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iansutton
iansutton

Posted: Mon May 02, 2016 5:44pm

Post Subject: Problems starting engine

Hi Tony I have noticed over the years that my engine has become increasingly difficult to start from cold. After spending a few days this weekend I have think I have traced the problem down to a faulty start key switch. I initially thought that there was a problem with the glow plugs as I had to keep the key switched to heat longer each time I started, but checking the resistance across the glow plugs at below 1 ohm led me to think that they were okay. I then measured the delivered voltage at the plugs and found it to be only 8.5 volts. I checked the battery at this point and it was around 12.5/13 volts, so I knew the battery was okay. I then measured the voltage exiting the keyswitch and it was around 9 volts. I checked the terminals on the back of the keyswitch and they appeared to be okay, but I cleaned them regardless, however this didn't make any difference. I am therefore assuming that the contacts within the keyswitch have become worn/corroded over the years, and the keyswitch would need replacing. Another boater suggested placing a relay between the battery and glowplugs, with the keyswitch activating the relay. After reading your TBTraining notes this seems a better solution, rather than having the high amperage going through the keyswitch. My questions are as follows:- 1. What amperage of relay do you think I should go for? Your TBTraining notes suggest a 180amp relay, but I can't find one with an amperage that high. Vehicle Wiring Products do a 70 amp Durite relay, would this be sufficient. 2. Also would the 9volt output from my current keyswitch be sufficient enough voltage to activate the relay, or would I need to replace this as well? 3. What fuse rating should I place between the battery/relay/glowplugs? I have a NanniDiesel 4.150HE engine and control panel, but I am not sure of the amperage on the glowplugs. Regards Ian

Tony-B
Tony-B

Posted: Mon May 02, 2016 7:23pm

Post Subject: Problems starting engine

The key switches have a sort of copper washer with bumps in it.The washer turns as you turn the key so the bumps contact the required output terminals so I think fitting a relay at present would only cover up a problem that could stop you starting at some point so I would sat fit a new switch as long as you are sure its not volt drop on any cables/terminals. I am not sure if your 12.5 to 13 volts was measured at the battery or on the input lead to the ignition switch with the switch turned to heat. If it was the former then it is still possible you have a wring fault. Glow plugs on modern 4 cylinder engines draw close to 100 amps the instant they are turned on that quickly drops to a stead 50 amps so a typical 10 or 40 amp automotive relay is not likely to give an extended life. You need a relay rated at over 100 amps. This would typically be a split charge relay OR a starter solenoid as fitted to older cars. VWP list a 120 amp and 200 amp High current relays on page 37 of the 2015/16 catalogue. The fuse would have to be rated in excess of 100 amps and that is why you may well find that your present circuit does not have one. Because of the fast fall in current you could probably get away with something like a 60 or 70 amp CONTINUOUS rated fuel that blows at 120 to 140 amps. Likewise a lower rated relay MIGHT be satisfactory but could just as well be false economy. As long as you do not have volt drop on the circuit I suspect a new switch will solve the problem for many years.

iansutton
iansutton

Posted: Tue May 03, 2016 11:41am

Post Subject: Problems starting engine

Thanks for the quick reply and your advice I will check the wiring a bit more thoroughly, however I suspect at the end of the day I will probably need to replace the key switch. Can you recommend a good key switch to go for, or am I best purchasing a replacement switch from NanniDiesel ( A R Peachment)?

Tony-B
Tony-B

Posted: Tue May 03, 2016 12:00pm

Post Subject: Problems starting engine

Nanni are, as far as I know, Kubota based engines so you may well get a better quality switch from a Kubota agent or, as you say, Peachment. The only "problem" is how Nanni chose to operate the stop solenoid. It could be from the ignition switch or by a separate push button. Some stops are operated by turning the key anti-clockwise form the off position but I do not know how Nanni do it. You need a switch with the same "positions" as the present one but the ones on the VWP website seem to use what are known a "Tractor" keys where one key fits all similar switches. Not so good from a security point of view. It all depends upon what type of key you have now. I fear switches from chandlers may use the same key. I do not think it is any longer possible to change the barrel of the switch, but if it is you could keep your existing key and fit the old barrel into the new switch.

iansutton
iansutton

Posted: Wed May 04, 2016 4:01pm

Post Subject: Problems starting engine

Hi Tony I have been at the boat today doing some more checks before committing to replacing the key switch. I have checked the voltage at each point at the key switch when it is in itâs different positions and have come up with the following results. Key Off - Battery 12.5v, Input to key switch 12.5v, Output to Glow Plugs 0v, Output to starter 0v Key On - Battery 12.5v, Input to key switch 12.5v, Output to Glow Plugs 0v, Output to starter 0v Key Glow - Battery 12.8v, Input to key switch 11.8v, Output to Glow Plugs 10.5v, Output to starter 0v Key Start - Battery 10.5v, Input to key switch 10.5v, Output to Glow Plugs 7v, Output to starter 9v Are these voltages typical when the system is under load with the glow plugs and starter? The engine seems to be starting now, so It might have been a fuel problem when I was trying to start it at the weekend. Regards Ian

Tony-B
Tony-B

Posted: Wed May 04, 2016 7:37pm

Post Subject: Problems starting engine

The battery may be considered serviceable if it can maintain 10 volts while cranking so as you have 10.5 that is fine. I note that you give no voltages for the Aux or ignition on terminal that feeds the warning lamps and gauges but as the current is very low I expect it will be 12.5. I can only assume that the 12.8 at the battery with the key to glow is an aberration. If anything it will be lower than 12.5. As soon as you put a load on the circuit with the glowplugs you cause a 1 volt voltdrop between battery and switch input. This could be an undersized cable but I suspect loose or dirt connections in the multi-plug on the main engine wiring harness. If you solve that then the glowplug terminal reading SHOULD then be more or less 1 volt higher. We must assume that the 1 volt of voltdrop will also be present when the switch is supplying both the starter solenoid and the glowplugs so as you find 10.5V it the start position we should assume the battery voltage is 1 volt higher at 11.5 yet you have it at 10.5 at the battery. This is not logical. However you are dropping 3.5 volts across the ignition switch to the starter and 5.5 volts to the glowplug terminal. This identifies another inconsistency in that without the starter operating the glowplugs only cause a voltdrop of 1.3 volts. It should be the same voltdrop from the input terminal to glowplug terminal for both glow and start positions. I think your first task is to sort out the voltdrop between battery and switch when the glowplugs and/or starter are operating. There still seem too much voltdrop across the switch so it will probably only get worse but solving the voltdrop on the input cable may keep you boating without buying a new switch. The inconsistent reading could be caused by the problem areas heating up and altering their resistance. The maximum voltdrop I would like to see between battery and the first glowplug is 0.5V with the same between battery and the starter solenoid energise terminal. The easiest way to measure voltdrop across a circuit is to connect the voltmeter to either end of the circuit (so that would be one end on the battery and the other on a glowplug) and operate the circuit. The reading while the circuit is operating will be the voltdrop. Relying on subtracting separate voltage measurements is open to error.

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