Testing Glow Plug Module

[tim292stro]

Start with a resistance check before pulling them.

 

[wisconsinz]

Okay, it went back to 24 volts. Didn't have to give it a whack either. Maybe I metered wrong the first time.

 

[MarcusOReallyus]

That's easy to do, and it can really confuse a fella!

BTDT.

 

[wisconsinz]

Alright, so I don't really know where to go from here, so I plan on doing the resistor bypass to the front battery with a 120 amp mega fuse, and 8 ga wire (cuz why not right?). Then I'll give it another multimeter test. Anyone have any opinions about my temp switch not having the optimal 800 ohms of resistance?

Like I said at the beginning, my issue is mainly that it takes forever to crank over usually, even in 50 degree F weather. The colder it is the more gurgly the relay sounds...or like it stutters rather than quickly switches back to "resting/off." And if I do this too many times, my batteries die and I'm screwed. When it does start cold like this it always puffs white smoke. I had the batteries replaced last winter, but it's always been risky to let it sit unplugged when it's below 20 degrees F (I added the freeze plug).

Thanks for reading. And all the info I've gained.

 

[tim292stro]

Just because it measured out fine once doesn't mean it's not the problem. The relay can just be sticky - which is even more annoying to trace.

It shouldn't take forever to crank. White smoke at cranking is usually cold unburned diesel (and usually accompanied with the heavy diesel smell). Let's take it all the way back to the basics.

A diesel engine is a compression ignition engine. When the cylinder compresses the air volume inside it, the temperature increases. GM 6.2L/6.5L diesels are so called precombustion chamber diesels - the glow plug is meant to heat up this little metal cup (aka a "pre-cup") in the cylinder head, and precup keeps enough heat from combustion to assist in the future combustion events as the cylinder heat retention in an indirect combustion diesel is not very high. What you need then for combustion in a 6.2/6.5 is: fuel, pre-cup heat, and good compression.

You can do the 12V/resistor-bypass if that's your please while doing these checks.

1. Load test your batteries. Even brand new batteries have been shown to fail within 6 months. In consumer products this is called infant mortality.
2. Remove and clean your battery terminals (both the top of the battery and the ends of the wires), reattach and clamp to spec.
3. Check your engine ground strap to the chassis and the one from the chassis to the battery, make sure the connections are clean and tight.
4. Makes sure your batteries are fully charged. Short trips to the store (less than 30 minutes) are not enough to recover the battery charge, and if it sits for more than a month it needs to have the batteries pulled and charged before the next use. At rest your charged 24V system should read about 25.4V from the low-battery "-" ground to the high-battery "+". Below that and you'll have cranking issues.
5. Do a resistance reading from all 8 glow plug tabs to the engine block. Anything over 1.5Ohms on each individual glow plug means bad. If you have replaced glow plugs with self regulating (like AC60G), you really should do the resistor bypass as they are generally incompatible with the ballast resistor setup on CUCVs (as they get hot the resistance goes up and the voltage can become unbalanced popping a cooler glow plug with higher voltage).
6. Reconnect the glow plugs, all 8 connections should be clean and tight.
7. With the engine cold, pull the GP card, turn the key to run, and measure the voltage on the pink/black wire to the GP relay (one of the little wires) to ground.
   • Pink/black terminal of the GP relay should measure at the same voltage as the 12V battery.
   • Remove the green wire from the fuel shutoff solenoid on the injection pump - there should be a substantial "click". Reconnect it and there should be another substantial "click"
   • If the above two bullet tests true, short the light-blue wire terminal of the GP relay to ground for the time specified below (there should be a good "clunk" when you do this):
     • Ambient temperature <32F = 35 seconds
     • Ambient temperature 32F to 50F = 25 seconds
     • Ambient temperature >50F = 20 seconds
   • Once the above time has elapsed, quickly jump in the cab, press the accelerator to halfway and turn the key to start until running or for 10 seconds.
   • Watch the fan through the hood as you crank, if the engine spins the fan fast enough that the blades are a blur, it probably spinning fast enough to reach ignition temperatures in the cylinders - if you can still very clearly see the blades and it sounds like the starter is struggling, your starter may be shot. (>=300RPM crank speed is REQUIRED for a start in all temperatures)
   • If it doesn't start at this point, you may have air in your fuel system (bad fuel lines - just happened to me recently!!!), or you may have bad compression (need to pull the glow plugs and use a compression/leak-down tester).

I have started my M1009 recently on 4 bad glow plugs with less than 10 seconds of cranking at 40F ambient. Once I replaced the Glow Plugs and repaired the GP harness that had corroded GP terminals, the truck will fire in 1 second or less of cranking at 36F (which happened the week after I replaced the plugs). I also had 30 year old fuel return lines start popping off during the week after I did the plugs, the rubber lines just started disintegrating... Once I had those fixed at my mechanic's (I didn't have the time, but I do now - ha!), the Blazer will now start with the slightest touch of the key when cold.

 

[MarcusOReallyus]

Let's take it all the way back to the basics.

Whenever you get to the "Now I've confused myself!" stage, this is what you need to do. Wipe the mental slate clean, start over, and go from the basics.


That gives you the maximum opportunity to smack yourself when you figure out what you missed the first time around.

 

[wisconsinz]

With the engine cold, pull the GP card, turn the key to run, and measure the voltage on the pink/black wire to the GP relay (one of the little wires) to ground.

• Pink/black terminal of the GP relay should measure at the same voltage as the 12V battery.
• Remove the green wire from the fuel shutoff solenoid on the injection pump - there should be a substantial "click". Reconnect it and there should be another substantial "click"
• If the above two bullet tests true, short the light-blue wire terminal of the GP relay to ground for the time specified below (there should be a good "clunk" when you do this):
  • Ambient temperature <32F = 35 seconds
  • Ambient temperature 32F to 50F = 25 seconds
  • Ambient temperature >50F = 20 seconds

So the pink/black wire is getting 11.98 volts. Batteries together measured 24.5 and alone they were good. Don't have a min/max feature on my meter, and I haven't had a chance to bring them in. Was I supposed to take the green wire off the injector while the pink/black wire was grounded or just with the card out? I did both with the ignition on "run", but I heard no click. I could hear the pump working, but no click. Am I doing this right? I also noticed that the engine ground wire (i'm guessing that's what it is?) was melted, but mainly intact. I replaced that wire with the proper gauge and cleaned the terminals (also cleaned all the other terminals/grounds you suggested). If you look at this picture you can see how it slightly melted one side of the harness/plug that connects to the fuel filter. I inspected it and it doesn't look like the wires are separated inside. Either way, no click and not quite 12 volts.

 

[tim292stro]

That voltage is low, both the pink/back wire and the battery voltages. A dead 12V lead acid battery reads around 11.85V - under very light loads, the battery should not drop below 12.25V, only with cranking is it allowed to drop down to 9.6V. If the indicator lights and a fer solenoids are enough to take your battery down to <12V you need a new battery.

Whoa - ground the light blue wire of the GP relay, not the pink/black - grounding the light blue wire emulates what the glow plug card does internally, grounding the pink-black wire is how you blow fuses (that's your +12V ignition circuit, we don't want to ground that)...

Ahh, andI see a color-code error in my last post regarding the fuel cut-off solenoid: that wire is pink!!!

The green wire goes to two different places on the Injection pump:

1. The high-idle solenoid
2. The timing advance solenoid

The two solenoids powered by the green wire are for starting a cold engine. The timing advance injects the fuel into the hot/warm cylinder earlier in the cycle so that the fuel has a longer burn time in the engine, the high-idle solenoid on the throttle body will not click, and it won't pull the throttle up, that's why the pedal needs to be pushed in half way (just enough strength to hold it high).


[EDIT:] I will also comment that the ground strap, or whatever that black wire you took a picture of, looks like it overheated as the insulation appears to have caught fire. Just from what I can see in the picture it also looks like it cut through a bundle of wires right there - maybe it's the camera angle, but that's the main harness to the engine from the looks of it... [/EDIT]

 

[wisconsinz]

Sorry, I didn't mean that I "grounded" the pink/black wire...I meant I had the positive of my meter on the pink/black and the black of my meter to a ground. Is there a way I could be frying these batteries so soon? Lately my gen 2 light comes on and off as I let of the gas, but tightening the belts usually fixes that. I rebuilt the alternators with a kit 2 years ago, but maybe I should test them to see if they could be overcharging or something?

 

[MarcusOReallyus]

Stick with the basics. One step at a time. I know it gets frustrating, and it's tempting to jump to something else, but that will get even more frustrating.


BTDT!

 

[tim292stro]

...Is there a way I could be frying these batteries so soon?

Cold (slower chemical reaction, freezing damage), sitting (self discharging), over-charging (water boil-off), undercharging (sulfation), dirt corrosion on the terminals... There's a huge list of ways to kill a battery or significantly shorten its life.

...Lately my gen 2 light comes on and off as I let of the gas, but tightening the belts usually fixes that. I rebuilt the alternators with a kit 2 years ago, but maybe I should test them to see if they could be overcharging or something?

That, plus the GP relay chatter you described in post #24, is sounding like a bad chassis ground.

I know that if you're working outside, and that the weather for looking at this stuff is terrible right now. Just checked, and it's 33°F (0.5°C) and expected to snow in the evening and the windchill takes the temperature below freezing. My dad grew up in Fargo, so I'm familiar with that particular brand of cold.

With that in mind, start a pot of coffee, tea, or hot chocolate (whichever is your preference), go out and pull both the batteries and bring them into the Garage for a 12-hour/overnight charge (each if you only have one charger). Then have a nice warm beverage. While the batteries are out, you can trace the ground circuits and make sure they are good. One way or another, you're going to need to diagnose and deal with that very ugly looking black wire you pictured in post #27. It appears to be a ground to the firewall, and may be a ground passed through the firewall to the dashboard and instrument cluster (you'll need to check and see if there is another wire on the inside).

Can you reply with the resistance values for the Glow Plugs?

Load test the batteries the next day (either take them to get done or use a battery tester yourself). This means that a high current load needs to be applied to the battery(ies). A battery tester simulates a starter being run from the battery. The voltmeter on the battery tester shows what the voltage is while the load is applied, if it drops below the "OK"region of the voltmeter for your battery's CCA rating, then the battery is shot.
https://www.youtube.com/watch?v=izSi29V5O2A

 

[wisconsinz]

The glow plugs all read around 1.2 ohms. That fried black wire was screwed into the firewall and connected to a bolt on the engine where another 4 or 6 gauge negative wire coming from the terminal board was also connected. I'm not sure where the engine ground wire is, but I was hoping that was it. Can anyone tell me?

I'll just fill my thermos with a hot toddy...that'll motivate me to get out there.

 

[tim292stro]

Check this thread (it's also in the TM).

 

[wisconsinz]

Alright...

Charged both batteries and took them in. Turns out they're both good. One rated at 800 CCA measured 898 CCA, 13.01 volts at 61 degrees. The other, rated at 850 CCA, measured 1136 CCA, 13.75 volts at 71 degrees.

Got 12.2 volts at my pink/black wire, and also heard the IP click after plugging/unplugging pink wire. Jumped the light blue wire and waited for 25 sec (47 degrees out) and she fired up immediately (cold). Fan was a blur, by the way. I tested the alternators and the right measured 30.2 volts (TM says it can't be over 31. and the left measured 14.2 volts (TM says it can't be over 16).

BUT, when I plugged the card back in, I waited for about the same time (relay clicked about that time) and cranked it, but it still took forever. Had to cycle the GPs a few more times before it started. Does this mean its the card?

 

[Chevybrit]

A cliff hanger of a thread ending .................. WHAT HAPPENED????????