Hello, I’m pretty new to this website. I have a 1985 M1028. Recently I’ve had to crank my truck a lot before start up. Even give gas while trying to start up to get it to fire. I can hear the relay click on and off. It does this multiple times, clinking on then a couple seconds later clicking off. The voltmeter doesn’t show any changes when the relay clicks on, when it used to show the draw. I love this truck, been great for me at school and want to get this figured out so I can have my daily driver back. Thank you for any help!
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Hard starting, glow plug relay failed?
- Thread starter jaako40
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MarcusOReallyus
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Well, start with a test light or multimeter. Your GP relay sits at the back of the engine compartment, just a bit to the right of the engine when you are standing in front of the truck looking back. There's a heavy wire coming in (should be the top, but not always) that provides the main voltage to the relay. Should be always hot. Opposite that is the output to the GPs. You want to see if that terminal gets voltage when you activate the relay.
There is also a smaller orange wire which should be hot when the key is in the "Start" position (energizing the relay and the GPs), and a small blue wire which goes to the GP controller card. When this wire is grounded, the relay should engage and send juice to the GPs. If the card is bad, it won't groiund that wire. If you can ground that wire and not get 12v out of the relay, either the relay is bad or you aren't getting juice TO the relay.
There's lots of good info in the "Helpful Threads" sticky, including all you'll ever want to know about the GP system.
There is also a smaller orange wire which should be hot when the key is in the "Start" position (energizing the relay and the GPs), and a small blue wire which goes to the GP controller card. When this wire is grounded, the relay should engage and send juice to the GPs. If the card is bad, it won't groiund that wire. If you can ground that wire and not get 12v out of the relay, either the relay is bad or you aren't getting juice TO the relay.
There's lots of good info in the "Helpful Threads" sticky, including all you'll ever want to know about the GP system.
I have 25v in at the top of my relay, 13v at the bottom and 25 initially on the turn of the key that drops to ~13v after a couple seconds. The relay is getting grounded but it doesn’t stay on long normally shutting off again after just a second.Well, start with a test light or multimeter. Your GP relay sits at the back of the engine compartment, just a bit to the right of the engine when you are standing in front of the truck looking back. There's a heavy wire coming in (should be the top, but not always) that provides the main voltage to the relay. Should be always hot. Opposite that is the output to the GPs. You want to see if that terminal gets voltage when you activate the relay.
There is also a smaller orange wire which should be hot when the key is in the "Start" position (energizing the relay and the GPs), and a small blue wire which goes to the GP controller card. When this wire is grounded, the relay should engage and send juice to the GPs. If the card is bad, it won't groiund that wire. If you can ground that wire and not get 12v out of the relay, either the relay is bad or you aren't getting juice TO the relay.
There's lots of good info in the "Helpful Threads" sticky, including all you'll ever want to know about the GP system.
The 25 down to 13 is at the glow plug itself. Thank you for the reply also. Guess it’s probably time to pull my card and check it out most likelyWell, start with a test light or multimeter. Your GP relay sits at the back of the engine compartment, just a bit to the right of the engine when you are standing in front of the truck looking back. There's a heavy wire coming in (should be the top, but not always) that provides the main voltage to the relay. Should be always hot. Opposite that is the output to the GPs. You want to see if that terminal gets voltage when you activate the relay.
There is also a smaller orange wire which should be hot when the key is in the "Start" position (energizing the relay and the GPs), and a small blue wire which goes to the GP controller card. When this wire is grounded, the relay should engage and send juice to the GPs. If the card is bad, it won't groiund that wire. If you can ground that wire and not get 12v out of the relay, either the relay is bad or you aren't getting juice TO the relay.
There's lots of good info in the "Helpful Threads" sticky, including all you'll ever want to know about the GP system.
MarcusOReallyus
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Yep, sounds like the card. Hillbilly Wizard carries new ones.
BUT! Before you pull the trigger on that, clean your grounds. There's one up under the dash right next to the parking brake mechanism. 6 legged creature. Remove, clean to bare metal, slap on some dielectric grease and reassemble. Then try again. Also use some contact cleaner on the card contacts. Pull the card out and put it back in a few times, spraying contact cleaner on the contacts each time.
Can't hurt, and it might solve your problem. If not, well, you probably need a card.
BUT! Before you pull the trigger on that, clean your grounds. There's one up under the dash right next to the parking brake mechanism. 6 legged creature. Remove, clean to bare metal, slap on some dielectric grease and reassemble. Then try again. Also use some contact cleaner on the card contacts. Pull the card out and put it back in a few times, spraying contact cleaner on the contacts each time.
Can't hurt, and it might solve your problem. If not, well, you probably need a card.
Ok I hate to ask a dumb question but how does this box open up? I feel like I’m missing something very simple here right now and have been fiddling with it for 30 min now
MarcusOReallyus
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Looks pretty good. My guess is the problem is elsewhere. Check the continuity on that light blue wire that goes up to the relay, and make sure you clean those grounds.
After changing all the glow plugs the relay started working normal again and truck fired right up. Now I’ve managed to crack one of my heater core tubes getting that pain of the passenger glow plug out. Looks like I’ll have plenty to keep my busy this week...