Standard Test Equipment port (A0's and?... why/why not utilize this more than we are doing now.

[GeneralDisorder]

FYI New FMTV's made by BAE had a Cummins.

The civilian Brazos had the under-powered Cummins. The military FMTV's built by BAE have the CAT C7. And The A1P2's are also still being produced with C7's.

 

[coachgeo]

The civilian Brazos had the under-powered Cummins. The military FMTV's built by BAE have the CAT C7. And The A1P2's are also still being produced with C7's.

sounds about right... though the Cummins was a step up from the 3116 and the Brazos was in that 3116 era of the FMTV's right? Does that Cummins exceed the 3126's?

 

[Reworked LMTV]

sounds about right... though the Cummins was a step up from the 3116 and the Brazos was in that 3116 era of the FMTV's right? Does that Cummins exceed the 3126's?

A scope can be a very useful thing. And there are decent options that are quite a bit cheaper than the Picoscope. The real benefit to buying their product is their software - part of which is geared specifically toward automotive diagnostics. But (big but) my fully decked out 4-channel Picoscope with pressure transducer kit, master probe kit, etc is about $5,000 and would not really be economically viable for someone that doesn't own a shop. I've used my Picoscope I think on ONE problem on my truck (and had ALL FOUR channels hooked up to boot). For sure it helped me narrow down the problem by showing me a bunch of things that were not the problem but ultimately it wasn't the silver bullet that time around.

The vast majority of electrical problems people are going to encounter on an LMTV can be diagnosed with some skill, a DMM, and a couple of different "test lights" of different amperage draw ratings.

Much like a Picoscope can be amazing in the hands of a master - so can a halogen headlight bulb and socket with flying leads. The "scope on a rope" as those of us diagnosticians refer to them.

Jarhead Diagnostics Load Test Light — Jarhead Diagnostics

Perfect for adding a load to any 12v circuit!

www.jarheaddiag.com

I get a bit nervous when I hear "Scope on a rope". I definitely will not be bending over to pick up my phone

 

[Reworked LMTV]

An interesting discussion would be "what are the possible engine swaps for an LMTV?" C7's are pretty plentiful, thus you can get one fairly cheap, but it would be interesting to hear what else might fit. Like the larger Cummins, or an older L series, big cam, etc. That kind of thing. If someone said a Detroit might fit (which I don't think one would) I would be interested. Another area that interests me is examining the areas that cause a 3116 to last about 300k. Could a few mods extend its life? (i.e. a larger oil pump, catch cans, etc) But that being said , if I put 300k on my FMTV, I will be a very old man.

School bus mechanics have a wealth of information on our engines.
C7=faster school bus
3116=slow school bus
3126=school bus on side of road

 

[GeneralDisorder]

sounds about right... though the Cummins was a step up from the 3116 and the Brazos was in that 3116 era of the FMTV's right? Does that Cummins exceed the 3126's?

No the Brazos was in the BAE era of FMTV's which was several years after the C7 was standardized. The Cummins has full diesel emissions systems including DEF. I think they are all round 2012 models. They only made like 50 of them.

 

[olly hondro]

The AO STE is very rudimentary. Basically you can read:
24v, gnd and regulator field duty cycle(how hard it is working) from the alt
A buffered/isolated flywheel tach signal(133 pulses per rev) from the frequency divider.
A 24V battery voltage sample from the PPD
A current sample seen by the instrument shunt,
you can sample or activate the run solenoid on the governor
You can sample or activate connection points on the Aux start solenoid, start solenoid and starter motor, perhaps even crank from the STE test box.

ALl that info is available on that plug, I have re-used some of it for my dual voltmeter...

The TCU is accessed by a standalone interface and computer or a prolink. Same with the CTIS, specific adapter set, interface and software you put inline with the connection to talk to that black box....

Not having seen one specifically, but having seen several similar on different systems over the years, you probably had a box that plugged into that STE cannon plug, that probably had a bunch of go/no-go lights, maybe some switches, that should come on as you activated the dash switches to start the truck. it had test points to measure specific voltages from those dedicated test lines, and current measured by the shunt... depending on what lights light, that would narrow down the area to look for trouble, for say a no crank...

Pretty quick IF you have it handy, but a competent tech would outgrow it pretty quickly, as just about any indication it can provide can be duplicated by other observations and a voltmeter, with a little hands on experience... In the case of the A0, the money spent on this system would have been better used to either incorporate it as a Built In Test Equipment, or BITE box(little black box with indicators and test points), or better spent on better drawings and documentation...

The later versions are a whole different ballgame as they bussed all the modules together onto data busses, accessed at a single point by an interface and a laptop... they also did away with all the standalone sensor wiring and current shunt...

This is currently out of my A0, my inclination is to not put it back in. Your thoughts?

 

[Ronmar]

This is currently out of my A0, my inclination is to not put it back in. Your thoughts?

I am not putting mine back in there is another small module down there, called a “frequency divider” that you can also pull. Small box with about 5 colored leads into a multi pin connector. Its actually an isolation amplifier that allows the magnetic pickup RPM sensor to feed more than one tachometer output without being loaded down. Like the dash tac and the STE test equipment…

 

[coachgeo]

I am not putting mine back in there is another small module down there, called a “frequency divider” that you can also pull. Small box with about 5 colored leads into a multi pin connector. Its actually an isolation amplifier that allows the magnetic pickup RPM sensor to feed more than one tachometer output without being loaded down. Like the dash tac and the STE test equipment…

ahhhhh. so one could pull their tach signal from there instead of half removing heater to get to that harness?

 

[Ronmar]

ahhhhh. so one could pull their tach signal from there instead of half removing heater to get to that harness?

Yep, its right there on PX26 pin 1 and 4. Pin 4 is referenced to ground(tb2) at the truck side of that plug.

 

[olly hondro]

Yep, its right there on PX26 pin 1 and 4. Pin 4 is referenced to ground(tb2) at the truck side of that plug.

View attachment 923669

Tachometer huh....I can hear the engine pretty well......it would be like checking the weather app on my phone instead of stepping out on the back porch...

 

[Ronmar]

Ears OK, unless you are looking for a specific number, like say when using a PTO, or determining TC stall…

 

[GeneralDisorder]

Ears OK, unless you are looking for a specific number, like say when using a PTO, or determining TC stall…

The electronic engines of course output tach through the J1939 for diag (such as the stall test) and the CAT ECM has two available high idle speed settings - one of which is used by the factory momentary rocker for PTO/warmup operation (set to 1350 RPM). In addition the cruise control accel and coast functions work as idle up and down controls when in neutral. If you know the high idle RPM, know the sound of your engine, and have the cruise buttons for fine adjustment I don't see any need for an actual tach. For PTO winch operation anyway - I know the high idle speed setting and line play-out/retrieval speed and engine sounds work in concert to tell me everything I need to know.

Perhaps for PTO operation using other types of equipment it may be necessary especially if the pump or whatever you are running needs a corresponding exact speed. Though you could just adjust the high idle speed in CAT ET, use the rocker switch, verify it's operation with live data and forget about the permanent tach.

I don't personally see the need with an automatic transmission. Just more distractions.

 

[Ronmar]

Mmmm high idle… Hey wait, i have a cruise control hand lever

 

[MatthewWBailey]

Mmmm high idle… Hey wait, i have a cruise control hand lever

It's like a motorcycle throttle wrist lock, never disengages when a curve approaches.