2008 C4500 dies when on the highway. NEED ADVISE

[SOAS]

I have a fleet of 4500 Ambulances. Two of them will die randomly on the highway, usually after being ran for an hour or more. We tow them home, because they will not restart. After the fuel system is worked on, new filter, prime it, release air, etc, it starts and runs great. A day later, same problem. Our GM shop is baffled. The have replaced the pump, filter, fuel caps, etc. The mystery problem continues.

Anyone out there have any ideas???? Please??

[SOAS]

Our ambulances can be seen on our website: www.soas.net (http://www.soas.net)

[Mark Rinker]

Bad situation when an ambulance might come to a stop...

My first thought is to check for proper fuel cap venting. If the cap isn't venting, then the fuel system could be creating a vaccuum in the tank, causing a stall after a few hours, that would correct itself over time, as air leaked back into the tank.

The Duramax 'draws' fuel from the engine mounted Injection Pump (IP) sort of like sucking it through a huge straw, all the way from the tank. You might consider adding lift pumps at the tank, to push fuel forward to the IP. www.kennedydiesel.com (http://www.kennedydiesel.com) sells these.

Beyond that, search these forums for threads on cracked fuel filter housings that let air into the system, causing stalling and running problems.

From your description, the scenario sounds repeatable and more like and on/off situation, which is more like total fuel starvation....

Q: Is the fuel cap a genuine GM vented cap that came with the cab/chassis, or a replacement? A simple test would be to loosen the cap and see if the situation repeats itself, or when one dies, have the driver loosen the cap and see if air rushes in!

[dually2002]

In an older thread Kennedy helped another ambulance company. I believe lift pumps solved the problem.

[Mark Rinker]

I have recently found out about a GM bulletin PIP4526 that addresses collapsing fuel lines. While the C4500 isn't specifically mentioned, the longer run and even higher fuel requirements might cause the same scenario.

Q: Are the same trucks affected each time? If the same, are these trucks heavier, or more likely to be running hills at the time of the stalls?