Last week, my 1981, 240D, glow plugs stopped working. Thanks to Diesel Giant , I had two bad glow plugs.



Replaced the bad glow plugs, then went to start. All I got was loud clicking noise , from the glow plug relay. I just left the car and went inside, and later reading posts on glow plugs.


One suggestion, was to tap the glow plug relay. I did this and sure enough, everything works.


WHY did tapping the glow plug relay, cause everything to work?

Broken solder traces, cracked fuse, or stuck contacts. Be prepared for the relay to puke on you sooner rather than later. Any time something electronic magically works after "hitting" it, the answer is ALWAYS a poor connection.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I interpreted your post differently. Do you mean the starter would not even turn the engine over? Until after you tapped the glow plug relay. Nothing worked got my attention.

If that is the case the relays behavior if it was that you heard . Was only the result of another issue. In that case tapping the relay actually in itself did nothing. I would clean the battery terminals and cable ends to start with if your starter did not function the first time.

You might clarify when you said nothing worked the first time you tried to start the engine. .The clicking noise you heard could have been the starter solenoid and not the glow plug relay.

Had no problems with starter. But with no glow plugs, the engine would just turn over , and after 15-20 seconds, I just stopped .



Then after tapping glow plug relay, the glow plug light on dash lite up, and then starting engine was just like normal.

Probably not a bad ideal to change the glow plug relay out. I have acquired them from auto wreckers before. I felt the cars were not sent to the wreckers for bad glow plug relays and they were cheap from that source. If you have any electrical background or not. I would at least inspect the fuse strip in the relay. Or for a loose connection.

If for example the fuse had cracked your hitting the relay might have re established a connection. Looking further into the relay might depend on your electrical experience.

I have paid as little as five dollars for a used replacement. If it failed once. Even If now working it probably will fail again. Unless you find the cause for the failure.

Replace the internal electrolytic capacitors and it will likely act like a new relay.

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Sam

84 300SD 350K+ miles ( Blue Belle )