1986 300sdl glow plug question and comments

[brandlj]

Hello all,
Thursday morning when I started my 300sdl I decided to do a double glow plug sequence. It was 36 degrees that morning and my car has been starting roughly all week. The first glow sequence was fine, glow light on. Second turn of the key and no glow light. I counted to 20 and started it and it started just fine. I thought perhaps the bulb in the dash burned out.
Late in the day leaving work, no glow light, started rough.
I was off Friday so I did a little diagnosis using the Factory service CD. Following the protocol, I found that the light bulb in the dash is fine, the glow plug relay is fine. I then tested the glow plugs using my ohmmeter.
Plug 1 .9 ohms
plug 2 .9 ohms
plug 3 .9 ohms
plug 4 .9 ohms
plug 5 .9 ohms
plug 6 158.6 ohms

I guessed that meant that plug 6 is bad. I took the plug out and tested it without the wiring and the ohms were 90.

Should I order one glow plug or get all 6? Does cylinder 6 routinely go thru plugs faster than the others? or is it just time to replace all 6 and start fresh?
The factory service CD is wonderful to have. The best $20.00 I ever spent.
I appreciate all input.

John

[Brian Carlton]

The question cannot easily be answered until #6 is fixed.

If the engine starts after one full glow cycle and doesn't kick and bang in the process, you can continue to use your old plugs.

However, like my '86, the old plugs don't put out the heat of a new plug and it's absolutely necessary to wait 30 seconds from the point of turning the key until you crank the engine. Just ignore that glow plug light...........it's useless unless the temperature is above 70°F. or the plugs are brand new.

There really is no reason to cycle the plugs twice. You'll likely get sufficient heat to start after 30 seconds............whether it will be a smooth start is the question.

[brandlj]

Originally Posted by Brian Carlton

The question cannot easily be answered until #6 is fixed.

If the engine starts after one full glow cycle and doesn't kick and bang in the process, you can continue to use your old plugs.

However, like my '86, the old plugs don't put out the heat of a new plug and it's absolutely necessary to wait 30 seconds from the point of turning the key until you crank the engine. Just ignore that glow plug light...........it's useless unless the temperature is above 70°F. or the plugs are brand new.

There really is no reason to cycle the plugs twice. You'll likely get sufficient heat to start after 30 seconds............whether it will be a smooth start is the question.

You are correct here. It does kick and bang unless it's over 70 degrees outside. Now I can plug it in for about an hour and it starts much better. I guess it has been a slow deteriation in the glow plugs. You don't really notice it until that first cold morning.
I believe I will order all 6 plugs and start fresh. The number 6 was so easy to get out too!!! Looking at the rest, this will be a challenge.
My car has Bosch glow plugs. Any difference between these and the BERU?
I am going to attempt this without removing the intake manifold. Have you done this before in this fashion?
Thanks for all your help.

John

[Brian Carlton]

Originally Posted by brandlj

You are correct here. It does kick and bang unless it's over 70 degrees outside. Now I can plug it in for about an hour and it starts much better. I guess it has been a slow deteriation in the glow plugs. You don't really notice it until that first cold morning.
I believe I will order all 6 plugs and start fresh. The number 6 was so easy to get out too!!! Looking at the rest, this will be a challenge.
My car has Bosch glow plugs. Any difference between these and the BERU?
I am going to attempt this without removing the intake manifold. Have you done this before in this fashion?
Thanks for all your help.

John

I've only changed two of them. If I was going to do all of them, I'd probably remove the intake..........the frustration factor and the lack of visibility would kill me.

The BERU plugs are fine.

Please post again with the results of the full new set...........I'm curious if you can get a clean start at the moment the glow plug light goes out.

[brandlj]

Originally Posted by Brian Carlton

I've only changed two of them. If I was going to do all of them, I'd probably remove the intake..........the frustration factor and the lack of visibility would kill me.

The BERU plugs are fine.

Please post again with the results of the full new set...........I'm curious if you can get a clean start at the moment the glow plug light goes out.

WHOA!!!! If you have only changed two before, maybe I should re-think this.I realize when looking at where they live, this would be difficult with the Intake manifold on, but maybe with some small 1/4 inch drive tools maybe I can do it.........

I will buy 6 plugs, replace number 6 and see what happens. If I still have problems then I will attempt the other 5.

[babymog]

The oddity here is that your glow-plug light didn't work.

Accroding to the FSM, for the glow-plug light to not work, you must have either: #1 glow-plug out, or 2 of the plugs #2-#6 out. You've only found one.

[brandlj]

Originally Posted by babymog

The oddity here is that your glow-plug light didn't work.

Accroding to the FSM, for the glow-plug light to not work, you must have either: #1 glow-plug out, or 2 of the plugs #2-#6 out. You've only found one.

You are right, that's what the FSM states, but the bulb is good. All the plugs except number 6 are good according to an ohmmeter test. I do not have the ability to check amperage on them when they are energized. I could have another bad one, I really don't know. I am going to replace number 6 and then see what happens.

[sixto]

Originally Posted by brandlj

I do not have the ability to check amperage on them when they are energized.

The brute force way is to get a half dozen 5 amp fuses and a 15 amp fuse. To the extent you can trust the fuse ratings, there should be enough current to each glow plug to burn a 5 amp fuse but not enough to burn a 15 amp fuse.

Sixto
87 300D

[a2t]

Did you just say #6 was EASY to get at? #1 is easy, it gets harder as you go back to firewall. #6 is a prayer at best w/intake on.

Make sure to ream the plug bores with the proper tool or you will be doing it again soon.

And beeeeee rellleeeeeee careful of the metal fuel lines. I disturbed them a bit R/R intake manifold. 2k miles later #4 line broke at injector, created huge mess. 2k miles later #5 broke at IP, created huge mess. I got the memo and went ahead and replaced #6 as it was looking questionable. These metal lines are all but impossible to find from dealer (they have been back ordered around country since March 08). Fair warning...

If it were me (and Ive been there twice now in 30k miles because I failed to ream bores 1st go round), Id replace all 6 at once.

I seldom wait 30 seconds, maybe 5 or so and it starts but stumbles a bit in cold.

All the hard starting (because I was too lazy to replace the glows) also resulted in me having to replace starter (after a tow home 100 miles outside AAA plus towing range). Fair warning...

[brandlj]

[QUOTE=a2t;2024850]Did you just say #6 was EASY to get at? #1 is easy, it gets harder as you go back to firewall. #6 is a prayer at best w/intake on.

Make sure to ream the plug bores with the proper tool or you will be doing it again soon.

Thanks for the hints. My car is a 300sdl and number 6 plug looks like the easiest to get to. If you have a 300D, I bet it really is tight back there at number 6.
When I pulled number 6 out it was very easy to remove. Does that mean that I need to ream out the hole? It did not even have much carbon in there. My car has only 113,500 miles on it.

[tangofox007]

Originally Posted by babymog

The oddity here is that your glow-plug light didn't work.

Accroding to the FSM, for the glow-plug light to not work, you must have either: #1 glow-plug out, or 2 of the plugs #2-#6 out. You've only found one.

The circuit that controls the light looks at the balance between the current to the #1 plug and the #2-6 plugs. Given the differences in resistance listed, it would not be unreasonable for the light to not illuminate.

[Jeremy5848]

Consider putting a very light coat of anti-sieze on the threads of the new glow plug before you install it. I have used anti-sieze for decades anywhere I have a threaded connection involving dissimilar metals such as a steel glow plug into an alloy head. Use very little and remove most of that – it's not plumbing, after all. Just a little bit and the glow plug will come out easily next time. Ditto for spark plugs (know what those are?)

Jeremy

[brandlj]

Originally Posted by Jeremy5848

Consider putting a very light coat of anti-sieze on the threads of the new glow plug before you install it. I have used anti-sieze for decades anywhere I have a threaded connection involving dissimilar metals such as a steel glow plug into an alloy head. Use very little and remove most of that – it's not plumbing, after all. Just a little bit and the glow plug will come out easily next time. Ditto for spark plugs (know what those are?)

Jeremy

Yes, I know what they are!!! All of my other cars are gassers. I will put a little anti-seize on the threads. I hope to change out the number 6 plug this weekend. Right now it's 29 degrees this morning and my car is plugged in and getting toasty. Even with the car plugged in though, it is a rough start.

[brandlj]

UPDATE:::::

I received my new glow plugs yesterday and started to get to work on my 86 300sdl. Number 6 was definitely bad. I replaced it and then checked my resistances with my ohmmeter and all was well except for Number 3 now.
When the old plug was in on number 6, the only resistance that was off was number 6. I replaced number 6 and now all were fine except number 3.
I replaced number three (intake manifold on ) and then checked reistances again and all was well. I turned the key, glow plug light on, waited for it to go out ( 16 seconds at 52 degrees outside) turned key to start and it was WONDERFUL!!! Success!!!!

While I was at it, I replaced my plastic clips that hold the hard fuel lines to the intake manifold. They were crispy and crunchy and melted in my hands.

Took it for a test drive and damn... a vacuum leak somewhere. Shifting really hard. Looked under the hood and I dislodged a vacuum line to the blue flying saucer. Hooked it up and all is well.

Tomorrow morning it should be about 38degrees out. We'll see how it works then.

[brandlj]

Well it went down to 36 degrees last night and this morning my new glow pugs worked great! Just replacing the number 3 and number 6 have transformed this car in the morning!

I am pleased!!!