isx 450 hard start

[Kiko]

Hello all. New to this forum. I am having trouble with an Isx 450 in a Volvo truck. When cold the truck is a few hard start. It cranks and cranks with no smoke. Once it’s running it runs great with lots of power. When running the fuel pressure on insite is about 250 at idle. Now I was thinking it’s a fuel prime problem. This engine did not come with a lift pump but has a Cummins lift pump that was added. When priming the fuel pressure is at 4 to 5 psi. Insite says it should be 10 +. When I take any of the lines off it has all kinds of flow and doesn’t seem to have any air in the fuel. I tried pressurizing the tank and could get prime pressure up to 12 psi. I thought this helped but when left overnight it was still a hard start with the same process. When monitoring the fuel pressure when cranking it slowly builds up to about 80 psi and then fires. Cummins wants 13000 for a new primer pump which is ridiculous. I did a cylinder cut out test and all cylinders are firing. Plus did a contribution test and all cylinders appear to pass. Now how long should the heat pump crank to build up pressure for firing when starting. Or could this engine need to see proper oil pressure to fire etc. kind of stuck on this one and could use some help.

[Rawze]

you did not mention what make/model year engine this is. Its anyopne;s guess if no one knows what engine you have.

Is it a Cm570?.. CM870?.. CM871?.. CM2250?.. CM2350?.. CM2350-X15?.. an ISX 12?... What?.


an engine ser# would help answer this too.

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As far as the ISX goes.. the engine needs to see 50 psi minimum while cranking before it will even consider firing the injectors. Sounds to me like you have a weak or restricted electric lift pump, and last I checked, they were not some ridiculous 13k$.

Could also be a snapped shaft on a gear pump. The CM570/870/871's are notorious for getting a snapped gear pump shaft and running just fine (because it would catch and start working) after cranking it up.. but would be a bear to start up because it would barely make 50+ psi fuel pressure (if at all) during cranking. Your symptoms sound similar to this.

Also, will the engine pass a properly done injector leak test?. if not, then that is the place to start.

[Kiko]

I did not try an injector leak down test as I don’t have an adapter fitting for the solenoid valve. It’s just funny how the engine runs good when running. It is a isxcm570. The fuel pressure also drops right off right away when the engine is shut off. Is this normal.

[Kiko]

Hello again. I have bought a tool and did an injector test. They all passed, no air bubbles. This engine is a long cranking before firing after sitting overnight. When it starts to crank the fuel pressure will build right away up to 50 60 70 etc. when I do initially turn the key on and hear the fuel pump come on it sounds like I have some bubbles come out in the fuel tank. I am really scratching my head on this one. Anybody have any ideas.

[Rawze]

sucking air?... cracked pick-up tube at the top of one of the tanks?.