4 plugs give ohm reading but front and back two don’t

[Jdog87]

My truck wouldn’t start this morning. I tested the glow plugs even though I just replaced them two months ago. The 4 middle ones give good ohm reading but the back two and front two don’t. Is there a problem that may have caused this or is this just bad luck? Would a bad injector cause this? Truck was blowing more black smoke than usual and the truck was running a louder than normal.

 

[IDIBRONCO]

I doubt that a bad injector would burn out a glow plug. Burn the tip off? Possibly, but not a burn out. Most likely bad luck. If you have any doubts on your readings, pull the "bad" ones out and test them again. I've had some give bad or no readings and then read good after cleaning all of the crap off of them.

 

[Jdog87]

I finally got to pull the gp out and both front and back on each side have the tips blown off. What should I do? And what would cause this? The middle gp had carbon build up. Is my relay staying on to long?

 

[IDIBRONCO]

It could be several things. Relay like you said, cheap brand of glow plugs (Motorcraft/Beru are the only ones to use- others will probably give you trouble), a bad injector can also cause this. If it leaks fuel after firing, it will burn hotter with the extra fuel and can certainly cause the ends to burn off. As for the carbon on the middle one, it's probably normal unless there's a huge amount of carbon. Then you would feel at least some resistance when you pull the glow plug out of the head. You will probably always have a thin coating of carbon on your glow plugs after the engine starts. Look at the end of your tail pipe.

 

[Jdog87]

Do I need to pull the heads for the fractured tip or should I use a vacuum .

 

[DaveBen]

Just turn the engine over and it should come out.

 

[IDIBRONCO]

Did the tips break off when you pulled the glow plugs out? If not, I'd assume that they burned away. If you had to really work to get the glow plugs out, then I'd guess that the ends were swollen and probably broke off. If you think that the tips broke off, I'd first try the vacuum trick. It's cheaper and easier. I'd empty the shop vac first and make sure that the filter is fairly clean. That way it's easier to inspect for the broken pieces. If all else fails, then it may be time to pull the heads. I feel that if you pull one head, then it's ok to try it with the engine in the truck. If you're going to pull both heads, it easier to pull the engine. Now if you have head studs, just pull the engine. It will save you a lot of headache.

 

[Jdog87]

Do I need to remove the injectors or will it come out of the gp hole

 

[IDIBRONCO]

Just turn the engine over and it should come out.

I didn't think of that. The cylinders will make WAAAAY more pressure than a vacuum will.

 

[Jdog87]

The plugs came out with ease. There was no resistance.

 

[UMR_Engnr]

Look at the end of your tail pipe.

What are you looking for? My tailpipe is black but it doesn't smoke when running so I always just figured it was fine.

 

[IDIBRONCO]

That's my way of pointing out why things would have some carbon on them if they are in contact with burned diesel fuel. A little bit of carbon on the glow plugs is normal. It may be burned off when glowing to start the engine, but it should accumulate right back on there when the engine's running.

 

[UMR_Engnr]

Got it. Thanks.

 

[bbjordan]

Would a bad injector cause this? Truck was blowing more black smoke than usual and the truck was running a louder than normal.

Yes it could. An injector with a weak spring will open sooner, and the timing for that cylinder will effectively be more advanced. Symptoms of advanced timing are:
1. a louder diesel knock/rattle
2. black smoke
3. eats glow plug tips

Like IDIBRONCO said, Motorcraft/Beru glow plugs are the way to go.

You didn't say whether it was a 6.9, or a 7.3. The 6.9 old style glow plug controller is notorious for failing in the closed position which will burn out the glow plugs.

Please put your truck particulars in your signature file, so we don't have to guess what you have.

 

[Jdog87]

It’s a 94 7.3 non turbo. I think it’s a couple injectors going bad as it has all three of the symptoms you said. Who is a good source to buy injectors from and do I need to replace the ip too.