Long Way from Home - Diesel Trouble

[Tia Bu]

Hi all:

Ran from South Carolina up to Maine so far this summer. Have just started back south as must be back to my teaching job by early August. Just stopped in Gloucester, Massachusetts, and am stalled and baffled by some diesel engine trouble. Any suggestions?

The engine is a Volvo MD7A. I had the injection pump rebuilt rebuilt this winter, and she ran fine for 200-300 hours on the way up. When we pulled in to Portland, Maine, though, a couple of weeks ago, after a 24 hour run on engine power, I found the engine wouldn't restart after it had been shut down for about an hour. I had to bleed it to get it running.

For the next several days, I had to bleed it to get it started nearly every time I started it, but it ran just fine afterwards. I assumed the problem was fuel filters, so we replaced both the filters yesterday. The engine started just fine afterwards, and we made a 9 hour run under power the whole way. However, several hours into the run, the engine started revving up 300-400 rpms for brief spurts. We never figured out why it did that, and after an hour or so, it stopped doing it and ran fine.

This morning, the engine started without bleeding. But it was slow to start. This afternoon, as we pulled into Gloucester harbor after about a 7 hour run, it just died. I tried bleeding it several times. It will bleed, start, run for a minute or two, then it will rev up 300-400 rpms, and it dies. When I bleed it again, I find the whole system is full of air.

Kind of baffled. Any ideas? My buddy saw me reading Cruisers Forum looking for help and suggested we post this tonight and see if we get any suggestions before we plunge back into the engine compartment in the a.m.

Thanks in advance.

[cal40john]

Originally Posted by Tia Bu

Hi all:

Ran from South Carolina up to Maine so far this summer. Have just started back south as must be back to my teaching job by early August. Just stopped in Gloucester, Massachusetts, and am stalled and baffled by some diesel engine trouble. Any suggestions?

The engine is a Volvo MD7A. I had the injection pump rebuilt rebuilt this winter, and she ran fine for 200-300 hours on the way up. When we pulled in to Portland, Maine, though, a couple of weeks ago, after a 24 hour run on engine power, I found the engine wouldn't restart after it had been shut down for about an hour. I had to bleed it to get it running.

For the next several days, I had to bleed it to get it started nearly every time I started it, but it ran just fine afterwards. I assumed the problem was fuel filters, so we replaced both the filters yesterday. The engine started just fine afterwards, and we made a 9 hour run under power the whole way. However, several hours into the run, the engine started revving up 300-400 rpms for brief spurts. We never figured out why it did that, and after an hour or so, it stopped doing it and ran fine.

This morning, the engine started without bleeding. But it was slow to start. This afternoon, as we pulled into Gloucester harbor after about a 7 hour run, it just died. I tried bleeding it several times. It will bleed, start, run for a minute or two, then it will rev up 300-400 rpms, and it dies. When I bleed it again, I find the whole system is full of air.

Kind of baffled. Any ideas? My buddy saw me reading Cruisers Forum looking for help and suggested we post this tonight and see if we get any suggestions before we plunge back into the engine compartment in the a.m.

Thanks in advance.

Air in the fuel line usually means a leak somewhere upstream of the lift pump. Check unions, banjo fittings, cracked hoses, hole in pickup tube in tank, etc.

You can test by running a hose from your lift pump to a gerry can, no more air then for sure a leak.

John

[DeepFrz]

The rev-ing up is most likely caused by fuel starvation. It sounds like you have some kind of restriction/blockage in your fuel system. I suggest you check your fuel tank vent, blow out your line from the tank to the fuel filter, carefully visually check all of your fuel lines, from the tank to the engine. Ensure your filter gaskets are installed correctly. Good luck.

[perchance]

Originally Posted by DeepFrz

The rev-ing up is most likely caused by fuel starvation. It sounds like you have some kind of restriction/blockage in your fuel system. I suggest you check your fuel tank vent, blow out your line from the tank to the fuel filter, carefully visually check all of your fuel lines, from the tank to the engine. Ensure your filter gaskets are installed correctly. Good luck.

Good point about the tank vent. Bugs seem to love them as nesting areas.

[capttman]

Check to see if your filter O rings set properly

[Kettlewell]

Another thing that can cause fuel problems is that the end of the pick up tube gets plugged up in the tank from crud. The crud gets stirred up offshore, causing more to get into your system, though this usually shows up in a very dirty or plugged primary filter first. I would check the primary for dirt and or water before looking too far for anything else. That will also tell you if plenty of fuel is getting that far.

[scallywag]

I would call the company that rebuilt your pump and ask for any ideas. One thought would be to bypass your main tank and hook in a small tank of good diesel. I would do this if you can not inspect the main tank. I would put the aux. tank higher than the engine so fuel would flow and not be sucked into the engine. I would also begin to look for a place to keep the s/v and fly home to make work on time.

John

[HopCar]

I vote with Cal40john on this one. Sounds like an air leak. As capttman says the filter o-rings are a common source of air leaks. The other ideas are also good. I've had an engine stopped by a wasp nest in the vent and by dirt in the pickup tube screen. The pickup tube screen drove me nuts. I couldn't run on my port tank. I went through the whole fuel system including pulling the pickup tube. Everything looked fine and there was no screen to clog on the pick up tube. About the third time I went through the system I realized that I could unscrew the pickup tube from the elbow fitting at the top. There it was! A screen hidden in the top of the tube, full of little black rock like things. I threw that screen as far as I could, put everything back together and haven't had a problem since.

[vintageray]

Is there fuel in the tank? This seems like a silly question, but a neighbor who is a diesel mechanic just spent a day and a half trying get a guys engine to run right and the air out of the system. The sending unit for the fuel gage didn't work and the tank was inaccessable. The owner said they'd just topped off the tank and only run it little since. End of story, there was only two inches of fuel in the tank.

[motion30]

A blocked vent line would not cause air in the line There must be an air leak somewhere in this system. Check all hoses and clamps If you have an eletric fuel pnu you could rig it to pressurize the system from the tank forward and check for leaks

[motion30]

I had a simular problem motor ran for 4 ten hour days and then just shut off. The racor filter was at fault

[barboak]

Browns Yacht Yard has an excellent diesel mechanic in Gloucester harbor. We live here and could ferry you somewhere if needed.

[CarlF]

In my experience, a clogged fuel supply will cause the engine to slowly loose RPM. It doesn't seem like your situation.

Air in the line, on the other hand, does exactly what you're experiencing. Remember also that difficult to diagnose problems often have two things going wrong at the same time. For example, clogging between the tank and the filter will cause more air to be sucked in at any air leak.

I really suspect those fuel filters. If they are Racor's did you replace the handle O-ring when you changed filters?

How old are your fuel hoses? If 10 years+ they need to be replaced anyways. There are lots of people in a fishing port like Gloucester who can do a good job replacing fuel lines. Of if they just use standard hose clamps it's easy to do yourself.

Carl

[mbianka]

Originally Posted by Kettlewell

Another thing that can cause fuel problems is that the end of the pick up tube gets plugged up in the tank from crud. The crud gets stirred up offshore, causing more to get into your system, though this usually shows up in a very dirty or plugged primary filter first. I would check the primary for dirt and or water before looking too far for anything else. That will also tell you if plenty of fuel is getting that far.

A good point. I converted to electric propulsion several years ago and just recently had a look inside my fuel old tank:
THE BIANKA LOG BLOG: IN THE TANK: Part One, Scene of the grime!
I was surprised that the bottom of the tank was coated with a tar like coating that could easily clog up somewhere in the fuel lines or pickup if it got dislodged.

[Kettlewell]

I really suspect those fuel filters. If they are Racor's did you replace the handle O-ring when you changed filters?

I second this suggestion--the logical first place to check. Also, on some engines, like mine, the on-engine filter (CAV type) is so hard to replace that it is very easy to not get it aligned or tightened quite right, or even to leave a second O-ring stuck on the filter mount like I did once. The only way for me to see it was with a dental mirror. Once I removed the second o-ring the air leak went away.