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Hey guys,

I’ve got a bit of a headscratcher here with a QSX15 CM570 and thought I’d throw it out there to see if anyone’s come across something similar.
The engine’s fitted to a road milling machine and is down on power under heavy load with no fault codes.

Here’s the weird bit. During milling, the fuel shut-off solenoid seems to close for a split second, fuel pressure drops away, and the revs fall from around 2100 to 1500ish before picking back up a second later.
I’ve been logging it through INSITE data monitor logger and checking the actual voltage supply from the ECM to the fuel shutoff solenoid. Sure enough, the voltage drops straight to zero at random times.

Here’s what I’ve tried so far:

1. Pulled the valve out of the fuel shutoff solenoid and gave it a run. The engine runs sweet as, but the supply voltage still drops out randomly, and INSITE still shows the fuel shutoff command going to “Close”.
2. Had a look at the previous wiring repair. The bloke before me replaced the wiring from the ECM to the fuel shutoff solenoid and also swapped the ECM, but apparently that didn’t sort it out. I haven’t gone through the wiring properly yet, but it looks like he might’ve just joined the new wire onto the back of the ECM connector instead of replacing the female terminal properly.
What doesn’t quite add up is that even if the wiring’s dodgy, why is INSITE still showing a “Close” command?
3. Ruled out a fair few fuel supply issues. New IFSM gear pump, lift pump and fuel filter. Checked the inlet screens and relief valves, and even tried running fuel in and out of an extra jerry can. No joy.
4. It only plays up under load. At rated RPM with no load, it runs fine as. The problem only shows up when the machine’s actually milling.

So, keen to pick your brains on a couple of things:

1. Is there any OEM wiring or external safety device that can send a shutdown request to the ECM and make it command the fuel shutoff solenoid closed? Could something on the machine side be telling the ECM to shut the fuel off?
2. If the keyon or main power supply has an intermittent dropout, could that make the fuel shutoff solenoid close for a split second and cause the revs to drop before recovering, rather than killing the engine completely? I haven’t had f/c1117 come up either.

At this stage, I reckon I might have to get stuck into the wiring harness and go through the lot — fuses, relays, power supplies, earths and connectors — if I can’t find the culprit.

Has anyone run into this sort of issue before, or got any ideas on where else I should be looking?

Any thoughts would be much appreciated.