My 1976 300D has been having issues starting and my Dad and I decided it was most likely the glow plugs. We went in a replaced all 5 finding the 5th burnt out. After replacing all 5 with brand new Monark non-pencil type glow plugs and hooking everything back up the car will not start. The starter will crank, the engine will turn over, the glow plugs will get hot, but to no avail.

The battery in the car is on the small side and needs to be changed next, but every time I try to start the car it will drain a lot of power and by the third attempt we have to either try and jump it or hook it up to a battery charger. Even while attempting to jump the car, the car will still not start, but would before the glow plugs were replaced.

We are totally at a loss and really have been trying to figure this out. After replacing the glow plugs everything went down hill, which should have been the opposite, haha. Any help will be greatly appreciated and I'll try to answer any questions to the best of my knowledge.

 

I have a 76 300D that will not start post glow plug replacement. I do not get power at the primary connection to the glow plugs and the glow plug indicator does not light. Continuity checks between all 5 plugs and ground. I have checked all the relays I can find. Is there a fuse some where I am missing?

 

Perhaps you lost your fuel prime? I had similar issues on my '78 300sd. But is seemed like it wanted to start. I figured that it HAD to be lack of fuel in the chamber. I held the throttle open and pumped the hand primer 10 times or so. besides the usual 30 pumps with the throttle closed. that did it for me. I honestly don't know for sure if that was the problem, but it started right up after that.

I also suspected water in the fuel lines so I added a bottle of Heet to the Tank at the same time and replaced the fuel filters, too. But I think it's unlikely that the Heet would work so well so quickly.