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Injection Pump Inlet Filter

Posted: Tue Oct 08, 2019 1:14 pm
by Colin6224#2
Hi
DB990 has a problem with fuel starvation. Difficult to start, it needs bleeding which in itself takes longer than usual.
The tractor only runs idle for about 15 minutes before the fuel runs out and needs bleeding again.
I have narrowed this down to a problem in the injection pump. There is I believe a nylon filter under the inlet connection which attaches to a spring and small mechanism to regulate fuel.
Do I need to take the end plate off the pump to work on the bench, or can I swap the filter on the tractor. I have a fear that as I lift the filter out a small part might drop down inside.
Any advice on the correct tools to use, small dentist type tools would seem to be the best option.
Thanks for any assistance.

Colin

Re: Injection Pump Inlet Filter

Posted: Tue Oct 08, 2019 4:09 pm
by db2d
There is no need to remove the pump or the end plate. Remove the input pipe and then the adapter connection and then you can carefully remove the filter. It is unusual for this filter to become blocked bearing in mind the fuel has to pass through several filters . The usual reason for the problem you describe is a fault between the tank and the liftpump. The filler cap breather can also cause problems. Be certain that the return line from the injection pump to the tank is clear of obstructions.

Re: Injection Pump Inlet Filter

Posted: Wed Oct 09, 2019 10:48 am
by Colin6224#2
Hi db2d.
Thanks for the feedback on removing the filter. My concern is that when I pull the filter out, there will be other bits that come with it or fall back inside misaligned.
I agree with what you say about the filter being unlikely to be the fault but after replacing the pump, filters and seals there are few suspects left.
When the tractor stops, I bleed the system. No air is found in the filter but the injection pump is difficult to bleed. When it does bleed, it only dribbles slowly rather than the jet of fuel I have seen before.
When I loosen the lift pump inlet pipe, fuel runs freely so that is neither blocked nor airlocked.
I took the injector inlet pipe off and turned the engine over for a few seconds, fuel flows from the pipe so the pump is working and fuel flows.
I suspect that fuel system may have been neglected in the past, or simply a sludge build up because it doesn't get used much.
Either way, I think I have to at least eliminate this as a problem before I call in a mechanic.

Any other thoughts welcome.

Colin

Re: Injection Pump Inlet Filter

Posted: Wed Oct 09, 2019 12:01 pm
by cobbadog
As suggested check that the fuel return line is not blocked as well, just for peace of mind and knowing that is not the issue. You should also check where that line connects to the fuel tank that it is also clear.
I'm sorting through some fuel starvation issues on another tractor and once you start looking it is amazing the things that you find are not quite right.

Re: Injection Pump Inlet Filter

Posted: Wed Oct 09, 2019 12:47 pm
by db2d
Have you changed the fuel filters ? Some of the filters on the market are very poor quality and reduce the fuel supply. The filter in the back of the injection pump can be removed without bits falling into the pump.
I suggest obtaining new filters from davidbrownparts.com
Is the tractor an Implematic or a Selectamatic?

Re: Injection Pump Inlet Filter

Posted: Wed Oct 09, 2019 3:27 pm
by rid54
If you get a nice flow into the injection pump by turning the engine, indeed the lift pump and the filters should be OK. In that case I would suspect that the final filter in the injection pump inlet actually does need inspection. Not having access to full info, I would nevertheless assume that parts shouldn't fall into the pump by just removing the inlet piece; the assembly should be made for service in the field, one would think.

Re: Injection Pump Inlet Filter

Posted: Thu Oct 10, 2019 2:56 am
by GeoffDEAL
Hi under the inlet nut there is a spring then a plunger then the filter just carefully hook them out with suitable tool and replace in same order, i had one injection pump that had a broken vane in the end of the pump behind the inlet housing could be worth checking as when the broken vane was replaced everything worked perfectly. There are some good U Tube vidios of working on the injection pumps well worth watching, thats how i learnt to work on them.

Re: Injection Pump Inlet Filter

Posted: Thu Oct 10, 2019 12:57 pm
by Colin6224#2
Hi All
Thanks for the support.
I will check the fuel return pipe for blockages. Hadn't thought of that so far.
The filters are bought from our local parts store who specialise in tractors and construction equipment so I have no worries on that point. Same place for the last 30 years for all the tractor spares.

I got a new filter and seals so I should be able to replace the filter next weekend. Will report back.

Colin

Re: Injection Pump Inlet Filter

Posted: Thu Oct 10, 2019 1:16 pm
by db2d
Can you please state the tractor type because there is a difference between the Implematic and Selectamatic fuel system.

Re: Injection Pump Inlet Filter

Posted: Tue Oct 15, 2019 9:54 pm
by bedwards1966
It does sound possible that there's a problem between the filter and injector pump, though it is rare. As said, pay attention when you undo the fitting on the pump, make sure everything is very clean and you should be fine.

Worth checking as you've made no mention of it is the lift pump push rod and the camshaft lobe that drives it. These seem prone to wear on DB's (both mine have suffered this, and rectifying the problem has made all the difference). Strange running problems can occur when the plunger or cam is worn. Remove the lift pump and measure the rod length, 36mm rings a bell but a search on here will confirm the correct length. 3/8 Silver steel is perfect for a replacement.

Re: Injection Pump Inlet Filter

Posted: Tue Oct 15, 2019 10:21 pm
by db2d
If the wrong steel is used to make the push rod the cam-shaft lobe gets damaged.

Re: Injection Pump Inlet Filter

Posted: Wed Oct 16, 2019 6:07 am
by ollek
As db2d says, the cam shaft lobe will get damaged if the push rod material is wrong. This will result in the need to replace the cam shaft, a major engine repair. Therefor, please use only the correct push rod and do not make your own.

Re: Injection Pump Inlet Filter

Posted: Wed Oct 16, 2019 7:49 pm
by bedwards1966
I used silver steel as it's good quality material but unhardened. It's not going to cause excessive wear in its soft state, and is ground to the exact size with a good surface finish so only needs making to length.

Cam wear is certainly an issue and I would never use anything hard - my 995 has a worn out cam lobe which necessitates an electric fuel pump. I can change out push rods very cheaply and easily if they wear and would choose that over a camshaft!

Re: Injection Pump Inlet Filter

Posted: Wed Oct 16, 2019 9:52 pm
by GeoffDEAL
Hi if replacing lift pump be sure to use the same thickness of gasket, some replacement pumps had a thin paper gasket where the old pump had a thicker gasket these didnt put so much pressure on the cam lobe. On one tractor i replaced the pump and the gasket that was with it and resulted in wearing out the cam lobe and had to use an electric pump in line.

Re: Injection Pump Inlet Filter

Posted: Mon Oct 21, 2019 2:03 pm
by Colin6224#2
Hi Guys
I thought that I would update you on the outcome of my investigation.
The filter was easier to remove than feared. First removed supply pipe. Then unscrewed adapter from pump. It has a copper washer for sealing.
Carefully lift out the spring, note that it has a plug insert on the bottom end.
Filter needed a little encourgement with a screwdriver to come out but it can be removed without damage if you careful. Happily nothing else came out with it.
There was some dirt in the filter, little bits that might have arrived with a filter change but nothing to block fuel. The white nylon filter looked like it had been in a teapot for forty years being dark brown and possibly coated with old oil, but again showed no evidence that it was a source of the problem. Replaced the filter and the copper washer with new parts when I reassembled it. Cost of parts about £3.
Tractor bled easily enough but after 15 minutes the engine stalled again.
This time I followed advice from others to blow out the fuel lines. Got a length of rubber fuel pipe and my compressor set to about 20 psi and blew out the various fuel lines in stages back to the tank, but not the filters themselves in case something burst.
After that the diesel did flow more easily so I assume that some dirt was patially blocking the flow.
When bleeding the injector pump the fuel would squirt out where before it had dribbled out.
Engine ran for 25 minutes until I stopped it.

Thanks to all for their comments and suggestions.

Colin