So this is my first diesel and I'm not sure the glow plugs are cycling correctly. The wait to start light stays on for about 10 seconds first thing then after that I hear clicking and see the voltmeter flopping around, this should be the "after-glow" right? The truck is hard to start and I was wondering if there's a way to troubleshoot the "after-glow"? The hard start might not even be glow plug related because the truck has almost 200k miles and I think it still has the original injectors.

A buddy of mine replaced the glow plugs with motocraft ones shortly after I bought the truck.

 

If you have new Motorcraft/Beru gp's you may want to troubleshoot the controller then. The easiest way would be to remove white wire from the controller and run a temporary switch from that terminal to ground.
It was discussed quite a few times how to run a push button gp switch. If she will start you will have a choice, either leave it like this or replace the controller.

 

It shouldn't be flopping around, just steady reading a little lower than normal.

 

​​​​​​That's what I thought. It's fine until the WTS light goes off. Any idea what to start troubleshooting?

EDIT: Sorry, I missed your previous post. I'll look into it thank you!

 

No "flopping" at any time, just below normal reading. How much below depends on how good your batteries are, as gs's draw almost 200 Amp.
Here is how to bypass the controller:
1. Disconnect white wire from controller's terminal and tape it.
2. Run a new wire from that terminal through a switch to a good ground.
3. Disconnect the connector on the wire running from the back on the controller (don't remember what color it is but there is just one wire with connector on it which goes to your wts light).
4. Temporary splice into that wire and connect to the same terminal where your white wire is and now the switch is connected to. This is to see wts light while you are holding your new gp switch.

And check all connectors on the whole circuit, pay specific attention to gp connectors. Clean and grease with dielectric grease.

If you run a temporary wire to the cab you will be more comfortable switching the plugs on, seeing wts light and cranking the motor.
Some people leave it like this for ever and are happy.

Now hold your switch for about 10 sec with ignition ON then crank the motor. It should start, or at least try to.

I wouldn't mess with injectors for now. I bought my truck with 220K miles on it and from what I can tell there are still original injectors and return lines/caps.
From what I know injectors just don't fail at once on these motors. They do degrade over time but don't fail just like that.
I did have faulty gp's though. WTS for 3 sec, then clicking and hard start even at 90*. Replaced the plugs and she starts and runs good.

 

the volt gauge varying is the controller turning the plugs on for a second or two to keep them warm, and it is supposed to do they.

before going crazy, put a test light on the output of the glow plug relay and see if it is actually sending power to the glow plugs when the wait to start light is on. you may have a bad glow plug relay.

 

x2 ^^^
Makes sense to check the relay before you start playing with controller. You need to have a good relay to run manual gp switch.

 

Honestly it's the stupid simple stuff that I usually miss, I figured since the light was on they must be working... I'll check that thank you!

 

Also, I've found that an old glow plug relay can build up corrosion on it's terminals inside, so when it's on, you are getting power through it... but not enough. I've seen 2V dropped just across the relay itself, which really messes with the heat being produced(i.e. 12V at the battery, 10V on the output of the relay) - If you put a voltmeter across the big terminals of the relay when it's on, you shouldn't see more than about 0.5V or hopefully less(because any voltage being shown here is wasted power).

 

Well I checked the voltage but I don't have a helper so by the time I got to the relay with the probe (I don't have clips, just those needle ends) it was clicking on and off but my digital voltmeter was popping up to 9 or so, idk if that's all it was getting or just couldn't keep up.

I'm strongly considering replacing the feed wires from the starter solenoid to the relay with some 4ga battery cable I have laying around. already has a fuse inline.

 

I personally don't see how this will help since you don't know how much voltage drop you have if any and where does it happen. Stock supply wire is just fine, you won't get noticeable voltage drop on this wire, rather on batteries themselves. Leave alone that the terminals on that #4 cable will be way to big.
Get a helper, even a kid can turn the key whenever you are ready to take the reading. And get alligator clip for ground, this will help significantly in getting accurate reading. If your wts light stays on for 10 sec as you said, you will have enough time to get the reading on both terminals (and you should), yellow wire from the battery and two wires on the terminal to gp's. At this time you need to know what is the difference on those two terminals if any. If there is a difference your relay needs to be replaced as there is probably a build up on it's terminals. If no difference the relay is fine. Doesn't matter what you see there, 9, 10, 11...you need to know the difference to determine if the relay is good.
After that you can think of how much lower it was comparing to normal 13V or so. If it drops below 10V on battery side of the controller you need to charge your batteries and check them under load. I usually charge at about 5% of battery CCA, meaning at 5 Amp for 1000 CCA battery. Slower but much better.
As soon as you have 100% charged and holding well under load batteries and working relay you will do the controller bypass if she will not fire by then.
And I prefer analog meter for purposes like that.
If you are not comfortable with splicing wires you can just leave wts light wire along as it is or simply disconnect it.

 

Well I will eventually be doing something to replace the power lead to the relay, the wiring just gets way too hot near the engine harness plug (it's already melted).

My brother in law was over earlier and we checked it. No drop across the relay but when the relay engages voltage drops to about 10v at the power in for the relay. I forgot to check voltage at the battery when this happens, I'll do that before long.

​​​My primary reason for the 4ga comment earlier is if there is extra resistance in the old wiring replacing it with new wire would remove the resistance and allow the glow plugs more power. I just happen to have the 4ga lying around and I'm not going to go out and buy 6ga just because 4ga is too big. I'm also not going to do what the factory did and run two 10ga wires when one 6ga (or 4ga) wire will do the same job and look cleaner anyway.

 

IF the connections are good and the wire isn't corroded. It /can/ easily produce a voltage drop as evidenced by melted connectors(voltage drop = resistance*current = heat)
Eh... #4 actually isn't that big(.203 thick copper). Connectors can be found in multiple hole sizes.

 

@mattnj

I apologize if my reply sounded harsh, I had a rough day and had misread both your comment and tone. I appreciate your help and don't mean to come across wrong.

 

Never mind, it didn't sound harsh to me.
You didn't mention melted wires/connectors before so I was assuming it's all good there.