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minimerc...
minimerc...

Posted: Sat May 15, 2010 9:01am

Post Subject: BMC 1.5 going flat out?

I have just got a boat with a bmc 1.5. (not been run for 1 year) Got her staryed and all was well 10min run. however when mooring up out of gear ideling engine started to speed up. ended up going flat out revving its self mad. if restarted still revs high however if left for 10 min or so it starts fine although after a few min starts to rev up again. process of revving up is very quick, its as if the throttle lever was pushed fully forward, its not. thanks

Tony-B...
Tony-B...

Posted: Sat May 15, 2010 10:32am

Post Subject: BMC 1.5 going flat out?

Dear Simon, most, but not all, BMC 1.5s use a hydraulic governor in the injection pump to control the speed and one of the peculiarities of this is when the fuel pressure in the injector pump drops the engine revs up. The first suspect must be lack of fuel at the injector pump so try the following (Check to see if it still revs up after each step):- 1. Make sure the fuel tap on the tank is turned ON. 2. Make sure you have at least 6 inches of fuel in the tank. Now things get difficult unless you know how to bleed a 1.5s diesel system. 3. Follow the pipe from the tank to the engine and clean any "filter like" object you find. If they contain an actual filter element then change it. Change the fuel filter on the engine. Remove the domed cap on the fuel lift pump and clean any gauze strainer you may find in there and also clean out the sediment tray below. DO NOT TAKE THE RUBBER SEAL FROM THE PUMP CAP, they swell and can be impossible to get back in! Bleed the system. (If you do not know how to do this please email a picture of your injector pump to Tony@TB-Training.co.uk). Do NOT remove or attempt to renew any seals in the filters etc unless they appear damaged. Some are hard to fit correctly and misfitting one could cause an air leak that will also make the engine rev up or simply stop. Please come back with a description of what you find in each item you service. If the system will not bleed make sure the bolt/screw in the lift pump cap has a soft washer under the head. 4. Work through the system ensuring all joints are tight and there are no air leaks. 5. Remove a main fuel line connector at any place that will allow you to have the tap open without fuel leaking out. "Bodge" a length of hose onto the tank side that will push over a car's tyre valve. Get a car's spare wheel and take the valve core out, very quickly pushing the hose over the valve. If the fuel pickup pipe is blocked inside the tank this may well clear it to prove its the problem. Re-bleed system as required. Try that lot and come back. I am about 85% certain this will sort it but it may not. Please let us know what you find and how you get on. Tony Brooks

minimerc...
minimerc...

Posted: Sat May 15, 2010 9:31pm

Post Subject: BMC 1.5 going flat out?

Thanks so much for the info. never had dealings with hydraulic governor. Makes perfect sense regarding symptoms as engine has not run for over 1 year so filter bound to be dirty/buged up. I will have no problem doing the above as my skill level is enough. I will not manage back to the boat for 1 week so after then I will get back to you with the news. Thanks again

minimerc...
minimerc...

Posted: Sat May 15, 2010 10:25pm

Post Subject: BMC 1.5 going flat out?

Tony, Have being reading about hydrolic governors.thats all ok. can explain why revs increase due to loss of fuel pressure? Not that it matters just to increase my understanding. I see how the oil pressure works. Thanks for your time

Tony-B...
Tony-B...

Posted: Sun May 16, 2010 8:44am

Post Subject: BMC 1.5 going flat out?

If this makes little sense look in the technical articles on my website ()TB-training.co.uk). Opening the "throttle" preloads a small spring which in turn pushes the governor towards fully open delivering more fuel. As engine speed increases the transfer pump gradually increases the pressure inside the injector pump body which acts on a small "piston" to try to close the governor against the spring. AS it does so the fuel delivered is reduced until the internal fuel pressure is balanced by the spring. If the fuel flow to the transfer pump is reduced (but not totally blocked) the pressure inside the pump will fall as fuel is used so the spring pushes the governor to the excess (maximum then some) fuel position. As long as there is some fuel delivery the wide open governor will allow the engine to rev up. Please note the CAV DPA mechanism is very small and light so a blob of water in the governor can jamb it up but I do not think that is your problem. Its more a warning to fight water in the fuel at all costs. Tony Brooks

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