2003 M1083A1 Does C7 replace 3126?

[Lugnuts]

I don't know where to look so I know the experienced here can help me out, please.
I had an earlier post about motor oil in coolant system and it wasn't oil cooler, so I proved what it was. Needless to say the engine needs replacing. I have a crated drop in from the Military and it doesn't have an ECM. The serial number starts the same way 7JZ but one says C7 and the one being replaced is a 3126.
Is this a drop in or what do I need. It appears to be the same but I understand there is a difference in the injection system.
What's a mother to do?
Lugnuts

 

[Ronmar]

well a quick google search shows that 6PZ and 7JZ are the prefixes used for the 3126B engines...

 

[Lugnuts]

Son of a gun, At your prompting sir I went to wikipedia and learned about the 7.2 Litre Cat engine. I did not realize that they changed the name of the 3126 to C7. But in 2003 to comply with EPA they gave it the new name. Hats off to you once again sir.
I really didn't know how to look that one up!
Thank you

 

[aw113sgte]

Son of a gun, At your prompting sir I went to wikipedia and learned about the 7.2 Litre Cat engine. I did not realize that they changed the name of the 3126 to C7. But in 2003 to comply with EPA they gave it the new name. Hats off to you once again sir.
I really didn't know how to look that one up!
Thank you

They didn't change the name, C7 is measurably different from the 3126.

 

[DeMilitarized]

I don't know where to look so I know the experienced here can help me out, please.
I had an earlier post about motor oil in coolant system and it wasn't oil cooler, so I proved what it was. Needless to say the engine needs replacing. I have a crated drop in from the Military and it doesn't have an ECM. The serial number starts the same way 7JZ but one says C7 and the one being replaced is a 3126.
Is this a drop in or what do I need. It appears to be the same but I understand there is a difference in the injection system.
What's a mother to do?
Lugnuts

The ecm will need to be reflashed at a minimum. There is a possibility that it is compatible with the C7 but some ecms are not compatible with other engines. Example most of the C7 ecms but not all are not flash compatible with the C12 in the mtvr but the majority of the 3126b ecms are. It really DEPENDS. I can do ecm bench tuning.

 

[aw113sgte]

The ecm will need to be reflashed at a minimum. There is a possibility that it is compatible with the C7 but some ecms are not compatible with other engines. Example most of the C7 ecms but not all are not flash compatible with the C12 in the mtvr but the majority of the 3126b ecms are. It really DEPENDS. I can do ecm bench tuning.

My experience is the C7 is not compatible. I tried it in Cat ET on the one I have and was a no-go. They are also constructed differently with the C7 ECMs having 4 tapped holes around the plugs for a cable protector.

 

[GeneralDisorder]

3126 and C7 use different ECM's. Not compatible at all. Also the 3126 ECM is less reliable and twice the price: ~5-6 years of 3126 production. 20 years of C7 production.

The primary difference is the HEUI pump/sensors and the C7 injectors have trim files for each injector serial number. 3126 ECM's have no injector trim offset files - they treat every injector the same.

But the 70 pin chassis connector is the same so the C7 will drop in and replace the 3126 without much drama.

 

[aw113sgte]

3126 and C7 use different ECM's. Not compatible at all. Also the 3126 ECM is less reliable and twice the price: ~5-6 years of 3126 production. 20 years of C7 production.

The primary difference is the HEUI pump/sensors and the C7 injectors have trim files for each injector serial number. 3126 ECM's have no injector trim offset files - they treat every injector the same.

But the 70 pin chassis connector is the same so the C7 will drop in and replace the 3126 without much drama.

Don't the 3126 have trim codes(versus trim files). The C12 is trim code based. I would assume that means not all injectors are treated the same but obviously we don't have the engineering data to know what changes codes or trim files actually do. Maybe it's just all stuff to make us feel like our trucks are special with no substance...DEI style.

 

[GeneralDisorder]

No there are no injector trims for the 3126 - it was the first HEUI engine and didn't use them. The C7 injectors used to come with trim files on CD but now you just download them from CAT SIS.

The 3126 (and C7) has FLS and FTS trims. Which are a slope and intercept that describes some part of the fuel equation but doesn't change with pumps or injectors (or can't be calculated without running it in a Dyno cell) so you just copy that information from the old ECM or from the timing cover sticker.

I suspect that both of them are mostly fine tuning for emissions. The C7 trucks have catalytic converters. The military will swap ECM's around for testing purposes and they seem to run fine. I've seen trucks sold with an ECM that was not programmed for the injectors or FLS/FTS and the owner didn't even have any idea.

 

[aw113sgte]

I've heard fts/fls are numbers to adjust the power to the standard engine spec- so you don't have lower and higher power ones out there. People have played with the values (along with injector trims) to get more power. I haven't seen dynos so maybe it's all butt calibration and placebo.

 

[Lugnuts]

Don't know if I need to post to another title? If I do I will
Engine is installed but I have not attempted to start because I am having difficulties with wiring and previous repairs that have been done.
So in order to clean up and be sure of correct locations for the connections, I do happen to have schematics for the A1. Numbers on wires were seemingly in wrong places or not listed in schematic and I went looking for a legend of numbers and where they go, or at least vague description of wire and function.
My schematic does not show the starter. Yet it is labeled as the schematics that go with my VIN. I looked under FMTV tech manuals and found nothing for the A1. Color me stupid but as you will, I still could use more help with this.
Another thing that was spoken about previously was the difference between C7 and 3126 but when I looked at the Engine Number they both start with 7JZ so I put the ECM on just to see if it will start. Haven't attempted yet. My question is how do you know the difference between an ECM for a C7 and a 3126? Part Number?
Thank you y'all
Lugnuts

 

[GeneralDisorder]

C7 ECM's have large square castings with threaded bosses at each corner around both plugs for aluminum covers that are part of the EMI/RFI suppression and they bond the harness stainless mesh braid to the ECM housing. This is probably part of the solution used to delete the deprecated EMI box that hung off the back two bolts of the 3126 ECM. Otherwise they are both 70 pin CAT ECM's and the only way to tell them apart unless you know what you are looking at is to hook them up to CAT ET with a bench harness and query them. Even if you know what family of engine they were used for, you can't tell if it's a 170 HP school bus flash file or a 370 HP military MRAP flash file that's loaded onto it. I've seen a C18 ECM from a HET that happily took a 3126B flash file and turned itself into a 3126 ECM with no issue. But the C7 ECM is not compatible.... Explain it I cannot.

 

[DeMilitarized]

C7 ECM's have large square castings with threaded bosses at each corner around both plugs for aluminum covers that are part of the EMI/RFI suppression and they bond the harness stainless mesh braid to the ECM housing. This is probably part of the solution used to delete the deprecated EMI box that hung off the back two bolts of the 3126 ECM. Otherwise they are both 70 pin CAT ECM's and the only way to tell them apart unless you know what you are looking at is to hook them up to CAT ET with a bench harness and query them. Even if you know what family of engine they were used for, you can't tell if it's a 170 HP school bus flash file or a 370 HP military MRAP flash file that's loaded onto it. I've seen a C18 ECM from a HET that happily took a 3126B flash file and turned itself into a 3126 ECM with no issue. But the C7 ECM is not compatible.... Explain it I cannot.

Again the threaded housing doesn’t really mean anything. It’s simply the BIOS on the ecm that is configured for a certain type of truck. If the ecm isn’t the compatible part numbers and you can’t get it to flash let me know and I can bench flash a known c7 ecm


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[GeneralDisorder]

Well I have a bench flash adapter and many versions of CAT ET..... I've played with wash files and some other stuff but I have run across ECM's that will just not accept some files. The threaded casting ECM's don't take 3126 files and the non threaded casting versions don't take C7 files and even some non threaded ECM's don't accept 3126 files of certain versions. There may be a way to do it by opening them and manually flashing the EPROM..... Not sure.

 

[Lugnuts]

C7 ECM's have large square castings with threaded bosses at each corner around both plugs for aluminum covers that are part of the EMI/RFI suppression and they bond the harness stainless mesh braid to the ECM housing. This is probably part of the solution used to delete the deprecated EMI box that hung off the back two bolts of the 3126 ECM. Otherwise they are both 70 pin CAT ECM's and the only way to tell them apart unless you know what you are looking at is to hook them up to CAT ET with a bench harness and query them. Even if you know what family of engine they were used for, you can't tell if it's a 170 HP school bus flash file or a 370 HP military MRAP flash file that's loaded onto it. I've seen a C18 ECM from a HET that happily took a 3126B flash file and turned itself into a 3126 ECM with no issue. But the C7 ECM is not compatible.... Explain it I cannot.

Does it harm anything to try???

 

[DeMilitarized]

Does it harm anything to try???

No it just works or it doesn't. If it doesn't then it needs to be flashed back to 3126. And anyone is going to charge $600 to touch it with Cat ET.