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evanmc

Low voltage to glow plugs

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1985 2.5NA 110

I was having trouble starting by 110 in cold weather (ok, what passes for cold weather in tucson, az) and started looking at the glow plugs, as it would start right up when the temperature was warmer in the day.

OK, when I disconnect the glow plug cable and measure where it attaches to the first plug, I read 12.2V when I engage the plugs.  When I connect the cable, I read 9.2V.

Anyone seen this problem?   Plugs are about 5 years old.

 

-Evan-

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Is your battery in good shape?

Have you taken the plugs out and energised them to see if they glow hot at the tip when 12v is applied to them?

Use a multimeter if you have one and check the resistance for each plug. High resistance = a bad plug. If you replace them, avoid cheap plugs. I only use Beru.

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Glow plugs draw a heavy current, voltage drop across them will be significant.

Though, 12.2V from your battery shows it is weak, this will also cause the voltage drop to be greater than normal.

I don't think you will find a problem with the plugs, operation sounds normal, even if at lower voltage. You can test them by removing and giving them 12V, the tip should glow a nice red/orange.

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My voltage drops to low 11v when the glow plugs are on. 

I would suggest you check/clean battery and starter connections first. Then I would give the battery a good charge via a mains charger or get it drop tested.

Mike

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finally got a chance to test resistance and install new plugs. Starts right up now.

 

Thanks for your help.

-Evan-

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Good to hear that the problem is sorted, did you measure high resistance on the old glow plugs?

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Yes, two of them showed high resistance.  forget what the actual values were. On to the next problem I will post today...

 

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