d47u Diesel won't start, fuel pressure low.

My situation is quite similar to this one:

https://acmoc.org/forum/discussion/d2-3j3006sp-fuel-transfer-pump

The situation is:

It used to show fuel pressure in green on the pony motor. But typically diesel would only start by throttling up and then popping compression lever. Reverse didn't work. Ran this way for years (used very lightly)

Machine sat for 6-7 years under cover. Recently I've been trying to get it back in service, after a radiator rebuild.

A buddy changed the fuel filters.

Initially the pony would not start. And the fuel rack was stuck. But I was able to get it unstuck with lots of juice and some gentle prying. I bled the diesel while towing the machine and got it started via pull-start, in 4th gear. I noted the fuel pressure gauge was in the green. It ran and operated well on diesel for 20 minutes or so until I shut it down.

Eventually I got the pony motor running reliably again. Figured I'm on the home stretch, but no...

With pony turning the diesel, it will not give a single puff of black smoke. Even If I throttle all the way up and then flip the compression lever, nothing.

I have bled fuel system fully several times, and see good squirts at each injector when loosening the caps.

So at first I was suspecting worn pumps in the injection pump. (and this might explain the situation from years before as well).

Then I noticed the fuel pressure gauge was in the white caution area when running on the pony. So I thought maybe this is the cause of present troubles.

Or maybe it is both: low pressure to the IP, and a worn IP.

I inspected the transfer pump bypass valve and everything was clean, no dirt under plunger. The plunger is the old brass+rubber type. Interestingly the seat underneath it appears worn/grooved as if it previously had the plastic type plunger.

I've ordered a new plastic plunger and it should be here tomorrow.

In the meantime, I lightly sanded the plunger area with 600 grit and stretched the spring a bit.

After bleeding again, the fuel pressure gauge now reads to right of the caution range, about 1/10 shy of green. So it improved, and I interpret that as about 9 PSI, if gauge is accurate.

I've seen reports on this forum of engines starting in the caution range with approx 5psi or more.

Since mine is not popping at all, it makes me think (again) that the injection pumps may just be too worn. afaik, injectors don't get harder to pop when sitting, so I can't imagine it's an injector problem affecting all 4.

But I would be more comfortable with that conclusion if I was getting full pressure, like it used to.

I do have 4 spare pumps of unknown condition off a parts tractor. So I am thinking of trying one, to see if it will generate some black smoke. Also I have a D6 with a seized engine (D318) that I could scavenge pumps from - I think they are the same.

I think I will wait until the new plunger arrives though, to see if that improves pressure.

I guess my questions are:

1. Should I sand down (lap) the plunger seat some more to get it flatter? Or is it supposed to have some indentation in it?

2. Do you agree that it sounds like the injection pump(s) are worn?

3. is it necessary to drain the fuel filter housing in order to remove bottom plate from the transfer pump, or to remove entire transfer pump?

Hi danda, not to sure on the depth your are asking about but all I can ask is if the pumps have been bleed themselves behind the injector line from pumps? I did notice with my 3J they needed bleeding a few times or no go

Hi Busso, good suggestion. In fact I haven't bled them behind, but not for lacking trying. They are painted shut and very stuck. I don't have the proper wrench/socket. I've tried using a 1/4" wrench on them but it wants to slip. So I backed off rather than damaging.

That said, in the past I bled the fuel system several times and every time all that was necessary was the 2 bleeders on the filter housing and then crack the lines at the injectors themselves. Indeed my understanding is that Cat decided these bleeders were not necessary and eliminated on later models.

Also, just to reiterate that I had it running for about 20 minutes via pull-start. So the system was fully bled at that point, and then when I tried to start it via pony afterward the diesel exhaust is just clear. no pops, no white smoke.

My belief is that the pony simply isn't cranking the engine fast enough for the marginal fuel transfer pump to generate enough pressure for the (marginal?) injection pumps to pop the injectors. But when I tow started it, it spun the engine fast enough that it crossed a threshold and lit off. I'm kinda wondering if others have had this experience, or at least if it sounds a plausible theory.

btw, that is actually another reason I'm considering trying the spare pump(s). They have loose bleeder screws.

Is the fuel line clogged from the tank to the transfer pump? You said it ran then shut down. Take the fuel tower apart and check all the passages. May have to remove the injector housing and clean the fuel galley that feeds the injector pumps and replace the seal between housing and fuel tower. Not all the that hard to do. When apart, check and make sure the lifters in the housing are set to: 1.736" @ TDC for each pump measured to the top of the injector housing and rack plunger lengths are: 2.6575" - 2.6577" and no more than .005" short from wear. They can still be measured with the housing attached to the engine and just remove each pump. Have you removed any of the injectors to see if any of the tips are clogged?

All of this is explained in the Serviceman's Reference Book.

I would say you need to open the bleeder valves on each pump. In 40 years of dealing with D 318 big brother to your D 315 engine ,TWICE on needing to prime I wasted hour bleeding with just line nuts loose. I have no idea of why, but on the one occasion I pressurized the fuel tank with air, had fuel flowing out the lines and not a pop for hours. This was a farm tractor being used every day. Fuel pressure fell at the end of the day and fuel tank very low. So started the next day with filters in hand. Not an unusual event to have low fuel be the last event of filter clogging. Not that it happened often ether.

Unfortunately I believe the newer diesel formulations are also part the trouble. We have been fighting Kubota MU 7040 ( mid 90's model, about 3500 hours). I have been the operator care taker since 2000. I honestly don't remember changing fuel filters in it the last time. Used in a 14 acre vineyard. Almost always left with full fuel tank. Years ago a crew ran it out of fuel. Then it has mostly sat since spring of 2020 when vines were removed. I rented it for 5 to 20 hours per year until 24 when I bought it. Spring of 25 it did not start had to prime it. Used less than 30 hours for the year. Used this spring discing around the yard. Then my son started it, before moving it died. It has plastic fuel bowl and could see water. Changed the filters, never getting it to prime. Son took it upon himself to have full time mechanic friend come help him prime. He concluded injector pump was gummed up and sent pump off. I am waiting to know how this ends. I am hoping the pump shop doesn't decide to hose me. I would of consulted another mechanic who has done pump work for me before.

Depending on your wishes danda get cheap 1/4 drive socket and smash until it is tight on the oval bleeder valve or just buy one from Cat. And if you think low flow to transfer pump is part of the problem have helper use a rubber tipped blow gun on vent in fuel cap. Or if no helper get rubber cap that fits fuel filler hole from hardware store, then install a tubeless tire valve stem in cap, then an airline pressure regulator and setup to about 5 psi on fuel tank. Much more could damage the tank.

When I said it shut down, I mean that I shut it down normally. It exhibited zero problems while actually running on diesel after the pull start and throttled up and down nicely.

Even still, I have verified the fuel line between tank and pump is clear. There is very good flow. I even can gravity bleed to top of filter housing and a good flow comes out of the top wheel bleeder.

this is the bleed screw being mentioned above. A socket used to fit the top of shock absorbers will fit the two flats bleed screw.

The engine should start and run with only fuel tank gravity feed head--it will be low on power if put to the test but it will run.

Hope this helps.

Cheers,

Eddie B.

Ray 54 on the Kubota M7040 when you change the filters you need to undo a little round bleed knob on injector pump to bleed fuel or you will never get it going. Other models have the screw but don’t always need it but 7040 will not go without opening it.

Danda have you tow started it again to make sure it will run. That would eliminate air in the system and work from there.

>The engine should start and run with only fuel tank gravity feed head

That's quite interesting to me if true. Because it means that the injection pumps must logically be at fault rather than the transfer pump.

And along those lines I have an update.

Today I received a "new" plastic plunger from ebay. Turns out it was used, but appeared in decent condition. I installed it and ran the pony. Fuel pressure was actually a bit lower (middle of white) than with the original metal/rubber plunger. So that's a bust.

Then as a test I took one of the (4) injection pumps from my parts tractor and installed it. These pumps are in unknown condition -- the parts tractor is in very rough shape but at least all 4 pumps were capped off, as if someone cared about it. So when I ran the pony and flipped the compression lever I got a strong puff of black smoke. It wouldn't start, but it was progress. This was not happening before.

So, encouraged, I cleaned the other 3 donor pumps and installed them. The first thing I noticed was that fuel pressure gauge was now higher, just over the line into the green. So that makes me think the old pumps were leaking enough to lower fuel pressure on the input side. I wasn't aware that was possible, but it makes sense.

Upon flipping the lever, I got more black smoke. With another bleed of injectors and flipping the lever a couple more times, eventually the diesel started.

Unfortunately fuel started gushing out the back of one of them, as if the bleeder screw were wide open. Perhaps it was... I had difficulty tightening it earlier and it might have jiggled loose. So I shut it down right away. Anyway the jet of fuel coming out of that thing was clear evidence there is no obstruction in the fuel filter housing or lines, so we can put those ideas to rest.

Tomorrow I will tighten it up better, and hopefully that fixes it.

So I conclude the injection pumps were the primary problem.

I think there's still something not quite right though. It only seems to puff smoke when the compression lever is first moved. After that, exhaust returns to clear if the diesel doesn't fully take off. Though to be fair, it could've been air. The real test will be 2nd cold start.

My gut feeling is that the donor pumps are quite worn, despite being better than the ones that were in there. Or maybe something else is going on like worn lifters under the pumps...

"So, encouraged, I cleaned the other 3 donor pumps and installed them. The first thing I noticed was that fuel pressure gauge was now higher, just over the line into the green. So that makes me think the old pumps were leaking enough to lower fuel pressure on the input side. I wasn't aware that was possible, but it makes sense."

Sounds plausible to me too. Once you get the leaks stopped (you may want to take the bleeder all the way out and flush it in case there's crud under the seat) and give it a good solid run, then a couple more cold starts should tell you where you stand regarding the shape those new injectors are in. Even if not perfect, if they're better than the old ones then you're moving in the right direction. You could also look into getting new injector nozzles which are relatively inexpensive and may also provide an improvement