CM570 Low Fuel pressure woes

[Johnny LongRifle]

Hello gents,

Pardon me if this question has been discussed here before. I searched around and really haven't found the answer to my questions or another thread with the same symptoms.

A little background... I am an auto mechanic for 30+ years, but I am green when it comes to heavy duty stuff and especially the fuel system on this truck. I am trying to help my brother with his Kenworth that contains this CM570. ESN 14006005. Non EGR engine. A couple weeks ago he was driving and said the engine cut off like you had turned the ignition off. No spitting and sputtering, just pulling one second and dead the next.

I have quickserve and a scan tool that I am using.

We have power to the fuel shutoff solenoid, the lift pump (is not intstalled on the IFSM like all the exploded views shows) is running and making lots of flow, but scan data shows 3psi KOEO. I pulled the return line off and fuel flow was wide open. With my thumb in the hole I was able to get it up to 50ish psi. Tells me the lift pump is ok. I have removed and inspected the 250 and 400 psi regulators and didn't see anything obvious. I am having him install a mechanical guage tomorrow to verify fuel pressure.

Currently it is setting code 482.

The engine will start and show around 250psi fuel pressure on the scan data. As soon as you try to foot feed some fuel or set the PTO, fuel pressure drops and the engine stalls. Quickserve tells me to check the overflow valve in the IFSM, but I don't know where to look for that. Any ideas?

I dont have a good idea of how the fuel flow works inside this IFSM. It seems that there were multiple iterations, and I get real confused trying to sort through the information trying to figure out something I know nothing about.

The engine stalls because it can't maintain fuel pressure above idle, Im sure. Is there something in the IFSM that is dumping pressure back to the tank? I did clamp off the return line (good or bad) and the symptoms persist.

What am I missing here? I dont think its a bad HP pump, but instead something is dumping all the fuel back to the tank, I just don't know where to look.

Help a newbie please?

[Nostalgic]

Maybe this will help:
https://www.youtube.com/watch?v=MWiSwgcwIoc

[Nostalgic]

I also seem to remember someone mentioning a broken fuel pump shaft - at lower pressure, friction is enough to make pressure, but then when pressure rises, it stops driving the pump. It's easy enough to pull the gear pump off and check it. Also make sure to check the gear on top of the ifsm that's driven by the cam.

[Rawze]

It sounds to me like your over-thinking it. Those older IFSM systems are pretty straight forward.

250psi is about normal for idle pressures. - What is NOT normal is It falling off when engine is loaded up. This leads towards a fuel starvation issue, or a bad gear pump.


Also, unlike common rail systems... it is normal to see a lot of fuel going back to the return lines, so your barking up the wrong tree on that one. - This is how they work... Once the pressure is met,.. ALL the fuel gets circulated back to tanks to keep the tanks warm (preventing gelling in winter while engine is running) and bleed off heat from the fuel system. It is also NORMAL to see bubbles in the fuel return lines btw. It is due to cavitation at the exit port of the IFSM and nothing else.

#1... Start by REMOVING all the guts from the fuel shut-off solenoid. They are notorious for going bad internally and starving the fuel system. The engine should shut down just like it did with the solenoid guts in place. If it has hesitation in shutting down with guts removed from shut-off valve, then you have leaky injector(s).

#2. DO A INJECTOR LEAKAGE TESTS... for all anyone knows, you may have a bad check-valve in an injector, blowing combustion gasses into the system and starving it of fuel. This is also possible... and not too uncommon. Use OEM ONLY replacement injectors, as they have updated check valves, etc.. and are not as prone to these types of failures.
info on how to do it: https://rawze.com/forums/showthread.php?...8#pid67948

#3. If the truck has a glass-bowl type of pre-filter... the type where the glass boll hangs down.. those are NOTORIOUS for letting air in at the seals after a filter change... and you will never see bubbles in the bowl. - Ensure this is not the issue.. bypass the thing if you have to for troubleshooting.

#4. Pressurize the fuel tanks to 5 psi, put lines that feed the engine into bucket, and see if there is air in the fuel. For all anyone knows, there could be a cracked pick-up tube in a fuel tank.

#3. Replace the gear pump (OEM ONLY) if it is more than 8+years old. A snapped shaft will often let the engine crank and it run, but not keep up when under load. Also an OEM-only part.