2 computers..... what is the 'command flow'?

[rancherman]

the 12 valve and 24 valve cummins running the cummins supplied computer, along with the chrysler supplied pcm... make up our 'management operations'. Am I wrong to think the cummins' ecm does the actual engine management.... but is 'guided' by the pcm?so when a person mods with a performance module, they are actually 'fooling' the cummin's ecm with 'false' info from pcm?? ( so to induce higher boost, more timing, more fuel, etc..)The reason I ask, is the '94 ranch truck I am getting ready to build this winter still awaits my decision on which power plant: A simple 12 valve, totally mechanical on one end of my choices, to a more expensive 24 valve common rail 5.9 ( or something in between).One part of me wants to keep it simple, (fewer computers and wiring the better)... but at the same time wants more than the stock horsepower.. My plans are to hang an Allison 1000 5 speed behind it. I want the overdrive. I realize there will be a tcm to wire up there, along with a trans position sensor (if I go with a mechanical 5.9). I have spent far too much on Dodge Automatic transmissions at the rebuilders.. (I've already strayed from my 'simpler' theory!:banghead: dang it )This truck has been stripped of most of the engine wiring. (originally a diesel model). This is where I need to know how to proceed! If I go with 98.5 and up engine, I have found suppliers who sell 'ENGINE RUN' harnesses. Which will require me to basically do a custom dash. Which leads me back to the top of my post! If I go this route, 'eliminated' pcm, have the 'reflashers' made progress in re-working the cummins ecm? so, this is basically a 'see what I can/can't/shouldn't attempt' type questionare. Any and all inputs.. I am ready to be schooled! bring it!Thanks!

[hex0rz]

the 12 valve and 24 valve cummins running the cummins supplied computer, along with the chrysler supplied pcm... make up our 'management operations'. Am I wrong to think the cummins' ecm does the actual engine management.... but is 'guided' by the pcm? so when a person mods with a performance module, they are actually 'fooling' the cummin's ecm with 'false' info from pcm?? ( so to induce higher boost, more timing, more fuel, etc..) The reason I ask, is the '94 ranch truck I am getting ready to build this winter still awaits my decision on which power plant: A simple 12 valve, totally mechanical on one end of my choices, to a more expensive 24 valve common rail 5.9 ( or something in between). One part of me wants to keep it simple, (fewer computers and wiring the better)... but at the same time wants more than the stock horsepower.. My plans are to hang an Allison 1000 5 speed behind it. I want the overdrive. I realize there will be a tcm to wire up there, along with a trans position sensor (if I go with a mechanical 5.9). I have spent far too much on Dodge Automatic transmissions at the rebuilders.. (I've already strayed from my 'simpler' theory!:banghead: dang it ) This truck has been stripped of most of the engine wiring. (originally a diesel model). This is where I need to know how to proceed! If I go with 98.5 and up engine, I have found suppliers who sell 'ENGINE RUN' harnesses. Which will require me to basically do a custom dash. Which leads me back to the top of my post! If I go this route, 'eliminated' pcm, have the 'reflashers' made progress in re-working the cummins ecm? so, this is basically a 'see what I can/can't/shouldn't attempt' type questionare. Any and all inputs.. I am ready to be schooled! bring it! Thanks!

Its a no-brainer in my book. A 12-valve...

[diesel4life]

The ecm is strictly engine management while the pcm does truck functions. Trans commands come from the pcm as well. On the vp 44 trucks the pcm is mounted on the firewall behind the air cleaner. Now as far as the swaps go, I havent ever done one but you wanting to keep it as simple as possible i would think sticking with a 47 re or 48re would be more practical . I personally think the allisons are a bit overated if you look at the duramax guys anybody who does any mods also have to beeef up their trans as well they just cant handle much above stock hp. For the money its going to cost you to convert an allison over and possibly have to rebuild you could build a more than adequate 47 or 48. You could look for a donor truck something that has been wrecked and even maybe find some extra useable parts as a bonus. Now obviously a 12 valve with a 5 speed would be the simplist choice no computers very little wiring to deal with but in the end its your project you do what trips your trigger Have you been on CF? Its a pretty big site lots of people doing all kinds of mods you may be able to find something there.

[Wild and Free]

Stick with a 12 valve and properly mod it for daily towing use and stick with a Dodge tranny, sounds like you need to find a better tranny builder. The 47RH "mechanical auto tranny" properly built will outlast the Allison, as posted above the Allison 1000 was designed as an automotive tranny and is not a quality tranny compared with to the older truck trannys most think of when they associate with allison, they have many issues as do every other tranny in stock form.