Glow plugs? No Codes-starts rough. - Page 7 - Chevy and GMC Duramax Diesel Forum
04.5-05 LLY 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 Ect

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Old 01-01-2013, 05:49 PM   eBay Motors  #61 (permalink)
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Okay, so the fuel heater is still showing open, so if I understand right, that means the heater is bad. Best to replace the whole filter head assembly if I followed the other conversations.

But . . . for peace of mind, can someone explain this to me . . .

I can get that warmed up fuel helps a cold start, but to me, for the fuel in the warmed up filter head to make it to the injectors, that would take some time, and a fair amount of fuel would have to pass thru the injectors before that warmed up fuel ever sees the inside of a cylinder. I can't wrap my head around the idea that in just a few seconds of cranking the warmed fuel plays a role.

Could someone enlighten me please?
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Old 01-01-2013, 06:08 PM   eBay Motors  #62 (permalink)
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camp I am with you on that. I forgot to prime my fuel filter the other day (oops) when I changed it while I was changing my gp. I started the truck it ran for maybe 20 sec then died. I then remembered that I did not prime it. After I got her primed it took a good 10-15 sec of crank before she would fire. I assume that the heater keeps the filter warm because it is isolated from the rest of the fuel and more prone to freeze/gel.
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Old 01-01-2013, 06:16 PM   eBay Motors  #63 (permalink)
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camp I am with you on that. I forgot to prime my fuel filter the other day (oops) when I changed it while I was changing my gp. I started the truck it ran for maybe 20 sec then died. I then remembered that I did not prime it. After I got her primed it took a good 10-15 sec of crank before she would fire. I assume that the heater keeps the filter warm because it is isolated from the rest of the fuel and more prone to freeze/gel.
Maybe I need to stop reading things, but now I found another thread that essentially says the fuel heater in the filter head aids in water seperation and has nothing to do with cold starting . . . I'll try to find the thread again and link to it . . .
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Old 01-01-2013, 06:26 PM   eBay Motors  #64 (permalink)
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This excerpt:
"From the EDU, the fuel passes through an engine mounted fuel filter. This filter has a water sensor, a water separator and a fuel heater. If necessary, the heater warms the fuel to 14 degrees C to prevent any waxing of the fuel."

came from: The Diesel Page News - Original GM announcement for the Duramax 6600 diesel engine.

Although now that I know the heater is shot, I will replace it, but I don't think it has anything to do with the cold start
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Old 01-01-2013, 06:37 PM   eBay Motors  #65 (permalink)
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I will do some more searching on how to test the contoller but I am sure that was my issue. I will let you know for sure tomorrow if my truck starts in the morning. I would go out now and try it but from the past experience once it was started it will start all day. It is interesting how you got that article. Kind of going against everything that I have been reading.
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Old 01-01-2013, 07:16 PM   eBay Motors  #66 (permalink)
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The fuel heater should have 12 volt power to the connection-- with the key on.

Inside the filter housing, the heater has a thermo switch connected in series to the heater wiring. That switch closes when the temperature in the housing is around freezing. If the temperature is around freezing, the switch should be closed, and the ohms should be about 1.5 ohms. If the temperature is above freezing-- the thermoswitch will be open and the ohm will show open.

You should also make sure the heater ground wire is attached to the primer cup screw.
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Old 01-01-2013, 08:00 PM   eBay Motors  #67 (permalink)
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I know the thread is a little broken up, but this is what I found:

I do have 12v+ at the filter heater connction when the key is on

I do have an open when testing the heater - outside air temp is 4*F

Ground is good on filter housing

I get that the filter housing fuel heater is bad, and I will get it replaced.

Per my link above, I still don't believe the fuel heater has anything to do with a cold start issue. Per GM docs, the fuel heater helps prevent waxing in the filter. If I was experiencing waxing to the point I didn't have enough fuel delivery to start the engine, I shouldn't be able to drive it at highway speeds without replacing the filter, but that isn't the case.

Does my logic make sense or am I missing something?
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Old 01-01-2013, 08:32 PM   eBay Motors  #68 (permalink)
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My 2 cents is = I think you got a controller issue= cause if bad glow plugs they would ohm out of range and flag light ( when glow plug go bad they stay bad) controllers/modules can be intermittent plus a bad module can not tell if itself is bad. Have had gas pot trucks not start in sub zero cause of a module .

Think you got to hook up test light and test every morning till you get a bad start and see if power to plugs??

Also they ask on import cars alot if you have no codes is to induce a code to make sure system works = unplug 1 of your glow plugs and do a few cold starts should flag a code.

And I believe your correct that fuel heater doesn't help for first little bit at fire up.. takes a bit for that "warm" fuel to get to injectors..
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Old 01-02-2013, 06:04 AM   eBay Motors  #69 (permalink)
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Quote:
Originally Posted by camping-guy View Post
I know the thread is a little broken up, but this is what I found:

I do have 12v+ at the filter heater connction when the key is on

I do have an open when testing the heater - outside air temp is 4*F

Ground is good on filter housing

I get that the filter housing fuel heater is bad, and I will get it replaced.

Per my link above, I still don't believe the fuel heater has anything to do with a cold start issue. Per GM docs, the fuel heater helps prevent waxing in the filter. If I was experiencing waxing to the point I didn't have enough fuel delivery to start the engine, I shouldn't be able to drive it at highway speeds without replacing the filter, but that isn't the case.

Does my logic make sense or am I missing something?


It's good to look at theory but either the GP module or the fuel heater can both cause issues with hard starting in the cold. Your issues make me wonder if you maybe also have water in your fuel which has turned to ice in the tank (possibly clogging the pickup or fuel filter). It would help alot in your case to be able to see rail pressure while cranking. That will help you narrow down if it's a glow plug or a fuel supply issue. Glow plugs themselves are easy to check and the module simply provides voltage so it too should be easy to verify when it comes on. If your fuel heater resistance tested open below freezing (I believe 37 degrees is the actual cutoff) first thing in the morning, then it needs to be replaced as you suggested. The fuel in your tank gets continually heated as you drive the truck because the both the injectors and CP3 will return fuel (and fuel that has been pressurized is quite warm) which often explains why the truck drives fine later but doesn't work as well when sitting overnight. You may have multiple issues at work so being methodical about testing and checking components will help solve your issue.
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Old 01-02-2013, 09:58 AM   eBay Motors  #70 (permalink)
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Correct me if im wrong but if the truck start after a while of cranking and then starts just fine the rest of the day cant you assume there is no fuel issue as far as freezing goes
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