Glow plug problems

[540milotalon]

This is a friends truck, ‘85(?) I think, definitely a 6.9 but the truck has a 1992-1997 front clip. She sounds good when running but had some serious air leaks. My buddy didn’t have time to work on it, I was getting over a surgery so he got this “young guy” to work on it. He replaced the low pressure hoses, caps and I imagine the “o” rings, and the glow plugs.

If it sits very long, you have to bleed the air still, the young guy installed a check valve in both the fuel side and the return side but forgot to tighten one hose clamp and siphon she did. I could NOT get it to start, checked glow plug relay (GPR) and with test light it cycled on/off.

I checked glow plugs with test light, as I have always done so, and they didn’t light up. I removed one and read it with an DVM, no good and showed my carpenter buddy how to test the glow plug with a jumper cable. Would not get warm, all 8 bad.

He said the young guy changed them, he changed them himself once a while back. This truck has not driven over 20 miles, multiple start attempts but has fried the original set he purchased the truck with, the set he replaced,
the set the “young guy” replaced and now there are 8 that test bad.
Other than reading for even a trickle of battery voltage feeding through the GPR, what else is there to consider?

Thanks for looking, any thoughts greatly appreciated!

 

[Big Bart]

Some thoughts.

If he is burning up 8 glow plugs in say 20 miles or even 2 months then likely his glow plug relay keeps coming on after he starts or sticks on at times. Leaving the glow plugs on would burn them all up in short order.

It could be cheap imitation Chinese glow plug parts but not likely all 8 would dies that fast.

Less likely but possible, he has a voltage drop on the positive side of the gp relay, causing high resistance and causing them to burn up prematurely.

It might be the glow plug timer is turning on and off when driving. It could be the glow plug relay is sticking on at times. He can replace both and the glow plugs and that would likely fix it. Your testing suggests right now the relay is cycling on and going off. So likely a intermittent issue.

He could also could replace the glow plugs with Motorcraft ones and rig a light in the cab to light when the glow plugs get power. Then see if they stick on. They probably do so he would likely replace the timer or relay anyhow. If he does both with the glow plugs he eliminates the most likely issues.

 

[CDX825]

The glow plug controller for the 6.9 was known for sticking on and burning up glow plugs. Thats why a lot of guys including myself wired them to a push button.

Also if no one has mentioned it stick with motorcraft glow plugs only. Stay far away from autolite glow plugs!

If you are wanting to start the truck and the glow plug system is no operating you can plug in the block heater for an hour or so and it should start if everything else is good.