2.25 Diesel with modified fuel return

[David Sparkes]

The question is, will the engine run OK under road conditions, when the only fuel return is from the spill rail to the top of the fuel filter?

At the moment the normal return to the tank is blocked, as the tank it goes to is removed for repair.

The background is:

I'm currently trying to make roadworthy an ex military 109" with twin underseat tanks, where a PO has changed the 2.25 Petrol to a 2.25 Diesel.

The RH tank is leaky, and out of the vehicle for repair.

The PO fitted just one fuel return, to this tank, and I've currently blocked it off.

Using fuel in the LH tank, I have successfully started the engine, and run it on tickover for long enough to get the thermostat open. The 'return' from the spill rail goes to the top of the fuel filter, and it was this junction I opened to bleed the system before starting the engine.

Thanks.

[Orgasmic Farmer]

Not a definitive answer but when running on SVO with a twin tank system the solenoid valves are set so that no veggie oil is returned to the tank from the spill rails and it just keeps circulating back to the FIP. This works fine so I see no reason why it won't work on DINO

[Serious Series]

On a 2.5 diesel the excess fuel is used to lubricate the injection pump I would assume the 2.25 is the same.Injection pumps are very expensive so best find away to get it back to the tank.

[David Sparkes]

On a 2.5 diesel the excess fuel is used to lubricate the injection pump I would assume the 2.25 is the same.Injection pumps are very expensive so best find away to get it back to the tank.

Thanks for the thought, but visually there is a world of difference between the injection pumps, although it's fair to say I'm not an expert on the fine detail. I guess if I was I wouldn't be asking the question :-)

On the 2.25 the injection pump sits in the hole where the distributor fits on a petrol 2.25 engine.

On the 2.5 the pump is mounted on the front cover, and I think you will find it's the incoming fuel that lubricates the pump.

On the one example I've experienced (a 19J turbocharged version) there is an excess fuel pipe from the pump back to filter port 3.

As far as the spill rail is concerned, injector 1 has a pipe to the boost pressure sensor on the pump (which I accept could be to lubricate that sensor). Injector 4 has a spill pipe going to the air bleed point on the top of the filter.

To state the obvious, as well as the specifics mentioned, the spill rail is daisy-chained between all four injectors.

Without going to look especially, and getting dirty tracing it through, I'm not sure where the return to the tank leaves the engine / filter.

Anyway, its 2.25 experience I'm interested in :-)

Regards.

[Snagger]

You must have a return line, but what you can do is tee the return from the injection pump to the feed line to the lift pump, recirculating the fuel instead of returning it all the way to the tank. This has one problem, however - any tiny leaks that allow air into the system will not be purged and will accumulate until the engine begins to run badly and eventually stop. Such small leaks are pretty common and are the usual cause for a diesel not starting instantly and needing a small amount of cranking. So, unless your engine starts instantly every time you use it, hot or cold, then this short loop method is inadvisable.

[David Sparkes]

OK, that makes sense. I suppose in the back of my mind I wasn't sure how any entrapped air would be handled if it wasn't sent back to the tank. The alternative would be to make a separation tank, but why bother, when there are two already on the vehicle :-)

The vehicle isn't currently in service, so I can't say whether it will start instantly every time I use it, hot or cold.

Regards.

[David Sparkes]

After a test today I can say the idea (only adopted because of a faulty tank) doesn't appear to work !!

After idling for a few minutes, spent looking around for leaks, both from the top and underneath, the engine started to surge. It had done this the last time I ran the engine, so I merely noted it and carried on. The surging got more noticeable, then the engine cut out. It wouldn't restart until after I re-bled the system. I noticed that as I released the bleed screw on the filter there was an audible hiss of air escaping, but it wasn't enough to just release the air, the system also needed bleeding via manual operation of the lift pump.

Oh well, move tank repair further up the priority order.

Regards.