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glow plug resistor fourtrak
Moderator: Tiny
glow plug resistor fourtrak
hi i have an old fourtrak 2.8 td engine in a landrover 90 the problem is getting the preheat timer etc working correctly. this has been a nitemare and am now thinking of just using a button on the dash and a relay to switch current to the plugs. the problem is the plugs take 7volts and the loom obviously puts out 12volts this burns out the glow plugs and requires a resistor to lower the voltage by 5volts, has anyone had this problem before and what did you use to get round this? if anyone can suggest a link to an appropriate resistor that would be great, this little fault is becomming a problem and expensive too two new sets of plugs allready
Although the glow plugs may be rated at 7 volts, running them from a 12volt supply shouldn't be an issue if your glow plug timer is working correctly. The timer serves two purposes - 1. pre heat the engine correctly for the given conditions, 2. protect the glow plugs from overheating.
The period of pre-heating is determined by the temperature sensor located in the lower thermostat housing (not the same as the temp gauge sender located adjacent in the head). Obviously the hotter the engine the less pre-heating required.
The current/temperature limiting of the glow plugs is done by switching the glow plugs on and off, via the glow plug relay, every few seconds or so. The glow plug timer determines when to switch the glow plugs off using a current shunt located between cylinders 3 & 4 glow plugs up on the bus bar section. The current shunt looks like a wavey strip of bus bar with a small wire from either end.
Basically the glow plugs exhibit a positive temperature coefficient (PTC) which means the hotter they get, the higher there internal resistance becomes and hence the less current they draw. The glow plug timer detects this drop off in the current draw using the current shunt. When the current drops below a pre-set threshold (indicating the plugs are red hot), it switches off for a few seconds to prevent overheating, then back on again repeating the process.
It sounds to me like your glow plugs must be coming on and staying on for a long period causing them to burn out. Given the engine is fitted in another vechicle first thing to do is make sure both the coolant temperature sensor and current shunt are fitted and functioning. Without these your timer will not work properly. Then make sure your relay is switching in and out when pre-heating. Initially from cold it will stay on for a number of seconds before it starts to switch in and out in order to get the plugs up to temperature quickly.
A push button switch directly driving the glow plug relay will work. It just means you have to remember to press it thats all.
Hope this helps. Sorry for the length but its quite a complex little beast
The period of pre-heating is determined by the temperature sensor located in the lower thermostat housing (not the same as the temp gauge sender located adjacent in the head). Obviously the hotter the engine the less pre-heating required.
The current/temperature limiting of the glow plugs is done by switching the glow plugs on and off, via the glow plug relay, every few seconds or so. The glow plug timer determines when to switch the glow plugs off using a current shunt located between cylinders 3 & 4 glow plugs up on the bus bar section. The current shunt looks like a wavey strip of bus bar with a small wire from either end.
Basically the glow plugs exhibit a positive temperature coefficient (PTC) which means the hotter they get, the higher there internal resistance becomes and hence the less current they draw. The glow plug timer detects this drop off in the current draw using the current shunt. When the current drops below a pre-set threshold (indicating the plugs are red hot), it switches off for a few seconds to prevent overheating, then back on again repeating the process.
It sounds to me like your glow plugs must be coming on and staying on for a long period causing them to burn out. Given the engine is fitted in another vechicle first thing to do is make sure both the coolant temperature sensor and current shunt are fitted and functioning. Without these your timer will not work properly. Then make sure your relay is switching in and out when pre-heating. Initially from cold it will stay on for a number of seconds before it starts to switch in and out in order to get the plugs up to temperature quickly.
A push button switch directly driving the glow plug relay will work. It just means you have to remember to press it thats all.
Hope this helps. Sorry for the length but its quite a complex little beast
If it doesn't have two sticks, I don't wana know about it!
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