i have a 94 f-250 p/s. it is hard to start. i changed the gpr. still hard to start. if i plug it in overnite , it will start right up w/ o hitting the glow plugs. ???????

 

how far does you volt gauge pull down? It should pull down to the white line on the left or so when you first turn the key on. Listen to hear if you can hear the relay click when you turn key on. I think there is another relay on the passenger fender that feeds the gpr that could be causing priblems. How old are your glow plugs they are prob bad. You can check them by unpluging valve cover harness and checking ohms. I dont remember the values. SOme one else will chime in soon

 

i dont hear any click at all when i turn the key on or hit the glow plugs. if i were to take the glow plugs out and check them for the price would it be better to just replace them?

 

It may be the Glow plug relay (GPR), it's not unusual. They last about 2 years.
Next cold start cross out the 2 large terminals on top of the GPR for 30-45 seconds.
If it starts right up the GPR is bad.

 

i just replaced the gpr.

 

You may have gotten a bad relay right out of the box ? seen that before

x2 what cuda said about crossing the two big posts on the relay with a big screwdriver

It could also be a grounding issue

 

Ok, I will add a little bit. You do not need to remove your glowplugs to test them. All you are looking for is suitable resistance. You do not even have to remove the valve covers to test your glow plugs because you can test resistance through the UVC (under valve cover) harness.

The best way to do this is as follows:
To test your Glow plugs using the UVC harness conection, first you must locate the connecters, carefully remove the connecter by pushing in on the latch and prying the connector apart (be carefully these are easier to break, they are even often brittle from wear and heat, the UVC harness may even need to be replaced). The glow plug wires are either the outside most pins on each of the 4 UVC harness plugs (2 per plug for a total of 8 wires). Or if you have a 99 and newer it will be the two outside most pins on each end of each of the 9 pin connectors ( 4 on each plug for a total of 8).

Get out your multimeter and set it to resistance (ohms) , using a straight pin and the positive lead of the multitester, (with the negative lead attached to a good engine ground) test the resistance across these glow plug pins mentioned above. Each of these pins should show a resistance reading between 0.6 and 2.0 ohms. If any one of them show a valve that is beyond this, either very low or all zeros (0.000) then it is bad and needs to be replaced.

If there are any typing mistakes in this I apologize but hopefully this will help you diagnose the glow plug problem a little more easily.

 

So is the engine warm or cold when it won't start? You said it starts hard but first thing in the morning it starts fine. That leads me to believe you have a warm/hot restart issue. Is that true? If so you may need IPR (injector Pressure Regulator) o-rings.

 

Not to hijack this thread, but I took a volt meter and one side of the GPR was 12.7 the other was 0 with the ignition off. I turned the ignition on, ran out and checked again. one side was 11.5(hot all the time side), the other side was 10.9. Does this mean the GPR is working properly?

 

Not necessarily. The GPR can show battery power on both sides but it may not be carrying the load to the GP's. Shorting out the 2 big terminals is a better test, low tech but works.

 

Disregard my warm start comments I now see that it starts fine in the morning after its plugged in. You have a GP issue

 

thanks fellas, i replaced the gpr. it starts perfectly everytime.