MD5A - MD5B Volvo Penta Diesel won't go? Try this!

Unfortunately, the first year we got our Sunbird 25 trailerable yacht, Volvo Penta diesel engine problems prevented us from embarking on our much-anticipated Christmas - New Year trip down the D'Entrecasteaux Channel south of Hobart, Tasmania - something which was becoming a bit of an institution, beginning with our former boat (a SpaceSailor 22).

Now, the engine worked fine during testing when I first inspected the boat prior to purchase. The vendors delivered it to our property by road from the north-west of the state, and we now had it proudly sitting on our hilly acreage nestled on its trailer. My initial focus was getting the cabin all ship-shape, and I certainly had my hands full - painting out the interior, rewiring various circuits, fibre-glassing and also an unexpected rudder rebuild. I had not paid that much attention to the motor except for an oil and filter change, and I paid the price when we launched it for the first time, and it would not start.

I am going to tell this story in some detail because I believe that it could help others, either in a direct way if you have one of these engines, or possibly in a more general way for other makes and models.

The inboard diesel would not fire up. It would turn over fine, but from what I could tell, the injection pump was not delivering any fuel to the high-pressure part of the circuit i.e. the high pressure line, or the injector. The engine repair manual described, amongst other things, how to bleed the fuel system. I carefully followed the directions more than once, and was quite convinced clean fuel (with no air bubbles) was reaching the injector pump. I had a marine diesel mechanic come and look at it for half an hour when he was in the area, partly as a favour. He likewise identified the injection pump as the probable culprit. His advice was to remove the pump, and also the injector while I was at it, and take both to his recommended specialist to service and check.
After doing this, and receiving back my now very clean and shiny components, I re-installed them with much anticipation. You guessed it, the engine still would not start. The specialist said the pump and injector had been fully serviced and both tested OK on their workbench, and I had no reason to doubt that.

My in-depth internet research of these Volvo diesels began. There had to be information out there - somewhere -  to help me. Eventually I found a post on a marine diesel engine forum with a person experiencing a similar problem to my own. I had found many other posts on the net concerning Volvo Pentas which would not run, or had other problems, and I quickly got the impression that these engines were a bit problematic generally, and this was backed up by a few conversations I had with experienced boat owners locally. On the other hand, not many folk are going to post an article on-line saying their motor works fine I suppose, and the motor served me very well for many years.
Lots of posts had suggestions revolving around fuel filters, diesel tanks etc, but one post caught my eye:

Marcus (Marcus)
Posted on Sunday, September 28, 2003 - 01:38 pm:

My 20yr old MD-5B won't start. I have bled the fuel all the way to the injection pump but nothing will come out of the pump itself. The lift pump is working and the injector was replaced last season. Is the pump broken or could it be something else before I strip it down? If I have to strip it down does anyone have any tips? Thanks.
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Dick Vosbury
Posted on Monday, October 06, 2003 - 08:52 am:

Marcus, Check that cold start latches down. If it does, remove high pressure line from pump.Loose delivery valve holder on pump.That is fitting that high pressure line attaches to. Use lift pump to vent fuel out of valve. When vented, tighten down and reattach high pressure line. should solve your problem Dick V.

Thanks Dick Vosbury.

The underlined text is the key. To successfully bleed the Bosch injector pump on these engines, it is not enough to just remove or loosen the high pressure line. You must also loosen the knurled delivery valve holder hex nut as shown in the diagram below with the black arrow pointing directly at it (specifically item 3 in exploded view at the bottom of this article). Remember to loosen the high-pressure line hex-nut just above it first to prevent the line from rotating and doing possible damage.
As soon as I did this and turned her over, fuel came flooding out of the pump on the high pressure side, and when I reconnected the high pressure line, the engine fired into life. What a sweet and joyous symphonic sound. I must add that the delivery valve holder appears to be an integral part of the pump, and it does not seem like it is something that should be tampered with. Just do it!!
But remember, injector pumps are high precision devices, and are not user-serviceable. Don't mess with it unless you want to compound your problems.

The extra page in the user guide

 

 

Just as a follow up, when I went back and had another look at the hard-copy Volvo MD5A user guide, (not the repair manual) I took particular note of an semi-attached page (shown above) - some sort of afterthought to the printed guide. It had a line drawing showing the pump, and in hindsight, information which would back up what Dick said in his post. This is the only indication I ever came across (including the downloadable MD5 manuals) of this "secret" step. Look exactly where that big black arrow is pointing.

Exploded view of injector pump - item 3 is your friend