Ok I have replaced my GPR 3 times this year. First of all can you test the GPR when truck is warm? Or does it need to be cold? Second of all are the small post supposed to read 8 volts. My truck is warm... 30 degrees today in Chitown. I was testing just to test because I have had cold weather start issues and the passenger side "live post" was 12.7 volts as well as the small post were 12ish volts. The drivers side post was nothing. Zero. But the truck was still very warm from driving. Now 2002 f250 4X4 Stroker. SCT Tuner. New batteries yesterday. Recent Buzz test good. Replaced ICP today. After I put the ICP it did not start. My fuel filter was old like 8,000 miles. Very dirty so I replaced it today. Replace GPR today with a brand new motocraft GPR and same reading as above mentioned. But remember the truck was still warm from an hour drive. New ford glow plugs by Heavy Metal Performance last year. Auto Enginuity said still good. . So the truck finally started after having it plugged in for well over an hour and some starting fluid. Please know the truck has sat for 2-3 weeks without driving. I will know in the morning whether or not the GPR is good. But a guy on a powerstroke forum said the small post should reed 8 volts and it has me nervous:-http://images.ford-trucks.com/forums/images/smilies2/mad0228.gifbanghead

 

I've never actually checked the voltage to the small terminals, only the voltage to the glow plugs, however the difficult start may have been do to air entering the high pressure oil system when you removed the ICP. Don't ever use starting fluid. It can be ignited at times and places that are not good, causing damage. Others that are more savy with electronics will chime in.

 

With the key on, one small post should read batt voltage. 12.5 or so anytime the key is on- engine warm or not. The pcm will ground the other small post to kick the relay in when it needs to based off of programming. Then the other large post will get voltage. It may not ground the relay after being driven an hr as eng temp and the other variables are higher than it calls for.

It is my understanding AE cannot test trucks with GPRs. That test is for CA trucks and EX's with GPCM instead of GPR. I may be wrong about that but fairly certain. How many miles are on the truck? It could be injectors if it has a lot. Changing to a different oil may help to ease that cold start a little if so.

 

165,000 well taken care of miles. Auot Enginuity and buzz test confirm injectors are fine. The truck cooled down and I am getting normal readings from the Volt Meter for the GPR now. When you say AE what does that mean Carlton Webb

 

THIS IS WHAT I SAW ONLINE FROM DIESEL BOMBERS...........Your relay's might not have necessarily been bad. When you tested your GPR's, did you only check to see if power was being transmitted between the two larger posts?

Because you should only see 12v constant at one big post (closest to the passenger fender), and with the key on you should see 12v at both. Now with the key on, you should see 8v at the smaller post (closest to the firewall) and 8v at the other small post.

Your "wait to start" light is a good indicator that your PCM is good and GPC (Glow Plug Controller) is working properly. How long does the "wait to start" light stay on before shutting off? It should stay on for a minimum of a couple seconds (like 5 or so if it's warm out) and shut off after say 20 or 30 seconds (depending on temperature). But in reality, your glow plugs are commanded on for a minimum of 10 seconds, and up to 2 minutes depending on outside temperature (the "Wait to Start" light does not stay on for the whole duration).

I went through this EXACT problem on my buddies 95', (I wasn't seeing 8v at the two smaller posts) it was the GPC harness from the GPC to the GPR

 

If you're getting voltage greater than 10.5 VDC on the drivers side Stud and a difference of less than .5 VDC drop your GPC is operating correctly under load.

The voltage at the pins is irrelevant providing there is enough to activate the solenoid. Corrosion, loose connections, and wire condition will adversely affect current flow and therefore not an acceptable technical reference.

If you're GPR passes the above, check the connections at the Valve Cover for loose, damaged, or missing pins.

A failure of the circuit on the load side should initiate a DTC

 

AE=autoenginuity

Here is the correct explanation of the entire glow plug system from an old thread. The WTS light is just a light. If it does not come on when cold , its an indicator that the pcm is not working but does not tell you if the glow plugs are actually working.

https://www.ford-trucks.com/forums/7...pr-system.html