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Old 07-01-2020, 14:12   #1
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Why my MD7a doing this?

Hello everyone!

Here is the video; https://youtu.be/b5za_OofLwM

Looking for all kind of suggestions except throw this old engine away as i love my old friend and so far he was so reliable

When i start the engine it runs like a normal (idle) then rpm increasing and normal up and normal, then it goes up and at certain point engine stops. If you watch the video you see it starts at idle and goes up. Always similar pattern.

What i did so far;

New water separator with pre-fuel filter installed (as my old lift pump was so dirty)
New lifting pump installed.
Did bleed the system but i have never seen an air bubble free fuel lines on this engine so i assume little bit air running through is ok or i should look for air leakage?

Also if there is air in the system engine should loose power right not increase the rpm?

Today i started to think that maybe injectors are not working well and spraying too much fuel and after certain point it is too much fuel and engine stops.

I have bosh injection pump installed, i am not sure if it has problem (hopefully not).

Thanks!
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Old 07-01-2020, 19:38   #2
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Re: Why my MD7a doing this?

Don't know your engine well, but almost all diesels with an injector pump have a governor built in to the injector pump. The governor controls the engine speed. When you move the "throttle" the linkage is just setting the governor to a new rpm. The governor then allows more fuel to flow to the injectors. If the engine speeds up on its own my guess is loose linkage or a problem with the governor.
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Old 07-01-2020, 22:51   #3
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Re: Why my MD7a doing this?

I would normally agree with governor or fuel pump problems, but that doesn't quite sound like either of them.

I'd try running the engine out of a separate jug of fuel to isolate any fuel supply/tank problems first, and then go to the harder and more expensive things.
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Old 08-01-2020, 00:49   #4
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Re: Why my MD7a doing this?

Agree with post 3. My guess is fuel supply or air . Make sure you use filtered fuel if you rig up a gravity feed to yr injection pump. It's easy to forget
Yr engine doesn't sound too bad when it's running so I'm not going to suggest throwing away. Just find the fault.
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Old 08-01-2020, 00:51   #5
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Re: Why my MD7a doing this?

Forgot to add if it's overfuelling it will be blowing black smoke. Have you checked exhaust?
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Old 08-01-2020, 05:06   #6
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Re: Why my MD7a doing this?

I believe the Bosch fuel pump does NOT have a governor. Long story I won’t repeat but at one point while docking in a gale the Volvo shaft coupling went, so was essentially in neutral. Not knowing that, I couldn’t hear myself think over the wind, I threw it into reverse hard, the the tachometer recorded a max RPM of something over 5,000.

Low bandwidth, can’t see video.

Have you disconnected the throttle linkage and tried it?

Else-wise it may be time for a pump servicing.
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Old 08-01-2020, 08:25   #7
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Re: Why my MD7a doing this?

Yes, the Bosch VE pump has an internal governor, and it may be that the governor is not controlling the fuel supply adequately.

But as stated earlier, feed the fuel from an independent source and eliminate any possibility of fuel starvation/ air in the system.

To me it almost sounds like the governor reacting to intermittent fuel supply, over reacting to the rpm loss, and subsequently dying from fuel loss.
Only after ruling out starvation have the injection pump checked.

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Old 08-01-2020, 11:57   #8
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Re: Why my MD7a doing this?

X2 on DougR post. Sounds like it's running out of fuel.
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Old 08-01-2020, 18:05   #9
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Re: Why my MD7a doing this?

If you run from a jug of fuel for any length of time don't forget to run the return line to the jug also.
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Old 08-01-2020, 18:16   #10
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Re: Why my MD7a doing this?

Is the engine running in neutral or in gear in the video?

If in gear, then I agree with the above comments about eliminating possible fuel problems first by using a seperate gravity tank / jug etc.

If in neutral, then I not so sure there will be fuel supply problems, more a governor or linkage issue (IMO).
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Old 08-01-2020, 18:19   #11
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Re: Why my MD7a doing this?

Run a can of LiquiMoly 2005 Diesel Purge through it. You would be amazed how well it works on cleaning pumps and injectors
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Old 08-01-2020, 20:31   #12
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Re: Why my MD7a doing this?

1) If a diesel has compression and fuel, it will run.

2) Every time our diesel acts up, it's because air is getting in somewhere and causing an interruption in fuel flow. Very small leaks can drive one crazy with exactly the symptoms you describe.

3) Seems your problem started when you installed a new separator.

4) Life has taught me over and over that when a new problem happens after I have done something, it's time to go back and find out what I screwed up.

5) IMO, you very likely have an air leak somewhere in the plumbing with your newly installed separator. Look for mismatched ftgs, missing or mis-installed o-rings, ditto with gaskets, small holes/cracks in old rubber hoses, etc..

Good luck.
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Old 09-01-2020, 10:35   #13
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Re: Why my MD7a doing this?

Hello Everyone!

It is fixed thanks to you all!
It was the clogged tank sucking line! System was trying to suck the fuel and getting air from the water separator inlet as it is the weakest in my system.

I made a plan and went onboard today and went inside the small hatch on the port side and took the suction line out from the tank.
As soon as I took it off, black jelly dirt came out then I took my hand pump and connected and started to suck a lot.
It is like a ketchup first small pieces then more and boom big dirt came out. Then clean fuel started to come.
I connected everything, did bleed the system and now working better than ever.

Once again thanks one more time I learned that always start with the simplest and cheapest one 
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Old 09-01-2020, 11:13   #14
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Re: Why my MD7a doing this?

Good for you. And thanks for reporting back.

I had a fuel line blockage and the MD7A behaved differently. You get a clue when it is hard to take the Racor filter lid off, if it is hard then you are likely pulling suction. Also I’ve used an air pump to blow back into the tank to clear a blockage. Anyway I’m surprised of your finding but very glad you did find it and shared your experience.

Before I’ve done these things I did a lot of other that took some time and blood.
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Old 09-01-2020, 17:52   #15
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Re: Why my MD7a doing this?

Glad for you it turned out to be the most common problem. Also very lucky you didnt have to go to the green engine shop for parts.
A further tip is always use a filter funnel when filling your tank & keep the o-ring on the deck fill cap in good condition.I'm amazed how much crap comes in the fuel from the pump & we buy diesel from a very busy auto fuel site. Sounds like you need a good tank clean.
Also glad you reported back.
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