Glow Plug System Diagnostic...

Can't you take them out one by one and watch to see if they glow cherry red?

Maybe you got a bad plug or two?

Nope... no can do. They are all underneath the intake manifold... Intake manifold has to come out along with a bunch of stuff that I do not want to do.

_____ Is the E300D glow plug system similar to the 300SD? If yes, then the plugs are the fast type and are powered in parallel via a large black relay. You can check each plug's resistance individually by pulling the connector away from the relay and checking inside the terminals. You should read something like 0.3 Ohms. Plugs like this usually fail open, and resistance will obviously be infinite. On my 300SD i found two bad plugs this way. You should read 12V at each terminal immediately after the ignition is turned on (connector plug removed). If not, the fuse may be bad. The large fuse (metal strip) is inside the relay just below the cover. Also, check all connections in the main supply cable to the relay for voltage.

You have to remove the INTAKE MANIFOLD to change the glo plugs?

Oh. My. God.

I thought removing the fuel rails was annoying enough even though it only takes

10 minutes:

Well, if you can't watch the glo plug glo can you measure voltage on that wire someplace?

Although it really seems to me that anything such as a relay is gonna give you a go/nogo for all the plugs and the only thing that would make individual cylinders work or not work would be the glo plug itself. I guess in a perfect world you test them before installing something that impossible to check in situ.

Yep... gotta remove intake manifold to replace all glow plugs. This is for all the 606 engines from 1995 to 1999. I will test the resistance. I have a feeling it is probably my preglow timer relay gone faulty.