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Old 11-05-2008, 10:29 PM   #1
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Question fuel pump?

hey guys

recently i noticed that when i try to start my truck it turns over longer then usual but eventually catchs and starts. If i shut the engine off then start it back up it will start normally...i only have this problem when it has set for a little bit. i have also smelled fuel after i get it started. does this sound like a fuel pump problem? any help is appreciated
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Old 11-05-2008, 11:32 PM   #2
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From your profile it looks like you have a 2006 with the 5.4. Do you have any activity on the check engine light? I had the dealer check my truck for the same problem...they found a TSB on it and reprogrammed the PCM.

He said it could also be a "fuel injector leaking down" I'm not sure what that means exactly but he said it's normal and as long as the truck runs normal and the engine light doesn't come on it should be fine.

Hope that helps...
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Old 11-06-2008, 07:45 AM   #3
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How many miles on the engine? It could be many things, but the fuel pump I'd rule out; if it were faulty, the truck would not start and run at all. Fuel pumps either work or they don't, there's no in between. When the key is turned to the on and/or start position, the fuel pump activates and pressurizes the two fuel rails (one on the left side of the engine block, one on the right side). The injectors are connected to one of these rails, and then into the cylinder head. One injector per cylinder, so you'd have 3 or 4 injectors connected on the left rail, and 3 or 4 on the right side rail (6 or 8 cylinder engine). The ECU/ECM (brain box) controls the pulsing of these injectors based on inputs from the various sensors on the engine (O2 sensors, Mass air flow, etc). In the case of an engine that has sat (cold), it uses a "map" setting in it's memory.

You could very well have clogged or dirty injectors; that would be indicated by the fuel odor you mentioned after startup. Injector leak down refers to an injector that does not close when the engine is turned off. The injector basically is a small tube with a needle in it's center. The injector has a solinoid that makes this needle move back and forth thousands of times a minute to provide a nice clean mist of fuel into the cylinder (controlled by the "brain"). If the needle does not "park" (close) when the engine is shut off because of the orifice being clogged, leakdown happens, meaning fuel passes by the needle into the cylinder. This is because the fuel rails are pressurized after the engine is shut off. If you ever replaced a fuel filter on a fuel injected engine, you are told to remove the pressure on the fuel lines (there is a pressure bleed screw/vavle in the system to releive pressure).
In your case, it could be that the fuel pressure bleeds down past a clogged or dirty injector after a day or two of the truck sitting. That's why it takes a few moments of cranking to start the engine upon a cold startup; the fuel pump is having to build up pressure to the fuel rails so that the injectors can spray.

Try this test: next time the truck sits for a day (or two), turn the key to "on" but don't engage the starter for about 5 to 10 seconds. This would allow the fuel pump to "pump" up the fuel lines and rails to injectors. Then turn the key the rest of the way to engauge the starter. If it starts faster, that would indicate to me that you are indeed loosing fuel pressure when the truck sits for a period of time.

When is the last time you replaced the fuel filter? A dirty fuel filter can also cause a low pressure fuel line system. Have you had the injectors cleaned? A good garage can perform this service as well. What type of fuel are you using (brand wise)? A lot of folks have started to used lower grades of gas to save some money. The better grades (Shell, Exxon, and Mobile to name a few) add injector cleaners into their gas to help prevent buildup. You could also add your own to every 3rd or 4th tankfull of gas.
If your injectors are dirty, adding cleaner now won't really help; it would take too many tanks of gas to clean them out. Best to take it into a garage and have then cleaned. Then use the injector cleaner to prevent it from happening again.

All of this is only if the injectors are at fault here.
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Old 11-06-2008, 08:42 AM   #4
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Great explination Bucko...

Is it true that the injector leaking is "no big deal" thanks...
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Old 11-06-2008, 11:48 AM   #5
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Quote:
Originally Posted by Dark Stone View Post
Great explination Bucko...

Is it true that the injector leaking is "no big deal" thanks...
To me it would be a big deal; if an injector is leaking down, it means it's dumping fuel into that cylinder. Maybe a small amount depending on how bad that injector is, but any amount over a period of time is contaminating that cylinder with raw fuel, washing away the film of oil for that cylinder. It's well known that a cold startup of any gasoline engine causes an initial "metal on metal" wear, until the oil pump has come up to pressure and is circulating oil. Again, we would be splitting hairs as to how much wear this really is during an initial cold startup, but in this case it may be worth getting the injector(s) checked and cleaned if in fact they are the cause of his slow start condition.

Always tough to do an "internet diagnostic", but his symptoms do lead to an injector leakdown condition as a possibility. One way to test is to connect a fuel pressure gauge on the fuel delivery line to the fuel rails. Most engines have a connector to do this. Then start and run the engine for a few minutes, then shut it off. Pressure should hold and the guage will show this. If the guage begins to show a drop in pressure when the engine is off, that can be an indication of an injector leaking down. It can be other things too, such as a fuel pressure regulator: this is a valve that diverts fuel back to the gas tank during de-excelleration or light load (cruising) driving. The fuel pressure regulator does as it's name implies, it keeps the fuel pressure in the fuel lines/fuel rails at a constant pressure, and diverts fuel back to the gas tank as to not "over pressure" the fuel delivery system (such as the injectors).

There's good reading material to be had at the book stores on the basics of fuel injection. This really is not hard stuff. I've sat my butt down at these book stores (they usually have a coffee shop) and I'll read about this on rainy days when my wife wants to go to the mall. I hate that part, so reading about autos will usually get me to go with her. Good thing they don't serve beer....I'd never learn anything!
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Old 11-08-2008, 12:03 PM   #6
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Thanks for all the replies!
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Old 11-09-2008, 10:17 AM   #7
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I guess it was just bad fuel....once i ran that tank out i put 93 octane and injector cleaner in it.....now it starts fine..... thanks for all replys
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Old 11-09-2008, 10:17 AM
 
 
 
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