Return Fuel Line 200 TDI ex Disco

[Dave64]

Hi All,

                    Came across a bit of an abnormality with this TDI 200 engine (ex Disco) where there seems to be a fair pressure build up in the return line from the top of the pump back to the tank. Enough to cause a fuel leak at the fittings.

You can remove the return hose from the tank end and drain it into a container and no probs. You can also put a bit of hose on the return line where it goes back into the tank and it will blow through alright, so doesn't appear to be any obstruction.

The tank is off a Mazda E3000 Diesel which has a NON vented screw type cap with a rubber seal. There is an additional vent line built into the tank which has a small nylon sliding ball in it, which is some sort of safety device to stop fuel escaping in case of a roll-over.

Funny thing is, when the tank only had about two inches of fuel in it, didn't leak. Filled the tank to about halfway up and I'm surmising that the extra weight of fuel is stopping the return line from operating correctly. I've had the fuel sender out to fit a new one and shown a torch in, the return line is roughly the same height above the bottom of the tank as the pick up line.

Wondering if it may be a combination of the original Range Rover fuel tank return fuel line just vented straight into the TOP of the tank and also the original may have had a vented cap. Often seen tanks where an excess fuel line returns to the filler neck and then returns to mix with the cooler fuel. I don't run it for very long the way it is.

I did notice last time I started the engine that it seemed a bit "smoky" at idle. If the return fuel line is not doing it's job as it was designed, could be building up TOO much pressure at the engine?

I was going to try swapping the lines for the return line and the vent line so the fuel returns straight to the top and leave the cap off so it vents to the atmosphere. As it's not yet on the road, can tinker a bit, but obviously have to have some sort of vent into a charcoal canister affair for eventual registration.

Any thoughts?

ALSO, have a boost gauge coming, 0-30 psi, and already have a bung in the fitting halfway along the INLET manifold. Someone told me that they run around 10-14psi, increases slightly under load??

Pyrometer would be nice but will be some time before I get around to the exhaust, currently drops straight down with a 90* elbow, 2&3/4".

Normally, where would the pyro be fitted i.e. just how close to the turbo outlet flange??

Thanks again, Dave

[Ex Member]

You are probably getting air into the injection system and the tank is not venting.  Both items should get fixed. The fuel return line is meant to go to the bottom of the tank.

[Dave64]

Thank You.

Dave

[TSD]

On 03/04/2018 at 11:32 AM, Dave64 said:

Pyrometer would be nice but will be some time before I get around to the exhaust, currently drops straight down with a 90* elbow, 2&3/4".

Normally, where would the pyro be fitted i.e. just how close to the turbo outlet flange??

Thanks again, Dave

Pyro normally fitted at the turbo INLET, as close as practical to the turbo / as far as possible from the individual cylinder pipes. In 300tdi theres a cast boss in the manifold for EGR that can be drilled if not already. Sometimes it's not possible /practical to fit it in the intake side, on my 2.8 I fitted it on the turbo outlet about 75mm from the turbo body. It still provides good info on the change in EGT, but there's more guesswork in deciding a safe limit, since the pistons usually melt before the turbo gives out.

[Dave64]

Thanks!

Dave

[Dave64]

Fitted a new excess fuel return line, whatever the problem seems to have stopped leaking, fair amount of fuel being returned though.

Gave it a big bootful and just about choked myself on the smoke.

Reading on another forum over here that a bloke over the West (Australia) had similar symptoms and he posted a link back to this one.

Seems that there is a diaphragm affair on top of the pump which monitors the fuel and when the turbo is working under load, meters the fuel. If I have this right, IF the diaphragm goes bad, it can let fuel back into the system causing "overfuelling".

The link to this forum was regarding a 19J engine, looking at the photos, mine being a 12L has a different pump.

What looks like a diaphragm housing sits on top facing upwards.

Don't know if the 12L suffers from similar symptoms as a 19J as I'm unfamiliar with them. Easy enough to get at, haven't taken the top cover off yet but maybe could have something to do with the initial problem??

Edited April 5, 2018 by Dave64

[Ex Member]

No, that would not cause that problem.  If the boost compensation diaphragm failed, you would have low power.

In your first photo, it does not look like anything is connected to the fuel return pipe on the injection pump.

[Dave64]

"No, that would not cause that problem.  If the boost compensation diaphragm failed, you would have low power.

In your first photo, it does not look like anything is connected to the fuel return pipe on the injection pump."

Photo taken when fitting removed to get correct size return line, which has since been re-installed, Leaks stopped.

Engine is only sitting in chassis, so can't test it under any type of "Load" conditions. When started after new return line installed, also added boost gauge, went to flight revs (no load) turbo pumped manifold pressure up to around 7-8 lb, (what's normal?), blew what I would call excessive smoke, didn't sustain that, shut it down after idling for a short time. Can actually smell "raw" fuel, so maybe the injectors need looking at. Pump had already been done not long before I inherited this engine.

Dave64

[Ex Member]

Ah.  You can't tell anything with the engine under no load.  You really shouldn't even be testing like that as it is hard on a diesel running with cold cylinders and they can't get warm without load.

[Dave64]

Thanks anyway, only ran it long enough to test for leaks etc. Dave