Cat 3406E no power/ miss while under load

Odd's are it's a sensor going bad, but with no other specific codes it wil be troublesome to find. Look at all your wiring to all the sensors etc. See if you can spot any place they might be chafing and worn through. Take a good look at the oil pressure sensor, make sure it's not leaking through the end and back into connector plug, also look closely at wiring to engine temp as it is mostly hidden from cylinder head down to sensor. Sometimes it's hard to find ghosts, hope you spot your troubles. If you've got a monitor, you can unplug sensors one at a time and see if you can pin down the one stealing your voltage, if it's sensor related. Without a monitor you'll just keep seeing the 21 Flash code though, and you won't know if it's for an open or shorted circuit.

 

engine harness.very common problem here in Michigan (snow,salt)have replaced more Cat harnesses than any other for some reason.seems when they are around 600,00 miles or so,they start to go.good luck.

 

I don't think we are talking same harness.I am talking the engine harness that plugs into ECM.If you can get that one for $243,let me know so I can buy 10 of them at same place!

 

You are going to have a pile of money tied up in that if you just throw parts at it. From what I hear you are working the truck, but it has minor issues. Here is my suggestions, do why you know is free and needs done anyways. Clean all grounds on engine, ecm, and batteries. Unplug ecm check for corrosion and clean with electrical spray. Unplug rocker plug, clean very well with electrical cleaner these are know intermittent issues with oil saturated harness, the oil runs through the wires. Rev motor at idle 1500 rpms have someone watch for check engine light and listen for changes in sound as you pull and wiggle wiring harness. I would exhaust your own labor before spending another dime. Just what I would do.

 

When a shop tells you that without a swap out with a test ecm, how do they know you need an ecm? Like the above posters have stated, disect and thoroughly, thoroughly inspect your wiring. I'm not saying it coud not be an ecm problem, but it rarely ever turns out to be that. Cover your basics first or have a test ecm to avoid spending more money. Usually the more complicated it gets, it'll be something simple, once you find it. The problem is finding it.