Engine/Transmission (1998.5 - 2002) Inside the ECU

[Jdonoghue]

This subject has probably been beaten to death over the years, then forgotten due to some of the products available today. But, I'm one of those people who just have to do everything myself, and I'm not satisfied until I know how everything works. So, if anyone's interested to follow me down the road of Cummins ECU exploration, my journey can be followed here: Dodge/Cummins ECU

 

[WTBurke]

JD,

I'm in your audience and reading. It's good stuff and I'll follow along.



William

 

[GDMRTN]

I'm watching too. It's not always the "big" companies that make the most of their truck!! Good job and keep it up! Keep us posted on progress. However slow and small it may seem to you.

 

[rweis]

This will be fascinatingly interesting, and will make a superior read.



Bob Weis

 

[JR2]

Nice work... . keep digging and don't let the smoke out of those little thingies in there. I hear once the smoke comes out they don't work so well.

 

[Jdonoghue]

Nice work... . keep digging and don't let the smoke out of those little thingies in there. I hear once the smoke comes out they don't work so well.

I won't even begin to tell of all the 'magic smoke' I've seen come out of electronic things in my time!

 

[KDoerr]

Keep up the good work I'm with you for the Imformation.

Keith

 

[John - K5AWO]

I'm also interested in such things but it has been a long long time since I did assembly and machine code. Never got into 'C' but would be willing to learn if for no reason more than to be able to change the parameters in my ECU.

 

[John - K5AWO]

I won't even begin to tell of all the 'magic smoke' I've seen come out of electronic things in my time!

"Magic Smoke", we always called "Well, I just tested it and all the Good Smoke has gone" :-laf

 

[Jdonoghue]

I'm also interested in such things but it has been a long long time since I did assembly and machine code. Never got into 'C' but would be willing to learn if for no reason more than to be able to change the parameters in my ECU.

The biggest problem right now is that all I have is a disassembly listing of the code. It looks like most of the code was originally written in C. It's not easy stuff, like the Z80 code that I disassembled and changed while working on a large mainframe project (1980's era mainframe). I have a background in microprocessors and electronics, much of this stuff is familiar, but 32-bit code disassembly listings aren't the easiest things in the world to figure out.



Also, I have not yet figured out which inputs go where - if I had a scrap ECM to poke around with, it would be easy to find out things like which analog input pin is the coolant temp. sensor, the APPS, MAP sensor, etc. I only have the ECM off my truck and really don't feel like having to replace it. In the next week or so I am going to have to go hunting for a junkyard ECM.

 

[John - K5AWO]

I appreciate that one JD. I have a spare for my truck, it is the OEM that came with the truck, but not inclined to take it apart. Might accidentally have to put it back in service if the hot rod version I'm using craters...

 

[ccie]

Actually the “smoke” is what makes it work. I know this because when I let the smoke out it no longer works.

 

[jmy]

The biggest problem right now is that all I have is a disassembly listing of the code. It looks like most of the code was originally written in C. It's not easy stuff, like the Z80 code that I disassembled and changed while working on a large mainframe project (1980's era mainframe).

______________________________________________



Z80 code brings back memories, sounds like console processor for and IBM compatible mainframe such as AS5000 or AS3000 from NAS or Itel. Did a bit of that in the late 70's and early 80's myself. Moved on to PC's X86 and microcontrollers later. Fully agree the 32bit stuff written in C and implementing custom ASICs are tough even with the best tools.



Good luck with your effort. Plenty of people are intrested in this kind of project.



Thanks for sharing.



Jim

 

[RoryTek]

Hey JD, is part of data in there for black box type data recording, like the stuff crash investigators would use for accident info?

 

[Jdonoghue]

Hey JD, is part of data in there for black box type data recording, like the stuff crash investigators would use for accident info?

I don't know for sure, but I think if something like that existed, it would be inside the PCM or some other module. The engine controller is only interested in reading the various engine sensors and sending the appropriate data to the VP44. It sends things like engine speed, oil pressure, coolant temp, etc. to the PCM. The writable memory inside the ECU would contain things like stored fault codes.

 

[rkressg]

Actually the “smoke” is what makes it work. I know this because when I let the smoke out it no longer works.

I can 't believe someone else actually says this. At work, we call it the Magic Smoke, because once we let it out, things quit working (we blow stuff up good on the Railroad).



But seriously, this is a good post. I am glad to see someone trying to rip the ECU apart and apply common sense to it.

 

[Jdonoghue]

J1939 messages

By luck, I stumbled upon a .pdf file with the J1939 info. Using this, I was able to identify where in the code the messages are generated and transmitted, and more importantly, where things like engine speed, boost pressure, etc. are stored.

This has enabled me to identify important parts of the code and the tables used to generate various data points. I'll post a complete update later today! This is getting really interesting!

 

[Gary - K7GLD]

A good thread, and a good start into understanding the "flow" of electronic info that controls our trucks!



I am pretty much in the dark as to exactly which device - PCM or ECM - that operates, governs and controls various operational aspects of the engine in particular.



This all became important again, as we just returned from a week long RV trip that involved below freezing weather the last morning, and resurfaced the notorious cold-weather random "miss" or erratic engine operation that has been covered on this board before.



It clearly relates to some portion of engine control that is sensitive to ambient temperature - and quite possibly actually a solid state device inside one of those control units that becomes erratic when the ambient temps drop to freezing or below - but WHICH unit is it - the PCM or the ECM? I don't have a clue...



Perhaps following this subject will give a better clue as to which unit is most likely to create specific problems...

 

[ERuhl]

Also, I have not yet figured out which inputs go where - if I had a scrap ECM to poke around with, it would be easy to find out things like which analog input pin is the coolant temp. sensor, the APPS, MAP sensor, etc.

There's a pinout diagram in the FSM, see attached PDF. Is this what you were looking for?

This all became important again, as we just returned from a week long RV trip that involved below freezing weather the last morning, and resurfaced the notorious cold-weather random "miss" or erratic engine operation that has been covered on this board before.



It clearly relates to some portion of engine control that is sensitive to ambient temperature - and quite possibly actually a solid state device inside one of those control units that becomes erratic when the ambient temps drop to freezing or below - but WHICH unit is it - the PCM or the ECM? I don't have a clue...

Neither, your truck has too much base timing. As does mine and several others on here. Search my post history, I installed a pigtail between the IAT sensor and its connector so I could splice a switch and potentiometer into the circuit without damaging the stock harness. When it gets cold and starts acting up I flip the switch and pull out timing by altering the IAT signal with the potentiometer. Switch off = stock, Switch on = potentiometer in parallel w/ IAT sensor. Works great. Start another thread or send me a PM if you need more info.

 

[Jdonoghue]

There's a pinout diagram in the FSM, see attached PDF. Is this what you were looking for?

Thanks for the PDF, that will be a great help! The one I had before was really grainy and there were several pin#s that I could not make out.



But, what I had been referring to, was which analog input pin on the CPU chip itself each input was connected to. I have since figured that out, with the exception of the coolant temp sensor. Most of my spare time these days has been spent picking through the program code to see what makes it tick.