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Fieldvole
Fieldvole

Posted: Mon Oct 27, 2008 2:10am

Post Subject: BMC 1.5: Volt drop to glow plugs

I have a problem with the glow plugs only getting 9 volts due to the size of the wiring to them, it seems a simple idea to use the existing cable to operate a car starter solenoid which would then power the glow plugs direct from the battery via a fuse. Does anyone know if this is alright and safe to do, and would it pass the BSS? Thanks in advance for any replies. Bryan

Tony-B
Tony-B

Posted: Mon Oct 27, 2008 1:34pm

Post Subject: BMC 1.5: Volt drop to glow plugs

There is nothing wrong with this at all providing you ensure your wiring meets the BSS requirements. All I will say is to try not to mount the solenoid on the engine in case the constant vibrations damage it. But before you actually do this please do a voltdrop test across the ignition switch because they can cause significant voltdrop as they get old. If this is the case it may be glowplugs today, but it will the starter very soon. On most boat it should be a fairly easy job to run a correctly sized cable from the ignition switch to the glowplugs and tape/zip tie it to the existing loom. Tony Brooks Tony Brooks

Fieldvole
Fieldvole

Posted: Mon Oct 27, 2008 8:36pm

Post Subject: BMC 1.5: Volt drop to glow plugs

Tony. Thank you very much for the reply, I hadn't considered that the switch may be faulty so will be checking that before going ahead with the change- over. Thanks again Bryan

blavster
blavster

Posted: Tue Dec 16, 2008 1:27pm

Post Subject: BMC 1.5: Volt drop to glow plugs

I'm having the same problem with the same engine. When I remove the wiring to the glow plugs, and turn the key to heat mode, the correct voltage (i.e. 13V +) is measured on the lead. However when re-connecting the leads to the glowplugs and measuring the voltage at the glowplug, again in heat mode, only 11 volts registers. The engine used to start fine, after 20 seconds or so of heating, now however alot of turning over is required, with plenty of smoke being produced, before the engine starts up. Once going the engine runs fine, with little smoke, and once warm will start up instantly. Could the glow plugs be damaged? Ben

Tony-B
Tony-B

Posted: Tue Dec 16, 2008 3:39pm

Post Subject: BMC 1.5: Volt drop to glow plugs

Dear Ben, first I will address the low voltage. It is very unlikely to be a glowplug fault. If it was then one or more would have suffered a very much reduced resistance so the increase in current flow caused voltdrop across the wiring and ignition/glowplug switch (see the first post). As long as the battery is delivering(say) 12.? volts across its terminal POSTS (not clamps) when the glow plugs are in use it is far more likely to be undersized wiring or a worn ignition switch. If the battery is only delivering the 11 volts when the plugs are in use then its a faulty or discharged battery. If you want to check the voltdrop connect a voltmeter set to 20 volts DC between the battery positive POST and one of the glowplug terminals. Ignore any reading you get - it will be about battery voltage - operate the glowplugs and take a reading. You should have less than 0.5 volts maximum. (0.3V ideally. If you have more then 0.5 volts start stepping the meter lead back from the glowplug terminal to each other terminal between the plug and the battery -e.g. glowplug - fuse output terminal - fuse input terminal (there may well not be a fuse)- ignition switch glowplug plug terminal - ignition switch feed terminal - main feed connection to battery/starter solenoid/junction box as appropriate for your boat. You will eventually find where you are loosing the voltdrop. I expect it will turn out to be the switch to plugs cable. Now I will address the poor starting. If this has only happened over the last month or so then its probably simply low air temperatures however if its been going on for a while then it might be one or more failed glowplugs but I can not tell you unless you give me a current reading. Typically each of your plugs will draw about 6 amps so all four plugs draw about 24 amps. If they only draw 18 amps you have one faulty plug. However current is not a 100% reliable guide because plugs occasionally fail with the heat being in the wrong place and BMC 1.5s also need the plugs taking out every 3 years or so and the carbon removing from the glow plug holes - the plug tips often snap off if this has not been done for a while! "Worry" each plug out by alternately doing up and undoing the plugs about 1/3 of a turn, gradually increasing the "undo". until the plug is out. Measure the tip and use a drill about 0.5mm larger than the tip (7/64" I think but check) in a HAND or low power battery drill to remove the carbon. Test each plug using jump leads across the battery. Smear the tip and thread with "Copperslip" copper grease and refit. If a tip snaps of ether pay a professional to solve it OR, if you fancy a lowish risk flutter, use the same sized drill bit. Cover it in grease and drill down the hole for about 30 seconds. Remove the drill, clean off the grease and swarf, re-grease and repeat until the drill "brakes through". Spin the engine on the starter whilst looking away in case any swarf is blown out of the hole. That should solve the cold starting problem and with it the white "smoke" which is vapourised fuel that did not get burnt whilst trying to start the engine. It will not solve the problem if you have low compressions or faulty injector spray patterns. Tony Brooks PS Unless you are using a battery charger a voltage of 13 + volts on the heater plug lead indicates either an inaccurate meter or something very odd with the battery or charging system.

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