Fault Code 1117
08-25-2020, (Subject: Fault Code 1117 ) 
Post: #28
RE: Fault Code 1117
(08-24-2020 )DVT873 Wrote:  Rawze, had the same problem on a N14 a while back. Fuel solenoid feed from ECM. Realize that there may be an ECM problem. A "go time" issue. Ran keyed power out of the fuse box. Came off the solenoid with 2 diodes. Hooked keyed power to one and the ECM feed to the other. Figured if the ECM didn't see the solenoid it would get pissy. The diodes should stop any back feed. Didn't want key power going to ECM or ECM power going to key. Been a week or so. So far so good and no codes. Truck stays within 30 miles. Miss the simple days of turning the little knurled knob on the solenoid for bypass. Didn't need anything more than pliers if that.

The diode trick is short lived the way you have it hooked up.
You need a diode also in reverse across the pin to ground to bleed off the kick-back current from the coil. That kick-back current will go somewhere every time power is dropped off and if you have only forward facing diodes, it will jump internally across one of them and destroy one of both or the diodes after a while (and consequently, possibly the ecm ) after a while.

It can be done properly with 2 diodes, however it sounds like you did it wrong. ... one forward facing from the ecm... the other reversed across the coil power feed to ground... and the key-switch wired directly to the feed point of the coil (thru a 3a fuse of course).

Also.. diodes have a 0.7 volt drop across them. This could be a problem all in itself if your battery voltage is below about 13.3 or so.


User's Signature: ->: What I post is just my own thoughts and Opinions! --- I AM Full Of S__T!.
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 Thanks given by: DVT873
08-25-2020, (Subject: Fault Code 1117 ) 
Post: #29
RE: Fault Code 1117
I need to think about this a bit more. Forgot about the kick back. Thanks
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08-25-2020, (Subject: Fault Code 1117 ) 
Post: #30
RE: Fault Code 1117
(08-25-2020 )DVT873 Wrote:  I need to think about this a bit more. Forgot about the kick back. Thanks

Yeah, when a magnetic field collapses, it creates a kickp-0back current and voltage. If it has nowhere to go, that voltage will climb into the tens of thousands of volts or more range until it finds and jumps across a pathway. Usually the relay or electronic circuit that is attached to ... hence the spark seen as the contacts open on a relay (wears out the relay eventually) .. or jumping the silicone substrate inside a solid state device like a transistor, Diode, FET, or SSR whatever is controlling it. The Only way to stop it is a diode in reverse across the power to ground so that the voltage can be safely bled off.

The 2 diode approach you used would be fine as long as that kick-back has somewhere to go (a 3rd diode in reverse from power to ground of the coil itself). ... or just using a single diode to protect the ecm, a second one in reverse across the coil to bleed kick-back off, and a small fuse to protect the ignition circuit (needed regardless of what approach you take) in case anything in the circuit fails.


User's Signature: ->: What I post is just my own thoughts and Opinions! --- I AM Full Of S__T!.
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09-20-2020, (Subject: Fault Code 1117 ) 
Post: #31
RE: Fault Code 1117
Update. First a thank you to Rawze for pointing out I needed a suppression or flyback solenoid.
This is a pretty old engine so some may want to skip this. Did did not have to add the kickback diode because ECM got replaced. I did not list all the problems with this engine. Obvious problem was occasional lose of signal to fuel solenoid which is why I added another key switched wire. There were other issues.

Truck is water tanker for a local VFD. First problem was I couldn't make sense out of a couple of codes Insite was showing .One code I couldn't even find. Learned that Insite doesn't work well with these very early N14's. Cummins had a tool back then called Echek. Was able to get the use of one. Codes about the same but some difference in definitions per the manuals included with the Echek.

Almost all pointed to the ECM. Some circuit checking reinforced that diagnosis. ECM NLA from Cummins. The local Cummins location which is a Cummins only facility, not part of a truck dealership, recommended a rebuilder. This location has a bunch of 20, 25, 30 year people there. Usually good info and work.

Based on what I have read here and other sites I did not want to be involved in getting the ECM. Passed info to customer and let them get it. We then installed it. All the codes cleared and stayed cleared. Running and intermittent misfire/stumble/smoke issues also cleared.

Something interesting about the Echek. Small private fleet that let me borrow the tool has a guy that has been with them since the 855 days. He told me he was pretty sure that somewhere in the past Cummins had put out a field letter saying not to use Insite on the N14's.

This post should probably be on an antique engine board somewhere!
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 Thanks given by: Rawze





  
  
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