My 4bt has suddenly started to act up. It used to start perfectly, cold, hot, what ever. Since 2 monts ago, all of the sudden it began to start bad after sitting overnight (I have to crank it a lot), it would be ok during the day, and since yesterday it starts very hard even 30 minutes after shutting it off. Nothing was changed that could affect starting.

No smoke is coming when cranking, I have a pre-filter which is transparent and that is never empty, I also have a non-return valve between the stock lift pump and the pre-filter.

Tried a new filter, no change. Manually priming the stock lift pump helps a bit. Using the heater grid also helps.

What can cause the bad start ?

Last valve adjustment was 200 hours ago and I will take the injectors for testing next week.
It's installed in a Case backhoe if that makes any difference and it has a Bosch pump.

Thanks in advance !

 

1st thing that comes to mind is a small leak in the line between the lift pump and the injection pump, or the lift pump and the fuel tank. It lets the pressure in the line drop while it sits which causes hard starting. If it's not the line itself, I'd look very closly at the lift pump. Sometimes when they start to fail, it'll cause that problem.

 

Lift pump to fuel tank should be ok since I have a valve there and all hoses are clean, even after running in very dusty conditions.

I'll check the line between the lift pump and the fuel filter.

 

Update:
I started it from a bottle and checked to see if it leaks fuel back. Nothing. The valve I added works perfectly.

Tested the line between the lift pump and the filter housing, as soon as I cracked the banjo bolt it oozed fuel, so it's ok there.

Re-adjusted the valves.

It still starts bad. Seems as though I have some sort of injector / glow plug in the intake instead of the usual grid heater. It cranks a lot without putting out any smoke. If I use the glow plug it cranks less but still a very bad start.

I also took the new fuel filter and filled it with fuel, thinking the valve doesn't work and it leaks fuel back in the tank. That didn't help either.

Going to test the injectors tomorrow and if that still doesn't fix it it's time to test the pump

 

Any idea what the fuel pressure is at the lift pump? Mechanical or electric, it needs to be around 15psi when cranking or starts will be miserable.

 

No idea but I will start to look for a gauge and test that.

Thanks !