I found an interesting thing, when I start the truck right away without waiting for the glow plug light to completely cycle (Engine at operating temp) the engine will lope REALLY bad. Now, when I wait for the glow plug light to finish and then start the engine, it runs as normal. I checked and cleaned the PCM pins for the chip and everything is good. Ghosts & gremlins.

 

I am often attempted to hop in and just go right to start myself once the engine is warmed up. But...then...I remember that the fuel pump runs for 20 seconds to build fuel pressure and I hold off for at least a few seconds. Since it is only when you say it's doing it I might be on the right track.

 

My truck always seems to take longer to fire if I just turn the key and go, even in summer or hot. Pretty much with any car I drive, I always wait for all the dash lights to go through their "self-check" and whatever else the computer does when you first turn it on. I turn the key, let everything light up and turn off, and then start.

I agree with Sous' comment (previous thread) that the fuel pump is really only re-pressurizing the fuel system, and there shouldn't be much volume at all to pump. The Wait-To-Start (glow plug) light is on a timer, I don't think the plugs are actually being lit at all if EOT is hot. You can watch your battery voltage to see if that changes.

Edit: Added WTS as per Marks comment below - good call Mark

 

But why the severe loping if I don't wait for the GP (wait to start) light to cycle?

 

Let's clarify something here...you say 'GP light'. Are you talking about the WTS light, or do you have an independent GP light hooked up?

 

Wait to start. It's OEM but for the GP relay, that's a HD relay.

 

The light being on or off doesn't have any relation to the glow plugs. If you have a GPR truck then you can rig a light to see when the plugs are actually on. The other way to tell is to monitor the battery voltage. I use a plug-in meter like this:

There is a noticeable voltage drop when the plugs are on. They stay on after a cold engine has started. Near freezing, I found that they stay on for about 30 seconds after starting. When the engine is at operating temp, it doesn't light them at all. Not even if you sit there and wait for the WTS light to come on. As I said in the other thread, immediate fuel pressure is available in my truck as soon as I turn the key to "on". So assuming that your fuel pump is healthy, that's not the problem. Note that I don't have a solution for you, but you can rule glow plugs and fuel pressure out as causes IMO.

Note that I have a GPCM truck so I won't promise that yours acts the same as mine. This is just based on my experience with the only 7.3 I've owned.

Edit: Actually I do have a suggestion. Do you have a way to monitor the engine while it's running? If you have a smartphone, there are apps and adapters to read codes and monitor live engine data. It's very useful for troubleshooting like this.

It also might be something as simple as a bad CPS, loose nut on the IPR or a bad IPR.

 

I can recheck the IPR, but I had cleaned it and applied loctite to the nut the other day with no changes. I changed the CPS with a known good gray one. So why does it lope severely when I don't wait for the light vs it idles awesome when I do wait for the light? Remember I'm at operating temp and it's upper 80's outside.

 

I second Andy's suggestion for a smartphone app like Torque Pro for real data as to what's happening. Our trucks are run by computers and electronic sensors. Maybe something electronic is still "turning on" during that 30 sec wait time, so your PCM is running off a default indication or something like that. I really don't know, but that's why I always wait to start any car that I care about.

 

I will be very interested in seeing what ends up being the cause. Someone more knowledgeable than myself is going to have to help you.

 

I believe "romping" or "romp" is the commonly used term around here.

My truck did that when I brought her home from Miami in the middle of winter.

I had to plug her in and still wouldn't always start.

Here's how I solved that.

1. New glow plugs
2. New injector orings
3. New UVCH on both sides
4. Switched to 5w-40w T6 synthetic
5. Hutch mod, replaced quick connect fittings on intake side of fuel pump, rebuilt fuel bowl, installed FRx.

"Thinner" oil (5w part instead of 15w) "helps" older and tired injectors. So does CLEAN and fresh oil.

I used to think it was "normal" for it to start that way, because as it warmed up, it would even out smoothly, just like it was a warmup feature or something. Found out that isn't the case.

My first suggestion is to change oil and use T6 5w-40w and run it about 100 miles. See if it starts better.

Air in fuel could be much worse when first starting. FRx allows some recirculation through the heads to remove air, the other fuel mods above help prevent air in the system.

My results? Until this injector puked, for the past approx 3 yrs, she started in less than 2 secs every time (except when the starter was puked).

Hope this helps!

 

I rebuilt the engine and installed new injector orings when I slapped the new injectors in. I've had FRx for five years, IF I wait for the wait to start light to cycle she runs normal. If I don't wait for the wait to start, she will romp terribly and no power as well, sometimes not running on all cylinders. If I shut it off and wait for the wait to start the romping goes away and she runs normal. Yes, new OEM valve cove gaskets at overhaul. Checked all connections and for wiring chaffing.

 

Do you have a fuel pressure gauge? How old is your fuel pump? How long before your power returns? I'm wondering if your pump is tired, and the WTS light gives it just enough time to build up full pressure where a healthy pump gives almost immediate pressure. Just thinking out loud here... Hope you get this figured out.

 

I checked the fuel pressure and it was 55 lbs. It doesn't seem to be a fuel problem. Since I can start the truck one moment (waiting for the wait to start light to cycle) it runs fine and the next moment I start the truck (not waiting for the wait to start light to cycle) it romps really bad. I can switch the sequence at any time with the same results.

 

Without actual data, all you can do is spend money and time and start swapping out expensive parts. Really, spend your first dollar on an OBD-II adapter and get Torque for your phone / tablet, or Forscan for your PC. The softwares are free (well, Torque Pro is $5).

Then we'll find exactly what's going on. Search the forums for Torque Pro, you'll find many suggestions for which adapter to get. And as always, there are many different opinions on what to get.