79 300TD glow plugs

[Rudder]

The other night I was at a evening gathering with my wife and daughter. My 1979 300TD failed to start when we climbed in and attempted to head back home because of a faulty glow plug, (# 5). (The glow plug lamp did not light as well) This I determined by testing the glow plugs with my ohmmeter that I luckily had in my crash kit that I carry in the boot of the wagon. Being quite late and the weather turning to rain I was motivated to to get my family home as quickly as I could rather than leaving the wagon in a parking lot overnight and hailing a cab. The 79 300TD glow plug system is wired in series and if one glow plug is bad then the whole system is dysfunctional along with the glow panel light. In order to get the glow plugs working again, I decided to rewire the glow plugs wire harness to by-pass the faulty #5 glow plug. I borrowed a steel coat hanger from the host of the party and fashioned it so as to go from #4 glow plug to the firewall relay/fuse-strip. This worked beautifully, the glow plug indicator lamp came on as normal and the engine started just fine although with a bit more smoke than usual.
So I figured the engine would start and run on four cylinders at first when the engine was cold but I thought that #five cylinder would start to combust and kick in as the engine warmed towards it's normal temp. As I drove home that night the engine ran smooth but a very real reduction in power was quite noticeable. So I"m thinking here that #5 cylinder never got lit! (I drove over 20 miles so normal running temp was achieved.) So my question to you all is, why didn't #5 cylinder fire off after the engine warmed up?

Low compression is my guess but the engine has run quite strong up and till this event. I have only 98,000 on the engine! I have yet to install a new plug and haven't driven the wagon since this event the other night!

Any insights or comments?

Thanks...

[1960mog]

The 5th cylinder should have fired as soon as the engine started, even with out a glow plug.
Maybe parts of the burned out glow plug got stuck in one of the valves and now you have low compression on #5.

[Rudder]

1960mog,
I believe your correct with low compression and quite possibly correct with the foreign debris in the valve seat. The GLP loop has a section out of it about 3/16" long at the lower end. The section looked as though it had melted or burn off! The GLP base looked clean otherwise! Any thoughts on how I should proceed with regard to a possible seat issue

Best..
R

[1960mog]

Is #5 running at all?
Start the engine and open #5 injector line.

Check valve clearance.
If you have to much, some thing may stuck between the valve and seat.

You can also check compression.