powerstroke glow plugs

to get a good smoke free cold start I have to turn the glow plugs on twice. does this indicate a couple of bad glow plugs or that they aren't staying on long enough? (although the on-time seems sufficiently long enough) is there any way to check each glow plug without removing the valve covers?

thanks for your time

you have to remove the cover

Yes there is. The glow plugs are the outermost two of the five connectors. Remove the connectors, and using either test light or an ohm-meter check the outermost two terminals for good ground. Any that are open are bad (or the undervalve-cover harness is).