Isx cm871 fuel pump.

[Bigmack713]

Hello all. I was driving down the road and the truck suddenly shut off. Check engine light says fuel pressure delivery. Usually in this truck this happens when fuel filters are plugged. I threw a fresh pair of fuel filters and yet truck will not start. Priming pump runs, but it seems like the geared pump would not take over and build pressure. I haven't checked the pressure at the gear pump. Getting 12 volts to the fuel shut off solenoid. I even took the valve right behind the fuel shut off solenoid to eliminate any fuel shutting off issues. Truck just cranks and barely starts running off of one or two cylinders until it runs out of fuel and dies. Another reason why I think the gear pump is bad is because lately I've been low on power. And usually I have to change fuel filters in between oil change. I only pump at pilot ,So I don't think bad for you is a factor .got the truck towed back to the yard and I'm looking for any help in what I should do next.

[Rawze]

871's are known for the shaft to snap internally in the gear pump as they get old, or if the electric fuel pump fails and sends debris into the gear pump. Then engine refuses to fire off. Once its running however, it stays running, as the friction in the broken shaft will often keep the pump spinning.


it can be checked by looking at fuel pressure in Insite while cranking. It should be 100+ psi during cranking, .. and a minimum of 50 psi, or the engine control module itself it will not even try to fire up a cylinder.

[Bigmack713]

I will start there. By any chance do you have the name or part number of the adapter that couples on to that pressure fitting.i have a pressure gauge and fittings but they are not that quick connect style.

[Rawze]

(10-22-2024 )Bigmack713 Wrote:  I will start there. By any chance do you have the name or part number of the adapter that couples on to that pressure fitting.i have a pressure gauge and fittings but they are not that quick connect style.

those fittings are known as 'Compu-check' fittings. Snap-on and a few other vendors have fuel pressure test kits, etc. that have those adapters and gauges needed.


Mechanical gauges or not ... you need also to FIRST check fuel pressure reading in the Insite software while cranking. You could have pressure, but if that ecm does not see above the minimum required, then it still will not open any injectors to let it fire any cylinders off.

[Bigmack713]

Just wanted to update.i replaced pump and all is good now.Seems like it has been progressively getting weak because engine now definitely has more power.I will definitely get the compu check fitting for future diag.Rawze thank you for your prompt responses.