glow plug warm up time?

[GREASE FIRE]

I am trying to figure out if my glow plug relay timer is working correctly on my 7.3.
The glow plugs are actually controlled by a manual, momentary push button switch but the stock relay is still hooked up so the "wait to start" light comes on when you turn the key on and after several seconds it goes off. Today i went out to start it, about 20 F outside, and counted to see how long that light stayed on for. I may have counted kind of fast but it seemed like close to 20 seconds which seeems long enough to fry the glow plugs. They were replaced by the previous owner and are whatever brand most parts stores carry (he probably just walked into a store and bought them, rather than special order some premium brand or whatever). So i don't know if they are self-regulating or not.
So does anyone know what the max time that light should be on for and what the longest you can have the glow plugs on for?
thanks,
paul

 

[Diesel JD]

They are in fact self regulating...now with standard non ptc 6v plugs that would fry them.

 

[Mr_Roboto]

Well the "system" is self regulating. When it's colder the glow plugs take longer to warm up so the controller stays on longer.

 

[greythorn3]

max i ever hold mine on is 8 seconds

Ray

 

[Agnem]

Not only does it take longer to heat them up when it is cold, but your battery voltage is probably lower also. The controller basically looks at the total resistance of the glow plugs and uses that in its decision as to when to turn them off. Much better than the 6.9 method. The problem with not holding them on long enough (for instance 8 seconds if it's cold), is you may not start, which could lead to holding them on again too soon. Once you've gotten past the first glow plug cycle, it becomes difficult how to estimate the time they should be on again, and how soon. A lot of manual systems burn up plugs that way. Your way better off to hold them for 14 seconds, and have it start on the first shot, then to go 8 seconds twice in a row.

 

[sle2115]

My 87 6.9 with the factory solid state controller as used on the 7.3 IDI's does the same. When it is warm out, I might see a 5 second burn. When it get's cold, 20 seconds or so sounds about right. As Mel said, the controller senses resistance and goes from there. I have a digital voltmeter and it is not at all uncommon to see my system start at 12.6 or 12.7 volts and be down in the high 10's following a cold glow plug cycle. One other simple test is how long do they "glow" once it warms up? If you see a much shorter gp cycle with the engine warm, I would guess it is working just fine.

After guys saying 8 to 10 seconds on the gp's with a manual controller, then getting this system working (my controller was fried) then I was scared to death to see those long glow times! I just knew I was going to ruin a set of gp's, but it has been like that for 2+ years with no problems. I even once went out and pulled all my gp's just to check them, they were all fine. Use a quality glow plug if/when you change them, Motorcraft is the most recommended and what I have. They are available from Autozone as far as I know (the bullet style we use, I guess they have sold out all the spade type according to other posts) and you should be good to go.

 

[rickrat]

I have a manual on mine. I hold for 8 seconds, then wait about 10 seconds, then hold and crank at the same time. Seems to work best. I only do it this way when it is colder than 35 degrees out.

 

[GREASE FIRE]

I have a manual on mine. I hold for 8 seconds, then wait about 10 seconds, then hold and crank at the same time. Seems to work best. I only do it this way when it is colder than 35 degrees out.

why do you wait for 10 seconds afterwards? i would think that time allows them to cool down - could you explain?

i realized my "wait to start" light really does stay on for close to 20 seconds when it is cold out - i timed it with a stop watch. There must be something wrong with it.
thanks,
paul

 

[yARIC008]

A lot of manual systems burn up plugs that way. Your way better off to hold them for 14 seconds, and have it start on the first shot, then to go 8 seconds twice in a row.

I dunno about that. An extra two seconds is going to blow them out? And it's not even the 16 seconds is equal to 16 consequtive seconds because you have a small cool down period. So maybe it comes out being something like 15 seconds...

I just burn mine for about 6-7 seconds on not too cold days for the first start only. Then on really cold days I do say 8 seconds, then crank, if it doesn't go off, then another 4 or 5 seconds and usually that does er. I've been using the same glow plugs since the rebuild 5 years ago.

 

[Snowdiver]

I have Wellman dual coil with a manual push button. After trial and error I hold it down and after 6-10 seconds start it and continue holding it until the truck starts. When it's real cold it might take up to 15 seconds to start. Then I push the button for a second or two a few times until the idle smooths out. I've had the same plugs for over five years and it starts fine every time.

When the weather is warmer it fires at six seconds real fast. Colder takes longer. No way these plugs will burn out on 15 seconds.

 

[Diesel JD]

Nothing wrong with the light being on 20 seconds if its cold, like 32 or colder with the 7.3 system. Once you get into manual glow plugs it could be different. I had a manual system before I switched to solid state. I never burned them out once I fixed my very advanced timing issue after the head gaskets, and other fuel problems. I still have 7 of the 8 ZD-1a glow plugs that worked well when pulled. I always held them on no more than 8 seconds. They weren't even swelled or distorted when I pulled them.

 

[Ford428CJ]

I use a start push button with Bosch GP. On really cold days (Like 10 deg or colder) I hold them for 15sec tops on my 6.9. Seams to work just fine. And when it is 30+Degrees, then its 8 seconds.

 

[Agnem]

Eric, I guess my point is that when you re-lite your plugs are not cold, and the amount of time needed to get to X degrees is a lot shorter than initially. If you've ever played with a glow plug on the bench you would see what I mean. The darn thing gets so hot it's too bright to look at in a much shorter time if it has been cycled once already. They really are incredible devices when you think about it.

 

[rickrat]

So I might be better off holding the button, and after 8 seconds start to crank without letting go of the button for up to 16 seconds?

My thinking was that holding for about 8 seconds, then letting the glow plug cool a little and re-aaplying after 10 seconds or so was actually easier on the glow plug. My thinking was that the cylinder would warm up a bit on the inital 8 seconds, the glow plug would actually cool a little while the cylinder was still warmer than before, then while cranking hit it again.

Just holding for up to 16 seconds, if the engine didnt start, what would be a safe time to wait before holding for 16 seconds and trying to start again?

 

[Agnem]

I'd wait a full minute or two. Generally speaking, if it doesn't start with a hot glow plug, you've got other issues. I'd probably just crank it until I saw white smoke, and then worry about lighting up the plugs.