Will a failure on Glow Plug #1 prevent the car from starting?

[grindMARC]

I've tested all the plugs and found that #1 is reading "infinity." The relay tests fine. The strip fuse tests fine. The glow plug dash light is not coming on (very recently).

Will the failure of just one glow plug (#1) prevent the car from starting? Or asking the question another way -- if the dash light is out, does that mean that the glow cycle is not happening when I turn the key?

I cannot get the car to turn over. There is no air in the fuel system (I have a hand pump installed on this 86 to purge air). I plan to replace at least the #1 plug tonight.

Its been in the mid 20s here the last few days.

[123Guy]

Typically if you have one or two bad glow plugs, the light won't come on. But are you saying the engine won't turn over, or it spins, but won't start?

[Brian Carlton]

Originally Posted by grindMARC

Will the failure of just one glow plug (#1) prevent the car from starting? Or asking the question another way -- if the dash light is out, does that mean that the glow cycle is not happening when I turn the key?

I would say that it would not prevent a start on the 603. It definitely will not prevent a start on the 617. The dash light will normally be out if the #1 glow plug has failed.........however, the remaining five might be working. Put a 12V test light or meter on a couple of them and make sure the relay is providing voltage.

You might have more than one problem.

[JohnS]

Typically one won't keep it from starting at that temp. I've had as many as three bad and still started, tho' it smokes quite a bit. Make sure it is only one that is bad - also it doesn't have to read infinity to be bad, they may read as low as a few ohms and still be bad. What do you mean by 'turn over" - the car is not cranking?

[grindMARC]

The engine tries to start, but doesn't fire. It fired up once, ran very rough up to about 3k RPM and then cut out after about 10 seconds with my foot on the floor. The block heater was turned on for a good 75 mins.

All the other GPs tested under 1 ohm. Most were around .8 and .9.

So, in answer to my question, even though the dash light is not going on, a glow cycle SHOULD be happening. Correct?

Now that I think about it... I never tested that the relay was actually providing power to the plugs. I confirmed that power was arriving at the relay and that the fuse was working, but not that it was sending power.

[nhdoc]

You need to confirm the glow cycle is working, I suspect it is not. You ought to be able to start the car with one dead GP. Simply confirm you are getting voltage at the plugs by checking them with a meter when the key is set in the glow position. Those relay fuses can develop hairline cracks and look and even test fine with a meter but not carry the current needed to glow.

[tangofox007]

Originally Posted by grindMARC

So, in answer to my question, even though the dash light is not going on, a glow cycle SHOULD be happening. Correct?

Correct. Can you hear the relay click on and off?

[grindMARC]

Originally Posted by tangofox007

Correct. Can you hear the relay click on and off?

I'm not positive, but I don't think so. I'll confirm that tonight. I can say though that I did not see the dome light get brighter after the normal glow cycle time (read about that test in another thread).

If power is not making its way to the plugs, should I bypass the strip fuse to isolate the relay or fuse? Is there another way to test that fuse? Its got continuity and its getting power on both sides.

[tangofox007]

Originally Posted by grindMARC

I'm not positive, but I don't think so.

The relay itself is pretty big and,therefore, usually quite audible. It's starting to look like you might have a new GP timer in your future.

[barry123400]

I thought I read somewhere that the first glow plug is also used in later models as a relay time refference. Probably in error but worth considering. Remember if #1 is out it can or does extinguish the glow light. As the glow plug needs replaced anyways change it before assuming something else is wrong. Just my two cents worth again probably wrong.

[nhdoc]

Originally Posted by barry123400

I thought I read somewhere that the first glow plug is also used in later models as a relay time refference. Probably in error but worth considering. Remember if #1 is out it can or does extinguish the glow light. As the glow plug needs replaced anyways change it before assuming something else is wrong. Just my two cents worth again probably wrong.

Yeah, I would also recommend replacing any known bad GPs before doing much else - but the fuses are known to be achilles heals on these so it would not hurt to replace it too.

[grindMARC]

Originally Posted by nhdoc

Yeah, I would also recommend replacing any known bad GPs before doing much else - but the fuses are known to be achilles heals on these so it would not hurt to replace it too.

Thanks everyone for the input. Look for an update later tonight. The fuse and a new set of GPs are waiting for me at my parts shop. It should only take a few mins to swap out the one bad GP and the fuse. If it starts, I'll do the remaining GPs when the temp is a little warmer and I have some sunlight.

[grindMARC]

Before I swapped out the strip fuse with a new one, I tested the voltage at each glow plug during the glow cycle. I am getting power at the plugs. So that suggests that the fuse is good after all. I also noted that I can hear the relay turning off after about 25 secs. I swapped out the fuse anyway just to be safe. I retested the ohms on all the glow plugs. I was wrong about which one is bad -- its actually #6. 4 of the remaining 5 GPs tested at between .8 and .9 and the last tested at .5. I have not swapped out the bad plug yet. It got dark on me.

I'll try starting it in a bit when the battery has had a chance to take a full charge and the block heater has been on. I'm not real optimistic.

Strange, even my 400K+ mile 617 will start pretty well with one bad GP (just a little rough). I really suspect there is something else going on too.

[Cervan]

i had a 616 engine that had all glowplugs bad. (dont know why they all went bad at the same time, but..) made one hell of a smoke cloud when i started her up.