Well after going to Napa, advanced auto, and finally oreilys, I bought a glow plug relay. Put it on about an hour ago, decided to try and start the truck, and it fired right up. At this point, I’m going to test the batteries individually, and see what I get. Now the real test will be to see how long this relay lasts.

 

I bought a NAPA GPR (GPR109, I think) a few years back and it had a 36,000, 3 year warranty on it. Still working fine.


I am glad that it is starting better. I busted my old GPR open to look at the insides and find out what was going on.... a lot of pitting and burned marks and bad contact points.

 

Just went out to do a little testing on the new relay. When I measured the battery voltage for both batteries, both read 12.63 volts. Odd compared to the other day, but I'm not complaining. When I went to test the glow plug relay, with key off, the post with power at all times read 12.63. With the key on, the post with power at all times read 11.8 volts and the post that gives power to the glow plugs also read 11.8 volts. Now while I'm happy that there is no drop between the posts, I'm wondering if this much drop with the key on vs key off is normal or do I have too much voltage drop?

 

I am assuming that your glow plugs are activating at key on with those numbers and you have less voltage drop than I do, you might want to ohm out your glow plugs to ensure that they are all good.

 

I don't have a problem with that voltage drop.

That is about what mine does. I also have about 5 ohms to ground from the switched terminal on the GPR (do NOT measure the resistance when the GPR is energized!). I think that is high, so I probably have some glow plug problems.

But the truck starts, so I'm not worrying about it this winter. It's too cold to work on something that isn't broken enough to notice.

 

Yeah I'm sure that glow plugs would also help as I'm pretty sure the plugs are original. Thanks for answering so quick guys, electrical problems of any kind have never been my favorite, but luckily glow plugs are pretty easy to diagnose. I'll probably ohm the glow plugs out this weekend and see what kinda numbers I get.

 

Get yourself a 12v voltage meter that you can plug into your 12v power port (cigarette power port)


This is what you should see on the 12v meter from inside the truck.


1) key off, truck not running... around 12.5v

2) key on, (wait to start) voltage should drop to around 11.5v. this shows you that the Glow Plugs are now on/hot. If the voltage does NOT go down, then the Glow Plugs are not on/hot... check GPR.


3) When 'wait to start' light goes out, try to start your truck...
Voltage should be above 10.5v, this drop in voltage is the Glow Plugs still on AND the Starter being engaged.

4) If the Voltage Drops Below 10.v.... Your truck will not start, as it needs to have at least 10v. to run.... If the voltage below 10v with Glow Plugs on and starter engaged..... check you batteries as being bad...

5) If/when the truck starts the voltage should go from 10.5v, back to 11.5v (starter not being used).... this shows that the Glow Plugs are still on. (GPR working)

6) when the GPR goes off and truck is running (GPR can stay on a minute longer than when the WTS light goes out), the Voltage will SLOWLY rise to the output of the Alternator. This voltage output show for the Alternator should be around 13.5v


This explanation shows your beginning bat voltage.
pull down (or not) when the GPR comes on.
Pull down when engaging starter.
Possible battery(s) condition.
Shows when the GPR goes 'off'.
Shows Alternator out put.


Any questions?

 

Nope, can’t say that I have any questions after that. Thanks for the write up, it answered any questions I had and then some.

 

Well I figured that I'd go ahead and include my test of the glow plugs themselves since this is a glow plug related thread after all. I grounded to the negative battery post, and tested each pin where the connector plugs into the valve cover. I started at the pin closest to the firewall and worked my way to the front. On the passenger side, I got .9 at the first pin, .9 at the second pin, 1.0 at the third pin, and no reading on the last pin (when I say no reading, the multimeter sits at a 1 all the way to the left on the screen and a decimal point all the way to the right when not hooked up to anything. This is what I got on the last pin, the screen never changed.) Again this is working from the pin closest to the firewall to the front.

Now on the drivers side, working from the pin closest to the firewall to the front again. I got no reading for the first pin, 2.5 for the second pin, 2.1 for the third pin, and 2.0 for the last pin furthest from the firewall. I was surprised at the difference in the numbers from the drivers side vs. passengers side. But considering I got no reading from two plugs and 2 plugs that were above 2.0 ohms, I'm just gonna replace them all. I'm fairly certain the plugs are the original ones, so they're overdue anyways.

I will post an update when I get plugs and install them.

 

Sounds like a solid plan. Remember to only get OEM/Motorcraft/Beru plugs.

 

Knock out the 50 cent mod while your in there, bust'n knuckles..😁