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Rough idle when engine cool

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  #1  
Old 10-11-2017, 12:50 AM
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Rough idle when engine cool

Now that I've been really digging into my truck, one of the things that bothers me is that the truck runs so rough when I first start. When cold, it is just louder and a bit more sluggish feeling. Once warmed up it purrs like a kitten... Well, a lion perhaps, but it's smooth and even.
What causes that?
 
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Old 10-11-2017, 06:25 AM
Walleye Hunter
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I don't know all the reasons but two that come to mind are some failing glow plugs and oil choice can make a big difference when cold. A good 5w-40 synthetic is recommended in colder climates.
 
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Old 10-12-2017, 09:09 AM
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Originally Posted by Walleye Hunter View Post
I don't know all the reasons but two that come to mind are some failing glow plugs and oil choice can make a big difference when cold. A good 5w-40 synthetic is recommended in colder climates.
I'm using Delo full synthetic 5w-40. when I say cold start, I'm talking like 60 degrees. It just runs louder and more obnoxious until it's been running for a bit. Not sure what could cause that.
 
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Old 10-12-2017, 09:20 AM
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Just curious but do you have a California Emissions truck with a glow plug control module instead of a relay?
 
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Old 10-12-2017, 09:24 AM
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Originally Posted by jimjokjv View Post
Just curious but do you have a California Emissions truck with a glow plug control module instead of a relay?
I am in CA, but not sure. It was originally an Oregon truck. I have the build sheet from dealer. Where would it say if it was California emissions? It says less catalyst, so maybe not?
 
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Old 10-12-2017, 09:39 AM
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This is a Glow Plug Control Module which should easily be seen on the passenger's side top of the engine just in front of the Turbo assembly.
The reason I ask is that I have the California Emissions set up on my truck and experience the same cold starting problems you are.
My research to this point tells me the glow plugs are operating but may not be operating as designed due to an incorrect PCM being installed by a previous owner.
 
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Old 10-12-2017, 09:40 AM
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Look under the hood for one of these:
Amazon Amazon
on the passenger side valve cover.

You will either have one of those, or two large brown relays on top of the motor, one for the AIH and the other for the glow plug relay. You will either have a GPCM or a GPR.

Ohm out your glow plugs and replace them if necessary. It's not that hard to do, just a little time-consuming, especially if it's your first time taking the valve covers off.
 
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Old 10-12-2017, 09:51 AM
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Originally Posted by andym View Post
Look under the hood for one of these: https://www.amazon.com/Glow-Plug-Mod.../dp/B009VI5G38 on the passenger side valve cover.

You will either have one of those, or two large brown relays on top of the motor, one for the AIH and the other for the glow plug relay. You will either have a GPCM or a GPR.

Ohm out your glow plugs and replace them if necessary. It's not that hard to do, just a little time-consuming, especially if it's your first time taking the valve covers off.
Thank you. It looks like I have a gpcm. Here's a picture.


I didn't know the glow plugs would affect the running of the truck, so much. I thought they just wanted it enough to start. I'll ohm the flow plugs this weekend. As far as the relay, it's this worse than the two modules? Is there something I should change?
 
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Old 10-12-2017, 09:57 AM
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Rhythmic misfire? If so, it's injector time (or shimming the armature plates at a minimum).

Rough, rhythmic (as in not "hitting" on one or two cylinders) misfire without smoke until the engine is warm means non-firing injector(s). The excessive noise or rattle is because the next cylinder in the firing order is working for itself and the cylinder before it.
 
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Old 10-12-2017, 10:09 AM
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Originally Posted by cleatus12r View Post
Rhythmic misfire? If so, it's injector time (or shimming the armature plates at a minimum).

Rough, rhythmic (as in not "hitting" on one or two cylinders) misfire without smoke until the engine is warm means non-firing injector(s). The excessive noise or rattle is because the next cylinder in the firing order is working for itself and the cylinder before it.
Uh-oh! It sounds like it is missing on one of two cylinders when it's cold. There is no smoke, but once I've gone a couple miles down the highway, it smooths out and sounds great. How do I know if this is it?
 
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Old 10-12-2017, 12:06 PM
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Originally Posted by cleatus12r View Post
Rhythmic misfire? If so, it's injector time (or shimming the armature plates at a minimum).

Rough, rhythmic (as in not "hitting" on one or two cylinders) misfire without smoke until the engine is warm means non-firing injector(s). The excessive noise or rattle is because the next cylinder in the firing order is working for itself and the cylinder before it.
How does engine temp change performance of injection?
 
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Old 10-12-2017, 01:37 PM
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Originally Posted by cleatus12r View Post
Rhythmic misfire? If so, it's injector time (or shimming the armature plates at a minimum).

Rough, rhythmic (as in not "hitting" on one or two cylinders) misfire without smoke until the engine is warm means non-firing injector(s). The excessive noise or rattle is because the next cylinder in the firing order is working for itself and the cylinder before it.
Would this require injector replacement?
 
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Old 10-12-2017, 01:42 PM
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Here you go....
 
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Old 10-12-2017, 01:43 PM
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Originally Posted by jimjokjv View Post
Would this require injector replacement?

Not always. I've successfully shimmed the armature plate on three sets of injectors and it buys a good bit of time.

Just google 7.3L injector shims and pick your poison.
 
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Old 10-12-2017, 02:40 PM
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Cold doesn't affect injector performance as much as it affects ignition. Remember the fuel in a diesel ignites spontaneously from the heat and pressure in the combustion chamber. A cold engine drawing cold air into a cold chamber injecting cold fuel will not run as nice as a warm engine.
 
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