differences between early and late IDI glowplugs?

[Dave Sponaugle]

Stock wiring harness should have a #4 AWG wire from the battery positive terminal to the glow plug relay. From there, you have two 10 AWG wires, one for each bank of glow plugs (head). The starter relay will work fine, it just needs wired a little different. You are only looking to close the relay for 10 seconds to heat the glow plugs which is about how long you would crank a gasoline engine with that starter drawing about the same power as the glow plugs. The relay Ford for the glow plugs has two small terminals and two large terminals. One large terminal for battery power in, one large terminal for glow plug power out. The trigger coil for the relay, one end is terminated at each small terminal on the relay. The mounting bracket does not supply a ground for the trigger coil. Starter relays have two large terminals and one or two small terminal. Again one large terminal for power in, one large terminal for power out. The difference is the trigger coil and the small terminals. There is an S by one terminal and an I by the other. The S terminal is where the wire from the start key position is hooked up and would be where you want to hook the trigger wire from your momentary switch to activate the relay. Starter relays also ground through the mounting bracket, so it must be mounted on a good electrical ground for the relay to work. Glow plugs should ohm out between .5 and 1 ohm each. So on a 12 volt system .5 ohms would mean a draw of 24 amps each. Like wise if they were 1 ohm each the power draw drops to 12 amps, but the time they take to heat will be longer. So if the glow plugs are at optimum ohm's, .5, the amp load to each cylinder head bank will be 96 amps, total of 192 amps for both. Starters for the diesel should draw about 300 amps if you are using a gear reduction starter, most of them are rated at 3.6 KW or 300 amps times 12 for 3600 watts. Battery grounds should be 2/0 cable to each battery negative. Battery positive cable should be 2/0 from the drivers side battery to the passenger side battery, the 3/0 from there down to the starter. 192 amps to heat the glow plugs, 300 amps to crank the starter, big dual batteries so you have more than one shot to start the engine when the temps get low and battery efficiency starts to drop. I guess the guys on that yahoo group were starting a 200 HP electric motor to run your truck with 5 times running load for the start up load, which is true for AC electric motors. And I almost forgot, I have never run Bosch glow plugs so I know nothing about them. Can you get an ohm reading on one of them? For what it is worth, Motorcraft/Beru ZD 9 or ZD 1A glowplugs are the best thing to use in these engines. All the others have issues of one kind or another, some worse that others.

[Marianna2003]

Ah the old issue of temperature limiting rears it's ugly head again. A temperature limiting GP is the only Idiot proof way to go. That way if your offspring leaves your glow plugs on, you can simply charge your batterys and go. Unless you like spending ~$100.00 for a set of GPs and enjoy changing them, why not try it. I know it goes against the grain for some of us, but the truth is that the ZD9s are NOT temperature limiting! Leave them on too long and you will have toast. They are slower than some of the other brands and may be slightly more durable. Spend about $10.00 and buy a Autolite 1109 and try it. You'll be surprised. They will heat up to red hot (approximately 800 Deg F and stay there. They will not continue to melt down. Dave is right when he says that the lower resistance ones are faster. They are also more senesitive to overuseage. Hook an 1109 up to your battery charger and watch. One last comment, always preheat your GPs before you install them. They can absorb moisture over time and will expand when heated for the first time. I bought a set of ZD9 when Oreielly's was giving them away and tried them. They draw ~10amps when first plugged in and continue to draw 10 amps until I chickened out when they got BRIGHT RED. If BERU makes a temperature limiting GP that would fit an IDI engine, I would consider it to be perfection.

[Marianna2003]

I left out AC 12G GPs because I worked in the lab that tested them and know they are good units. AC became Delphi which just screwed me, so you know what I think of them now. Regardless, I should have stated AC 12Gs or Autolite 1109s.