So our 7.3 with roughly 330,000 on it will not start below 40 unless it’s plugged in for about an hr. I have changed the gp relay as it was bad. Tested the gp and found they all are good except 1. And just changed the map sensor as I had a low turbo boost code which is now gone. What should I go for next? Batteries are in good shape and always plugged into a maintainer. Thanks

 

Did you get the relay from Ford or the corner store??? Never get parts from the corner store for these engines. Batteries maybe the exception. The internet is even more dangerous to our engines and pocket, with very few exceptions.
Did you prove you are moving current to the glow plugs?
Also your truck should not need the glow plugs online at 40 degrees to start easily, colder maybe.
You may have tired injectors. The block heater is a clue. If you are not using 5W-40 try that and if it starts easier that is another indication of tired injectors.
How are you proving your batteries are in good shape? A voltage meeter showing 12.6 or more after several hours sitting and disconnected is a basic check but not the entire story. Take them to your local truck stop not the corner store and have them put them on the big inductive and resistive load tester, not the hand held corner store junk.
Have you checked your primary cables and proved they are tight, clean, and absolutely no damage or corrosion anywhere?
Are you spinning clean and fast on key turn? You need if I remember correctly more than 150 rpm to fire the engine, a slow crank to that speed is not good.

 

[QUOTE=Jimmy's Pilot Service;20797116]Did you get the relay from Ford or the corner store??? It’s from rock auto and a motorcraft.

Did you prove you are moving current to the glow plugs? Checked the harness and it showed power.

How are you proving your batteries are in good shape? Batts are a year old and we’re checked by a mechanic friend of mine thsy has a large load tester.
Have you checked your primary cables and proved they are tight, clean, and absolutely no damage or corrosion anywhere? Cables are newer and look clean.
Are you spinning clean and fast on key turn? You need if I remember correctly more than 150 rpm to fire the engine, a slow crank to that speed is not good. Will have to check this


Thanks for the reply

 

Cranked it over tonight after it’s been plugged in for about an hour it fires after the 3-4 crank.

 

Is there a way to test injectors?

 

What else’s should I check on?