is it the glow plugs or intake heater

[needbigtruck]

My truck has been very difficult to start all winter long. Much below 20 degrees it has to crank for a while before it fires, and it has not started at all when it less than 0. I originally thought it was because I had mostly summer fuel in the tank because I didn't drive it much after September, my first refuel was late in December. After driving it extra and even putting in some kerosene I am still having the same issue. So I noticed the other day I turn it on the wait to start light comes on and the voltage is around 11 volts. It used to be after I started it the volts would stay low for 10-15 seconds maybe even a minute after it was running. Now the volts come up to normal, about 14.5, right away after it starts. So I got to thinking one of the 2, either the glow plugs or the intake heater has quit on me. I'm hoping someone can diagnose which one it could be from the info I've provided. I've read what I can about the GP and intake heater relays, and since they appear to be pretty expensive and it's starting to be spring finally and the truck seems to start OK above 20 degrees and I am getting a new truck this summer, I probably will just ignore it. But I'd still like to know...Thanks

[rapidoxidationman]

Got codes?
If there are glow plug issues there should be a CEL and some codes stored.

[DmaxMaverick]

Correct. Any problem with the GP's or intake heater will have the computer complaining.

I'd suspect the fuel, or a much slower cranking speed (cold/bad batteries, thick conventional oil, etc.). Adding kerosene won't do much to help summer fuel until you get too much kerosene. A good anti-gel additive is much better, and it won't dilute what little lubrication that remains in modern fuel. According to every publication I've seen, my experience, and shared experiences here, the Duramax engines see little difference with starting success as the temp drops. Until it gets well below 0°F, it should start just fine, even with the GP's and heater disabled (I tested this a few years ago). After start, that's a different story. Below zero, it's a bit rough and rattles some, but straightens out in 15 seconds or less. In any case, if you have good fuel and a healthy electrical system, it should start well in all but the coldest climates, with or without the heat help.

[needbigtruck]

I've had a P0107, manifold absolute pressure, code for a couple of years now. I comes on after I start the truck and I clear it and it doesn't return until I start the truck again. My batteries are OK, not new but not old either, so I don't think it's a "how fast does it spin" concern, it seems to spin like it always has. Granted when it doesn't start when it's so cold I've had to re-charge the batteries after I've cranked for a while and it doesn't start. With the temps in the 30's and 40's it's been starting fine. I know one of the 2 are bad based on the voltage coming right up to normal right after the truck starts cold, it never did that before. You say either of them will throw a code, but my truck is a first generation, 2001 could that make a difference?

[DmaxMaverick]

That is correct, regarding the codes. Mine is an October 2000 build, so it's as old as they get. I've visited this issue a few times on my truck, and others as well.

The GP/heater feedback voltage is monitored when they are commanded on, and it will detect when only 1 plug is bad. Same for the heater.

The P0107 won't have any affect on a start, hot or cold, but it will have a significant affect on economy and perhaps other issues, once running. Probably should get that fixed. Check the sensor and harness. The connector may be dirty/corroded/disconnected, or something simple like that.

I still think your deep-cold starts are fuel related.

[Kennedy]

The plugs on the LB7 (excluding CA and some NE emissions) are tied together by a steel rail. This rail often rusts off dropping power to some or many of the plugs. The diagnostic side of the glow plugs is not as strong on Fed emissions trucks.