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Diesel Return Line

Diesel Return Line

Diesel Return Line

Hello guys.  I have a little question which I am hoping a knowledgable Diesel person can help.  I purchased a stationary engine from a local supplier.  Its a 4cyl Chinese naturally aspirated engine with inline injector pump.  I have been having real problems with starting.  It will start sometimes, never first pop, but after cranking for around 2-3 seconds, sometimes a little longer.  However, for most of the time, it will not start at all.  It is a brand new motor.  I have spoken with the supplier who insists that it was test run before it was delivered.  But has not really been much help other than suggesting that I bleed the fuel system (I am sure that there is no air, and I have bled the system extensively).  The problem that I am in is that I have fitted this engine to a hydraulic pump platform and will be an absolute pain to remove let alone replace with another type of engine.  I would rather try to get this problem sorted.

The engine will start best when it is primed.  However, if started then left for a while I would expect to not have to prime it again.  When it runs, it runs perfectly.  Looking at the fuel supply, it has one fuel filter with the two inlets and two outlets.  One outlet goes to one side of the injector pump, the other outlet goes to the other side of the injector pump.  For the inlet to the filter, one side is from the prime/feed pump, the other inlet is from the bled off from the injectors.

This is the question I have.  The bled pipe from the injectors feeding into the filter has a 'T' in it which then feeds off to the tank.  Is this normal?  I cannot seem to be able to prime the fuel system to a 'Solid' resistance because it just feeds back to the fuel tank.  I would of thought the return to the tank should be at the opposite side of the injector pump?

Please, any ideas.


RE: Diesel Return Line

I am not sure I understand your system.  Does it have a centrally located injector pump with lines to each cylinder or does each cylinder have its own unit injector.  For the former, it is necessary to bleed each line, as any trapped air will compress and make injection sporatic.  If it is the latter, the return line must have a restriction somewhere to ensure the injectors are flooded with fuel.  One of the sytems I worked on had inlet and outlet banjo fittings that were nearly identical, except for an orifice and often assembled wrong, resulting in what you describe.

RE: Diesel Return Line

Thanks for such a speedy reply.  The injectors have a return pipe each which feeds into one pipe leading to the filter.

Effectively the way I see it, the return from the injectors feeding back to the tank and also to one of the inlets at the fuel filter.

What I am trying to get my head around is whether there is air being fed back into the fuel system via the filter inlet, or whether I have another problem like a injector pump issue?

RE: Diesel Return Line

Since I don't know exactly what you are running this is what we do with our diesel trucks. Dodges-Cummins.
Generally anytime the fuel system is opened on a diesel, you will have to at least prefill the fuel filter if it was opened or changed. Then there must be some kind of "lift pump" or transfer pump unless the Injector pump is gravity fed so this must be cycled to more or less precharge the IP. In other words get the air out of the fuel feed section. From there you usually can loosen the injector lines at the injectors and crank the motor over. Use caution as the diesel fuel can be under a lot of pressure here, enough to "inject" it right into your skin. I usually loosen half of the injectors at a time so the motor will at least run. This will usually get you started. The motor will run very rough at first as it is purging the last of the air from the lines. close up the lines while it is running.
Since you seem to be having a problem after shut down it appears you have a leak in a line somewhere or a restricted line. Can be either side of the fuel system. Water in the fuel can cause this. Not at all uncommon. It happens to all of us. I don't know if you have glow plugs or grid heaters for starting but if you do make sure these are working. Our truck ones come on below 50* F for starting. I don't know if this motor has a compression release to get it spinning over or not but if it does make sure it is sealing. Diesel needs all the compression it can get. One last thing check the air cleaner.

I think your lines are return from the IP then there is a return from a pressure relief on the lift pump teed into it, then it goes to the tank. There is probably a check valve here too. You might look at this but these are pretty reliable. I forgot the IP may have a check valve on the inlet side to prevent leak down after shutoff. check this too.
Let us know how it works out.

99 Dodge CTD dually.

RE: Diesel Return Line

That plumbing does not sound right. Return fuel from injectors is sometimes run through a restricted fitting and nearly always routed directly back to the tank. This is done to help rid the fuel of air and to allow it to cool. I don't recall ever seeing return fuel put directly back into a pump. The entire system needs to be setup in a way that helps to purge air. As mentioned you may need a check valve to keep fuel from flowing back out of the inlet side of the injection pump.

RE: Diesel Return Line

Thanks for your help guys.  I had another think about it and looked at it today.  I blocked the return to the filter so the return feeds directly into the tank.  It primes up the way I expect it to and more importantly starts first time, each time.  

I am a very happy man!

Thanks again

RE: Diesel Return Line

The fuel return from the injection pump and the leak-off from the injectors is often returned to the filter on European vehicle systems as a means of warming the filter for cooler climate operation.

I think there's also a small benefit for filter life as the return fuel has already been through the filter element and (once the debris from a new system has been removed) return fuel will be cleaner than tank fuel.


RE: Diesel Return Line

I didn't read all the posts. The return is best sent back to the fuel tank, I did read the post about returning to the filter. On a small setup, ie average heavy equipment etc. There would likely be heating issues returning to the filters. As far aa the prime problem. Try using a check valve inline. Also an electric boost pump.

RE: Diesel Return Line

I have a related problem and hope someone can help.  I likewise have a Chinese diesel Generator (Shanghai New Holland 495AD engine).  According to the manual the fuel injection pump is designed for gravity feed and there is no lift pump.  However the unit came mounted on a base tank and has to suck up the fuel about 12".

I primed it by filling the fuel supply line while inverting it, then quickly reconnecting the fuel line to the base tank.  It starts and runs fine.

The problem is that after it sits a while the fuel starts to drain back into the tank and an air bubble expands.  I originally didn't see that as problem, as there is a hand pump and air relief screw.

But I now am worrying that by starving the supply side of fuel I could be damaging this hard to replace injection pump, which by the way does have the return line into the filter system, see the picture at the link below.

So I am wondering if I can just put a simple low pressure electric lift pump on the supply side of the filter system, with maybe 4-5 psi.  If that runs continously would that cause any problem or do I need to rig up a pressure regulator and return.  Thanks for any help!


RE: Diesel Return Line

TheSaintToo .........
Some years back, I was experimenting with simple fuel delivery systems for diesel cars for my employer and was using AC Rochester low pressure gasoline lift pumps and Ford 1 bar TBI/CFI pumps.

What I found to be simple was a brass 'T' piece with one of the legs blocked with epoxy and drilled out to, say, 1 or 1½mm dia. The return to tank was taken from this leg, preventing fuel pressure from getting too high. Both these pumps were turbines, so their dead-head pressures weren't too high either. For a simple system the AC pump worked fine.

The only problem you ight see with using any old gasoline fuel pump is brush and commutator wear - diesel fuel tends to hasten this unless the brush material and copper alloy have been chosen to suit.

You could always try a solenoid type pump that stalls/shuts off at a set pressure.


RE: Diesel Return Line

Thanks I was thinking to use the E8016S low pressure pump pictured below.  I don't think this is really rated for diesel though as you say.  It produces about 2-4 psi.  There is currently no return line to the tank though (the injector return is to the fuel filter).  So It would be a bit of a pain to install one as the large base tank is currently full.  Are there electric pumps that would stall or shut off at a low set pressure, which would eliminate the return?  Thats what I am a bit fuzzy about electric pumps in general.  If I install the E8016S with no return, I am wondering if it just effectivelky stalls at low pressure as its rated or does that cause it to wear excessively and burn out.  Thanks again.


RE: Diesel Return Line

Well, I had a quick Google on the Airtex E8016S and found that it's recommended for a lot of old British cars that had no fuel return lines, so I suppose it's OK for your application. I couldn't find a proper speicifaction or description for it though.
I found this:
....and this Carter pump looks just like the E8601 so I imagine that the E8601 is a solenoid type (self regulating, so won't burn out).

Sounds like a good bet to me.


RE: Diesel Return Line

Interesting and thanks for the info.  I am going to try this and see what happens.  I found a lot of articles on the net about replacing failed diesel lift pumps with a little bigger unit, the E8012S.  In this application though, with a 4 cylinder Chinese engine designed for 500 mm of gravity feed only to the fuel filters, I am thinking I should go as low pressure as possible.  Regards - Steve

RE: Diesel Return Line

Yes, I think this is the way to go.

But don't only rely on my and other peoples suggestions read up on it, I am sure you don't want to get it wrong as we all know to do it right is much easier than correcting errors.


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