immediately when this happens, as when aftermarket exhaust is installed, you will see a considerable amount of white smoke while the engine is running. The turbo will spool up at idle, and the smell of unburned diesel fuel will be very powerful. You WILL notice it! After a short period, the ECM will realize the regen is not working due to the aftermarket exhaust, and will place the vehicle in “limp mode”. At this point you will need a product to clear the timers and codes to get out of “limp mode”.

100 ohm

On every calibration we have monitored, installing 100 ohm sims will 100% keep the ECM from commanding a regeneration. HOWEVER, the 100 ohm sims will also cause an immediate CEL that cannot be cleared until the sims are removed. If you are attempting to use a product that clears codes and counters on startup, and are expecting to be code free, do not use 100 ohm sims. The way 100 ohm sims work, is that the temperature the ECM sees in the exhaust is far above what it deems a safe level for the DPF, and disables regeneration. The bad part is that because of this high temperature, the ECM thinks there is a problem with the DPF, and turns on the CEL. Until you remove the sims, the codes cannot be cleared. 100 ohm sims are a great option if you want to remove the exhaust, want to guarantee regen will not happen, but do not mind if the check engine light is on. The bottom line is that if you have no way of clearing the counters, and don’t want to eventually regen, 100 ohm is your best option.

Pressure Sensor

Another topic I feel needs to be touched upon is the pressure sensor. There is a sensor mounted to the upper passenger side of the transmission that has 2 metal lines coming from it that end in the exhaust pipe. (A common misconception is that these are fuel lines, but they are not. They are for reading backpressure). The sensor uses these lines to determine back pressure in the DPF, and the ECM takes this reading into account when determining the soot load in the system. The lower the sensor voltage reading, the lower the estimated soot load.

Pressure sims

330 ohm
On some calibrations, the ECM needs to see a certain voltage at this pressure sensor, roughly 1.1V, to keep it out of a regen and not cause a CEL. A common practice when NOT using a tuner designed to eliminate regen, is to use a pressure sim on this sensor. Some calibrations see 1.1V as too much soot load, and will try to regen, thus causing a major problem. How do you know if you need a pressure sim on the current ECM calibration of your vehicle? As a rule of thumb, if you are using a device to clear codes on startup, and using 330 ohm sims, start by NOT installing a pressure sim. Install your 330 ohm sims, clear codes on startup as you normally would, then drive the vehicle for 5-10 miles. If you get a “Catalyst Full, Service Required” message during your FIRST drive cycle, AND it is accompanied by a P244a trouble code, you will need the pressure sim to be code free. If it takes 2 drive cycles to get a P244a code, and the code is NOT accompanied by a “Catalyst Full, Service Required” message, DO NOT install a pressure sim. Doing so will cause the timers to speed up, and will result in a regen for sure. Pressure sims are not commercially produced anymore as they are not easily understood how they work, and are a headache to troubleshoot. Also, the vast amount of factory calibrations, and the differences in these calibrations, is the reason that what may have worked for your friend may not necessarily work for you. Do it yourself sims are easily made using 2 specific resistors, and is easily searchable online.

100 ohm
If you are going to be running the 100 ohm sims, and need to know whether or not you need a pressure sim, here is the test. Install 100 ohm sims. Unplug the 3 wire electrical harness that connects to the pressure sensor. Take a 5-10 mile drive and watch for a "catalyst full, service required" message on the FIRST or SECOND drive cycle. If you do, then you need the pressure sim. If not, you should be good to go.

Dyno test misconceptions

Many people have made the assumption that because 100 ohm sims cause the ECM to think there is a problem with the DPF, it will de-rate or de-fuel the engine, causing a loss of horsepower. This is simply not true. We have installed both 100 ohm and 330 ohm sims in a vehicle, then ran numerous dyno tests with both setups. Horsepower and torque readings on every test were identical.

Is it legal?

Removing the DPF or EGR is NOT STREET LEGAL. A common misconception is that because you may not have emissions testing in your state/county/area that it is OK to remove the emissions equipment. This is simply not true. As a rule of thumb, if a vehicle came with emissions equipment installed on it from the factory, it is illegal to remove them. The exception would be if the vehicle is not registered or certified for highway use, AND is 100% of the time used for racing competition.


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Last edited by hsperformance; 01-18-2010 at 08:47 PM.
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post #2 of 24 (permalink) Old 01-16-2010, 04:49 PM
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Sweet info!!! thanks guy...

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post #3 of 24 (permalink) Old 01-16-2010, 04:51 PM
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Nice write-up.

You run out of things to do?

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post #4 of 24 (permalink) Old 01-16-2010, 04:58 PM
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This is wonderful Info. Thanks!

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post #5 of 24 (permalink) Old 01-16-2010, 04:59 PM Thread Starter
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Originally Posted by ksseabrd View Post
Nice write-up.

You run out of things to do?
I wish! The days just aren't long enough....
Just something I wrote up a while back but never posted it. I have seen several arguments lately as to what sims to use so I figured I would post it up. Might be helpful, might not. Figured was worth posting at least....

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post #6 of 24 (permalink) Old 01-16-2010, 05:31 PM
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post #7 of 24 (permalink) Old 01-16-2010, 09:55 PM
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Good info, as far as the regen counter goes, will it reset with a reflash??? Also wil a 100 ohm resistor bring you out of a limpmode if you are running 330 ohm???

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post #8 of 24 (permalink) Old 01-16-2010, 10:30 PM
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Do you know what EGT's the 330 and 100ohm resistors duplicate?

Is there a mid-level resistor that will ensure fewer regens, or no regens, but not so "hot" you get an CEL?
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post #9 of 24 (permalink) Old 01-17-2010, 12:18 AM
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This should be a sticky for sure. It would be a great reference to send the new owners to.
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post #10 of 24 (permalink) Old 01-17-2010, 12:36 AM
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I agree it should be a sticky

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post #11 of 24 (permalink) Old 01-17-2010, 01:14 AM
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Being one of those new owners, I couldn't agree more. Great info, definitely cleared up a couple things!!

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post #12 of 24 (permalink) Old 01-17-2010, 05:38 AM
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Great info and service as always Casey!

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