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Old 01-10-2020, 11:53   #1
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Volvo MD7A not starting - fuel pump?

Hello everyone -


a couple of weeks ago, my MD7A would not start. It had run fine for a month or so (after a fuel saga and successful filter replacement and bleed), but one day heading out for a sail after a few days of non-use, it just simply wouldn't start.

I bled the system again, following the correct CAV fuel pump procedure. I noticed the delivery pipe closer to the flywheel had a spurt-spurt-spurt pattern, but the other pipe had much less pressure. Still, I was able to get the motor started. It revved up well and sounded ok. But, I noticed the exhaust had a lot of white smoke, and there was a a lot oily discharge.

I then bled just that back lower flow pipe and the motor actually started in the bleeding process just on the one cylinder! Fuel is coming that pipe, just not as much.

I connected it back, and can't start the motor. It tries to catch, sounds like it's spinning up, sometimes runs/coughs for a second or two, then quits. That's where I'm at now.

Fuel, air, compression. Filters look good. Don't know what water would look like in the separation filter...all the liquid is uniform. So fuel should be ok? Air should be fine - it was a sudden failure vs bird's nest over time. Compression?

Is the CAV designed such that one side could fail? So one cyllinder gets full fuel and the other gets a small amount?

thank you!
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Old 01-10-2020, 12:12   #2
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Re: Volvo MD7A not starting - fuel pump?

Yes you have a fuel delivery problem by the sound of it.
Fuel delivery must be equal for each injector line. I'm not familiar with that engine so this is just general advice. I would try a gravity feed of filtered fuel to the injector pump for a start & see if it will go then.
If it runs then you need to check lift pump & all lines & connections.
Someone will be along who can help you with specific Volvo advice.
DougR knows them.
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Old 03-10-2020, 07:33   #3
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Re: Volvo MD7A not starting - fuel pump?

I agree with Compass 790....sounds like a fuel issue.

I think I would check:
- the fuel pressure from the lift pump going into the high pressure pump
- make sure the stop lever and stop cable on the injection pump is returning all the way to the “run” position

Do you use the “cold start” device on the injection pump when trying to start the engine? I’ve seen one that would crank and crank and not start, but start right up when using the cold start device....
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Old 03-10-2020, 07:58   #4
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Re: Volvo MD7A not starting - fuel pump?

Most obvious reasons:


- air in the fuel lines,


- no fuel (clogged),


- battery low,


- compression lever open,


- neutral rev set too low.


Have you eliminated all these?


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Old 03-10-2020, 08:18   #5
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Re: Volvo MD7A not starting - fuel pump?

Your specific case:


1)


Compression - make sure the decompression level is down. PULL THE STOP CABLE OUT - position "STOP". Now grab the wheel and turn it. How hard is it to turn?


If compression is low, it is very easy to turn. If compression is good, you cannot turn the wheel much - you can actually feel as you compress the air - it is 'springy'.


2)


Fuel at the injectors:


When you undo the last nut (the one around the injectors) and then crank vigorously - does fuel come out at both injectors? If so, good, if not - one is not getting fuel.


MD7A start on one cylinder. You can hear when the other kicks in. The older the engine, the more obvious the delay.


3)


If fuel gets to both injectors and the engine starts on one only and the other does not kick in, it may be anything there on the 2nd cyllinder - start checking at the injector - pull and test.


In my experience with MD7A (nearly 20 years now) they are hell to start after filter changes, dirty fuel problems, etc. They are hell to start if there is any air leak on fuel lines. They are hell to start when the lift pump ages (!!!). And the battery must be full and good too - these are old heavy engines, they do ask for plenty of battery juice.


Still, I would gladly buy a new one any day - once you sort our the fuel side these engines are hard to kill.


PS - if in the water - do NOT forget to close the intake seacock, then DO NOT FORGET to open it - when the engine starts. If you forget you will first flood it , then burn the raw water pump .... ;-))))



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Old 03-10-2020, 12:57   #6
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Re: Volvo MD7A not starting - fuel pump?

One other thing worth checking, make sure that the Stop lever goes all the way back on the fuel pump when you push the handle back in; my MD6A behaved just like yours, took ages to discover what was going on: I added an additional external spring on mine to make sure it fully returns, miracle cure. Completely agree about how good these old engines are...... Good luck.
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Old 03-10-2020, 14:36   #7
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Re: Volvo MD7A not starting - fuel pump?

Quote:
Originally Posted by goodoldvega View Post
One other thing worth checking, make sure that the Stop lever goes all the way back on the fuel pump when you push the handle back in; my MD6A behaved just like yours, took ages to discover what was going on: I added an additional external spring on mine to make sure it fully returns, miracle cure. Completely agree about how good these old engines are...... Good luck.

I have a MD7b and have installed an extra spring on mine as well. The problem in this case I suspect might be water in the fuel. I would suggest cleaning the fuel tank out and starting again with fresh fuel and new filters. Make sure the pick up is clear of the bottom of the tank.

I also installed a 12v fuel pump between the primary and the main fuel filter and I power this with a jumper lead just for fuel bleeding. The best $20 you can spend. Bleeding is now a breeze if the seals on the filters are airtight. Engine seems to jump to life on the first revolution. It probably isn't but it feels like it! These are great engines.
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Old 04-10-2020, 04:56   #8
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Re: Volvo MD7A not starting - fuel pump?

We have an MD 11C. [U]Every[U] time we have had troubles like yours, there was a small air leak on the suction side of the fuel plumbing. Frustratingly hard to find, certain that all was done correctly when I changed the filters, but nevertheless that was the problem.

Several years ago, while waiting for a replacement primary pump, I installed a 12v back-up fuel pump between the tank and the first filter. It also proved useful for finding a leak. Positive pressure on the system from the 12v pump revealed a tiny seep on the canister filter rubber ring gasket. The tiniest air bubble, when it hits the injector pump, causes a loss of prime and all the troubles you are having.
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Old 12-10-2020, 07:08   #9
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Re: Volvo MD7A not starting - fuel pump?

I had the same issue on an MD-2 until learning (after continual re-bleeding) to bleed way longer than common sense dictated. On that installation the last bubbles were about a solid stream quart behind the first bubbles every time. Not normal with Volvo but it happened on this one.
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