Engine Specific Info and Questions > IDI Engine

After engine stalls, fuel backflows from return line thru IP to filter (& tank?)

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Otis2:
Hi again all, it looks like I spoke too soon in saying the vehicle runs great.

After a test run today, after about 35 minutes of driving with fantastic power, the engine staggered to a stall.

I re-started it and examined the clear fuel lines, while it idled like crap.

There were obvious air bubbles in the clear line between the fuel filter and the injection pump, and there were so many tiny air bubbles in the return line leading from the IP to the tank that it looked like a frothy milkshake in there.

After shutting it down, I could see the air bubbles being sucked *backwards* up the return line and into the injection pump, as well as the bubbles moving backwards from the IP back to the fuel filter.

There is a check valve between the fuel tank and the filter, so I guess it would keep a nice vacuum in the fuel feed circuit, leading to this backflow.

So is this a symptom of a plugged fuel feed at the tank?

I think I have some crappy fuel in there, as the vehicle has not been used much since COVID started, and when I changed the fuel filter when installing the new injectors, the filter was full of some really dirty crap.  I may have algae problems in there.

Another possibly relevant symptom, the stalling initially happened while idling at a traffic light, facing down hill, as I said after about 35 minutes of great power.

Vehicle is a 2wd Vanagon, converted from a gasser, so it has the odd flat-shaped fuel tank up front.

I'm not looking forward to draining about 1/3 of the fuel tank, but will do so if necessary.  Probably about 25 litres of fuel in there.

I would appreciate your comments and analysis.  The backflow of fuel after shutdown is worrying.

Where should I be looking next?

Thanks.

(Edit - I drained a bit of fuel from the bottom of the filter, and it was nice and clean.)

Rabbit79:
One thing you can check is to make sure the gasket from the old fuel filter didn't stick to the filter flange. I did that once on the Rabbit and it acted a lot like what your symptoms are.

libbydiesel:
It sure sounds like an issue with the fuel flow from the tank.

Otis2:
Thanks. 

I'm going to try running it directly from a fresh jerry can of diesel, and see if I still get the milkshake coming out of the return line towards the tank.

If so, then I fear it is the pump itself leaking air, but given the tremendous vacuum in the circuit going back at least as far as the filter, I am hopeful the pump is still good.

I pulled the brand new fuel filter, with only 35 minutes of run time, and I got this mess from the spillage over the top as I removed it. 

Hopefully none of this crap went as far as the pump, but as I mentioned above, the plastic drain valve in the filter bottom drained out only clean diesel.  I hope that valve drains from the pump side of the filter, and is an indication that only clean diesel reached the pump.  I certainly never saw any of this crap in the clear line feeding the IP when it was running, anyway.

Gasket on the fuel filter was correct, so that's not the issue.

Looks like I am in for at least a new fuel tank.

libbydiesel:
Is that rust or is it algae?  Either way a new tank is probably the easy way to go.  If algae, though, it means that water is getting into the tank.  Make sure the fuel system is sealed well.  Also keep the tank relatively full if it is going to sit, in order to avoid the potential of condensation forming.   

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