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Re: Injection Pump Inlet Filter

Posted: Mon Oct 21, 2019 9:47 pm
by GeoffDEAL
Hi most likely the fuel lift pump not keeping up if yours has a glass bowl the washer under the bowl can get a slight air leak especially if bowl has been removed for cleaning and washer is old, had one tractor that kept stopping and that was the problem, also the pump valves maybe old and worn, there is a pump kit with these and washer ect or replace the whole pump, also check pump operating push rod length Do not swap ends on this as the cam shaft end will be beded in to the cam, the cam could be worn and not giving enough lift to the pump only way to fix is an in line electric fuel pump. As noted in another thread if replacing lift pump Be Sure to use a gasket of original thickness as some pumps have a thin paper gasket where old pumps can have a much thicker gasket, the thin gaskets can put excess pressure on the cam shaft lobe resulting in excess wear and failure. Pump push rod length 36mm.

Re: Injection Pump Inlet Filter

Posted: Sun Oct 27, 2019 6:20 pm
by Gard
I think if the tractor was running OK for awhile, that indicates the lift pump is OK.
I had a similar issue on my tractor which I eventually tracked to crap in the bottom of the tank, I would blow out the line between lift pump and tank, it would run great for awhile then die and be unable to start until I blew out the line again, I repeated this several times. The last time was way up in the woods on a very cold day on a steep icy slope. Had to drag a spare battery and portable air tank up there. Once the line was blown out it started easily after bleeding.

When I got back to the barn, I used 1/2" id tubing to syphon the fuel out of the tank as I slowly moved the tubing across the bottom of the tank. I poured the fuel back into the tank using a funnel that has a fine gauze filter in the bottom. The amount of crap caught in the filter was quite impressive, bugs, rust, feathers sawdust etc. I repeated this several times until the funnel filter was clean. That was over a year ago, no problems since. I now use the funnel with filter every time I fill any equipment from gas cans.

The other thing that has been mentioned before is to try bleeding the system using the engine starter, if the pushrod is not the right length for the gasket used, you can still get good flow with the primer lever but not as much when cranking.

Re: Injection Pump Inlet Filter

Posted: Sun Oct 27, 2019 6:56 pm
by bedwards1966
It's surprising how well they can run when there is an issue with the lift pump or the pushrod.

My 995 used to conk out sometimes and you'd have to bleed air out of it to get it to go, then it might do it again five minutes later or it might go two years without missing a beat! Drove me nuts checking for air getting into the system and wondering why it would run fine some of the time but then die.
Eventually found the fault to be that the lift pump plunger was worn out, along with the cam lobe. Simple issue but strange how it would run for hours at a time without missing a beat and with plenty of power, then at other times just conk out. That's why I always suggest checking the pin if there's any fuel issues as it's easy to do, cheap to sort (even if an electric pump has to be added) and can cause a huge amount of headaches.

Both my DB engines have had worn push rods. The 990 engine used to only run with perfectly clean fuel filters as it would run great but couldn't provide enough pressure to go through a filter that was even a little dirty (had a lot of dirt in the tank, filters were getting changed every couple of hours). Cleaned the tank at the same time as doing the push rod and the fuel pressure went from about 1 psi to 7 psi and it's never stopped since.

Re: Injection Pump Inlet Filter

Posted: Sun Oct 27, 2019 11:22 pm
by Gard
Thanks for the additional information Bedwards, how did you measure fuel pressure? I was thinking about making an adapter for the injector pump bleed valve to see what pressure is getting to the pump, not sure how well this would work but it would be nice to have a quick way to see how much fuel is getting to the injector pump.

Re: Injection Pump Inlet Filter

Posted: Mon Oct 28, 2019 5:19 am
by cobbadog
Some speed accessory shops sell in line fuel pressure gauges.

Re: Injection Pump Inlet Filter

Posted: Mon Oct 28, 2019 9:21 pm
by bedwards1966
I had a piece of rubber fuel hose between the fuel filters and injector pump (the original pipe leaked so rubber hose became a quick repair), this meant I could easily Tee into it with a pressure/vacuum gauge. I'm not sure what would be practical for checking the pressure without butchering the metal pipe.

I'd be curious to know from those who know the DPA pumps better than I do whether the bleed nipple would give accurate results, I'm not sure?

Re: Injection Pump Inlet Filter

Posted: Tue Oct 29, 2019 11:34 am
by ALANJ
A good test for like problems is to disconnect the leakoff pipe from the upper front face of the DPA pump and run a plastic pipe from the exposed stub fitting into a clear container located next to the driver . Then either load the engine onto a dynamometer ,if available, or drive up a steep hill etc. to load the engine to 80/90 percent min.
If fuel then emanates from the pipe ,this indicates that the fuel injection pump, the FIP, is receiving more than enough fuel . The fuel from the pipe being the excess to FIP requirements and normally returns to the tank along with excess leakoff from the injectors. This excess return fuel from the pump indicates the lift pump, filters, pipe work etc are good.
If the engine normally dies after a few minutes running this indicates a blockage on the return line from the said FIP / injector return line.This blockage back pressures the two pumping plungers in the rotor head against charging transfer pressure resulting in no injected fuel, Hence engine death.This failure is commonly associated with waxed fuel in cold winter conditions.
Therefore the leakoff pipe removal testwill also simultaneously check for engine dying cause after a few minutes running as well as the low pressure fuel feed circuit to the pump condition. Hope this is of interest and assistance. AJK.

Re: Injection Pump Inlet Filter

Posted: Tue Oct 29, 2019 11:35 pm
by Gard
Alan, thanks for the tip, I think I will give that a try since the tractor is running good now.
How would you go about trouble shooting a engine that will not start? How much fuel should come out of the return line when cranking the starter?
It seems that a pump should output a specific flow at a specific pressure, one point on the pump curve. This could be done by fitting a pressure gauge followed by a needle valve. Not sure how practical this is. Just measuring pressure with output still attached to the injection pump may be good enough?
Bedwards, it would make things easier if there was rubber tubing, it seems like anytime I remove a steel pipe I never know if I will be able to get it to be leak free on reassembly. I suspect the copper hardens.

Re: Injection Pump Inlet Filter

Posted: Wed Oct 30, 2019 7:44 am
by ALANJ
In answer to your query re non starting engine , as long as there is any fuel emanating from the pump return line that is enough.The FIP is then receiving all it needs.This return fuel is surplus to the pump requirements so the actual flow amount is irrelevant.
Actual pump,FIP, output can only be satisfactorily checked on a Hartridge type test bench. Home made tests and test equipment can damage the head/ rotor assembly. Hope this helps, AJK.

Re: Injection Pump Inlet Filter

Posted: Wed Oct 30, 2019 10:11 am
by rid54
The feed pressure from the lift pump is determined by the return spring in the lift pump, the status of the filters, and the flow ratio through the injection pump. Unless the lift pump is bad or the filters clogged, the pressure itself should be good enough for the injection pump to work on. The return pipe from the injection pump is hooked up with the leak return from the injectors purely from practical reasons, neither of these lines should have any pressure - they just lead the return flow back to the tank.

A non-starter problem has basically three reasons: no air (unlikely), no compression (happens) or no fuel (happens). Each of these branches off into several things that need to be checked.