Another gp thread... 24v resistor failure

[iacucv]

Ok guys, I apologize in advance for yet another gp system thread. I picked up a m1009 2 weeks ago and am slowly going through the systems to make sure it is reliable. Started with dog head mod, next on my list was new ac60gs and 12v resistor bypass. Well new gps in and then I discovered that the resistor had failed and was putting 25.3v to the gp relay. Had to stop after checking a couple gps for resistance, one or two starts didn't seem to hurt them but now I have a no start. Gps are obviously not heating up though voltmeter drops as usual. When I get a helper I will get the multimeter to work, but in the meantime I'm looking for advice on what likely fried. Hopefully just the relay? I have just ordered a new relay and a gp card from antenna climber, but want to make sure everything is fixed and won't harm my new parts. Thanks guys!

 

[reaper556]

I have the exact same symptoms on mine. I removed my resistor because it was smoking and I don't think it was from crap being stuck on it. After I removed it My WTS light only flashes once when I turn the key forward, Voltmeter drops down and I hear no click from my relay. My truck still starts fine. If I turn key forward press accelerator pedal down then let it up and start the truck fires right up in high idle. I live in TX and its garage kept, don't know if that's why mine seems to start fine

It actually fires quicker it seems after I removed the resistor. I'm not sure if my plugs are glowing or not

 

[iacucv]

My relay still clunks and wait light stays on longer now, but plugs are obviously not warming up. Exhaust smells like fuel and smoky. It was approx 60 degrees when I tried last. It's about 10 degrees warmer now, I'm about to go try it again and give the multimeter some field time.

 

[MarcusOReallyus]

Well new gps in and then I discovered that the resistor had failed and was putting 25.3v to the gp relay.

When? At what point in the cycle?


When the GP relay is OPEN (not putting power to the GPs), the output from the resistor (input to the relay) should read 24 volts.

That's the CORRECT reading.

The GP resistor will only drop the 24v to 12v when the relay is CLOSED and putting power to the GPs.

It does NOT drop voltage unless the current is flowing.


If the resistor output shows 24v when the GP is CLOSED (putting power to the GPs), then either the resistor is shorted, OR, you have an open circuit downstream of the resistor. That could be a relay not engaging (a clunk doesn't prove it's working), or it could be broken wires, or all of your GPs are fried.


Have you disconnected the resistor and measured its resistance?

 

[iacucv]

Ah yes I missed that Marcus. I did not test it under load, assumed it bad and did not want to send excessive voltage to my new gps. Anyway, after some more testing with the multimeter, I believe my relay is bad. After the 12v bypass, I am not getting any voltage out of the relay, and no clunk when grounding the blue wire terminal with a jumper wire.

 

[acesneights1]

There is only one proper way to test a glowplug. Take them out, make a set of small jumpers and put power to each one and look at it(don't touch the end or you will get burned). It should glow nice and hot at the TIP. if it does not glow or glows in the middle, it's junk.

 

[MarcusOReallyus]

Ah yes I missed that Marcus. I did not test it under load, assumed it bad and did not want to send excessive voltage to my new gps. Anyway, after some more testing with the multimeter, I believe my relay is bad. After the 12v bypass, I am not getting any voltage out of the relay, and no clunk when grounding the blue wire terminal with a jumper wire.

Yep, sounds like a bad relay. The good news is, that's an easy and cheap fix. 20 bucks at your local NAPA and you're good to go.

 

[iacucv]

Marcus I have a question about that for you. So before the 12v bypass, the truck would start though slowly as if it had bad gps. After I did the bypass, no start at all. Was there additional voltage/amperage before the bypass that allowed the plugs to heat up at least slightly?

 

[MarcusOReallyus]

This is a common complaint here on SS. Do the bypass, kill the truck! The usual cure is to replace the relay. It's likely that your GP relay has carboned up contacts.

 

[iacucv]

That makes sense. Surely has carbon, the relay looks factory, at least likely hasn't been touched since it left service. Going to try to get the new relay in tomorrow if I get off work in time to get the part. Also ordered a new gp card from antenna climber, save the stock unit as a back up. Hopefully those parts and mods, along with a good block heater, will keep her starting right up all winter long. Thanks guys, especially Marcus!

 

[iacucv]

Quick update, new st85 relay in ($40 bucks about at jobber cost!), truck starts right up. However only getting about 10.4v at the glow plugs. Obviously working fine, hoping to see 12v and end of my battle.

 

[MarcusOReallyus]

Great!


Now about that 10.4 volts, where and when are you measuring that?

 

[iacucv]

That is being measured at the 1/4" female spade connector while plugs are cycling. Hopefully it's another easy fix!

 

[MarcusOReallyus]

Well, you have some resistance between the battery and the GPs, but it's not much. I've never had reason to measure the joltage at the GPs while they are energized, so I don't know how bad that really is.

I suggest a good contact cleaning all the way back to the battery terminal.

 

[iacucv]

Sounds like a plan. I did come across a battery terminal I was less than impressed with, and the smaller ground cable that comes off of the front neg terminal needs some attention. Like I said, new to me and trying to do all the SS tricks to get her reliable. Many thanks to Marcus and all who replied, I know gp questions get old around here. I try to search as much as possible, but though I had a 1008 it was converted to push button... This gp system diagnosis is new to me so thanks for being helpful and understanding. Now to the high idle fix, some new epoxy paint and spray bed liner inside after some floor panel replacement!

 

[PJL]

After I installed the AC-Delco 60G's I checked voltage at the relay. As soon as the key was on the voltage was about 8 volts. It climbed up as they warmed which makes sense as the resistance increases as they heat up and the current required is reduced. That is the self regulating feature. When the engine started it cycled a few more times with the afterglow. The engine starts right up so I'm inclined to think this is normal. I did see a lot of smoke come off the resistor pack the first time. I suspect the old GP's had been bad for so long that the resistor wasn't getting warm enough to burn off the dirt and crud.

 

[MarcusOReallyus]

Good points.

 

[iacucv]

Makes sense to me. I will address that terminal and ground for good measure and call it a win. Many thanks guys!