2001 F350 7.3

Below 35 degrees, truck is hard to start. Cranks for a while, sputters, dies. Repeat a couple times, finally starts running rough, surging and loping for 10-15 seconds before it settles down and runs smoothly.

Recently had all glow plugs replaced. Next cold start didn't show much improvement (not as bad as sometimes, but wasn't very cold either).

Surfing here and other forums, I see suggestions about letting glow plugs heat longer after WTS light goes out. Some suggest as long as 60 seconds. In the past, I have tried waiting a little while longer after light goes out, or turning key off/on and letting it cycle again. But I've never really timed how long I was waiting.

We're having a warm spell right now, so I can't do much testing. But yesterday morning was about 30. I timed the WTS light and it went out after 10 seconds. I waited another 20 seconds.. about 30 seconds total. Starting seemed a little better than usual, and there was about 1 second of roughness before it settled down.

I need to do more cold weather testing to be sure, but it does seem like it might be better to wait longer than I have been.

On the other end of the scale, I saw a comment that glow plug cycle is dependent on oil temp, and they don't come on at all if oil temp is above 40. Is this correct? If so, is there any good reason to wait to start in warm weather? I'm usually pretty diligent about waiting for the light regardless of weather, but the truck doesn't seem to object if I get impatient and start it sooner in warm weather. If the glow plugs aren't even on, why wait?

Should I just totally ignore the light, and wait for some interval (or not at all) based on a semi-educated guess about how much glow plug time might be necessary for the current temp?

 

I think that oil temp is 140, not 40.

New glow plugs, what brand? Anything other than Motorcraft and it was a waste of time unfortunately.

Did you test the Glow Plug Relay? If voltage is being lost across the GPR, that will inhibit the GP's from working to their top efficiency.

 

Thanks. 140 makes more sense than 40. Can't remember where I read that, so I can't double-check to see if I mis-read it or it was a typo.

Not sure what the new glow plugs are. The shop receipt doesn't say. They did tell me that they would probably have to get them from a Ford dealer, but maybe NAPA would have them, so I'm hoping they got Ford/Motorcraft.

GPR should be good. I replaced that myself a couple of months ago. Old one seemed to be "working", but I did see some voltage drop. Not sure if it was a bad relay or just a normal drop from the plugs kicking in, but a new relay was easy and cheap so I did it.

 

I wouldn't call the WTS light "worthless", but it comes woefully short on being informative. Many people install the glow plug LED mod to know exatly what the glow plug relay is doing... and for how long.

GPs are active for up to two minutes, depending on the oil temp. Tune your radio, activate your OBDII gauges, situate your coffee, whatever it takes to make the wait time pass. I don't even load my stuff in the cab until I turn the key... then I use at least a minute or so to get my backpack, coffee, and lunchbox.

 

Doing some more searching, it looks like WTS light just stays on for 10 seconds, no matter how cold it is. Or maybe 10 seconds cold, 1 second warm. Reports vary, and I haven't done much testing. But it does sound like it will never be on longer than 10 seconds.

If I'm too lazy to install the LED mod, I'll just wait a little longer before start. It seems that one advantage to waiting for the full cycle vs. just waiting "long enough" is that waiting for glow plugs to turn off makes more juice available to the starter. That may not be as important to me here in central KY as it is to some of you in colder climes, because I'm usually not driving the truck when it's cold enough to seriously impact the cranking voltage.

Without the LED, would I be able to detect the voltage difference between glow plugs off/on by looking at the dash gauge? Or is it not that accurate?

 

Turn your dome light on and watch it. It will brighten up when the plugs go off. I see it in my headlights at night as I leave my driveway. About a minute after it starts, they get brighter.

 

Change your oil.

Try a 5w-40 synthetic oil. My truck is rough to start when it's cold out if I'm running 15w-40 conventional oil. Doesn't matter how long I let the plugs warm up for, it will still romp and run rough a bit. The 5w-40 makes a large difference.

Also, check to see if you have a programmer on it. I have a hypertech programmer that came with the truck and if I have the program in, it will run rough on a cold start.

 

I've been playing a little more. It's about 55 degrees here today, so I can't really tell what effect anything will have in cold weather. But I recently got an ELM OBD adapter, and the Forscan Lite iPhone/Ipad app. I"m a Mac guy, so I couldn't get the laptop Forscan version. I'm not sure why the app is called Lite, it seems pretty well loaded. I can read and reset DTCs, and display all kinds of info from the PCM.

There are several indicators related to glow plugs. There's "Glow plug control", which reads 0 or 100% (presumably on/off). Glow Plug Coil On time, I assume says how long glow plugs should stay on. Two Glow Plug Current indicators, one for left bank and one for right.

When i turn the key on, Glow Plug control goes to 100 %, Coil on time 50 seconds. After about 50 seconds, they both go to 0. That seems pretty self-explanatory.

But during that time, both glow plug current indicators read 0 amps. To me, that suggests either something isn't being read correctly, or the and plugs aren't getting juice for some reason.

Haven't tested the voltage at the GPR recently, but I just replaced it a couple of months ago. If the relay is good, and the output terminal is energized, is there something else that could go wrong between the relay and the point where the current is being measured?

 

#1 rule of the OBDII scan tool universe: If it's listed, flip a coin. While trucks with GPCMs might have a GP current sensor, trucks with GPRs do not. Ignore that one.

Look at the volts on the dash or the OBDII tool. You will see the voltage is lower with GPs active on both devices (running or not). For proof, let the GPs time out and see what happens.

 

What I have been doing, as it gets cold, is this:
1.) Turn key on and wait for 1- 2 minutes
2.) When sufficient time has passed, I cycle the key again, and wait for the WTS light to go out, then immediately start the truck.
I only do this on the first cold start in the morning. It seems to start a little easier and somewhat less smokey.

I know some guys will laugh at cycling the key, but there is a good reason for it. As has been mentioned, the glow plugs can stay on for up to 2 minutes after the WTS light turns off. So, letting it sit for that time, on the first key cycle, allows more heat, and for that heat to spread out into the metal of the head, instead of just the one tiny hot spot of the glow plug.
When you turn the key on, the fuel pump comes on for a short period of time, and then turns off. It is off long before the approx 2 min. wait period. On these engines, once the fuel pump turns off, fuel pressure drops almost immediately, to pretty much zero. So, if you simply wait for the 2 min or so, then go right to cranking, you are cranking with no fuel pressure. Yes, the pump should turn on again right away, but there is going to be a delay, before the system is fully re-pressurized; especially if you are also attempting to empty the rails simultaneously by trying to start the truck.
By cycling the key the second time, and then cranking as soon as the WTS light goes out, you've added a little bit more heat, and you are cranking with full fuel pressure (or close to it) in the rails/injectors.

 

If in doubt, while sitting in truck, door closed, turn the dome light on, turn ignition on till WTS light comes on while watching dome light. The dome light should noticeably go dim, and stay that way until the GP's turn off. Usually about a minute or 2. Today's cold enough for them to work.

 

Didn't notice a difference in the dome light. Voltage, reported through the PCM via OBD, reads 11.56 V when indicator shows glow plugs on, jumps to 12.02 when glow plug reading shows off. So there's definitely some drain when the glow plugs are supposedly on.

At this point, I'm going to assume that my glow plugs are good, and that the 10 seconds that the WTS light is on is not adequate for cold weather. Cycling the key to get fuel pump active again seems reasonable. Next time it's cold, I'll try leaving the key on for at least 30 seconds, maybe longer depending on how cold, then cycling and waiting for the 10-second light.

 

Get a helper. Be under the hood at the relay. (Farthest one back is for GP's). Let helper cycle key you should be able to hear and feel the relay operate if you have your hand on it. Use a stop watch if you want. After 2 min or so you will hear/feel it click off. Assuming it is working. Even in 70 degree weather at first start with all fluids at ambient temps. If no click you need to investigate further. If you have good hearing and know what to listen for you can hear it in cab. Led mod is well worth you time.

 

I would think the only trucks that you'd be able to monitor the left and right bank current draw through the data stream would be pre-99.5 with CA emissions.

 

If he has the GPCM, I could see this. I just worked on Scott's e99, and his has the GPR. There is absolutely no sensor for current anywhere near the GP circuit on a GPR-equipped truck.