Northern Lights Genny Lift Pump

[MikeP]

Our NL 16kw genny quit at anchor a few nights ago. It slowed down to about 1/2 speed, ran at that speed for a bit and then quit. It would not restart.

It's an obvious fuel issue - there was no fuel at the injectors after it quit. Flow through the primary filter is fine; I replaced the secondary and bled the system. I got a SLIGHT amount of fuel at the injectors but the engine still would not start.

The lift pump puts out a very small quantity of fuel at each pulse - maybe a bit over a teaspoon. Unlike standard automotive fuel pumps of this type, I am not familiar with these particular, very small, diaphragm pumps so I don't know how much fuel they should be moving with each stroke. Can't be too much since they are quite small/short stroke but it seems like very little volume to me. So I'm wondering if anyone has an idea of the volume they should produce at each stroke before I proceed with further troubleshooting.

 

[Canuck Dennis]

Not able to answer that, but, if you find out and the diaphragm is ok, check the spring, may have weakened over the yrs, neighbour had that on a gas job here..

 

[Boatsb]

mike a lift pump supplies volume not pressure. It brings the fuel to the injector pump. Fuel lubricates the injector pump. If your not getting fuel to it your injector pump will fail too. this may not be the answer you want but I believe the answer you need will not be the cheap way out.

contact someone at northern lights. you will at least get the right answer. here not so much.

 

[Avenger]

A teaspoonful per stroke may be okay. These are very low fueling engines, and the injection pumps usually don't have a fuel return. They just dead-head, so they don't need a lot of volume.

My recommendation would be to tee a pressure gauge into the injection pump inlet. Those pumps have to be pressurized in order for the pumping plungers to charge themselves. It doesn't take much, a few pounds is what you'd need to see.

 

[Colwyn D]

Mine is only an 8kW NL using the Kubota engine. I've recently done work on the fuel side and was thinking exactly the same thing when purging the filter and lines, took ages and was sure something was wrong with the piddling little amount coming from the lift pump but when bled it started and ran fine. Seems 'normal'.

 

[MikeP]

Thanks guys, appreciate the info and will do a pressure gauge test. I found the specs for the pump pressure which call for 1/2 bar (a bit over 7PSI) of pressure at the output side so I'll see what it actually does. I put my finger over the output port and IMO, there's hardly any pressure there. I'd guess it's not more than a pound or two at most but I don't have a calibrated finger so maybe I'm wrong!

There is fuel getting to the inj pump (and the injectors) but the pulses at the injector with the line cracked seem rather weak, as if insufficient volume was getting to the inj pump but I can't say that for a fact at this point.

The diaphragm/all gaskets appear to be fine - no cracks, etc. As noted, if the spring is weak, it appears it would reduce the volume and pressure.

FWIW, I swear I've seen accelerator pumps on a Holly 4500 put out more fuel than this lift pump!

 

[doc g]

Bypass the entire fuel system and pressurize it with an electric fuel pump right at the pick up pump. You may still have air in the system or you may have vacuum leaks in the inlet side allowing air back in the system,I keep a small electric fuel pump with a bunch of different fittings around to do this. I found that two of those banjo fittings were leaking air into mine but never leaked fuel out. Once i corrected that no more fuel issues. Be usre it's primed first then move on .........Pat

 

[Pascal]

We have two NL 20 on the boat I run, these little pumps do not put out a lot of volume when you manually reprime. Is it a teaspoon per stroke, maybe. Keep in mind that while one stroke isn't much, all the strokes add up to quite a but of fuel when the genny is running, or even cranked.

I checked one a couple of years ago, I m pretty sure you can pull the bolts off th pump and check the diaphragm. If it s good then the pump should be fine. In our case, th fuel tank levels are higher than the gensets and one day I found fuel in oil prompting me to check the diaphragm. It turned out the injector pump was leaking fuel into the crankcase (about 4000 hrs at the time)

As much as I hate throwing new parts at a problem, they re pretty cheap so it may be worth just replacing it especially if high hours

 

[mr hatt]

I'm with doc g. Our kubota users a small electric lift pump that I believe the previous owner used to replace the mechanical one. I have a harness I use when I change filers that let's me prime the system. For all of $50 you can install an electric lift pump. Just my opinion take it as such.

 

[Pascal]

My Norpro 18 (Isuzu engine) uses an electric lift pump. The nice thing is that when you change the secondary or open the fuel system, you just have to turn the key and for the pump to to bleed the system instead of having to manually flick the lever on the NL pump.

 

[Avenger]

Speaking of bleeding,... those little injection pumps are an absolute horror to bleed because they dead-head and pump so little fuel that it's near impossible to get the air out of them. Some of the newer ones have bleeder screws, but most don't. I'd say 90% of the ones we see had nothing wrong with them except the inability of the operator to bleed them. Then they assume something is wrong with it and try to take it apart. That's when they suddenly have something wrong with them.

 

[MikeP]

No luck so far...

Well, maybe partial luck:

I rigged an elec fuel pump and bypassed the lift pump. With the E-pump the genny will start but it still won't reach normal operating RPM (1800). There is a bit of diesel "clatter" at the reduced RPM (there was never any at normal operation/RPM). I bled all four lines at the injectors with the engine running and each "cracked" injector reduced engine RPM, as it should. Unfortunately, I have to quit work on it to get ready to leave the boat for a while. So further troubleshooting will have to await my return in September.

Forgot to add:

NL tech suggested I take a look at the muffler to see if it may have collapsed internally/causing a serious exhaust restriction. He thinks it's very unlikely that there is an issue with the injection pump itself. I'll check out the muffler when I get back to the boat in Sep - it's the original muffler installed with the genny in the mid 1990's.