glow plugs - pop went the fuse - PeachParts Mercedes-Benz Forum

psfred · #1 12-07-2003, 07:05 PM

Loop type plugs are series, not parallel, and the fast glow pencil type are paralle. You must put the series wire and relay in if you want to go back to the series type. You will burn out the loop type glow plugs doing this too, they aren't intended to be hooked up individually.

FastLane on this site has the large base plugs and the converstion kit.

Peter

wheelguru · #2 12-07-2003, 07:40 PM

'78 300 d. I decided to switch the glow plugs back to the pencil type that came in the car - not the motor, since it is a different one than what I started with, but the car is the same. when I got the car it had stickers that said that it had been converted to fast glow.
I checked my plugs by just putting some current to them. Four are good, and one is not. The old motor started well with this set up, four of the plugs all I could find a couple years ago when I needed new ones (large thread for the plugs, not the even more updated smaller thread) .
AAAnyways, I put the new pencil type in place of the old loop type, put everything back together, got in and turned the key. The glow light came on dimmer than normal and even with the doors closed, there was an audible pop as the light went right out. The pop was the fuse on the firewall burning up. I got the exact same result with another fuse. (well maybe it just works way too well)

Obviously the new plugs are drawing way too much current. What do I check or change? The plugs are wired in a string with the original jumper wires as far as I know the arrangement is just like it used to be but it does not work now.
Would the shop that did the motor swap have needed to change anything in the car to make the loop type plugs in the replacement motor work?
thanks.

wheelguru · #3 12-07-2003, 09:16 PM

I checked the plugs out of the car, one at a time with a battery and jumper cables. Clamped them in a vise, connected negative to the vise and pos. to the plugs, as per a post I found yesterday when I searched. they glowed quickly (four of them).
Let me make sure I got series and parallel right - and this is a part that confuses me, more on why in a minute. Series is hooked one to the next to the next to the next. Parallel is a separate wire coming from the source to each each plug individually.
It confuses me because the plugs were hooked one to the next to the next for both set-ups - and both worked, I could not tell any difference in starting between the two.
Two years ago, before the old engine broke a piston, I had to get a 4 plug conversion kit when the car stopped starting. I put in four and left one, hooked up the little jumper wires as they had been, one after the other and BANG! it started right up and idled smooth very quickly with temps in the teens.
I am thinking of just going back to the loop plugs, but I must have at least one bad one, car is hard to start up and barely keeps running for the first few seconds.

wheelguru · #4 12-07-2003, 09:21 PM

Also, I am going on the assumption that the newer relay etc. were installed with the fast glow kit (prior owner). The sticker was a Bosch one, something to the effect that a fast glow system had been installed in the car - now I am beginning to wonder how it could have worked with both types of plugs and the same wiring set up, but it did.

Stevo · #5 12-07-2003, 09:24 PM

When you hooked up the new GPs you disconnected the grounding strap at the fwd end, right. I installed the new style plugs an a couple of cars and I would NEVER go back to the old loopers. I used the old relay and 50 amp fuse, no problems.

Stevo · #6 12-07-2003, 10:13 PM

Dont feel too bad, I left out the oil gallery glugs

when I rebuilt my engine last spring, that was a big.... DAH

psfred · #7 12-07-2003, 10:38 PM

Well, you CAN, but be prepared for sparks and VERY hot conductors.....

Hard start and poor initial running can be bad glowplugs, but I'd also check the condition of the primer pump and suction hoses to the lift pump -- bad hoses will allow air in, and that will cause problems starting and initial running.

Peter

wheelguru · #8 12-07-2003, 10:58 PM

DOH!
That's it, I did not disconnect the ground strap! makes perfect sense! I am such an idiot, of course I can't hook negative and positive together.

wheelguru · #9 12-08-2003, 12:01 PM

thanks for the help all. I stopped at the parts place down the street this morning and got another strip fuse for the princely sum of $1.35. I don't doubt that once I unground the plugs I all will be well. After thinking about it I have a grasp of parallel v. series on the plug system also.
If the plugs don't make starting easier I will take a closer look at the hoses to make sure I am not sucking air.

wheelguru · #10 12-09-2003, 11:53 AM

Yup, starts right up now that I am not trying to short everything out. Still need that 5th glow plug, what a treat that would be. My plan it to make an adaptor from an old loop type so that I can put in the common pencil type plug in the last hole. Should get it done about April.

Stevo · #11 12-09-2003, 07:14 PM

"adaptor " ....... The problem is that the 18mm, new style GP for the pre "77" cars are close to twice the price of the 12mm GPs that fit in the post 77 cars. So if one had a 18mm down to 12mm bushing we could all use the 12mm new style. Sombody around here made a set but most dont have the skills, tools or time. So if anyone could come up with this bushing, post it pronto

Rick Miley · #12 12-10-2003, 10:58 AM

leathermang and rickg, are you watching? This is a money making opportunity!