Volvo tmd31b restricted revs

[moodyfinn]

Hi All, I’m hoping someone can help me with an issue ok my tmd31 which is causing much frustration both with mechanics and my bank balance.
I had a leak on the diaphragm breather hole with diesel pouring out into the bilge. I was informed that it was better just to get the pump rebuilt as it was just a bit more work than just replacing a seal. The pump was rebuilt by an authorised and respected Bosch injection specialist. The pump was put back on with all the marks lining up. The boat was taken for a run and did about 6 hours all fine. When I lifted the anchor a few days later, I could not rev the engine past 1000 revs in gear but had full Rev range in neutral. I struggled out and headed off. The next day I still had no revs over 1000 so I headed for port. Once again I replaced the pre-filter and main filter, still no joy. I replaced the lift pump but this did not work either. I then ran fuel direct from a fuel can to eliminate tank/pipe issues, still no joy. Air filter was changed and the operation of the turbo checked. Then the engine ran normally for an hour or so. The next day the engine would once again not rev past 1000. I called a marine engineer and he checked all the obvious bits with no conclusion. He spoke to the injection pump engineer and it was agreed that it should be removed and returned for a check over. This was done and all outputs were to specification. Replacing the pump and the engine ran fine. I have just returned from another trip and once again the revs stuck at 1000 for 20 minutes then burst into life and revs returned to normal. After catching a fish I needed the engine to get out of irons and the engine was limited to 2000 revs not the 3200 that it should do. I reduced it to 1800 and then the black smoke started on every engine setting. I had to return to dock and get it sorted so I sailed back and used the engine just for entry where it worked perfectly until I put it in reverse to stop the boat, yes you’ve guessed it, 1000 revs and crew flying everywhere to stop the boat. Any ideas anyone?

[Lepke]

If the injector pump is operating correctly, diesel rpm is controlled by fuel and the load. If when trying to exceed 1000 rpm you have black smoke, then there's a problem with too much load - prop, shaft, transmission. If the exhaust is clear, then it's not getting enough fuel. Black smoke is too much fuel for the rpm.
One thing to check is the linkage/cable between the injector pump and controls. Have someone at the controls and another at the pump. Make sure it's operation is smooth and the controls move the injector pump lever thru the full range of movement.
Another possibility is an air leak. With air in the lines, the engine isn't getting the right amount of fuel. It could be a very small leak and could be intermittent. So make sure there's no air in the fuel. Bleed the pump and look for bubbles.

[moodyfinn]

Thanks for the reply. I have been moving the throttle by hand directly off the pump and it still does it. Also there is no smoke from the exhaust when stuck at 1000 revs.I can also move the prop shaft by hand so no loading issue. I do suspect the action of the governor in the pump itself but let’s just say the injection specialist is in denial.

[Searles]

Check the fuel tank breather ,must be clear and rising all the way,,also maybe a intermittent air leak in the fuel lift pump,try an electric on line pump before filters and lift pump ,but it really sounds like a sticky govener ..please post all test results ,most interested ⛵️⚓️

[johnn33]

Following

[Scubaseas]

Originally Posted by Searles

Check the fuel tank breather ,must be clear and rising all the way,,also maybe a intermittent air leak in the fuel lift pump, try an electric on line pump before filters and lift pump ,but it really sounds like a sticky governor ..please post all test results ,most interested ⛵️⚓️

Distinct possibility. Open the fill cap and it should resolve issue within a minute or so. Or alternately loosen cap and see if the problem comes back at all.

Assume you tightened the pump to specs and equally? just to toss out a few ideas.....Not syaing I'm right or wrong just offering possibilities of what may be. It's either a not enough fuel or blocked exhaust. Blocked exhaust should not come and go unless it's a ball sized chunk of junk. Like a broken catalytic converter in a car/truck. Highly unlikely in a boat. So fuel side of the mechanical and fuel makes it go equation.

You might also check for exhaust back pressure either by eye balling the elbow or taking the salt hose off and putting a pressure gauge on it. Should be less than 2 psi back pressure. It should not come and go like your symptoms though. Improbable but possible.

Governor getting stuck is very possible but rule out everything else.

When it happens try smearing thick grease on any of the inlet fuel line fittings to try and rule out vacuum leak. This incudes line into the lift pump, in and out of the filter and inlet at Injection Pump. Clean off later with a rag/cloth and brake/parts cleaner. If you have a smoke generator that's another way to test for leaks. Or air pressure and soapy water. Apply air pressure (2 to 5psi) at inlet line from tank and check the line all the way to the injection pump. You'll have to purge the fuel from the lines first though for either air pressure or smoke generator method.

You might try advancing the pump about 5* and see if it helps. Or retiming it all together but if memory serves you need some tools a DIYer probably won't have. You might be able to rent or borrow needed tools from the rebuilder if he has them.

You have checked the pickup in the tank just for sh*ts and giggles but running on a separate tank without joy should rule the pick up being intermittently clogged. I had one car years back that drove me nuts and ultimately turned out to be the foil cap off a fuel treatment bottle the owner had mistakenly put into tank. Would randomly run fine until it didn't. Shut off the car and it would run fine for a week or an hour. This was before screens on pickup tubes. Weird problems sometimes have weird solutions.

From your descriptions I would bet a small amount that there is an issue with the rebuild in the governor assembly. Can we assume there was no issue other than fuel leaking out of the top of the pump prior to rebuilding it? As in no running issues as described before you removed the HP/Injection pump? After pushing a wrench over 50 years the first place we usually look for a weird problem is who just did what to it, just to rule it out. This includes the washers and the fittings, pump timing, etc. etc. If the issue wasn't there before the pump came out but is there after the pump went back in, I'd look at both the install and the rebuild. I would not rely on marks made to time it.

[moodyfinn]

Thanks for your comments people! Just to cove a few points, the boat is a 30 year old swan so generally very well put together and I had no engine issues before the leak repair/rebuild. My next move would be to connect the generator pumped fuel supply to the engine and see if that makes any difference. Not sure if I mentioned it but I fitted a new lift pump just to eliminate that. Breathers are an interesting point but the same amount of fuel is pumped into the pump regardless of fuel used so any vacuum in the tank would be present at Tick over on load or off load. Will speak to mechanics today to see what they have done and will keep you posted I think they will be scratching their heads also.

[Scubaseas]

You could have a restricted tank vent where if it sits a while there is no vacuum, run the engine and the vacuum slowly builds to the point of fuel starvation which leads to lower RPMs. Diesel speed is determined by how much fuel is injected as there is no intake throttle. Your symptoms as stated could be caused by a restricted tank vent. Seen a lot of cars where they fail evaporative emissions due to a spider nest in the tank vent hose. Simple to check by taking fuel fill cap off.

Or you could be sucking air from one of the banjo fittings especially if you reused them. If you replaced the lift pump that could be a fault. Not sure if your generator pump will have enough pressure to feed the HP Injection pump. Check the manual but I think Volvo of that vintage needed 4 to 6 PSI lift pump pressure. I could be easily wrong on that number though.

I keep a 6 to 8 PSI electric pump as a fuel transfer, emergency lift pump, fuel polishing pump (when used with a mongo sized 10 micron truck filter I picked up ages ago). etc. Cheap and effective. Noisy though.

Good luck. Do tell if you find the fault.

[chasfgr]

My Yanmar had exactly the same problem - found an air leak in the flexible pipe from the top of the tank.
Fuel ran perfectly well when disconnected at the engine pump, only leaked when the engine demanded more than the gravity induced flow (which reduced as the tank came off being full).
Three engineer attempts at clearing it - involving pump and filter changes - were NU - in the end I found it myself.

[kryg]

I had the same problem, with my Vitus 33 hp, Twice, in different years. First time, it was a golf ball size carbon buildup in the manifold outlet restricting gas flow. this carbon ball was created because I used the engine to charge the fridge engine run AC compressor. And not motoring enough to burn out the accumulating carbon build up over years. Once I remove the carbon golf size ball the engine ran fine. I was told by the mechanic I needed a new engine, as mine was worn out not so, as I found out.

2nd time was when I installed a new gearbox that had failed, the engineer installed a gear box with the wrong gear ratio, that would not Rev beyond 1000 RPM.

Good luck finding a solution. It maybe not what you first think the problem is.

Originally Posted by moodyfinn

Hi All, I’m hoping someone can help me with an issue ok my tmd31 which is causing much frustration both with mechanics and my bank balance.
I had a leak on the diaphragm breather hole with diesel pouring out into the bilge. I was informed that it was better just to get the pump rebuilt as it was just a bit more work than just replacing a seal. The pump was rebuilt by an authorised and respected Bosch injection specialist. The pump was put back on with all the marks lining up. The boat was taken for a run and did about 6 hours all fine. When I lifted the anchor a few days later, I could not rev the engine past 1000 revs in gear but had full Rev range in neutral. I struggled out and headed off. The next day I still had no revs over 1000 so I headed for port. Once again I replaced the pre-filter and main filter, still no joy. I replaced the lift pump but this did not work either. I then ran fuel direct from a fuel can to eliminate tank/pipe issues, still no joy. Air filter was changed and the operation of the turbo checked. Then the engine ran normally for an hour or so. The next day the engine would once again not rev past 1000. I called a marine engineer and he checked all the obvious bits with no conclusion. He spoke to the injection pump engineer and it was agreed that it should be removed and returned for a check over. This was done and all outputs were to specification. Replacing the pump and the engine ran fine. I have just returned from another trip and once again the revs stuck at 1000 for 20 minutes then burst into life and revs returned to normal. After catching a fish I needed the engine to get out of irons and the engine was limited to 2000 revs not the 3200 that it should do. I reduced it to 1800 and then the black smoke started on every engine setting. I had to return to dock and get it sorted so I sailed back and used the engine just for entry where it worked perfectly until I put it in reverse to stop the boat, yes you’ve guessed it, 1000 revs and crew flying everywhere to stop the boat. Any ideas anyone?

[Madehn]

following--my gut says that if you had no issues prior to taking the pump off then issues after the rebuild then the pump is most likely culprit - however you might want to take a look at any other fittings -lines that could have been disturbed during the replacement of the pump- somebody leaned on something while reaching to tighten a bolt etc- sometimes that can create intermittent air leaks from small cracks or shifts.