Help! Pesky MD7A Air-in-Fuel Problem!

[Geoff Safron]

Symptoms: After a minimum of two hours motoring and as late as five hours, the engine revs (up 2-3000 RPM's and then back to running speed) several times over twenty minutes; visual inspection of Racor clear filter bowl during this time looks like a percolating coffee pot; and finally she stalls. I prime her using the bleed screw and manual secondary pump lever and get her running again (I've gotten very good at this); She runs for twenty minutes to an hour and then revs/stalls again; and so on until we limp into port.

I have replaced all fittings (except the proprietary aluminum "L" tank fitting) and hoses from tank to secondary filter (Racor primary is new as well); and bedded them (twice) with teflon compound. The vent resists a little but not enough to starve the line. The tank is clean, the down-tube doesn't appear to leak. WHERE ELSE CAN THIS &%$#@! AIR BE COMING FROM??!! Has anybody else had this happen? Is there a portion of the fuel system I haven't investigated (eg, the return line...for that matter, can someone explain to me the dynamics of the fuel return line)?

Please (on hands and knees) help me if you can! This one stupid flaw in an otherwise flawless CD30 has delayed, annoyed, worried and even endagered us...and is all by itself a major impediment to winning my wife over to the Sailing Life. Help!



brainstorm@unidial.com

[Ben Thomas]

Symptoms: After a minimum of two hours motoring and as late as five hours, the engine revs (up 2-3000 RPM's and then back to running speed) several times over twenty minutes; visual inspection of Racor clear filter bowl during this time looks like a percolating coffee pot; and finally she stalls. I prime her using the bleed screw and manual secondary pump lever and get her running again (I've gotten very good at this); She runs for twenty minutes to an hour and then revs/stalls again; and so on until we limp into port.

I have replaced all fittings (except the proprietary aluminum "L" tank fitting) and hoses from tank to secondary filter (Racor primary is new as well); and bedded them (twice) with teflon compound. The vent resists a little but not enough to starve the line. The tank is clean, the down-tube doesn't appear to leak. WHERE ELSE CAN THIS &%$#@! AIR BE COMING FROM??!! Has anybody else had this happen? Is there a portion of the fuel system I haven't investigated (eg, the return line...for that matter, can someone explain to me the dynamics of the fuel return line)?

Please (on hands and knees) help me if you can! This one stupid flaw in an otherwise flawless CD30 has delayed, annoyed, worried and even endagered us...and is all by itself a major impediment to winning my wife over to the Sailing Life. Help!

Geoff, I had similar problems last year with my md7a. heres what I found and fixed. the fuel line running from tank to racor was comprimised, that got replaced. also where this fuel line enters tank its best that it drops immediatly down to racor. mine rose above fitting, looped up then downto racor, avoid that configuration. air gets trapped in loop and is a bear to bleed out. to test your fuel delivery system for leaks this is upstream of your transfer pump(fuel pump) I used a vacuum gauge, plug inlet of line insert other end of fuel line into vacuum pump, create vacuum in line and watch gauge. if it moves you need new fuel line. loose fittings etc. on the pressure side of system make sure all fittings are snug those brass washers collapse to a point that they fail. i would replace them.
check archives on bleeding diesels. daunting at first but after first time its really easy. with engine off and compression lever off and throttle at full pump through racor, then fuel pump. I go directly to injectors full throttle. after this I start the egine and do the injectors again.
back injector one at a time off just enough that engine starts to falter, a little bit of fuel and hopefully all the trapped air will come off injector onto the rag or paper towel you have set up there, leave end wrench on nut for fast action. there will be differing opinions on the safety of this, but remember the fuel has not passed through the small injector orifice yet and is not at full high pressure found inside of cylinder downstream of injector.
my engine would run fine for hours but if I shut her down it wouldn't start. this went on for way too long. along with bad fuel line the fuel pump was malfunctioning as well compounding problem.

heh if you can do this, which you definitly will. hands down. your wife will b e so impressed that when you mention the cd36 thats for sale down the way you will have passed way beyond any potential stink eye and be in that etheral place of "clear sailing"

good luck keep progress posted, ben



btlandscapers@imagina.com

[John D]

Goeff - I had a similar problem on my MD7A. If you have taken (or attempted) the cover off the transfer pump, the seal has been compromised and you will get air through this fitting. You will need a new gasket and an extremely clean surface for it to seat on.
John



john_dupras@hotmail.com

[Dave Bristle]

I don't have one, but your symptoms (and Ben's) sound a little like a fuel line that's too close to the manifold or block, causing boiling (not air), and thereby a "vapor lock." This can especially cause the failure to start after shutting down a hot engine. Restoring the flow can cool it temporarily... See if you have any hot spots in the fuel delivery system, and if you can reroute or insulate to reduce them.

Smooth motoring,
Dave (in the market for a CD25D or CD26)




bristle@att.net

[John R.]

Symptoms: After a minimum of two hours motoring and as late as five hours, the engine revs (up 2-3000 RPM's and then back to running speed) several times over twenty minutes; visual inspection of Racor clear filter bowl during this time looks like a percolating coffee pot; and finally she stalls. I prime her using the bleed screw and manual secondary pump lever and get her running again (I've gotten very good at this); She runs for twenty minutes to an hour and then revs/stalls again; and so on until we limp into port.

I have replaced all fittings (except the proprietary aluminum "L" tank fitting) and hoses from tank to secondary filter (Racor primary is new as well); and bedded them (twice) with teflon compound. The vent resists a little but not enough to starve the line. The tank is clean, the down-tube doesn't appear to leak. WHERE ELSE CAN THIS &%$#@! AIR BE COMING FROM??!! Has anybody else had this happen? Is there a portion of the fuel system I haven't investigated (eg, the return line...for that matter, can someone explain to me the dynamics of the fuel return line)?

Please (on hands and knees) help me if you can! This one stupid flaw in an otherwise flawless CD30 has delayed, annoyed, worried and even endagered us...and is all by itself a major impediment to winning my wife over to the Sailing Life. Help!

Check those copper banjo fitting washers on anything you've loosened or disassembled prior to the problem. They are notorious for air leaks if they've been compressed more than a couple of times.