Measuring fuel pump pressure on the BX tractor.

[cerlawson]

As some of you may note I have been struggling with stalling ever since purchase and now about 225 hours on ths BX. Currently will be trying to verify if there has been air sucked into the system, starving the engine. However, even before that I'll attempt to measure fuel pump pressure. This newer pump was instlled along the way of these problems in case the original was bad. Original does produce clicks when 12 v is applied,but that's without any fuel. I'll test that one also with fuel.. First attempt is on the one now in place.

I purchased a low.pressure gauge, 0-15 psi which is fluid filled. It has an instruction to vent it at its installed location. I intend to use this low pressure gage with some of the gear that came along with a fuel pump pressure testing kit from Harbor Freight. However, their gage is for a higher pressure range and this pump is supposed to be 3 to 5 psi or so. My question is "Why is the instructions for the Harbor Freight kit saying "not for diesel engines"??? Doesn't make sense, except it is obvious the parts with the kit are mostly for gasoline engines. I suppose this is because the box is labeled "Fuel Injection Pump Tester". Anyhow the stuff is there for fuel pumps.

Is there any precaution (position, etc,) for the fluid filled low pressure gage? It might not sit vertical.

 

[Grouse Feathers]

They probably mean it is not for checking the injector pump as it would be much higher pressure. It should not be a problem for the little electric pre-injector fuel pump on the BX.

 

[Grouse Feathers]

They probably mean it is not for checking the injector pump as it would be much higher pressure. It should not be a problem for the little electric pre-injector fuel pump on the BX.

The only thing with the gauge at such low pressures it to make sure the elevation of the gauge is the same as the pump or that you correct for the elevation.

 

[Dave_eng]

My thought would be to test for the quantity of fuel delivered by the pump as a first step by having it discharge into a container whose volume is known.
My reasoning goes like this. I am assuming you are going to connect your gauge directly to the discharge of the pump. If the pump can suck a low volume of fuel and deliver it to the gauge the gauge is going to produce a reasonable pressure. If the fuel line is crushed or in some way restricted or if their are problems in the tank , the pressure gauge, only needing a small volume of fuel to show a discharge pressure, might mislead you into thinking every thing is OK when in fact the problem is the injection pump is not receiving enough fuel.
Dave M7040

 

[cerlawson]

In general the problem does not seem to be involving rate of flow. When things stop, it is abrupt even with load removed from engine. With the gage on a "T" fitting at the inlet to the engine I get 2 psi. That remains even when engine is running. I did not try it with load on the engine, since 2 psi is below the rated range of 3-6.
The 2 psi was the reading with the slightly used filters in place and also after replacing both. The original pump was given a no-flow test from a container of fuel with a reading of 3 psi and this points to weak fuel pump being one main culprit.

Plan now is to install the second pump in line with the one there now. Local dealer seems to think it will work and not exceed the 10 am rating of the fuse. He guesstimated about 2 amps total. A no-load, no fuel test on spare pump is 0.4 amps. This work will wait until no need for the tractor for a few days due to having to take off so much stuff to have a working access and my age, 88..

 

[D2Cat]

What would happen if you quit changing out fuel pumps and just applied the 3-5 PSI pressure to the fuel tank?

Take an old inner tube and cut around the valve stem with enough material to cover your fuel inlet. Fasten it with a clamp. Turn your compressor way down to 5 PSI (or use a regulator like for a spray gun). Use the self clamping nozzle to clip on your valve stem.

Start you tractor and see how it runs.

I've bled the air out of a couple diesel systems using the 'ole inner tube method!!

 

[Grouse Feathers]

How accurate is your gauge? You can check the calibration by rigging up clear plastic tubing as a manometer. If you use diesel fuel 1 psi will raise the level in the manometer 2.7 feet. With water 1 psi will raise the level 2.3 feet.

 

[cerlawson]

an update on this post. A second pump was installed in line. Result was 5 psi for two pumps in series.. Put about an hour on the tractor and the gauge on always showing 5 psi until suddenly 2 psi. Tractor still worked for a little while until I put it up on blocks to see what is wrong. Disconnecting the add-on pump electrical connection dropped pressure reading to zero. Disconnecting the original pump electric connection, with add-on doing the job, gauge red 2 psi.
A new pump came today via Hong Kong cost about$18 free shipping. It is different style and is termed "heavy duty". Installed where the original and the pressure came up to 5 psi. Noise from the two pumps is considerably louder than before.

Checked resistance of the old pump both ways +\- and -/+ and with low resistance range reading of zero both ways New pump with same setting had a significant reading of resistance.

I'll leave the pressure gauge on for the next few hours of use to see if all stays OK. Will let tank fuel level drop to see it things still run, whereas in the past many a stall. at 1/2 and higher fuel level. Fuel filters are almost new. My thought now is most past problems due to weak fuel pumps. We shall see.

 

[D2Cat]

You'll soon have it ironed out. It's too bad you have this many hours of trouble caused by a faulty fuel pump.

I had similar troubles on a 1995 Chev with 6.5. NAPA and O'Rielly pumps would not pump the pressure the book called for.

I had replaced the lift pump for my 5.9 Cummins with an aftermarket pump and was going to use the original Dodge pump on the Chev. The fitting were different and both stores told me there were no fittings available to adapt the dodge to the chev.

I chopped off the fitting on the Chev and welded them to the Dodge pump. I added a gauge and it keeps 10-12# all the time on the 6.5, and it's been working fine for about 4 years!

 

[Hondarancher4435]

Just a thought due to your sudden pressure drop assuming you pump is good any chance there is debris in the fuel tank that sucks the pick up line shut and once the vacuum of The pump stops it floats free and let's you restart engine. I have has this problem before with similar symptoms to yours.

You could also replace a piece of fuel line with clear tubing temporarily that way you can see if it has a steady full flow of fuel when it's cuts out and you can also see if there is air bubbles in the fuel

 

[Diydave]

You may also want to check for debris in the tank, blocking outlet, or a clogged tank vent...

 

[ipz2222]

Haveing a restricted line before the pump will do the same thing as a bad pump. You can put a vacumn guage between the pump and tank to see what it does when the engine stops. I remember someone haveing a dead bug in their tank that caused this.

 

[cerlawson]

Plugged tank outlet certainly seemed like a possibility. However, took the tank off at 210 hours and did as much work on it as the dealer said they would do and nothing came out. Flushed with fuel and it showed no such stuff. Before that I even got the dealer to put in new fuel gauge with float thinking it was not reading empty when if fact it had plenty. Appearance of that later sender showed no rust, like brand new. The word "lemon" keeps cropping up in my vocabulary.

 

[DVoss]

There is the possibility that a rubber fuel line has delaminated internally, causing a restriction.

 

[cerlawson]

More news. With two fuel pumps in line and pressure drops to just above zero, a test was to be run on each pump. Before that, attached a copper tube to the hose coming from the tank and I blew into that causing bubbles to be heard in tank. Tried to see if that would affect pump pressure at injectors, but no change.
Taking both pumps off and measuring their output pressure the first pump purchased at ebay did not operate at all. That has about 3 hours on it and it had been for a Yanmar tractor. Pump that came from Hong Kong, a different configuration than Kuboto's, puts out 6 psi. Instead of the failed pump installed a small length of copper tubing. So with all back together and installed new final filter and now the gauge at the injectors reads 5 psi. Mowed a city lot for about a half hour and all went fine. Hours on tractor now 233. By the way, the original and replacement pump (from Messics) still run and put out 3 psi. I'm not ready to take the label "lemon" off this tractor.