Diesel Suction Leak Troubleshooting

[Birken Vogt]

I have a customer unit, brand new under warranty, that is failing to start after it sits a week or so.

We suspect possibly a suction leak.

I am thinking of taking the ends off the suction line and pressurizing with a slight bit of air and looking for diesel leaks and/or soap bubble checking the whole thing.

Any wise tips and tricks would be appreciated. This unit is some distance from the shop.

 

[mg2361]

I have used about 5 psi of air to test fuel system suction side integrity. Cap the line to the injection pump and pressurize the pickup tube end. Just had one this week with a fuel water separator bowl leak. It would lose prime, but did not leak fuel. Pressurizing the circuit revealed the culprit.

I have also used clear lines as well. Place clear plastic lines on the suction and return sides with vertical loops. Run unit to fill the lines. While running see which has air in it, if any. Let sit then see if one of them is empty.

 

[Vetech63]

I can't add anything........MG covered this well!

 

[Muffler Bearing]

Agree all the way,

who's warranty is it under? why not let the major corporation pay for the repair?

 

[Birken Vogt]

I'm the one performing the warranty under flat rate. Which is why I ask here. I have already been out on it once. It seemed at the time that it was just never primed, brand new. But then a week went by and this happened.

 

[John C.]

It this a single unit or one of multiple units pulling from the same fuel source?

 

[funwithfuel]

I always scrutinize the water separator and priming pump. So many issues arise from a rolled o-ring or flat used o-ring. Have also had bad crimps on brand new outta the box filters. The pressurised low side has always revealed itself. The only difference between my way and MG2361, I only cap the return to tank. That way I get all the emissions and possible flame start solenoid or any other consumer that might introduce air. Good luck.

 

[Bluox]

Do we get extra points if we guess what you are working on?
I use an old gear transfer pump driven with a drill and a liquid eye to check for air .
Hook it up at the transfer pump intake on your motor.
Bob

 

[Birken Vogt]

It is a Mitsubishi 4 cylinder generator motor pulling from a tank right under it. Bosch style A pump. I have been meaning to get some clear hose on the truck, will pick up some tomorrow to help with the job.

 

[Zewnten]

Clear hose is usually the easiest but some times i cheat and put shaving foam on connections to see if it gets sucked in with the air.

 

[Birken Vogt]

Got out on the job today. There was an updated flash so installed that first, it starts with a much more aggressive fuel position. At least it started but it started terribly again, seemingly one cylinder at a time with shaking and smoke. I am sure the customer will not be real happy. After it got started, it was very clean each time after that. Installed clear line on the return, from a distance you would say it was 100% solid fuel but up close with a flashlight you could see very fine bubbles whizzing by. The thing has a check valve at the top of the dip tube, not leaking at all, zero fuel drops back to tank. Pulled dip tube, same deal, it's clear plastic and does not lose any fuel back to tank over any amount of time. Pressurized the entire system from dip tube to return with air including transfer pump and main pump, soap bubble check, zero leaks. The only part of the system that is under vacuum is the dip tube, first check valve and a rubber hose between the check valve and the transfer pump. After the transfer pump is pretty significant pressure on these A pumps IIRC and even checked all of that with air pressure, nothing. Pulled a fuel sample, looks perfectly clean.

Somebody will go look at it next week and see how it starts after sitting 1 week.

 

[thepumpguysc]

I don’t know for sure, but I don’t think they came with the check valve.?? I’m thinking someone put that inline to stop a drain back problem.??
MAKE SURE IT’S INSTALLED CORRECTLY.. (1 way check valve)
Good luck

 

[Birken Vogt]

Yes, the check valve is just a pipe fitting type valve screwed on right above the dip tube. It works perfectly when I was testing it, never drained a drop back into the tank, let it sit a couple minutes and watched. And I was able to re-prime the dip tube just by yanking the pipe up and down until fuel came out so I know it opens and closes without much resistance.

Here is a picture of the pump numbers, looks a little different than what I have seen in the past.

 

[thepumpguysc]

That pump should have an overflow valve on the outlet side of the pump.. banjo bolt.. if u have one in your arsenal, replace it with yours and then you’ll have to wait to see if it works..

 

[Birken Vogt]

You mean the bolt with the ball/spring/washer stack relief valve in it, might be leaking away?

I may or may not be able to scrounge one of those from an old Isuzu or Mitsu in my yard, are they all the same setting? This one has the injector leak off rail teed into it, so I wonder if that might make it a different size or length.

 

[thepumpguysc]

Post a pic of whatcha got..

 

[Birken Vogt]

Isuzu 6 cylinder. This one looks promising but it is old, mid 90s I think.

 

[Birken Vogt]

Mitsy S3L2 but this one seems to be dead headed with no overflow valve so probably no use.

 

[Birken Vogt]

Isuzu C240. Overflow valve is on top of the filter head with the rubber hose connected to it. Injector return might interfere.

 

[Birken Vogt]

The installer has been back after a week, and reports it just as bad as ever. Smokes and sputters and shakes like it is only running on 1 or 2 cylinders, until it picks up and takes off eventually after several crank attempts. It makes a lot of smoke too because it is a turbo engine with no anaeroid so it is going full fuel on 1 or 2 cylinders for quite some time until it finally catches them all. Once they all catch, it runs fine the rest of the day.