LB7 no start <45F weather - Chevy and GMC Duramax Diesel Forum
01-04.5 LB7 Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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  • 1 Post By stevewaclo
 
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post #1 of 8 (permalink) Old 11-01-2019, 10:04 AM Thread Starter
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LB7 no start <45F weather

I have a crank but no start on my LB7 when sitting overnight with temps below about 45F. I have a lift pump and the plunger on the filter head is hard with the key on. Injectors and CP3 have about 200 miles on them (did them myself so no shop to go complain to). Its a CA truck so a single glow plug going out will throw a code - no codes (but I have read where these should start in temps well below 45F without the glow plugs working). Batteries are newer and it cranks fine and starts no problem in warmer weather. All the threads I have read go towards losing prime, bad glow plugs, weak batteries, or even bad injectors but I think I have all of those covered - typically the threads that aren't priming related just fade away without a firm solution I haven't tried the block heater yet - but 45F? Really? I had no starts in cold weather before the lift pump but didn't know about the loosing prime thing until fairly recently so I may have been able to start it back then with pumping the plunger but honestly don't remember if I did that more than once. When it wouldn't start in the past I'd be going to work and just take my car without screwing around with it and it would start right up when I got home.
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post #2 of 8 (permalink) Old 11-01-2019, 10:52 AM
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Be forewarned I am far from an expert in reference to the Duramax or anything to be honest. If it were my truck and I was sure it was not losing prime I would check the easy stuff first like fuel filters and possibly even add some additive to see if that made a cold start difference. I would even check electrical connections that may be contracting with cold. This is more of a bump for you. I hope to see the resolution to this issue after you solve it.

2003 Silverado 155K. S&S stock SAC injectors, Kennedy dual lift with mega filter, aFe intake, the rest is bone stock.
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post #3 of 8 (permalink) Old 11-01-2019, 11:37 AM Thread Starter
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Thanks for the reply. An electrical issue makes the most sense - but where/what? Is there a weak solenoid or relay that can't function below a certain temp? I did the CP3 before doing the injectors so I probably disconnected/reconnected most/all of the connections on top of the motor multiple times.
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post #4 of 8 (permalink) Old 11-05-2019, 01:39 AM
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Hey, Livermoron!

Luv the name .

Interesting on your glow plug set-up, since I have a 03 CA truck and GPs are tied to a bus down each side of the block. Frankly, I dont know what it would take to throw a code in that situation, but suspect Id have to lose connectivity of all 4 on one side or the other. What I do know is when I go key-on, the voltmeter takes a massive dive as they come on and voltage rises fairly soon afterwards, as they cycle off, depending on temp, of course.

At around 45*, even without GPs, I would also suspect the engine would at least sputter and try to fire, and most likely start.

You noted a hard primer button, which should assure fuel to the CP3 so, like Durtynuby Im suspecting electrical harness connections. In our aging trucks it doesnt take much for a pin to be pushed back in its holder enough to become temperature sensitive.

I once discovered a no-start issue with a hair dryer. Heat, crank, repeat.

2003 GMC Sierra 2500HD SLE ExtCab CA Emissions; 155k; Allison 1000 w/Transynd X2 Flush & Fill; 8' bed; AFE/CAI; MBRP 4" Exhaust; Side Tint, 33% VLT, rear, Limo; Smittybilt Stainless Side Nerf Bars; Sprayed-in Bed Liner; MadJack Fuel Filter Access Door; Regular Used Oil Analysis (latest available on request), Blackstone Labs; EGT/Boost Gauges; Dual Chrome Dipsticks, JC Whitney; Stainless Steel fuel filter head bleeder screw; New WP and Hydroboost; Billet Aluminum Fuel Filter Housing Spacer; Professionally repaired instrument cluster (new steppers and lamps); Does anybody ever read this s%#t?; Injectors under warranty @ 70k; 2nd set DIY @ 155k
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post #5 of 8 (permalink) Old 11-05-2019, 08:59 AM Thread Starter
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Hi stevewaclo. Funny you mention using a hairdryer - that is my plan for this weekend. I think I will start with the FICM and then move to the under hood fuse/relay block. Although if I can confirm the 12v power wire to the FICM I might check that first. I called a module repair place and they said they haven't come across my symptoms before and typically fix issues around 1 or multiple (but never all) injectors not firing.

Can't comment on your glow plug set-up versus mine. I do know that when one plug goes out it will throw a code for the circuit and not indicate the individual plug. Mine are less than 2 years old and have about 2000 miles on them if that.

I will report back after I do the hairdryer testing.
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post #6 of 8 (permalink) Old 01-16-2020, 03:59 PM Thread Starter
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Update - after I posted about this issue the weather warmed up enough to where if I wanted to test it would be before the sun came up. And soon after that I started experiencing slow crank and high draw on start-ups. Eventually the starter fully shorted and I replaced it last weekend. And as luck would have it we started experiencing frosty mornings again. And guess what? With the new starter it starts right up even in the mid 30s. Now when I was trying to start it at the beginning of this thread I didn't notice the starter turning any slower than normal and I can't say for certain that the new starter turns faster than the old one did over the years I have had the truck - but it now starts when freezing when it didn't before. So I am going to say it wasn't turning over fast enough and the new starter fixed the problem.
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post #7 of 8 (permalink) Old 01-16-2020, 10:04 PM
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Thanks for reporting back!

Too many posts just fade away...

My batteries are 8 years old and Ive noticed that LB7s on YouTube crank much faster than mine, which fires faster than I can release the key.

Best and luv the happy ending.
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2003 GMC Sierra 2500HD SLE ExtCab CA Emissions; 155k; Allison 1000 w/Transynd X2 Flush & Fill; 8' bed; AFE/CAI; MBRP 4" Exhaust; Side Tint, 33% VLT, rear, Limo; Smittybilt Stainless Side Nerf Bars; Sprayed-in Bed Liner; MadJack Fuel Filter Access Door; Regular Used Oil Analysis (latest available on request), Blackstone Labs; EGT/Boost Gauges; Dual Chrome Dipsticks, JC Whitney; Stainless Steel fuel filter head bleeder screw; New WP and Hydroboost; Billet Aluminum Fuel Filter Housing Spacer; Professionally repaired instrument cluster (new steppers and lamps); Does anybody ever read this s%#t?; Injectors under warranty @ 70k; 2nd set DIY @ 155k
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post #8 of 8 (permalink) Old 02-13-2020, 04:40 PM Thread Starter
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Update - this morning with the mirror temp reading 44 it took multiple long cranks to fire. I am thinking back to the drawing board. On the plus side winter is nearing its end and I may not need to think about this for another 9 or so months. BTW - before replacing my starter I borrowed a battery tester (puts a draw on the batteries and indicates good/bad/marginal) - they both tested good.
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