OK guys, the season is here, the trucks have been running good all year and now as the temperature is begining to drop our 7.3's are acting grumpy. I want to take you through some steps (easiest and least expensive to the worst) These are things we see every year at our shop.
General Info: I was once guilty of this and have had to fight hard to move my focus and start thinking beyond so listen up and I will hopefully save some of you some headaches:
"Your glow plug system has ALOT LESS to do with cold weather starting than you think it does!"
The idea that glow plugs are essential to starting understandably carries over from the preceeding IDI models where is was in fact critical, however, with the powerstroke the injection timing is more precise and the fuel is better atomized due to much higher pressures. If you have a hard start cold condition, more often than not it is a tired injector issue and not your glow plug system<--- that being said the glow plugs (although not essential) do assist in cold weather starting so here are the stepd that I will go through when we get a truck in for this complaint:
1: glow plug relay (commonly mis-stated as a solenoid but this is in fact a relay) the two small wires are pointless to test unless you are diagnosing a PCM issue as they are not a simple ground vs. switched hot scenario... one of these is key-on hot and the other is grounded via the PCM. In very rare cases the PCM will fail for this circuit but like I said... rarely.
Working with the large terminals, take a test light and ground the clip to the negative of the battery and probe the booted side of the terminals, this should be 12v. Now clip the clamp side of the test light to the other large terminal and stab the handle end into the negative post of the battery (make sure its a good connection) jump in the truck and turn the key to the run position, the test light should illuminate (special note: the ambiant air temp needs to be cold enough generally for the PCM to activate the relay, if this test fails, unplug the Oil Temp Sensor and repeat the test) in addition to the test light you may want to feel the relay and insure a mechanical "click" takes place. If either of these tests fail, replace the relay (replace with the apropriate relay, a common ford starter relay WILL NOT work the same)
2: Make yourself a test lead of some kind that has an alligator clip on one end of about 4' of medium guage wire and a semi-rigid "probe" or "poker" on the other end. Clip the alligator to the positive terminal of the battery. Disconnect the UVCH connectors and brush the probe against the 4 outermost tabs (these are the larger terminals, two on each end). You should get a very slight spark or light blue arc, this indicates a good glow plug. In most cases a bad glow plig will present with no spark at all, in rare cases a larger arc may occur but this also indicates a shorted plug.
If all but two or three of your glow plugs test good (assuming the relay test passed) you may have injector issues.
3: This is going to be the removal of the valve covers and inspecting connections but be sure to do step #4 before this (this is #3 because it is cheaper than #4)
4: Obtain a scan tool!, at this point you will need to do an injector buzz test when the engine is cold, in most cases the bad injectors will present with a "lazy" or "tired" buzz. Its time to pull them and have them tested and replaced as needed.
From experience, if you have a hard start cold and when it starts the engine "lopes" and/or "chugs" for a bit after starting, glow plugs WILL NOT fix this issue, you have injector problems. The good news is you can limp it by, you will just have to get up a little earlier and let the truck warm up before it will go anywhere.
Final Note: I am from Michigan and these are conditions typical to this and similar climates. If you are from Juno, Alaska install 4 additional batteries- leave the truck plugged in and underground out of the wind and start a fire under the engine 1 hour before cranking. Better yet just leave it running ALL the time and wire the PTO driven generator to your house
A little humor there but the info above is apropriate for the northern/lower 48 on most days of the year, I do agree that a truck sitting outside in single digit temps and below can really benefit from a proper working glow plug system but not as much as plugging her in.
In closing: while using a block heater in combination with good injectors, the ONLY thing your glow plug system does is reduce smoke during start-up. All of this has been laid out to help some of you look beyond the glow plugs for hard starting as I was once so guilty of myself. Remember, all the dodge guys like to delete their grid heaters and they dont have plugs at all to begin with, lots of them running around here with no cold start issues all year.
Thanks for reading and hope it helps!