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Glow Plug Relay Question

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Randy smith

03-31-2002 19:14:10

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I use this site for as a valuable resource for my AC IB Tractor. I thought I would ask a question out of line with the forum in hopes some one can answer the question tomy problem. I own a 8hp mini excavator with a two cylinder diesel. The pre-glow is not working and I am attempting to find my problem. I've manually checked the glow plug relay and I can hear it clicking. My question is on the relay there are two large leads and two small leads. One of the large leads goes back to the glow plugs and the other to an unknown destination (I assume a 12volt source). I have no idea where the two smaller leads go (I assume to my ignition switch but the wiring is a mess of old black electrical tape wound around this, that, and everthing). Any ideas on how a basic diesel pre glow works? What shuts down the pre-glow condition (when the yellow light turns off indicating the plugs are warm)? Thanks.

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Clooney

04-01-2002 09:33:51

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Re: Glow Plug Relay Question in reply to Randy smith, 03-31-2002 19:14:10

Randy, I know nothing about your AC IB Tractor so can't give you any specifics on the glow plug system for that tractor
~Not all glow plug systems are the same & some just apply 12 volts (or battery voltage) to the glow plug until warm & others pulse 12 volts to a 6 volt glow plug so the plug heats faster. There are also other different type systems that use fast initial heat then lower to maintain glow plug temp .
~Do you have battery voltage to the glow plugs when you turn the key on? If so & they don't get hot, the glow plugs are probably burnt out. ~If your system has a pre-glow position on the ignition switch there might not be a any timer or temp protection in the glow plug system & uses the fact that the ignition switch must be turned to the run position after cranking. If that is the case all the relay does is hook battery voltage to the glow plugs when in pre-heat & probably during cranking. That will be easy to repair as you will have battery voltage to the relay & when in pre-heat the relay will hook the battery voltage to the glow plugs. Make sure the relay has battery voltage to it & the pre-heat position on the ignition switch makes the relay function.
~If you don't have any power to the glow plugs & you can hear the relay click, it sounds like your control side is functioning & the problem is in the power supply side. Of the two big wires going to the relay, does one wire go to the glow plugs (it probably should) & does the other big wire have battery voltage (it probably should) if the big wire, (the one that doesn't go to the glow plugs) doesn't have battery voltage you might want to see if there is a burnt fusible link in that wire or blown fuse or other problem. Glow plugs require a large amount or power to heat so the wiring from the battery (sometimes the power is picked up from the large stud on the starter) to the relay & then to the actual glow plugs is usually large in diameter. The control side is usually low amperage & uses smaller wires. ~I have no idea how your system knows when the glow plugs are hot, some systems use a timer, others use the change in resistance in the glow plug circuit (when the glow plugs get hot the resistance changes), still other systems use a head temperature sensor to shut the system off when the head is warm, some of the old systems even used the rise in alternator charging voltage to turn the glow plugs off. There are probably even different types of over-temperature & shut off controls that I haven't seen or mentioned.
~With the key on, start at the injectors with a volt meter or test light & work your way towards the battery, junction block or starter stud & see if you can isolate the problem, if the glow plugs light up for just a second or two then go out there is probably a problem with the glow plug resistance, head sensor (if used) or timer (if used).
~What you really need is a wire diagram of the glow plug circuit for your tractor & then it will be easy to isolate the failure.....

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Jake

04-01-2002 08:49:02

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Re: Glow Plug Relay Question in reply to Randy smith, 03-31-2002 19:14:10

Diesel plug controllers have a 12v batt terminal, an output to the glow plugs, 1 wire to the wait, 1 terminal to the activaton switch. The control should upon being turned on will heat the glow plugs for 30-60 seconds, the wait light will go out and the engine ready to start. I used the 82 Olds contol on my replacements, they were cheap at about $13.00.

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Randy Smith

04-01-2002 08:59:56

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Re: Re: Glow Plug Relay Question in reply to Jake, 04-01-2002 08:49:02

Jake..thanks for the reply. Can you tell me what actually cuts the flow of current from the 12v battery to the glow plugs. In other words, what determines when the wait light goes out in 30secs or 60secs. I guess I am wondering if the actual shut off is within the relay or is there another componet responsible for changing the relay to the open or off position. Is it some type of breaker? Any info greatly appreciated.

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Jake

04-03-2002 21:00:28

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Re: Re: Re: Glow Plug Relay Question in reply to Randy Smith, 04-01-2002 08:59:56

The wait timer is connected to the ign switch then in the case of autos on the intake manifold. When the ign is turned on current is passed on to activate the relay beteen the batt and glow plugs. In the case of a bad glow elay the wait light will remain on and the only way to start engine is to jump it 12v to the glow plugs. When the engine is hot the wait delay senses this and the wait light will not go on

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Jake

04-03-2002 21:00:13

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Re: Re: Re: Glow Plug Relay Question in reply to Randy Smith, 04-01-2002 08:59:56

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Jake

04-01-2002 21:50:02

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Re: Re: Re: Glow Plug Relay Question in reply to Randy Smith, 04-01-2002 08:59:56

I just found my Small diesel engine service manual. Starting procedure states if the engine is cold and below 55 F or above hold the preheat switch for 3o sec before starting, between 30 and 50 heat for 1 min, below 30 heat for 2 min. According to the diagram both glow plugs are attached to a manifold heater then attaches to the relay and battery. It does not show wiring away from the motor. I may be able to hook up my scanner this week. Just click Jake at the Posted by.

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RickB.

04-01-2002 17:43:36

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Re: Re: Re: Glow Plug Relay Question in reply to Randy Smith, 04-01-2002 08:59:56

Many systems have a time delay relay to control the time the indicator lamp stays lit, but that TDR has no control over the power to the glowplugs themselves. Systems like this are typical of Japanese-built compact tractors.

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