Hey everyone. I purchased a gpr 109 to replace the glow plug relay. What is the large relay/solenoid next to it. It's an 03 7.3psd truck. Is that part of the glow plug circuit?

 

It might be the AIH (air intake heater) relay, it its very similar to the GPR.

 

Is there only one relay for the glow plugs on an 03? Will this relay bieng bad cause it to start hard? When should it be energized? Appreciate any help.

 

Only 1 glow plug relay that I know of.
I think the gpr stays energized for up to 2 minutes from when you turn the key on.
Yes a bad gpr will cause it to be very hard to start perticularly when cold.

 

That other relay is the Air Intake Heater relay. Makes a good emergency glow plug relay in a pinch. Yes, faulty relay will result in hard starting. Is it smoking and/or romping? When energized, both large terminals should show the same voltage to ground. If not it is faulty.