Won't Start Hot - Chevy and GMC Duramax Diesel Forum
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post #1 of 12 (permalink) Old 10-15-2008, 08:24 AM Thread Starter
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Won't Start Hot

I have a 2003 Silverado 2500 6.6L Duramax. I replaced the fuel filter 6 months ago with a Purolator. Before the replacement the engine ran fine and would start instantly under any condition, hot or cold. Starting a month ago, the Duramax would crank longer and longer before it started. Now it won't start at all hot. I have to prime the fuel system with every start. I know there is a leak somewhere causing the fuel to lose pressure. Now, no matter how much I prime it, it still won't start hot. When I let it cool for 4 or 5 hours it starts, still with lots of cranking. I have an ACDelco on the way, hopefully it solves the problem. Any other ideas?

Thanks, Andy
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post #2 of 12 (permalink) Old 10-15-2008, 09:17 PM
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Welcome to the forum!

Id changed the filter and makes sure you use some grease or vaseline on all the O rings and threads for the filter.

If that doesnt work there are 2 things. I heard before that the filter housing where the primer is would have seals go bad. Causing air to leak in the system. Also, your lift pump could be going bad causing the no starts.

Make sure to post up after the filter is in!

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post #3 of 12 (permalink) Old 10-15-2008, 09:25 PM
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I would have to agree with Tow Master...

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post #4 of 12 (permalink) Old 10-16-2008, 06:53 AM
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X2 Change the filter and make sure the old seal is not still in the housing. If you still have a problem, it could be a cracked housing or leaking primer pump. You could pressureize the fuel tank about 10 lbs MAX, or use the pressure side of a shop vacuum to check for leaks.

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post #5 of 12 (permalink) Old 10-17-2008, 09:36 PM
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Do you have any other bad injector symptoms such as bad economy smoking at idle, rough running diesel in oil??

I may sound crazy but you could have bad injectors.

My truck did the same thing as yours, I had perfect balance rates, no smell of raw diesel, no diesel in the oil, no rough running, no smoke at idle, just hard starts and poor economy which would lead one to think it was an air leak.

Well turned out my injectors were actually bad. Get them checked, it never hurts.
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post #6 of 12 (permalink) Old 10-18-2008, 03:39 PM
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Injectors with high return rate can cause a no start. This means the injectors are returning so much fuel back the return line the injection pump can not make sufficient pressure while cranking to let the engine fire.

Also Duramaxs do not have lift pumps, the injection pump draws fuel from the tank under a vacuum. This is why they easily draw air in if there is a leak anywhere.

If you are sure there is not any air in the fuel system the it is probably the injectors. 03 and 04 models do not usually fill the crank case full of fuel because they already had an updated injector in them. But they still can have high return rate.
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post #7 of 12 (permalink) Old 10-18-2008, 08:00 PM
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Make sure they check the return rates too. Many dealerships wont and will tell you you have a bad batch of fuel.
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post #8 of 12 (permalink) Old 10-18-2008, 08:24 PM
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Cool Right on....

Yep,the return rates are what tell the tale...An injector is designed to flow at diff rates to make up for imbalances,returning excessive fuel means it is not being burned,rather returned...

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post #9 of 12 (permalink) Old 10-19-2008, 10:24 AM
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Originally Posted by daddysLBZ View Post
Yep,the return rates are what tell the tale...An injector is designed to flow at diff rates to make up for imbalances,returning excessive fuel means it is not being burned,rather returned...
Thats not entirely true. The injectors are, by design, ment to flow the exact same amount of fuel at any given pulse with. When injectors are new the balancing rates are near 0. But as the injectors get more miles on them they wear a little and their flow rate changes a little. So the computer has the abiltiy to add and subtract fuel to any or all cylinders to attain the smoothest idle.

When an injectors return rate gets high that means the ball seat inside the injector has worn and is letting fuel past it into the return line. This high return rate does not affect the amount of fuel any one single injector delivers, but, when it gets high enough, will start affecting fuel rail pressure. In other words the injection pump will not be able to keep up because so much fuel is being returned back to the tank. This problem also can set P1093 fuel pressure codes and can cause extended crank times and no starts.

The first thing the dealer needs to do is command the fuel pressure to 160Mpa (23000 psi) and see if it gets there with the engine at idle. If it does not then it is either the injectors or the injection pump.

You also, if you have the ability, is to watch the fuel pressure while cranking. The computer waits for about 1500 psi before it will allow the injectors to turn on. So if your cranking and the fuel pressure is only 800 psi then the computer will not let the injectors turn on. Low fuel pressure while cranking is caused by injectors with high return rate, air in the fuel system, or posibility a weak injection pump.
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post #10 of 12 (permalink) Old 10-26-2008, 08:49 AM Thread Starter
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I finally got the new fuel filter in the mail and got it changed. Everything seemed to be working fine for a while. The engine would start right up without any priming when cold and hot.

I drove thirty minutes to get gas one afternoon and it started up quickly after the short stop at the station. That same afternoon I stopped for about an hour at the store and it wouldn't start afterwards. I primed it and cranked it several times wiht no luck.

The priming pump is always soft, like there is no fuel in the lines, at idle and when the engine is off. Is this normal? I double checked for an extra o-ring when I replaced the filter, nothing there. The truck doesn't even have 100,000 miles on it. COuld the injectors really go bad that soon?

There isn't any smoke at idle or upon start-up. As far as I can tell the idle is smooth. No funny noises.

I am with the military overseas so I don't have the resources I would back in America. Wouldn't know how to explain the problem to a mechanic, or to even find a reliable mechanic. I'm hoping that with all of the little turbo diesel cars here, the mechanics will be pretty good with this kind of thing.

The thing that confuses me most is why it won't start hot? Cold starting problems seem more likely!!
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