[cjowett]

I'm missing something - maybe someone can help.

According to the Chrysler's wiring diagrams the exhaust pressure switch with ports on either side of the DPF is two variable resisters. One would assume that the ecm is comparing the pre-dfp pressure to the post to determine if the dpf is clogged up enough to need regeneration. So some guys have posted that you can fool the ecm with a constant resistance of 110 ohms on the pre side and 330 ohms on the post side. When I did that I got various error codes including a catalyst full message. The remarable thing is that the overhead even changed the percent full, sometimes starting at 100% sometimes 90 and counting it down to 80 and then 70 and then the message disappearing and yes it was in regeneration mode. It attempts regeneration often with those values so I've experimented with various resisters to try and get the false pressures close enough that no regen occurs and no error codes appear. All to no avail. I've had the full gammit of codes - P1451, P1453, P2453, P2451.... But with 330 on the backside and 330 in parrallel with 2k on the front, the regen didn't occur. So I hooked the factory switch back up with both sides seeing the same pressure and left the 2k resistor in parallel to the front side. I measured the resistance with the engine off and had 2.6k on one side and 2.66 on the other. But as soon as I started the truck I lost continuity on both sides (my ohm meter only goes to 40k.) What the [email protected]#$?

I'm also confused by something else. On the left side of the transmission there is a connector (either C108 or C128 I can't remeber which) that has wires from all three EGT probes and one wire for exhaust pressure. What happend to the other wire? Also none of the wires on that connector match the wires on the pressure switch. On dial-up I haven't had time to trace all the wiring for these things but does anyone know what happens between the pressure switch and this connector? Or is there another pressure sensor somewhere? (If nothing else this connector may be the ideal place to plug foolers in for anyone willing to do constant voltage feedback.)

BTW I'm not fooling the EGT. I have probes in place.

 

[HDMechanic09]

Put easy and simple get an xrt or the smarty and you dont need sims

 

[cjowett]

in due time I will. Right now I'm not working so I can't afford that kind of outlay. So I'm trying to improve my mileage on the cheapy.

 

[HDMechanic09]

something free you could do is unplug the egr. you'll get a check engine light but you wont have the recirculated soot going into your engine anymore. if im not mistaken you might see a mpg gain.

 

[cjowett]

I'll try the egr unplug/delete for sure. I was hoping to get a code-free dpf delete first so I would know which caused any errors that come up. I may end up putting the dpf back in place and then unplugging the EGR. If I'm not getting all the soot through the dpf it might not need regeneration as often and hence the improved fuel economy (and reduced trips to the dealer for a de-soot).

 

[dad2bike]

I'm missing something - maybe someone can help.

According to the Chrysler's wiring diagrams the exhaust pressure switch with ports on either side of the DPF is two variable resisters. One would assume that the ecm is comparing the pre-dfp pressure to the post to determine if the dpf is clogged up enough to need regeneration. So some guys have posted that you can fool the ecm with a constant resistance of 110 ohms on the pre side and 330 ohms on the post side. When I did that I got various error codes including a catalyst full message. The remarable thing is that the overhead even changed the percent full, sometimes starting at 100% sometimes 90 and counting it down to 80 and then 70 and then the message disappearing and yes it was in regeneration mode. It attempts regeneration often with those values so I've experimented with various resisters to try and get the false pressures close enough that no regen occurs and no error codes appear. All to no avail. I've had the full gammit of codes - P1451, P1453, P2453, P2451.... But with 330 on the backside and 330 in parrallel with 2k on the front, the regen didn't occur. So I hooked the factory switch back up with both sides seeing the same pressure and left the 2k resistor in parallel to the front side. I measured the resistance with the engine off and had 2.6k on one side and 2.66 on the other. But as soon as I started the truck I lost continuity on both sides (my ohm meter only goes to 40k.) What the [email protected]#$?

I'm also confused by something else. On the left side of the transmission there is a connector (either C108 or C128 I can't remeber which) that has wires from all three EGT probes and one wire for exhaust pressure. What happend to the other wire? Also none of the wires on that connector match the wires on the pressure switch. On dial-up I haven't had time to trace all the wiring for these things but does anyone know what happens between the pressure switch and this connector? Or is there another pressure sensor somewhere? (If nothing else this connector may be the ideal place to plug foolers in for anyone willing to do constant voltage feedback.)

BTW I'm not fooling the EGT. I have probes in place.

From what I'm reading it sounds like you have decided to the DPF delete in your own fashion. I suggest you go to this thread and see an already proven delete that works.
http://www.cumminsforum.com/forum/6-7l-powertrain/137901-egr-dpf-budget-how.html

It sounds to me like you installed the 110/390 Press SIM backwards. Been there, got the same results. Also it is very important to install the 3-330 ohm EGT SIMS. They are critical to a DPF delete.
There is an abundance of information available on this site. I suggest you do plenty of homework. :thumbsup:

 

[LSmith]

Hopefully someone will post who knows for sure but my understanding is the resistance increases as pressure rises which means you have the resistors backwards. The post DPF pressure normally runs only about 1/2 PSI (there is really no back pressure on this probe because the muffler is straight through). Pre-DPF pressure (unclogged @ idle) is about 3X that, thus the 110 and 330 ohm resistors..... It should be easy to check?! Just reverse them and see.........

 

[LSmith]

Dad2bike types faster than me......

 

[dad2bike]

Hopefully someone will post who knows for sure but my understanding is the resistance increases as pressure rises which means you have the resistors backwards. The post DPF pressure normally runs only about 1/2 PSI (there is really no back pressure on this probe because the muffler is straight through). Pre-DPF pressure (unclogged @ idle) is about 3X that, thus the 110 and 330 ohm resistors..... It should be easy to check?! Just reverse them and see.........

I just did before you. The correct values are 110/390. Having them revered will give the results posted. It is possible using a 330 might also due to the lower ratio between the resistors.

 

[menarje]

Been having problems with the truck complety shutting off for a second or two and then coming back on while driving 70 in traffic. DANGEROUS
Was told to unplugged my EGR last week so i did---Milage went from 15.7 to 18.3 and truck runs great.
I ordered a DPF-R and will install it over the weekend.

 

[KhakiCummins]

I'll try the egr unplug/delete for sure. I was hoping to get a code-free dpf delete first so I would know which caused any errors that come up. I may end up putting the dpf back in place and then unplugging the EGR. If I'm not getting all the soot through the dpf it might not need regeneration as often and hence the improved fuel economy (and reduced trips to the dealer for a de-soot).

I don't know that you'll see much change in regen frequency with the EGR unplugged. You're still creating the soot, it's just not going through the engine.

With my DPF in place and EGR unplugged, I did see an increase in fuel economy (about 1.5 MPG) but regens were just a frequent as with the EGR plugged in.

 

[LSmith]

but regens were just a frequent as with the EGR plugged in.

My frequency dropped at least in half. My truck will no longer do a DeSOx/DeNOx regen -- only DeSoot.

 

[cjowett]

From what I'm reading it sounds like you have decided to the DPF delete in your own fashion. I suggest you go to this thread and see an already proven delete that works.
http://www.cumminsforum.com/forum/6-7l-powertrain/137901-egr-dpf-budget-how.html

It sounds to me like you installed the 110/390 Press SIM backwards. Been there, got the same results. Also it is very important to install the 3-330 ohm EGT SIMS. They are critical to a DPF delete.
There is an abundance of information available on this site. I suggest you do plenty of homework. :thumbsup:

I did go through that thread and as near as I could tell it wasn't code-free. I also believe that if you are fooling the soot deferential switch properly that the ECM shouldn't be attempting a regen and as you point out with the method described there the EGT sims are necessary ergo to my way of thinking that method isn't "proven to work".

Having said all that, I have tried setting up the resistors as described and did get it code free but immediately go into regen. So I methodically moved the 330 up and the 110 down in unison but to no avail.

I pulled the switch out of the truck and measured the resistance across the poles and go quite a surprise. From 1 to 3 there was 8.4 k-ohms. From 2 to 3 there was 9.2 k-ohms and from 1 to 2 there was 1.4 k. So obviously when you fire up the truck and pressure hits this siwtch they all change. So this switch isn't at all as depicted in the wiring diagrams. Its shown there as fixed resitance between 1 and 3 thw 2 to 3 being variable.

 

[cjowett]

my next trick is to wire in two potentiometers so I can vary the resistance in both spots and see if I can hit it spot on where there ar no codes and no regen.

 

[LSmith]

Fooling the pressure differential alone will not prevent regens. As Dad2bike stated, the only way to prevent regens is for the EGT to be too high (thus the Sims fooling the ECM into thinking EGT's are >1100. Unplugging your EGR will prevent DeNOx regens, but not DeSoot regens. The only way to stop regens completely is with the Temp SIMS. The pressure sims prevents code and overhead messages (CAT Full)

 

[cjowett]

Fooling the pressure differential alone will not prevent regens. As Dad2bike stated, the only way to prevent regens is for the EGT to be too high (thus the Sims fooling the ECM into thinking EGT's are >1100. Unplugging your EGR will prevent DeNOx regens, but not DeSoot regens. The only way to stop regens completely is with the Temp SIMS. The pressure sims prevents code and overhead messages (CAT Full)

So what causes the soot regens if its not the pressure differential?

 

[LSmith]

DeSoot regens are activated by the pressure differential if the delta gets high because of "unusual" driving conditions. However, best anyone can tell (there were long discussions about this awhile back) it seems that the ECM initiates a DeSoot regen just because it hasn't done one in a while. On my truck it's about every 250 miles (or twice per tank of fuel). Fooling the ECM into thinking EGT's are high stops the regen because dumping raw fuel into a hot exhaust may cause a fire.

I'll look for the explanation and try and post the link.....

 

[LSmith]

Here ya go -- kinda long but lots of info....

http://www.cumminsforum.com/forum/6-7l-powertrain/67960-dpf-filter-load-what-do-numbers-mean.html

 

[cjowett]

I'll take a look. But your previous post got me thinking: if the ECM wants to do a regen of the catalytic converter and/or the NOx accum, something must trigger that. So I unplugged my O2 sensor and went for a spin. Vola. No regen occurring. So I swapped out the dfp delete pipe that replaced the dfp and NOx accum for one that just replaced the dpf. After a short regen of the NOx accum, no more codes, no more constant regen'ing going on.

I wouldn't want to not let these occur as long as either of those devices are in place (and when I stop the egr they will be very infrequent I would think) so that's another reason not to fool the EGT probes. But the biggest reason is that if the ECM is seeing a constant 1100 degrees, what happens if your boost fooler or tuner pushes the egt to 1500 or 1600. You'll melt the piston domes unless you're constantly watching your aftermarket gauge. Not something I want to rely on if I'm towing my RV through mountains or something like that.

So end of the day, I'm happy with what I have working. Thanks for your input.

 

[LSmith]

There is a LOT of stuff going on with the emissions on these trucks.

With the O2 sensors unplugged, you may be okay for awhile, but based on what has been reported over the past year, I think you're gonna get the good ole lightning bolt on the dash. During my experimentation, I went over 100 miles one time code free, then while driving down the interstate got the lightning bolt and the truck went into limp mode.

A lot also seems to depend on the flash level you are running. Different flashes give different responses to changes.

Maybe you'll get lucky -- someone finds out new stuff on these things every day!