3126 w/ABS vs 3116

[ramdough]

I have an M1083A1 from @fuzzytoaster


I highly recommend him as your source when you get ready to buy.


Sent from my iPhone using Tapatalk

 

[GeneralDisorder]

Personally I'm reconsidering the need for the high speed gears. You may go faster but your fuel economy is heavily tied to wind resistance and that will not change so you'll eat up a lot of fuel trying to "go fast" - personally I put my cruise control on at 50 mph and enjoy the drive.

Source: Daily Driven C7 M1079

For an overland build I would suggest the 3126b or the C7. They both support cruise control, and in general are considered longer lived and more reliable than the 3116 by the guys that work on CAT equipment.

Skip to 3:17 for discussion of the engines relevant to us.

 

[Reworked LMTV]

Personally I'm reconsidering the need for the high speed gears. You may go faster but your fuel economy is heavily tied to wind resistance and that will not change so you'll eat up a lot of fuel trying to "go fast" - personally I put my cruise control on at 50 mph and enjoy the drive.

Source: Daily Driven C7 M1079

For an overland build I would suggest the 3126b or the C7. They both support cruise control, and in general are considered longer lived and more reliable than the 3116 by the guys that work on CAT equipment.

Skip to 3:17 for discussion of the engines relevant to us.

A healthy and respectful debate is a good thing, when people's intent is gaining knowledge. I will explain my Modus Operandi for choosing the 3116.

First, there is no doubt that the 3126 and C7 are more powerful than the 3116. In my opinion, "intended use" is the most important factor. On-road, heavy, "have to get there fast" and local, is a completely different set of failure dynamics than Overlanding.

Now for the gray hair opinions. The the older I get, the less I like electronic controls, and I have been trained in electronics. I note that older discrete transistors, resistors and capacitors, tended to be more reliable than IC's found in most ECMs today. Electronics rarely age well, relative to their mechanical counterparts. While any component can break on any engine, electronics seem to be more prone to failure. The smell of burned electronic components is one that I know well. Electronics don't like extremes in temperatures, which these trucks get a lot of. I don't want a dead ECM leaving me stranded 10 miles into the back country. At some point, Matt's off-road recovery may not be able to rescue you. I can limp a mechanical with a dropped injector cup, but not the typical ECM failure. ECMs tend to die in a catastrophic fashion. No nothing on the outputs. You're stuck and your GF is looking worried. Unless something has changed, you have to bring the engine and ECM to CAT for a new ECM. That is typically going to be very, very, expensive if you are not traveling in a group.

Yes, setting the fuel rail on a 3116 is not fun, but I have the rare Meyer-Carpenter setting kit, which makes it a breeze. Watch a simple video, and any mechanic can do it.

 

[GeneralDisorder]

Now for the gray hair opinions. The the older I get, the less I like electronic controls, and I have been trained in electronics. I note that older discrete transistors, resistors and capacitors, tended to be more reliable than IC's found in most ECMs today. Electronics rarely age well, relative to their mechanical counterparts. While any component can break on any engine, electronics seem to be more prone to failure. The smell of burned electronic components is one that I know well. Electronics don't like extremes in temperatures, which these trucks get a lot of. I don't want a dead ECM leaving me stranded 10 miles into the back country. At some point, Matt's off-road recovery may not be able to rescue you. I can limp a mechanical with a dropped injector cup, but not the typical ECM failure. ECMs tend to die in a catastrophic fashion. No nothing on the outputs. You're stuck and your GF is looking worried. Unless something has changed, you have to bring the engine and ECM to CAT for a new ECM. That is typically going to be very, very, expensive if you are not traveling in a group.

Yes, setting the fuel rail on a 3116 is not fun, but I have the rare Meyer-Carpenter setting kit, which makes it a breeze. Watch a simple video, and any mechanic can do it.

ECM failures are absurdly rare. These engines are in 100's of thousands of school busses, FMTV's, equipment.... etc.

I have pointed this out before, but people seem to ignore the fact that the A0 trucks have a LOT more problems with their older generation transmission computer than the A1+ trucks have with theirs so you'll want to carry a spare of that anyway. And you can bet I have a spare ECM on hand also. Along with a starter, voltage regulator, MMDC, etc, etc. Overlanding in ANYTHING means carrying spare parts and tools. I'll take cruise control and a spare ECM over the A0 trans computer, lower power, and all the other upgrades the A1+ trucks have that literally doubled their reliability according to military stats.

 

[coachgeo]

Good call. I think your quote broke. You quoted the number, btw.

good call. Will proceed to self beating lol Fixed break and number

 

[Ronmar]

Well in just the few years I have been in this hobby, I have seen a lot of people diagnose to failed ECUs on 3126s. More so than any other EFI system I have ever worked with. HEUI systems are fantastic genius level diesel tech, but I believe the 3126 was one of Cats first entries into EFI and I think mistakes were made, like the method they chose to retain memory with an unserviceable battery…

I am not recalling too many 3116 MUI core issues, I think someone needed a injector a while back, but most every issue I have helped with/recall circled back to ancillary systems, like primary fuel/air leaks, or run solenoid and power wiring. The MUI system in the 3116 is the pinnacle of over 100 years of active service and development. It is not as easy to modify, and 290 HP is probably closing in on its limit though.

You really dont need any special tools to work on it. the top end alignment doesnt require that kit, it just makes it easier to accomplish the task. Since tech has moved on, finding someone with the knowledge to figure out how to do that work is getting more difficult. I would rank an injector cup replacement as more difficult, but that is a task that could be potentially required on all these engines as they use the same fuel gallery and injector cooling scheme, so the tools and talent for that are still readily available. At their core, they are basically the same engine…

Diagnosing or upgrading the HEUI does require specific hardware, software, experience and permissions, as someone here just recently related. But those services are more readily available.

I hate the term high speed gears. Making 15-20K# of ex military vehicle go faster down the highway is not a good idea IMO. What they do accomplish for you is to make a normal highway speed more comfortable by lowering the cruise RPM closer to the peak torque point instead of riding on top of a cat screaming at 100% rated RPM… The second and possibly more important benefit is to lower the RPM on driveshafts that have pretty extreme angles.

Unless you throw a lot of HP and a different transmission at it, these trucks are never going to be fast uphill, deal with it

As always, my .02…

 

[Reworked LMTV]

ECM failures are absurdly rare. These engines are in 100's of thousands of school busses, FMTV's, equipment.... etc.

I have pointed this out before, but people seem to ignore the fact that the A0 trucks have a LOT more problems with their older generation transmission computer than the A1+ trucks have with theirs so you'll want to carry a spare of that anyway. And you can bet I have a spare ECM on hand also. Along with a starter, voltage regulator, MMDC, etc, etc. Overlanding in ANYTHING means carrying spare parts and tools. I'll take cruise control and a spare ECM over the A0 trans computer, lower power, and all the other upgrades the A1+ trucks have that literally doubled their reliability according to military stats.

The discussion was 3116 vs 3126, not AO vs A1 etc.

"ECM failures are absurdly rare" ????? I concur with Ronmar.

How did you get CAT to flash another ECM with the same serial number, miles /hours etc?

Engine ECMs and Trans ECMs are two different subjects.

 

[GeneralDisorder]

The discussion was 3116 vs 3126, not AO vs A1 etc.

"ECM failures are absurdly rare" ????? I concur with Ronmar.
etc?

My sources in the military have noted that it's very uncommon and electrically the FMTV's weak point and most common failure was the 100a alternator. Having to order an ECU is rare and most of the time didn't fix the problem they were having - IE: misdiagnosed.

I agree that surplus trucks have a potential for failure with age, but as with anything - like tires, etc - change it out when it approaches what you consider too old. 30 years is probably asking a lot of electronics and I would suggest a new one if you plan on going overlanding with that junk. They are available brand new and if you do some looking they can be had pretty cheap with much newer production dates, etc.

The benefits outweigh the disadvantages for me.

How did you get CAT to flash another ECM with the same serial number, miles /hours etc?

CAT isn't the only game in town for programming. I was a software engineer in a former career. I dabble in the electronics side of things also.

Engine ECMs and Trans ECMs are two different subjects.

You're correct. But the fact remains the A0 trucks have TCM's and they are a weak point. You're just as stuck without it as I would be without my ECM.

 

[Stratosurfer]

I appreciate all the data, and look forward to joining the community soon with my own rig.
A1 3126 derivative.
Best All
S

 

[Reworked LMTV]

My sources in the military have noted that it's very uncommon and electrically the FMTV's weak point and most common failure was the 100a alternator. Having to order an ECU is rare and most of the time didn't fix the problem they were having - IE: misdiagnosed.

I agree that surplus trucks have a potential for failure with age, but as with anything - like tires, etc - change it out when it approaches what you consider too old. 30 years is probably asking a lot of electronics and I would suggest a new one if you plan on going overlanding with that junk. They are available brand new and if you do some looking they can be had pretty cheap with much newer production dates, etc.

The benefits outweigh the disadvantages for me.



CAT isn't the only game in town for programming. I was a software engineer in a former career. I dabble in the electronics side of things also.



You're correct. But the fact remains the A0 trucks have TCM's and they are a weak point. You're just as stuck without it as I would be without my ECM.

My sources in the military have noted that it's very uncommon and electrically the FMTV's weak point and most common failure was the 100a alternator. Having to order an ECU is rare and most of the time didn't fix the problem they were having - IE: misdiagnosed.

I agree that surplus trucks have a potential for failure with age, but as with anything - like tires, etc - change it out when it approaches what you consider too old. 30 years is probably asking a lot of electronics and I would suggest a new one if you plan on going overlanding with that junk. They are available brand new and if you do some looking they can be had pretty cheap with much newer production dates, etc.

The benefits outweigh the disadvantages for me.



CAT isn't the only game in town for programming. I was a software engineer in a former career. I dabble in the electronics side of things also.



You're correct. But the fact remains the A0 trucks have TCM's and they are a weak point. You're just as stuck without it as I would be without my ECM.

Ok, you are certainly entitled to your opinions on these trucks. The alternator to me is an issue, but a fairly minor one since it can be replaced with an upgraded one or an aftermarket. This was an engine discussion. Please share your sources for ECMs, programming etc, so the others may get spares and programming.

 

[GeneralDisorder]

Ok, you are certainly entitled to your opinions on these trucks. The alternator to me is an issue, but a fairly minor one since it can be replaced with an upgraded one or an aftermarket. This was an engine discussion. Please share your sources for ECMs, programming etc, so the others may get spares and programming.

That's a rabbit hole. Suffice to say it can absolutely be done and it's simply a matter of googling a bit. It's easier for the 3126b than it is for the C7 but both require some level of proficiency and understanding of software, etc. I bought a military crate C7 take-off ECM on ebay ($450 shipped) that was already basically programmed for what I wanted and then uploaded the injector trim settings from my existing ECM. I went further and got someone with CAT SIS online access on a forum to generate passwords for CAT ET that allowed me to also change the FLS and FTS to match from my old ECM. I now have a two ECM's that can run my engine. The bonus is that the newer crate ECM is programmed for 370 HP and 930 Ft/lbs

The upgrade from CAT for the 3126b to go from 275 HP to 330 HP is free (because it doesn't change the peak torque rating). It only costs a couple hours of labor at the CAT dealer to flash to it. With the C7 you have to purchase an ECM that has the military serial prefix of the desired HP rating (275, 330, or 370 HP) and then transfer injector trims, etc.

 

[Reworked LMTV]

That's a rabbit hole. Suffice to say it can absolutely be done and it's simply a matter of googling a bit. It's easier for the 3126b than it is for the C7 but both require some level of proficiency and understanding of software, etc. I bought a military crate C7 take-off ECM on ebay ($450 shipped) that was already basically programmed for what I wanted and then uploaded the injector trim settings from my existing ECM. I went further and got someone with CAT SIS online access on a forum to generate passwords for CAT ET that allowed me to also change the FLS and FTS to match from my old ECM. I now have a two ECM's that can run my engine. The bonus is that the newer crate ECM is programmed for 370 HP and 930 Ft/lbs

The upgrade from CAT for the 3126b to go from 275 HP to 330 HP is free (because it doesn't change the peak torque rating). It only costs a couple hours of labor at the CAT dealer to flash to it. With the C7 you have to purchase an ECM that has the military serial prefix of the desired HP rating (275, 330, or 370 HP) and then transfer injector trims, etc.

Some will be very interested in this. You will likely get a lot of questions. How hardened are the ECMs for EMPs?

 

[Reworked LMTV]

I felt that this article was very interesting and relevant to the 3116, 3126, and C7: https://thecampingadvisor.com/is-the-cat-c7-a-good-engine-problems/

 

[GeneralDisorder]

Some will be very interested in this. You will likely get a lot of questions. How hardened are the ECMs for EMPs?

All the important bits going into the ECM/TCM, etc are shielded with braided stainless loom. The ECM itself is entirely enclosed in a metal box. I have no way of testing it, but I'm assuming the military did.

 

[GeneralDisorder]

I felt that this article was very interesting and relevant to the 3116, 3126, and C7: https://thecampingadvisor.com/is-the-cat-c7-a-good-engine-problems/

That article states quite a few "facts" that are either incorrect or do not apply to military applications. Such as the "claim" that they run hotter and don't run the fans till 235 - this is false. The FMTV C7 runs the fan at the same 200 degrees that all prior engines ran them at.

The military spec ECU's are not setup with emissions AT ALL. They have ZERO emissions equipment and CAT is still providing the C7 for brand new Oshkosh A1P2's still being actively delivered to units. I rode in a truck built in April of 2021 a few months ago.

They go on to moan about how the C7 is "only" a 450,000 to 500,000 mile engine and only gloss over the fact that the 3116 and 3126 both have lower B50 ratings (but they do mention it). Yeah - we all know ULS Diesel has less lubricating properties. You should be adding additive to all of the engines ever equipped in the FMTV's. Especially those delivered prior to the introduction of ULSD. The military could generally care less since first of all their expected vehicle lifespan is 35,000 miles, and they variously run Diesel, Jet-A, and Jp-8 depending on what's available.

 

[Reworked LMTV]

That article states quite a few "facts" that are either incorrect or do not apply to military applications. Such as the "claim" that they run hotter and don't run the fans till 235 - this is false. The FMTV C7 runs the fan at the same 200 degrees that all prior engines ran them at.

The military spec ECU's are not setup with emissions AT ALL. They have ZERO emissions equipment and CAT is still providing the C7 for brand new Oshkosh A1P2's still being actively delivered to units. I rode in a truck built in April of 2021 a few months ago.

They go on to moan about how the C7 is "only" a 450,000 to 500,000 mile engine and only gloss over the fact that the 3116 and 3126 both have lower B50 ratings (but they do mention it). Yeah - we all know ULS Diesel has less lubricating properties. You should be adding additive to all of the engines ever equipped in the FMTV's. Especially those delivered prior to the introduction of ULSD. The military could generally care less since first of all their expected vehicle lifespan is 35,000 miles, and they variously run Diesel, Jet-A, and Jp-8 depending on what's available.

Still love my 3116. Not concerned about winning a race, just enjoying the ride...
Oh hey, it's cold outside. Better get a blanket for the little CAT to keep her warm : )

 

[GeneralDisorder]

Still love my 3116. Not concerned about winning a race, just enjoying the ride...
Oh hey, it's cold outside. Better get a blanket for the little CAT to keep her warm : )

Yes the 3116 isn't a bad engine - as you note it absolutely needs help cold starting so maybe a heated blanket for tabby.. The EFI engines really don't exhibit that behavior. More of a snow leopard than a tabby.

And I agree - I cruise at 50 mph. I'm also out to enjoy the ride. But the 370 HP and 931 Ft/lb of torque pulls me up grades like you can't imagine. It allows me to *maintain* my desired 50 mph much more easily.

 

[Reworked LMTV]

Yes the 3116 isn't a bad engine - as you note it absolutely needs help cold starting so maybe a heated blanket for tabby.. The EFI engines really don't exhibit that behavior. More of a snow leopard than a tabby.

And I agree - I cruise at 50 mph. I'm also out to enjoy the ride. But the 370 HP and 931 Ft/lb of torque pulls me up grades like you can't imagine. It allows me to *maintain* my desired 50 mph much more easily.

That is an awful lot of power to put through such a small block and a LOT of heat to dissipate on such an old design. Reliability is likely to suffer. I'd watch those EGTs like a hawk. I'd go with a bigger block to run that HP and TQ regularly. Maybe a newer technology Cummins or something like that.

 

[GeneralDisorder]

That is an awful lot of power to put through such a small block and a LOT of heat to dissipate on such an old design. Reliability is likely to suffer. I'd watch those EGTs like a hawk. I'd go with a bigger block to run that HP and TQ regularly. Maybe a newer technology Cummins or something like that.

The Oshkosh M1240 M-ATV uses the C7 @ 370 HP. This in an off-the-shelf dyno tested CAT sanctioned flash for this engine. The M1240 weighs 25k lbs BTW. The flash file in question is dated November of 2009. No one in the military or CAT has seen fit to derate the engine from that specification despite 2000+ units being fielded and 15 years of operation. AND Caterpillar has to warranty them. The military gets a warranty on new equipment just like you do when you buy a new truck.

The C7 @ 330 HP, 860 TQ is used on the FMTV A1P2 armored cab wrecker along with the same transmission that's in my truck. The LTAS armored wrecker weighs 40k lbs and is rated to pull 55k lbs behind it with a 25k lbs vertical load on hook. It must do this in the worst desert conditions with the lowest rank soldiers operating it. Just to do the math - that's 95 thousand pounds being pulled in 130 degree ambient temps up whatever grade PVT Snuffy and his co driver PVT Pharts deem unlikely to strand them before they make it back for hot chow.

So you're saying my 21k lbs M1079 might be too much for the engine with 40 more HP and 61 more Ft/lbs of torque?

Does that pencil out in your head? Really?

 

[Reworked LMTV]

The Oshkosh M1240 M-ATV uses the C7 @ 370 HP. This in an off-the-shelf dyno tested CAT sanctioned flash for this engine. The M1240 weighs 25k lbs BTW. The flash file in question is dated November of 2009. No one in the military or CAT has seen fit to derate the engine from that specification despite 2000+ units being fielded and 15 years of operation.

The C7 @ 330 HP, 860 TQ is used on the FMTV A1P2 armored cab wrecker along with the same transmission that's in my truck. The LTAS armored wrecker weighs 40k lbs and is rated to pull 55k lbs behind it with a 25k lbs vertical load on hook. It must do this in the worst desert conditions with the lowest rank soldiers operating it.

So you're saying my 21k lbs M1079 might be too much for the engine with 40 more HP and 61 more Ft/lbs of torque?

Does that pencil out in your head? Really?

Actually what pencils in my head is HP and TQ vs long term reliability. Have you not had physics? I will take the reliability bonus. Why would they need to de-rate if the military expectations of a 35K life (to quote you)?

By the way, the Steyr 12m18 only has 177hp.