SUBJECT: “Glow Plug PROBLEM SOLVED, Wagon Up and Running”

1982 300 TD (Turbodiesel Wagon)

After considering all the good and thoughtful advice you all provided, I decided to heed the advice of those who counseled me to “work the problem, first”. If the 80A Strip Fuse was blowing, then concentrate, first, on solving that problem (and ignore any other possible problems until after solving that one)!

The Glow Plug “GP”) testing methodologies recommended on many websites and forums are based upon GP resistance, in Ohms. Based upon that methodology, I did not have an obviously bad GP (not open or infinite!), as the readings, reported elsewhere in this thread, indicate.

Because I did not have a high comfort level working with battery-size currents, I decided to use my relatively small shop Battery Charger (“BC”) which puts out 8 Amps, has a built-in Ammeter, and is protected by an internal circuit breaker.

Both to remove the wiring harness from my experiment as a variable, and to protect it from current, I removed the 8 mm nut from each of the five GPs and then removed the wires coming from the large connector in the GP Relay. The GPs were to be tested in the cylinder head, however.

To test my experiment methodology, I removed No. 1 GP from the cylinder head and laid it down on the concrete driveway. I hooked up the Negative of the BC to the body of the GP, and the Positive to the threaded end of the GP. I plugged the BC into the extension cord, and watched as the element of the GP first smoked, and then grew a bright red. After 40 seconds or so, I unplugged the BC and allowed the GP to cool. When it was cooled, I reinstalled it into the cylinder head.

For the next stage of my experiment, I knew I wanted a good ground, so I took the negative cable of my shop jumper cables and hooked it to the battery ground. I was not looking to get battery power, just the good ground provided by the battery negative. I hooked the negative lead of my BC to the other end of the grounded jumper cable coming from the battery.

To review, I now had each of the five GPs isolated in the cylinder head with no wires connected to them. I knew No. 1 GP was good outside of the cylinder head, but just for good measure I tested it again in the head. I connected the positive lead of my BC, and then plugged the BC into the extension cord. The Ammeter pegged itself at 8Amps and held steady. After about 40 seconds, I unplugged the BC. No 1 GP checks out as good.

I moved to No. 2 GP, connected the positive lead of the BC, and plugged the BC into the extension cord. The Ammeter pegged itself at 8 Amps FOR ABOUT FOUR SECONDS, then the circuit breaker in the BC made a relatively loud noise as it tripped, and the Ammeter went to zero. I unplugged the BC and waited several minutes for everything to cool down and for the circuit breaker to reset itself. For the second try, to reproduce the experiment, the same exact thing happened: 8 Amps for about four seconds, and then dead short.

GPs No. 3-5 tested good, exactly like GP No. 1.

Next, I connected the wires coming from the Glow Plug Relay to GPs 1, 3, 4, and 5, only. I left No. 2 unconnected. After replacing the 80 A fuse in the Glow Plug Relay and making sure the large and small connectors were connected, I turned the ignition, watched as the GP light lit up, and cranked the engine which caught quickly and started up!

Sometime later, I removed the new GP Relay and reinstalled the old relay I had replaced with the new one. After installing a new 80A Strip Fuse, the old GP Relay lit the lamp in the instrument cluster, started the engine, and now does not blow the Strip Fuse. It seems to be just fine!

I will now proceed to replace all the GPs (believe it or not, I think the Beru s are all original) and ream out the precombustion chambers before installing the new GPs. I have quite a lot of carbon in there! Can anyone suggest where I could find an image of the section, shape of the precombustion chamber so I would have a better idea of where I should try to remove the carbon from?

What I learned, of course, is that that you can have a GP that tests just fine using the resistance method, but will quickly short out as it begins to draw current! By the way, I think several “experts” on this website said as much.

Thank you all so much for your thoughts.

-Bill