Well this past week when a cold front came through Houston I noticed it took a good 5-8 seconds for my truck to start. I let the glow plug light go off, start truck, only for it to turn over and over and over (seemed like forever), but eventually fired up after about 8 seconds. It happened more than once as well. So after the few times it happened I waited a bit more after the GP light went off. Go to start and it took less time. Probably 5 crank turns then it fired up. Truck only has 87k miles on it. Any ideas? I changed the fuel filter out my last oil change (5k miles ago). To add I did not have this problem this past winter.

 

How cold? Glow plugs will stay on up to 2 minutes, even after fuel pump and WTS light go off. Make sure your voltage is not dropping while glow plugs are running. If it is, could be your batteries. Glow plugs and/or glow plug relay (GPR) could be going bad. I would just give it 5 to 10 more seconds of warm up and see what happens.

 

It got down into the high 40s. Mainly 50s. Though this past winter it got down into the 20s. When I let it sit a bit longer after the light went off it started a lot faster than not waiting a few after the light went off. I will just let it sit a bit longer starting it now when it's cold out.

 

I would definitely check the GPR. When active, each of the big lugs should show the same voltage. If the switched lug has a lower voltage, it is worn out. Mine was dropping 6V!

If it is good, then move to checking the glow plugs. You really have pretty low miles for an '03, but it still has the years on it.

 

What voltage range is for a good relay and what is bad? From a quick YT search it seems I use the Digital Voltage Reader and place the positive on the left large cable (+ side of the relay) and ground out the negative on the meter? Also do I need to have the ignition into the "on" position when checking the GPR?

 

The youtube video does provide a shortcut measurement, but first I'll explain a longer test. It helps understand how the system works and helps understand what to expect overall.

When you turn the key on, the GPR turns on. The WTS light goes out in a few seconds, but the GPR remains active for up to two minutes.

If you measure battery voltage before turning the key on, you should see about 12.6 volts. When the GPR is active, the glow plugs draw a lot of power and your battery voltage will drop about a volt. Lets call it 11.7V for discussion.

So on the big "always hot" GPR lug measured to ground, 12.6 before key on and 11.7 with key on.

If the GPR is good, you should see 0V on the big switched lug before key on, and almost 11.7V with the key on.

Now lets assume the GPR is weak... It does not make a good solid connection between the two lugs. Mine dropped 6V but for discussion let's assume it drops 3V... So the always hot lug might read about 12V when the key is on, and the switched lug will read 9V. So there are two things going on here... The battery voltage did not drop as much as it should since the GPR is weak and the glow plugs are not drawing as much power as they should. And the other thing is the switched lug voltage does not match the always hot lug.

So now to the example in the youtube video measuring across the GPR... A good GPR will have a small drop, maybe a tenth or two. But in my example in the previous paragraph, the drop is 3V.

That 3V is enough to call the GPR bad, but lets now pretend you saw no drop when it is active... Does that mean the GPR is good? It could be, or the glow plugs may not be connected to it at all. That earlier test showing the 1V drop in battery power (12.6V dropping to 11.7V when the GPR is on) indicates the glow plugs (at least many of them) are drawing a lot of power.

So the shortcut test across the relay can confirm the relay is bad, but not that it is good. Hope this helps. There are some additional tests to look at the glow plugs, but I think the above is enough for the moment.

 

Thanks for the good write up. I will check this out later this evening to see how everything pans out.