Volvo Penta MD6b Cold Start System - SailNet Community

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Diesel This is a forum dedicated to diesel engines and their applicable accessories.


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Old 06-04-2014
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Volvo Penta MD6b Cold Start System

My first post- most assuredly not the last!

I have a 1977 Volvo Penta MD6b in my new-to-me 30' Santana (W.D.Schock) she takes a LOT of cranking to fire up when cold. Once she has been started she runs perfectly. If she is restarted within a few hours she starts up easily. But if she sits a few days, its back to 10 minutes or so of cranking (during which she fires intermittently and displays burnt exhaust smoke). This was completely disclosed by the previous owner, no issues there, I knew what I was getting into. Getting her home took two 6-7 hour runs during which the engine ran fine (once started)

I have been told if she runs fine once started, that the injectors are nominally OK. I believe this person as they are a mechanic and could have sold me new injectors if he wanted to, but he didn't. He is an honest guy.

I also had diesel in the oil, so this led me to believe that the lift pump had a bad diaphragm which caused the fuel in the oil and the hard starting.

I have replaced the lift pump and the fuel filter, and the pump did indeed have a very small tear in the diaphragm. Buttoned all up, no leaks bled everything and- itís better but still hard to start - as in I have to crank for a while. So the fuel in the oil is probably fixed, but the fuel system must be leaking pressure somewhere over time.

I am going to do two things- First, create this post , to solicit ideas and second , I am going to crack the injector nuts and use the hand pump to try to bleed everything up to the injectors BEFORE I start cranking- and see if this helps.

Questions:

I have read in my searches that there is a cold start system fitted to the engine - as there are no glow plugs it must do something with the fuel. It is supposedly activated by shutting off the fuel when you stop the engine, which sets the cold start system for the next start, No mention of this is made in the service manual. I am dying to know how this works and how I can determine if mine is functioning correctly.

Second, where should the throttle be when the engine is being started? I typically have it at idle but I have read about people using 1/2 or even full.


Thanks in advance!
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Old 06-04-2014
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Re: Volvo Penta MD6b Cold Start System

I'm not all that familiar with the MD6A, but if the engine starts and runs fine once warmed up, then it sounds to me like it could be a compression issue rather than a fuel supply one. If you've bled everything already, I wouldn't be doing it again.

I'm sure someone will come back with the cold-start system details. In the interim, try starting at full throttle instead of idle. Here's a link to the Workshop Manual if you don't have it already:

http://www.bluemoment.com/manuals/Vo...A_Workshop.pdf
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Last edited by Classic30; 06-04-2014 at 09:42 PM.
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Old 06-07-2014
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Re: Volvo Penta MD6b Cold Start System

Low compression is a likely candidate given the age. I need to eliminate any fuel delivery problems too. I will bleed her again. Thanks for the suggestions.
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Old 06-10-2014
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Re: Volvo Penta MD6b Cold Start System

Does it start when you give it some throttle when you crank? That makes a huge difference on my MD7A (5 seconds vs. minutes- though admittedly mine may have its own issues)

My throttle/gear shift lever has a pull knob to disengage the gearshift from the throttle so you can give it ~1/4 throttle in neutral for starting- it's limited to this amount by the knob blocking the throttle when pulled out. Does yours have a similar system?
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Re: Volvo Penta MD6b Cold Start System

I've a MD7a and that engine starts very easily. Even after being laid up all winter.
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Old 06-24-2014
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Re: Volvo Penta MD6b Cold Start System

I would really suggest not cranking for more then 20 seconds at a time. A diesel can actually build compression after you stop cranking. Really. So I would crank for 20 secs wait a few secs and crank again. the cost of rebuilding or buying a new starter is not an interesting thought!!

I would agree it is a possible compression problem. I had a similar problem with a very old tractor. I used Lucas engine oil conditioner. The problem was cleared up.

If you have a glow plug that is not working, it is an easy replacement once you locate its location. I might suggest downloading a parts book so you can see how each piece fits together and it will give you and idea of how to change your glow plug or wire, which ever system is in your engine.

Hope this helps
Rochelle
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Re: Volvo Penta MD6b Cold Start System

I did kill the solenoid- but installed a new one. (volvo used the same solenoid on 1977 cars as well as the Md6b engine) I found a fitting that is not visible except with a mirror. It is the line from the low pressure pump to the high pressure pump- at the high pressure pump, the fitting was slightly loose. I was able to give it 1/8 turn pretty easy , once i got the wrench on it with the help of the mirror. The engine then started up relatively quickly ( but still had air in the lines, so it took some cranking) once it started it ran much better, idle was smoother and she revved up nicer. She restarted instantly . I have left it sit for 4 days and will see if she starts up more easily after sitting. Wish me luck !
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Re: Volvo Penta MD6b Cold Start System

Quote:
Originally Posted by txmatt View Post
Does it start when you give it some throttle when you crank? That makes a huge difference on my MD7A (5 seconds vs. minutes- though admittedly mine may have its own issues)

My throttle/gear shift lever has a pull knob to disengage the gearshift from the throttle so you can give it ~1/4 throttle in neutral for starting- it's limited to this amount by the knob blocking the throttle when pulled out. Does yours have a similar system?
Thanks ! Yes i have the same system- I am using about 1/2 throttle.
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Wink Re: Volvo Penta MD6b Cold Start System

I have a Newport 30 with the MD7 Engine, which is essentially the same as you have. first, check to see that you don't have any air in the line...mine was hard to start and I had a small air leak in the fuel line...replaced it and now no issues. The engine is historically a cold beast...I put mine to full throttle and it usually catches within 8-10 seconds...if it doesn't , then let it rest for about 30 seconds and do it again. As soon as it catches, pull the throttle back to about 1000 RPM and let it sit for a couple of minutes, then take off. Mine runs best between 1800 and 2200 RPM and tops out at about 2600 RPM.
Good Luck
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Re: Volvo Penta MD6b Cold Start System

Just an update- a new starter spins the motor 2X faster and it started immediately- however after sitting 2 weeks I was not able to get it started again ( however with starting fluid it started immediately again) It still must have an air leak . I also see a lot of unburned diesel out the exhaust.
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