Issues with Glow plug start on cold since rebuild.

[Zol]

Hi all. I have a 2.8 deisel Turbo GQ & I have just changed the timing belt & valve stem seals. My ol man took the glow plug railings off & didn't realise there were plastic spacers between the long & short glow plug rail as the rear 3 glow plugs are duel resistance. Spacers fell out as he pulled it off & just re-installed it without them & clearly shorted out the system.

I started the truck & the glow plug light kept flashing while engine was running. I sussed out that there should be spacers, ordered new ones, installed it properly & checked the resistance on all glow plugs (all good). But now the primary glow plug light on console & glow plugs don't stay on long enough to pre-heat the chambers. I have to wait for ages while the secondary glow plugs slowly heat up & then it starts 8 out of 10 times.

The relays sound like they work (both are switching) but the primary relay just times out too fast.

How is the time controlled on the relay? Is it by the computer or is there a heat sensor somewhere that controls the preheat temp? OR does the computer sense a resistance change on glow plugs?

I'm a bit stumped & need some help here.
Cheers
Zol

[MyGQ]

The Temp sensor for the glow plug is on the side of the block near the temp gauge sender, it has 2 wires rather than 1. the computer could have taken a hit also by the glow plugs shorting out and not keeping the voltage going to the plugs long enough to keep it warm.

[Zol]

Thanks MyGQ.

I found the problem. The short out blew the cold start plug relay. Though the relay still sounded like it was working, it burnt out the bridging wire inside & plug was not getting power. You would think that the fuse would go first but the factory fuse wire is twice as thick as the one in the relay....Go figure???!! I'm sure there's some sense in it. So we have temporarily soldered it back together until I get another from the wreckers.
All works fine now.

Cheers
Zol