Why does my rabbit start without glow plug relay?

[DrAnonymous]

So if I drive my 83 1.6 rabbit for awhile and shut off the engine, it won't restart unless I remove the glow plug relay (the big honker on the right of the driver's fuse panel). I just hear a click with it installed when I turn the key. The yellow glow plug warming light will flash, but nothing else happens. If I pull that relay, starter works right away.

I looked at the electrical diagram in the Bentley manual and it doesn't have enough detail in the relay portion. It doesn't appear the relay should affect starter power.

What's going on? Don't want to spend $40 or so on another relay if that's not the issue.

[TylerDurden]

Automatic tranny?

It sounds like the GP circuit is dragging down the juice. I'd check the fusebox for good connections.

[DrAnonymous]

Yes, I have the automatic tranny.

If the GP circuit is dragging down the juice, why is it only when the engine is hot? I don't ever have an issue when starting it cold, so the fuses should be ok right? Asking to understand more.

There's a temp sensor for that circuit so that you don't heat the glow plugs when the engine is hot right? Shouldn't that part of the circuit keep current from going to the glow plugs. I'm assuming the relay is supposed to handle that.

[TylerDurden]

The temp sensor connection may be stuffed. You might connect a 12V LED from the cabin to GP #1 to see if the GP buss is getting juice when it shouldn't.

Auto tranny locates the starter too close to the exhaust manifold. The automatic tranny starter was designed to have a heat-shield - it may be missing. I suggest the heavy-duty starter, since a hot starter has effectively 1/2 or 1/4 the power of a cold starter, due to the increase of resistance in copper as temperature rises.

[Fatmobile]

The most common reason for poor hot-starting seems to be slow RPMs.
When the engine is hot the pistons and things are expanded and harder to turn.

The glow plugs on during hot-start would slow the RPMs down.

Sounds like your glow plug circuit is messed up,.. if the yellow light flashes.

Like mentioned; a light wired directly to the glow plug bus bar will tell you more than the yellow timer light.

[DrAnonymous]

I'll take a look today. I don't think this is directly heat related. If heat was affecting the starter, it wouldn't start when I unplug the relay.

It's definitely an electrical thing, but heat might be affecting the relay somehow.

[TylerDurden]

With certainty the starter has more resistance and less turning power when it is hot... Perhaps enough resistance also in the solenoid that energizing the GPs w/ 50A will drop the battery voltage below pull-in voltage.

I'd check the battery voltage when the starter fails and check the GP relay, sensor & wire...

The relay can be checked by:

• grounding the wire and turning the key to glow: should be no (or brief) juice to the GPs
  disconnecting the wire and turning the key to glow: GPs should have juice for max time

The sensor can be checked in a pan of hot water (or heat gun): as the water heats, the resistance should drop.

Check for continuity from the GP relay connector to the sensor connector & ensure the GP relay connector hasn't backed-out of the connector block.

[greg lousy]

the glow plug relay on my caddy recently failed resulted in continuous power to GPs.
The starter didn't really want to turn. I'm not sure what the connection was between the two because I ended up replacing the main ground wire to the chassis, adding a ground to the starter, loosening the timing belt a bit, and replacing the battery which was fried from me tooling around - probably before I realized the glow plugs were always on and I would charge and drain, charge and drain...

It makes sense though, as both GPs and starter require high voltage, and they are wired to never operate at the same time...

It became clear when I noticed the GP wire was warm with the ignition in the off position.

I ended up going relay-less and wiring a push button switch into the relay plate. I love it, haven't looked back. One less thing to worry about, especially after my problem cost me new GPs, a new battery, and much head scratching.
(granted the head scratching and battery were mostly due to my being an amateur)

[mtran]

It makes sense though, as both GPs and starter require high voltage, and they are wired to never operate at the same time...

They do that for short time after GP light is off,and you start engine.