3126 ECU mystery box

[Keith Knight]

Can anyone identify this box to the right of the engine ECU that has two threaded plug connectors with nothing attached to them.
This is a 2003 M1078A1 with the 3126B engine.
Each plug has two pins in it. The box had been by passed before I picked it up from the air force base. With a short harness connecting the two plugs together.

In the last picture you can see it, its the short harness with the long blue and white label on it.
My only guess EMP (electromagnetic Pulse) filter.
I hate extra parts so if it not necessary I'll remove and replace it if it is necessary.
Thanks

 

[coachgeo]

bump out of curiosity.

 

[MD 1083]

I had the same question...did you ever discover the purpose? Mine is corroded from the inside out and I think may be the reason the truck will not start. I want to bypass mine but need some guidance. I learned that it's called an EMI filter, Hale is the Mfg, but they don't service the part. Do you mind sharing how yours was bypassed? It has pins/sockets A and B on the upper and lower connectors. Best I can tell the bottom pins are + and - (continuity to the battery pins on the ECM connector) and the top are connected to the various ECM sockets (9, 11, 32, 34, 36, 42, 50, 62 and 70). Many thanks!

 

[Pope]

That is an EMI filter to prevent electroagnetic interference from affecting the ecu. Battery power to the ecu runs through the filter. There was a harness that was made to bypass the filter that I think was part of an MWO.
Later on the filter was omitted from production.

 

[Keith Knight]

Pope is correct. Mine had a harness, by passing it. When I had to replace my ECM/ECU I removed that EMP box.

 

[MD 1083]

Many thanks for confirming that I can stop trying to source the EMI filter. I've got a duplicate OEM side 70 pin harness being made that I intend to use to power up the ECM to see if I can at least get it started and get some Cat-ET data so I know what I'm dealing with. The Cat dealer bench tested the ECM and it's good, just need to get the power and other inputs sorted out. One obvious question and I hope I'm not being a total dope, but is there a start interrupt button or switch somewhere? The A0s look to have a push button but I don't see one in the power panel on my A1. The relay is good but I don't see where the operator can actually trigger the interrupt. All fuses are good and I get power to pin 70 but nothing on 24+ and battery pins. Thanks again!

 

[Pope]

The A0 trucks with the 3116 cat were the only ones to have the start interrupt switch. I'm not sure of the serial number range of your truck, which is important in some aspects of wiring. Does your truck have the DRIC (dual relay interconnect)?
You could connect the wiring directly to the engine ECM and eliminate the extra portion of the harness that went from the filter to the ECM, the fewer connections the less likelihood you're going to have problems with shorts, and loose connections later.

 

[MD 1083]

Thanks for the response. I'm not sure about the DRIC, all I can confirm at this point is that it has a single interrupt relay (truthfully I'll have to research more about the DRIC issue, I may have missed your point completely). I jumped in head first into the Military truck scene after the hurricane/flooding and determined to be in a position to really help friends family and neighbors if the circumstances get that bad again. Anyway, my education continues and I'll be in good shape once I figure out what the 1083 needs to make it run again. I'll post the solution once I get there!

 

[BHathaway52]

Just had the EMI Filter fail on my truck, couldn't figure out what was going on until I came across this thread. Thanks guys! Here was my diagnosis process.



Diagnosis I used:

- Placed inductive voltmeter on the injector wiring harness at the front corner of the valve cover and did not have any power going to my injectors. (Picked up this trick from Adept Ape on Youtube in his crank/no start video for CAT engines) The inductive volt meters say they will only read AC current, but I tested after I got the truck going and it will flash if power is being sent to the injectors. Be careful it's 90-120 volts!

- Disconnected the rear ECM connector or P1 on CAT diagrams. (All inputs come through P1 connector and all outputs to engine go through P2) Check for power at pins 70, 52, and 53. 70 is switched power from key switch, 52 and 53 are unswitched power from the battery. This unswitched power comes through the EMI Filter first then to the ECM. Switched power tells the ECM to turn on and unswitched power gives it the energy to power up. I had power at pin 70, but not pins 52 and 53. (Side Note: Pins 65 and 67 are your grounds for the ECM)


- Disconnected the EMI filter and bypassed it with jumper wires to test. Connect A to A and B to B; you will see the letter on the end of the connector. I just stripped both ends of some wire and shoved it into the pins, don't let them touch each other. Was then able to start the engine right up! Clipped the wires at the EMI Filter connectors and butt connected them together permanently.

 

[MD 1083]

Good work! I eventually did the same thing hoping it was correct. Adept Ape is a great resource - although I learned one thing about a no start condition that was downplayed on one of his videos. The injection actuation pressure sensor was bad. I was under the impression they are very reliable so I was looking everywhere else for a solution first...live and learn. JC Smith, Youtuber, also has a number of good troubleshooting videos for Cat 3126 in case others need pointers on troubleshooting no start issues....FYI.

 

[lshoening]

I have an 2002 M1078 here with that has the same box. The one on this truck is toast. I've been trying to find a replacement but no one seems to know what it is. Lol...

Is there a way you could send me more detailed pics of that jumper between the connectors? Specifically which wires are connected together between the 2 plugs? I know there's a 50/50 chance of getting them reversed, I'd like to build a bypass for this one.

Thanks,
lynn@militarytrucks.com