I know the glow plug relay issue is posted all over the forum, I couldn't find my exact issue so wanted to post it out there, maybe I am missing something. So a couple days ago we had a real Florida winter day, (low 40's) went to start the truck didn't start, I was in a rush and did the unthinkable I know.. a small shot of ether.. anyway that got it going, so when I got home I let the truck cool over night and went to test the relay. I have power to the battery feed 12.5V. Now when the ignition is turned on, I can hear and feel the relay click over, but still read 0V on the output terminal to the glow plugs. So that has me confused if the relay is switching why would I still be reading 0V?? When I put the key on and the meter on the key on control lead I do get 12V but then drops off. Any thoughts I just don't want to just throw parts at it without knowing whats going on. (For ground on the my meter I am using the negative term of the battery so I know I have a good ground) Thanks in advance!

 

I've seen them click & not have power to the output post, when that happened I cut one apart & sure enough there was carbon everywhere & was no way there was contact being made to the output post.

 

Relay can close but still be bad. The coil portion is working but the contacts that send the batt voltage to the glow plugs could be pitted, burned, or broken. If it's closing but no voltage to the glow plug side you have narrowed it down to a bad relay.

 

That makes sense, thanks for the input will get a new relay.

 

In response to jtak's comment about throwing unneeded parts at the truck, I understand his reluctance. However, there are certain parts which get abused by frequent use and will fail and possibly cause a no-start.
I highly recommend replacing the glow plug relay or module if it has a lot of miles on it. High amperage circuits cause a little bit of damage to the silver contacts every time they are used. If you consider parts like this as a replaceable device much like an oil filter, only with much longer change interval, you will be less likely to be sitting somewhere with a dead motor in the middle of winter. At a certain temp, no glow plugs, no start.
Larry

 

Yeah I agree with you, I just wanted some reassurance on this since I thought it was odd that the relay would close but not carry voltage across, .. I ordered the Relay today on Rock Auto so will put in as soon as it arrives... although its back in the high 70's here our winter day is over. But will test it out and measure the voltage across with the new relay once installed.
Thanks

 

Agreed with all the above. A relay can still "click" and still be bad. No power going out to gp's is a big sign of a faulty relay. However, things to consider. If you are getting power leaving the relay and just not long enough, you need to check further. Your PCM sends a signal to the relay telling it how long to send power to thr gp's based upon readings of the EOT and AIT. If you ever notice the WTS light does off faster after the vehicle has been driven versus after sitting it's because the EOT is higher and thus your relay does not need to activate the GP's as long. So if you are getting power leaving the relay but it's closing within a few seconds and your vehicle isn't starting, you could possibly have a separate issue. The 12volts going to the glow plugs should remain on even after the vehicle starts. The WTS light going off doesn't mean 12volts is no longer going to the gp's.

 

^^^^ this was my problem. Ended up running a ground wire to a switch, to control gpr function manually

 

over tighten the large studs can make them turn internally and make small contact point which will burn out quickly, just like the old starter firewall solenoids do

 

One common indication of the contacts starting to fail is the studs actually change color from excess heat. If either of the studs is dark in color, buy a new relay.

 

Got the relay last night, now I am getting a voltage across but only 11.3V, I'm getting 12.4V to the relay, that seems like a big voltage drop, any thoughts on that?
Thanks

 

that's a big drop


cycle the GPS a few times and see if it improves, if not then get another relay

 

Have you heard of White-Rodgers 586-902 Heavy Duty Monster Glow Plug Relay ?

Not sure if it will solve your problem but...

BBD

 

That's not a large Voltage drop....1.1 Volt? Load drop.....

 

That's more than I would like to see across the contacts for a new relay. To the OP, please clarify. Is that the voltage drop across the contacts, or the voltage drop when the glow plugs energize? Did you measure voltage at each large terminal while the glow plugs were energized and the difference between was 1.1 volts?