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LLY Rail Pressure/Cold Start Question

3K views 10 replies 3 participants last post by  frank2 
#1 ·
Hey guys, I am trying to figure out why my lly starts so hard in the cold. Anything under 30°F and the truck doesn't want to run. If I plug it in the truck starts fine at any temperature. My motor and injectors now have roughly 2500 miles on it since the rebuild. I run the lighter Rotella T6 oil, additive in my fuel, and have two new batteries that are less than six months old. All of my glow plugs are around 6 months old as well. I have had multiple fuel filters on the truck and rebuilt the fuel filter head. I just had my injectors tested and they are all within spec.
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I checked my rail pressure to see if the cp3 was going bad. My cp3 over performed the desired psi throughout the entire RPM range with no spikes or sharp drops in pressure at any point. However once I shut off the truck the rail pressure dropped from 5,000 to a couple hundred in a few seconds. Shouldn't the truck hold rail pressure for a while once it gets shut off? Does that mean I have a leak somewhere between the cp3 and the injectors (bad fuel pressure valve or leak in injector/cp3 lines? Also, if that was the case, why would the issue only happen in the cold?

Going with the idea that the truck is losing prime around the cp3 and has a harder time priming with cold fuel, I unplugged my engine harness so it would not start and turned the truck over for four cycles. I then plugged in the motor and the truck fired right up without even cycling the glow plugs. Does this validate my idea about a leak in the fuel system between the cp3 and injectors?

I was battling a fuel prime issue when I got the truck running and replaced the two rubber hoses that run from the filter to the FICM and made new braided stainless fuel lines which seemed to resolve my issue.

Any info you guys have for me would be great and much appreciated. I am just banging my head on the wall at this point. Thanks.
 
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#6 · (Edited)
My trucks fuel pressure will go down to a few hundred after being shut off as well after about 10 seconds or so.

You said if it's plugged in it will start just fine at any temperature. I'd would think you'd have bad glow plugs which you said you replaced. I would test them. Then I would check the control module.

Fuse isn't blown for the fuel heater?
 
#7 ·
I replaced the fuse just to be safe and even cleaned off the terminals. As for testing the glow plugs, is there a way to keep the glow plugs on so they have continuous power while is check them with a volt meter. Also, what should the plugs read on the meter? I have cali emissions if that matters. Is there a way to check the control module other than buying a new one?
 
#8 ·
Other than having someone turn the ignition to the run position and holding a volt meter on a glow plug(s) I think the glow plugs are 4.7 volts. If you removed a glow plug you can test it with a ohm meter. I'd check first for power at plugs first. That would eliminate the controls module as well.
 
#10 ·
Glow plugs won't always throw codes when they are bad, I think you can put a ohm meter on and test them without pulling them, I've never tried that way before though
 
#11 ·
Hmm I'll have to look into that, I'd rather not pull them if I didn't have to. Looks like my truck is gonna keep me busy once spring break finally starts. I noticed a large puddle of coolant under the drivers side, looks like its coming from the water pump. If I m replacing the water pump I figure I'll do my leaking power steering pump too while I'm at it. This truck sure likes to keep me busy.
 
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