I have an 85 300TD wagon with about 320,000 miles. I installed a new Bosch fast glow plug relay kit about 3 weeks ago. I needed to replace 3 plugs anyway so I thought why not get a new relay and plugs to boot.

I do not know how long the previous plugs were in there so I replaced all five for a nice baseline with the new relay. Fired up great for about 3 days and then I noticed longer and longer cranking time for the rest of the week. I parked it and staring driving one of my other cars.

Now the gp light stays on for 3-4 seconds, turns off and sometimes I can get the car started after 1-2 minutes of cranking. Most times only starting fluid will work.

I am really pissed off about gp's. I am having gp issues on my F350 as well. Almost ready to dump them all.

I bought a reamer from someone on the forum that had made and sold them about a year ago. Problem is that I can't find it I know I'll find it after I order a new one. I thought I might have lent it to one of a few local MB buddies but they all say no not them.

I tested the system per Diesel Giants instructions from his site and all five gp's ohm tested "dead". WTF? Less than a week for gp's.

Forgot to note that the car will easily start when plugged in, via block heater, for about 4-5 hours. Also, a valve adjustment was done about 1500 miles ago.

Find the reamer or buy one, ream, report back...
sounds like carbon build up shorting out the plugs...

Just bought a new reamer from ************** on ebay....I'll ream and see how it goes.

Remember to use some heavy grease on the threads and go progressively farther in and out...cleaning when out and recharging with grease..... to keep any metal or carbon out of wrong places...

Finally got around to the GP replacement. I pulled all 5 plugs as they all ohm's bad. I was shocked at the condition. The ends of the plugs were eaten away. On a couple of them I could see the filament or whatever it is that makes up the inner workings of the gp's.


I reamed the holes, installed new gp's. I was surprised at the lack of carbon that the reamer removed. I also clipped notches in the orings on the gp wires. Made for a much easier reinstall of the wires. That enabled me to install the new gp's with the wire nuts already on the gp's.

I also removed the fast glow relay and went back to my old relay. Fired right up.

Attached Thumbnails