Low voltmeter, hard start, then burning smell.

Morning y'all. I have an m1028 to which I recently changed all the glow plugs (A.C. 60g), gp relay, and controller card and was getting perfect effortless starts. Today I started up the truck as usual and shut it off. A little later I went to start it up again and saw that the voltmeter dropped lower than it usually did while the relay was on. Wait light went off, and upon cranking it took a lot longer to start than usual, but no white smoke and I didn't smell fuel. I looked at the voltmeter and saw that it was still dropped all the way as if the plugs were still heating, and I wasn't hearing or seeing the methodical clunk of the relay cycling the plugs in it's post start phase....all of a sudden, boom, the voltage shoots up to were it should have been and the relay begins to cycle properly..right at this time I noticed that I started to smell something like burning electronics/wiring. I shut off the truck and inspected but couldn't find anything. I waited a few minutes and tried the truck again, and same thing, higher than normal voltage drop and burning smell..

The gp resistor cover plate felt extremely hot to the touch, could itnhave gotten fried? And would that result in those start up symptons? Havnt checked the gp card, and I would be pretty upset if I burned the brand new one..but it didn't feel like the smell was coming from in the cabin.

Thoughts?

Ok, upon further sniffing around, I'm pretty certain it's coming from one of the wires just above the gp resistor, looks like the wire that connects the 24v to the gp relay...im not sure if it's the heat from the resistor or the wire itself...I tried to see what the voltmeter is doing when turning the key again and its just dropping even lower, I can hear the gp relay open for the wait light but I don't hear it close after after it shuts off, although now I can't even remember if it's supposed to.

Are the batteries strong and have they been load tested? The resistors do get hot. How are the glow plugs?

Batteries are good and have always kept proper voltage, on or off, however I havnt gotten them load tested. The plugs were changed out a few weeks ago, but ill check if any of them gave out during this. The only concerning thing is whatever it is that's burning or melting.

Voltage is not the issue with batteries. The amount of amperage. Low amperage will create heat and that could very well be your issue. Get the batteries load tested and that will be the deciding factor. Good Luck.

Well, bad battery...replaced it and voltmeter read properly and truck started up great. However, I let it run for a few minutes and noticed again that the gp relay was not cycling correctly, and I started to smell burning again. I let it run and finally saw smoke coming out of the resistor.

Is that conclusive that it's shot? I know I read that it can smoke from just crud sitting on it but it's never smoked or smelled burnt.

I'll try bypassing and see if it fixes the issues, but would a bad resistor affect the relay function? Hoping i didn't fry the brand new st85.

The resistor is not the problem you plugs are staying on. Find out why.

Btw lower voltage = more amperage for the same load.

Hmm...that would make sense. Only thing I can think of is that the voltmeter still shows like the gp Relay is stuck open after startup...but what would cause the relay to go bad with it being so new?

lol you think something being new means anything? I would put a used relay on before a new one. It's all made in china garbage.

check for the trigger on the relay (not sure if its power or ground) with the truck off... then glow plug it and see if the triggers cuts off... if it does but the relay stays ON... suspect relay... if the trigger stays on... look at other things, GP card, temp sensor, etc.

Pretty much you want to see if the relay is sticking or if something is commanding it to stay on.

Resistor is just a wire... it does nothing but pass power...

I mean I guess you could have a short too maybe... make sure your power wire is not grounding out anywhere but as soon as the plugs shut off that resistor is doing nothing.

I mean... I am not sure if it can fail where it draws current... it would need a ground to complete the circuit...

So I know this might be a stupid question, although I'm sure most of what I ask here is lol, but how do I go about checking the voltage/output at the relay? I have a cheapo multimeter with needle prongs. I know the positive should go to whatever I'm testing, so the large post to check for voltage from resistor, but then I ground the other end where? I tried the plate area where the relay mounts but I'm not getting a reading.


Also starting the truck a few times, it seems like the relay will open again...but much later than it used to and with a very weak "thud" voltage jumps up and no smoking resistor. Starting it again the relay remained closed and obviously the resistor got hot after a while until I shut off the truck. So I'll figure out how to test the relay and rule it as the issue or not.

I do hear the relay close every time I turn the key to run, and it opens after shutting it off, so something is keeping it closed after startup...the controller card is new from antennaclimber.

If you want to check for voltage... red to power black to *ground* battery negative is likely the best location as you know its a good ground...

I mean it sounds like you got the issue... for some reason the relay is staying closed...

New anything means nothing... never assume new = good.

To test the relay all you need to do is test the *small* wires... Again off the top of my head I don't know if this is a negative or positive trigger system, I am sure someone will post it (or I mean you could figure it out with meter but I would wait as you seem to not be very well versed with the DMM) lets assume positive for this example so you would check for power on the terminal... then once the plugs should shut off you should see no more power on the terminal. If this happens BUT the relay stays on... bad relay. If the power stays on... something else is wrong...

Those resistors are another set of 8 glow plugs... its alot of juice they are burning off... the bigger issue too is, your plugs are getting beat the **** too as they are running way too long. I hope you have self limiting plugs in.

Ok...slowly learning...thanks for all the patience. The plugs are the AC60g which if I'm not mistaken are self limiting.

So I was able to test voltages and these were the numbers I got:

At bus terminal for gp resistor: 24.6v
At gp relay post from resistor wire when key in 'off: 24.6
At gp relay orange wire on post: 0.00

With key in run:
At gp relay post from resistor: 12.2v
At gp relay orange wire post: 12.1v

Gp relay small post pink/black wire: 10.5
Small post light blue wire: .8v

So a few concerns after looming through the TM, the pink/black wire should show 12v
And the resistance between the pink/black wire and light blue wire should be 6-10 ohms. (If I tested correctly I put both ends of the multimeter one on each of the posts to the pink and blue wires) my reading was 18.8 ohms, way more resistance.

So, and again, I don't know much, but based on this the resistor appears to be working properly, and something else is afoot.

Well, problem persists but I might be narrowing it down...

I took a look at the gp controller from antennaclimber while the truck was warming the plugs and after startup. All led lights are on and yellow goes out appropriately after wait light goes out. Red light, which indicates a closed relay remains on even after startup.

I disconnected the small blue wire at the relay and had the key on "RUN" while manually grounding the relay, it opened and closed appropriately, indicating to me that it functions properly.

Then I disconnected all the glow plug wires and tried again, keeping an eye on the controller card. The relay goes on and off continuously, which I believe is appropriate when the system doesn't get voltage from the gp' s. During this constant on and off, the red light on the card would turn on and off in sync with the relay, showing that it's able to send proper signals to the relay......so...whats telling my card to keep the relay closed?

I replaced the temp sensor on the drivers side head about a month ago, but how do I test it or the connector for function? What else could be telling the card to hold the relay?

Did you replace the connector for the temp sensor? I replaced that same temp sensor and the connector as the new sensor is different. The connector wiring on my old connector was corroded d/t torn wiring insulator.

From what you described, the card is functioning normally. With the glow plugs disconnected you have reduced the load on the system. The controller is getting a higher than normal voltage input (orange wire) and is cycling the relay to protect the glow plugs.

The relay will stay closed for a little while after the engine is running, this time is based on the resistance of the temp sensor and the voltage to the glow plugs.

Well sounds like it may be that old temp sensor connector then. I only replaced the actual sensor, the connector isn't in great shape but it's also not terrible. I'll try to replace it. Anyone know of a replacement switch part number that will fit the original sensor? If I change to the new style I'll have to replace both.


Edit: on second thought it seems autozone sells the new style sensor with connector in one package.

Twigiestdrip said:

Well sounds like it may be that old temp sensor connector then. I only replaced the actual sensor, the connector isn't in great shape but it's also not terrible. I'll try to replace it. Anyone know of a replacement switch part number that will fit the original sensor? If I change to the new style I'll have to replace both.


Edit: on second thought it seems autozone sells the new style sensor with connector in one package.

Click to expand...

if you want to use old style sender the napa part number is ts 4032.

No one here can diag anything worth a ****... don't just replace crap non stop, atm sorry I can't look up what you should be seeing but what you want to do is test the temp sensor wire as close to the GP card as you can... it will likely be a resistance value that corresponds to a temperature. Not sure if unplugged would result in no glow, if someone can confirm unplugging should result in no glow you can try that (easy free) and see what happens... Or just keep replacing stuff...

Remember what you replaced may not be good either... so with out testing your just making things harder everyone here is just like "replace this replace that"....

Fair enough.

The tm says the yellow wire at the gp card should measure 800 ohms, I'll try to test it from somewhere, but what am I looking for? Less resistance as the gps heat yes?

On a side note....i just realised that the original sensor I put in had fricking red thread lock on it and I didn't think about it....if i end up replacing it, am I safe to just torch that hole thing to get it off? Anyone removed one like that?

You should be fine to remove it with out heat.

Resistance is not going to change, the water is not going to warm...

The resistance is a temp I would assume seeing as the GP have a variation in time.

Quick google while waiting... https://www.steelsoldiers.com/showthread.php?45857-glow-plug-temperature-switch/page3

On that page a link is posted to a resistance vs temp chart...

so the short is... both of those numbers are temps... I would do this engine cold (so your in FL thats like what 100f lol...) so engine cold overnight, see what you get you should be ballpark what 60-80f?

So what like 3000 omhs?

If its like 10,000,000 we got issues... you can test this at the sensor... then you can test it at the wire in the cab... should be pretty much the same.... (3000 at sensor 3200 in cab fine)

This will tell you one if the sensor is working and 2... if the correct temp (remember F is for humans... and ohms is for the cucv same thing) if the wiring is good between the sensor and GP card.


Can't tell you what pin on the card or anything else as I lack the time atm. Maybe someone else will chime in but it gives you a start.