Cm 870 fuel shutoff problems

[Precisionw900]

My cm 870 randomly drops dead with cel. Code 255, open circuit to fuel shutoff. Has died 4 different occasions, once while parked and idling.
Replaced fuel shutoff since I had one and just to rule out. Couldn’t make it duplicate problem until next day when it died crossing highway. After sitting for about 10 minutes it fired right up. Truck ran another few hours and died again. Luckily I took a voltmeter along and had zero power at shutoff.
At this point I hooked up a jumper to fuel shutoff and it fired right up and ran the rest of the day.

Checked harness and continuity test from pin 51 to shutoff will moving harness every way possible and have inspected plugs well. Passes every time.

I know 870 ecm’s tend to be a little wonky and as far as I can tell this one is original. Is there a possibility that it’s on the brink? Maybe ecm is momentarily killing shutoff circuit?

[mikkhh]

https://www.rawze.com/forums/showthread.php?tid=8608
Knock on ecm and see if the fault comes up again.

[Rawze]

(05-02-2025 )Precisionw900 Wrote:  ...
I hooked up a jumper to fuel shutoff and it fired right up and ran the rest of the day. ...

I hope like all h$ell that you disconnected the wire going to the ecm before you jumpered that solenoid. ... otherwise it burns out the circuit chip inside the ecm that feeds it (ecm commanding it OFF as engine shuts down, and you have it wired to 12volts = a conflict that damages the chip).

and like mentioned above.. you should bang on the ecm and see if it is not a floky ecm.. it is common on those CM870 and CM871's for the ecm itself to randomly shut off as they get old, or if no one has ever changed out the crank shaft damper in the last 500k miles ... higher frequency vibrations take out that ecm when crank shaft damper start not working so well.

BTW: I removed the guts on my shut-off solenoid to get me off the side of the road a long time ago in my own truck, .. I never put them back in...lol.

[Precisionw900]

(05-02-2025 )Rawze Wrote:  

(05-02-2025 )Precisionw900 Wrote:  ...
I hooked up a jumper to fuel shutoff and it fired right up and ran the rest of the day. ...

I hope like all h$ell that you disconnected the wire going to the ecm before you jumpered that solenoid. ... otherwise it burns out the circuit chip inside the ecm that feeds it (ecm commanding it OFF as engine shuts down, and you have it wired to 12volts = a conflict that damages the chip).

and like mentioned above.. you should bang on the ecm and see if it is not a floky ecm.. it is common on those CM870 and CM871's for the ecm itself to randomly shut off as they get old, or if no one has ever changed out the crank shaft damper in the last 500k miles ... higher frequency vibrations take out that ecm when crank shaft damper start not working so well.

BTW: I removed the guts on my shut-off solenoid to get me off the side of the road a long time ago in my own truck, .. I never put them back in...lol.

Yes. Disconnected harness wire. I hate jumping anything but was stuck in roadway and didn’t have Allen wrenches to pull off shutoff and remove guts. I had remembered reading a post you had on this situation. I gave ecm a couple of solid whacks this afternoon and never missed a beat . I overlooked or maybe didn’t mention a inactive code (can’t remember #) that was power lost while key one.) I started checking power supply connections and haven’t found anything concerning. No cel at this time.

I believe I will remove shutoff guts and be forced to run it until it shows a code again and start over from there. If it is on shutoff circuit it shouldn’t die. If ecm losses power and dies then I know which direction to head.

[Pigpen 2869]

I had a key power fuse for the ecm cause this recently. A lil bit of corrosion a New England rumble strip down the middle of the highway and Im on the side of the road.